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'[OT] Solar Steam Engines...'
2005\09\23@073205 by Byron A Jeff

face picon face
part 1 5643 bytes content-type:text/plain; charset=us-asciiI think it's time for a subject change too...

On Thu, Sep 22, 2005 at 05:29:31PM -0700, James Newtons Massmind wrote:
> > But the difference is that the heating block/head  would not
> > require cooling - it would remain substantially at the same
> > temperature and just be used to flash the water spray to
> > steam. The hot steam would then be ejsvted in the exhust
> > cycle ready for the next injection. I like the idea but think
> > that the running speed would be limited.
>
> I'm glad someone gets it. I'm amazed at the number of replies that show a
> complete misunderstanding of the idea.

New ideas sometimes take time to get.

> No, it doesn't require cooling.

Cooling is the worst thing in the world for a heat engine yes?

> No, it doesn't require high pressure injection: No compression and the
> injected water is NOT boiling.

But here's where all the questions arise:

Without high pressure can you inject sufficient water to generate a useful power stroke?
Won't injecting cold water impact the efficiency of the engine due to thermal cycling?

> Yes, you probably have to increase the surface area inside the cylinder head
> to ensure a rapid transfer of heat.

Se we should be looking at larger displacement engines then?

> Yes, it will turn over slowly, who cares?

I do. If it's possible to double or triple the efficiency by better equalizing
the temp and pressure of the intake water, then it's worth the effort to examine.

> No, preheating the injected water isn't a big deal, just bodge up a heat
> exchanger from copper tubing with the exhaust steam and the intake water.

Actually I was thinking that since this is fact a solar engine, why not simply use
concentrated sunlight to preheat the water. How hard can it be to construct a steel
injection chamber that takes in cool water and has focused sunlight on it? Use a
fresnel lens to concentrate a portion of the light hitting the engine to preheat
the water under pressure. It lessens the thermal cycling of the engine and ensures
that sufficient water for a decent power stroke is injected.

> No, it isn't supposed to be efficient, the sun is free: trash 99% of it but
> get that 1% at very low cost without high pressure danger.

The problem I see is that though it's free there's only a limited amount available
every day to utilize. So if there are ways that are still simple and low cost, and
yet wastes 95% of the sunlight instead of 99%, that's a vast efficiency improvement.

> Sure, a sterling engine would be better, but that isn't the point...

It's not better if it's inaccessible. Or if the efficiency of an accessible engine
is 10 times worse than your setup.

> ...this is cheap, simple, safe, and accessible to the little guy.

As a little guy in this I only have two questions:

How much is it going to cost?
How much electricity can I get out of it?

Any ballpark figures on these?

> Where can I buy a sterling engine right now? How much does it cost?
> Sterlings are pipe dreams.

Any Sterling with useful power requires extemely high pressure and difficult working
fluids. So it's inaccessible.

ICE's and water are extremely accessible. I have water. I have a 3HP Briggs and
Stratton engine from a scrap edger that's been sitting in my basement for the last 3
years. Is it possible to build a useful steam engine from it? It'd sure like to know.

[Snipped the ICE/water discussion]

> Another thing my dad made was a solar powered boiler for energy generation.
> The mirrors were each held by a scrap of sheet metal with the ends bent up
> at the tip and then bent at the center into a V. The mirror was held at the
> top of the V by the bent tips and the bottom was welded to a bit of narrow
> rebar which was then welded to a frame and bent to align the mirror. The
> frame was 12'x12' made from electrical conduit and strengthened by guy wires
> to posts along the central axis.

A Curnutt solar furnace. I can't figure out why 25 years later why every backyard/
rooftop doesn't have one.

> This entire frame was suspended in the air in a cradle that allowed it to
> track the sun. It flexed like all heck, was very heavy and we never did put
> all the mirrors on it.

I'm still thinking that this XenoTech Research idea of using flexible Mylar may
simplify many of those issues:

http://xenotechresearch.com/solvari1.htm

It's little more than an airtight drum with a mylar cover and a vacuum pump to form
a collector. Light, cheap (very cheap), and no mirrors involved.

{Quote hidden}

My gut keeps telling me its better to put the engine on a base below the collector.
Find attached a rough sketch of the idea.

Snippage...

BAJ


part 2 6734 bytes content-type:image/gif (decode)


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2005\09\23@140936 by James Newtons Massmind

face picon face
> > No, it doesn't require high pressure injection: No
> compression and the
> > injected water is NOT boiling.
>
> But here's where all the questions arise:
>
> Without high pressure can you inject sufficient water to
> generate a useful power stroke?
> Won't injecting cold water impact the efficiency of the
> engine due to thermal cycling?

Yes, but that is offset by the reduction in cost of not needed an injector
that can managed high pressure.
http://www.flashsteam.com/L912_Injector.htm is one such device. If memory
serves, he was selling them for $2,000.00

The incoming water can be heated as long as it isn't pressurized past what a
fuel injector can manage. That was why I suggested a heat exchanger with the
outgoing steam pre-heating the incoming water.

> > Yes, you probably have to increase the surface area inside the
> > cylinder head to ensure a rapid transfer of heat.
>
> Se we should be looking at larger displacement engines then?

Possibly. But keep in mind that larger surface area does not necessarily
mean larger displacement. A more convoluted surface can provide more surface
area in the same space. I personally think that the stack of razor blades
would be a good thing to try. Water sprayed down into that should flash
well. It might be possible to use a standard head and mill thin grooves into
the inside of it to approximate that razor blade stack.

> > Yes, it will turn over slowly, who cares?
>
> I do. If it's possible to double or triple the efficiency by
> better equalizing the temp and pressure of the intake water,
> then it's worth the effort to examine.

AFTER getting the thing working at all... Assuming that is possible. I don't
know that this idea will work... I just don't know that it will not work.

But what I really meant by "who cares" was that while this engine may not
(probably will not) be as efficient as other designs, the efficiency isn't
the point. Cost, availability, and safety are. When you have a FREE source
of energy, you don't NEED to be efficient. WANT, sure, but not NEED.

{Quote hidden}

My only concern would be OVER heating the water and boiling it.

> > No, it isn't supposed to be efficient, the sun is free:
> trash 99% of
> > it but get that 1% at very low cost without high pressure danger.
>
> The problem I see is that though it's free there's only a
> limited amount available every day to utilize. So if there
> are ways that are still simple and low cost, and yet wastes
> 95% of the sunlight instead of 99%, that's a vast efficiency
> improvement.

Absolutely. But it seems like people don't want to do anything cheap and
simple if it isn't as good or better than the expensive, complex, caustic,
unsafe, high-pressure, pie in the sky crap that is out of reach. Baby steps.
Start simple.

> > Sure, a sterling engine would be better, but that isn't the
> point...
>
> It's not better if it's inaccessible. Or if the efficiency of
> an accessible engine is 10 times worse than your setup.

Err... I think I agree?

> > ...this is cheap, simple, safe, and accessible to the little guy.
>
> As a little guy in this I only have two questions:
>
> How much is it going to cost?
> How much electricity can I get out of it?
>
> Any ballpark figures on these?

I think both depend on how well stocked your local junk yard is. Old MC
about? Heat exchanger? Spare head? Milling machine? The mirrors are cheap in
any case. Needs something to keep the engine in the focal point. The point,
again, is to do SOMETHING and if it shows any promise at all, do more. If it
doesn't work in any way, scrap it and try something else.

> > Where can I buy a sterling engine right now? How much does it cost?
> > Sterlings are pipe dreams.
>
> Any Sterling with useful power requires extemely high
> pressure and difficult working fluids. So it's inaccessible.

Bingo!

> ICE's and water are extremely accessible. I have water. I
> have a 3HP Briggs and Stratton engine from a scrap edger
> that's been sitting in my basement for the last 3 years. Is
> it possible to build a useful steam engine from it? It'd sure
> like to know.

I have seen a 5HP Briggs converted to steam by my father. Now, this was a
conventional steam engine, not the type we have been talking about here. He
took out the cam shaft, removed the hardening by heating and slowly cooling
it several times. Then he welded or silver soldered extra metal to one side
of the existing lobes and ground the results into the timing he needed for
the valves. I don't have the details on that.

If I had a spare unit like that, I would just vice it, take the spark plug
out, put a torch to the head and spray water from a bottle into the spark
plug hole to see what happens. Err... Wearing a heavy glove of course. If it
makes a nice puff of steam, I'd move on.

Then I might go and buy a fuel injector from the local auto parts place and
see about finding a way to screw it in place of the plug and feed it with
some water from a tank and hose. Then disable the intake valve, move the
engine to just past TDC, heat the head up and spark the injector.

If it turned the crank, even a little, I would work on changing the exhaust
valve timing so that it prevented any compression. And figure out a trigger
for the injector based on TDC.

Somewhere in there, if I had a mill, I would try to increase the surface
area inside the head. Maybe build a shroud to keep more of the torch heat
focused on the head.

It might actually start to run... Or not... Either way, it would be good to
know.

> [Snipped the ICE/water discussion]
>
> A Curnutt solar furnace. I can't figure out why 25 years
> later why every backyard/ rooftop doesn't have one.

A) Safety. Both from the amount of weight that needs to be moving through
the air and from the need to use a high pressure boiler to generate steam.

B) Cost. That is a lot of metal to weld up. If you aren't a welder yourself
and you don't have access to scrap metal, it costs $10k or more and
generates about 4KWh if I remember correctly.

> I'm still thinking that this XenoTech Research idea of using
> flexible Mylar may simplify many of those issues:
>
> http://xenotechresearch.com/solvari1.htm
>
> It's little more than an airtight drum with a mylar cover and
> a vacuum pump to form a collector. Light, cheap (very cheap),
> and no mirrors involved.

It's a very interesting idea. My only concern, and one that has been voiced
by others as well, is the ability to resist wind.

{Quote hidden}

Good idea. My only concerns would be with the extra work involved in
focusing it and with the possibility of heat losses through 2 mirrors. But
if enough heat gets through, who cares?

I really think the thing to do is put the mirrors on the ground. They won't
flex, they won't move, they won't loose focus. Even 1,000 1' square mirrors
can be focused to a 1' square area if they are on stable enough mounts.
Otherwise, you get 1,000 1' square mirrors focused on a 2' area and that
is.... Think about it.... HALF as good. 500 focused to 1 is as good as 1000
focused to 2. So the stability of the mirror mount and the alignment of the
mirrors is more critical than all the existing designs take into account. I
know from experience: You can't get even 144 mirrors focused dead on when
they are mounted to a metal frame that is light enough to move through the
air. It flexes. It bends. It melts very slowly over time. Things happen. The
best thing would be a huge concrete pad poured right on bedrock formed to a
perfect parabola with the mirrors glued in place after adding a little sand
or something to adjust each one to be dead on to the target.

Failing that, a nice hard dirt lot with one edge stuck in the ground and a
good sized, roughly triangular rock to prop them up at the right angle.

Why make it complex? I swear people do that just so they don't have to try.

---
James Newton, massmind.org Knowledge Archiver
spam_OUTjamesTakeThisOuTspammassmind.org 1-619-652-0593 fax:1-208-279-8767
All the engineering secrets worth knowing:
http://techref.massmind.org What do YOU know?




2005\09\23@152936 by Peter

picon face
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On Fri, 23 Sep 2005, Byron A Jeff wrote:

> I think it's time for a subject change too...

Thanks for that.

> Actually I was thinking that since this is fact a solar engine, why not simply use
> concentrated sunlight to preheat the water. How hard can it be to construct a steel
> injection chamber that takes in cool water and has focused sunlight on it? Use a
> fresnel lens to concentrate a portion of the light hitting the engine to preheat
> the water under pressure. It lessens the thermal cycling of the engine and ensures
> that sufficient water for a decent power stroke is injected.

Water requires about 2.2 MJ/kg to boil. There is no way around that. If
you think of the engine in terms of mass flow, it takes about 0.05 kg of
fuel to boil a kg of water in an unspecified amount of time. It also
takes a 1 meter mirror in full sun (1kW) about 37 minutes to boil the
same amount of water (assuming no heat recovery).

So 1 sq. meter of mirror used for an hour will equal ~0.03 kg of fuel
(about 1 oz). You can take this as a base for cost calculations I think.
I don't think that mirror life can be counted on to be longer than 2
years. With 200 days of sun/year and 8 hours of usable sun/day = 3200
mirror hours (not so bad). The fuel equivalent is 96 kg (

{Quote hidden}

I don't think that a 10% efficient (with heat recovery and very high
temperature steam) steam engine is practicable in garage build mode.

{Quote hidden}

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2005\09\23@160836 by Peter

picon face

Oops, the previous message went out unfinished and uncut. Wrong key.
Sorry. Here is the sequel:

Water requires about 2.2 MJ/kg to boil. There is no way around that. If you
think of the engine in terms of mass flow, it takes about 0.05 kg of fuel to
boil a kg of water in an unspecified amount of time. It also takes a 1 meter
mirror in full sun (1kW) about 37 minutes to boil the same amount of water
(assuming no losses in either case).

So 1 sq. meter of mirror used for an hour will equal ~0.03 kg of fuel (about 1
oz). You can take this as a base for cost calculations I think. I don't think
that mirror life can be counted on to be longer than 2 years. With 200 days of
sun/year and 8 hours of usable sun/day = 3200 mirror hours (not so bad). The
fuel equivalent is 96 kg (~36 gallons at density 0.7). At $2.6/gal ~=
$94. Say $100. The equivalent in heating costs is probably half that.
This does not take into account system losses for the sun system, which
are going to be huge.

So assuming the solar system efficiency is 50% (a good figure imho) the
equivalent gas price equivalent of a 1 sq. meter mirror for 200 sun
days/year, 2 years, and 8 hours/day is about $50 over 2 years. If I read
heating costs correctly for USA the bills are about $150/month per
(small) house so $150/month in mirrors would be at least 81 square
meters of sun collectors (about half floor surface of the liveable part
of the house ?) not counting the storage arrangements.

> How much is it going to cost?
> How much electricity can I get out of it?

I don't think that a 10% efficient (with heat recovery and very high
temperature steam) steam engine is practicable in garage build mode,
even if using a burner with fossil fuel.

I also think that using solar for heating makes a lot of sense but using
it for making electricity (at least via steam) is not a good
proposition.

I would think in terms of sun heat + heat storage for heating and
cooling (adsorbtion process) and co-generation for electricity, with the
extra heat from co-generation supplied to the sun system. The fuel for
co-generation will have to be fossil but may be supplemented with
vegetable oil, biogas etc.

I think that efficient electricity generation is reserved for large
plants whoch can afford the hardware to maximize efficiency (I heard
60+% is possible using diesel + steam turbine or gas turbine + steam
turbine).

Peter

2005\09\23@174325 by Peter

picon face

Re: price of mirrors:

According to this site:

http://www.peswiki.com/energy/Directory:Synchronous_Solar_Heliostat

1 sq. yard (~ 1 sq. meter) of mirror is $6.

Peter

2005\09\23@192739 by Peter

picon face

re: moving mirrors

All high efficiency/high temperature systems move the mirrors.

If you want to be cheap you can use 'trough' mirrors (fixed) for
preheating and a single parabolic mirror for the final fun. Although the
major power input is needed at the parabolic mirror.

If you would just switch to another working fluid (other than water),
like propane (at low temp.), nitrogen, CO2 or whatever, it would be much
easier imho. Even welding gas (Ar+He) is interesting.

If you go for efficiency you will have to go for high temperature. There
is no choice imho. Just pick the highest temperature materials you dare
to use and try for it. Either that or use a solar-chemical processes
(like ZnO->Zn + 1/2O @2300K ... Zn(s)+H2O(steam)->ZnO+H2, repeat (add
water vapor, extract hydrogen + oxygen). Obtaining 2300K is going to be
interesting. Small crucibles sold for casting can take almost as much.

Imho, if you boil water, you lose. It's ok to use water, as a gas
(steam). This can be achieved, f.ex., by using a vacuum in the system on
the cold side. Power plants use this.

How hard would it be to make a closed circuit system in which liquid
water is not allowed to circulate (condensate sump at bottom) and a
Rankine cycle is used, with a pump or roots blower recirculating cold
gas (steam) to the heater (hot steam).

Water is great for low temperature systems (up to about 200 deg. C).
After that it becomes impossibly hard to prevent it from destroying the
installation. Power plants have entire divisions concerned with feed
water treatment and hundreds of treatises were written on the theme.
Keeping feed water clean in a small system is a sisyphic enterprise
imho. And even so, who is going to work in the garage with 210at steam
at 350 deg. C ?! Just to drive a point home:

http://www.gcsescience.com/r3.htm

Pick 2nd or 4th from top depending on what your engine is made of.

All I can say is, I hope that the water injection scheme works out.
Against all the numbers. It has happened before.

Peter

2005\09\23@201230 by Byron A Jeff

face picon face
On Fri, Sep 23, 2005 at 11:08:33PM +0300, Peter wrote:
>
> Oops, the previous message went out unfinished and uncut. Wrong key.
> Sorry. Here is the sequel:
>
> Water requires about 2.2 MJ/kg to boil. There is no way around that. If you
> think of the engine in terms of mass flow, it takes about 0.05 kg of fuel
> to boil a kg of water in an unspecified amount of time. It also takes a 1
> meter

m^2 I presume?

0.05 kg of which fuel? Each delivers is different amount of energy per unit.

Natural Gas: 105.5 MJ/therm
Electricity: 3413 MJ/kWh

liquid propane has its own value.

> mirror in full sun (1kW) about 37 minutes to boil the same amount of
> water (assuming no losses in either case).
>
> So 1 sq. meter of mirror used for an hour will equal ~0.03 kg of fuel
> (about 1 oz). You can take this as a base for cost calculations I think. I
> don't think that mirror life can be counted on to be longer than 2 years.

With the mylar sheet on the form I referred to before the replacement cost are
minimal.

Also James pointed out a stability issue. There's no reason such a plant
simply could not be housed to minimize wind effects. Clear polycarbonate
panels are inexpesive and sturdy.

> With 200 days of sun/year and 8 hours of usable sun/day = 3200 mirror hours
> (not so bad). The fuel equivalent is 96 kg (~36 gallons at density 0.7). At
> $2.6/gal ~= $94. Say $100. The equivalent in heating costs is probably half
> that. This does not take into account system losses for the sun system,
> which are going to be huge.

All true. However you are missing the point that the engine also serves as a
heat sink. So it'll retain some of the previous heat energy that was previously
captured. A huge thermal mass will assist in the process of heating the water.

> So assuming the solar system efficiency is 50% (a good figure imho)

Too good.

> the equivalent gas price equivalent of a 1 sq. meter mirror for 200 sun
> days/year, 2 years, and 8 hours/day is about $50 over 2 years.

Again which gas? Is it possible for you to recalculate your figures in MJ?
It's important because the cost of fuel is all over the place. My Natural Gas
price has nearly doubled in a year's time, and it's likely that it'll start
moving toward tripling depending on the damage of Hurricane Rita upon the
refinery and distribution supply from East Texas.

> If I read
> heating costs correctly for USA the bills are about $150/month per
> (small) house so $150/month in mirrors would be at least 81 square
> meters of sun collectors (about half floor surface of the liveable part
> of the house ?) not counting the storage arrangements.

$150/month for electricity? At what time of the year? What rate plan?
Dollars isn't a good measure here. Too variable. What I've been doing is
converting everything to MJ. You also need to take those losses into
effect. Here's an example:

Last winter in December I used 160 therms of natural heating the house.
Each therm produces 105.5 MJ. I'm going to be generous to my furnace and
give it 70 percent efficiency (though at its age, it's really probably 65%).
To equalize cost with electricity I have to know the equivalent number of
kWh that matches up with those therms. Electricity generates 3.6 MJ per kWh.
You can find such figures on pages like this:

http://www.combust.com.au/tips/hottips.htm

Electricity burns with 100% efficiency. So the equivalent amount I would need
is 160(therms)*105.5(MJ/therm)*0.7/3.6(MJ/kWh) = 3282 kWh.

Now we can talk price. And it's all over the place. Currently I'm at the end of
a 12 month contract paying 0.88 USD/therm for Natural Gas. So that 160 therms
right now costs $140.80. But today I'm choking on the price. Fixed rate prices for
the next 12 months are averaging $2.50 a therm! So that same 160 therms would now
cost me $400!

See why you can't compute solely with costs. You need to know the energy requirement.

Now onto electricity (which here in Georgia, USA is a regulated utility). The
price per kWh depends on the time of year and time of day you use it. The
Summer fixed rate is about 9 cents a kWh. However there is a time of use plan
where the price is lowered for off peak usage, and raised very high during peak
usage times. For example from 2-7PM M-F from June to September has a 19 cents/kWh
charge! However in the winter, from October to May, any kWh after the first 650
only costs 5.1 cents/kWh with a fixed extra charge of 2.2 cents/kWh for the first
650.  So let's compare with that number.

0.051$/kWh *3282 kWh = $167.38 + 650*0.022 (fixed charge) = $181.68

So the dollars are meaningless without the MJ behind them.

You can see why I'm purchasing an electric furnace and having it installed.

Also I just got an additional insulation estimate today. I hope I don't choke on
it when I get it next week. I may have to blow it in myself.

{Quote hidden}

That didn't answer the questions. But let's take a stab at it. Full Sun is
1 kW/m^2. Say we get 5 percent efficiency. so we get 50W/m^2. A reasonable
collect is about 3 m on a side. So we can collect 9 m^2 and concentrate it
on the engine. So in full sun we can expect to get 450W of power. With 5 full
sun hours per day the engine can produce 2.25 kWh of power per day.

Anemic. Solar space heating is a much better bet.

James, this is why efficiency is important. If we can get the efficiency up
we can get useful power during the time that the sun is out.

{Quote hidden}

I'm looking at this because I know that next summer I'll be facing 19 cents/kWh
costs at certain times. Any useful output I can get from solar during those times
would help.

My game plan there is to build a battery charge bank. I'll charge the batteries
during off peak hours, and use that charge during peak hours. The off peak price
is 2.5 cents cheaper than the regular price of electricity (6.5 cents/kWh vs.
9 cents/kWh) while the 19 cents/kWh is flat off the chain.

Any solar electrical supplement would help. I'm wondering about concentrated solar
onto a PV panel now.

BAJ

2005\09\23@223149 by William Chops Westfield

face picon face

On Sep 23, 2005, at 5:12 PM, Byron A Jeff wrote:

>> it takes about 0.05 kg of fuel to boil a kg of water in an
>> unspecified amount of time.
>
>
> 0.05 kg of which fuel?
> Each delivers is different amount of energy per unit.
>
Not really.  All the hydrocarbons are approximately CH2(n) and
deliver significantly similar amounts of energy per gram.  Coal
(pure C, sorta), hydrogen (pure H) and more complex fuels (wood)
may be signficantly different, but they're not that common as "fuels"

BillW

2005\09\24@025545 by Peter

picon face

apropos cogeneration turbine (probably not cheap):

http://www.microturbine.com/technology/index.asp

Peter

2005\09\24@030240 by Russell McMahon

face
flavicon
face
>>> it takes about 0.05 kg of fuel to boil a kg of water in an
>>> unspecified amount of time.

>> 0.05 kg of which fuel?
>> Each delivers is different amount of energy per unit.

> Not really.  All the hydrocarbons are approximately CH2(n) and
> deliver significantly similar amounts of energy per gram.  Coal
> (pure C, sorta), hydrogen (pure H) and more complex fuels (wood)
> may be signficantly different, but they're not that common as
> "fuels"


Extracted from various place in my "energy" file with no attempt to
give them context.

There are a few contradictory figures here but overall it gives a
reasonable indication.

Hydrogen is king :-)
Ethanol has over 25% more energy per than Methanol but is well down on
liquid hydrocarbon fuels.
Anthracite is better than alcohols (but really hard on the injectors).
Interestingly, diesel is notably higher in energy content than petrol
(depending which of my 'data' you believe :-( ) -  and is far cheaper
per volume in this country than petrol - and "super" petrol is
slightly lower in energy content than standard grade ie octane rating,
which relates to resistance to compression ignition, and energy
content are not well correlated,



   RM

________________________________

Propane         12.9 kWh/kg  7.5 kWh/l
LPG gives 14 KWH/Kg
LPG             27 MJ/l
Petrol          35
Diesel          46
Mobil petrol    Gross calorific value
       91      47.5 MJ/Kg
       96      47   MJ/Kg      = 13 KWH

Fuel           Btu/lb  cal/g =?Joule

Petrol          20500   11400
Kero            20000   11200
Diesel          19000   10500
Alcohol         11500    6400
Hydrogen        61000  ~34000


               kJ/kg
Carbon          32780
Hydrogen       142017   39.45 kWh/kg        <-- !!!!!!
CO              10111
Methane         55533
Ethane          51923
Propane         50402
n-Butane        49593
isoButane       49476
n-Pentane       49067
isoPentane      48955
neoPentane      48795
n-Hexane        48767
Ethylene        50325
Propylene       48958
n-Butene        48506
isoButene       48324
n-Pentene       48195
Benzene         42296
Toluene         43033
Xylene          43382
Acetylene       50014
Napthalene      40247
Methyl Alcohol  23860
Ethyl Alcohol   30612
Ammonia         22485


     Energy Content   Heat of Vaporization   Oxygen Content
             Net MJ/kg          MJ/kg                   wt%
Methanol        19.95             1.154                  49.9
Ethanol         26.68             0.913                  34.7
MTBE            35.18             0.322                  18.2
ETBE            36.29             0.310                  15.7
TAME            36.28             0.323                  15.7
Gasoline       42 - 44            0.297                   0.0

Typical values for commercial fuels in megajoules/kilogram are [37]:-

                             Gross        Net

Hydrogen                      141.9       120.0
Carbon to Carbon monoxide     10.2          -
Carbon to Carbon dioxide      32.8          -
Sulfur to sulfur dioxide      9.16          -
Natural Gas                   53.1         48.0
Liquified petroleum gas       49.8         46.1
Aviation gasoline             46.0         44.0
Automotive gasoline           45.8         43.8
Kerosine                      46.3         43.3
Diesel                        45.3         42.5

Lignite         8  - 10 Mj/kg  70% moisture     > 40,000 yrs
Black Coal      24 - 28 MJ/kg   3% moisture     65-1-5 M yrs
Anthracite      32      MJ/kg

               yrs are "received" age.

2005\09\24@034133 by Peter

picon face

Sorry for replying out of thread, I do not use a threaded mail reader
and I get digests in the evening normally.

Re: fuel heat value I used in calculation: I used gasoline which is
rated at 45 MJ/kg and priced as of yesterday in Texas (average about
$2.6/gal), according to the web. I assumed that the cost of other fuels
would be cheaper since gas is considered very expensive now.

Re: cost of heating $150/month: this is a figure I got from several
discussions wrt heating costs on the web, for the last year (2004), for
somewhere in the central US afair, using kerosene I think. It may be
double now. I was just trying to get some numbers.

Re: mylar mirror: The vacuum formed mirror is not really new but its
efficiency is only 0.8 or so afaik. You can make a better mirror using
the spun cast method or by using a dish as a former for a fiberglass or
composite concrete copy. The mirror you make need not be round (pita to
handle), it can be a rectangle inscribed in the mold or a petal
(triangle as above). That way you lose some surface but the thing is
much easier to make, handle and array.

The problem with the parabolic shape proposed is, you cannot make an
array from them (the focal point is way too close). So it turns out that
just taking plain glass mirrors (at $6 / sq. meter if what I read was
true) and warping them slightly in a frame (they will warp anyway) will
yield something closer to the 10 meter focal distance needed for an
array. Then the secondary mirror can be on a pole, and IT can be
hyperbolic (using a parabolic dish as casting form and mirroring the
'wrong' side), and the target on the ground and fixed, where you can get
at it.

Imho the bad news with the array is, the mirrors need to move. The good
news is that arrays scale. You can start with 2 mirrors and increase to
50 later. The bad news is that a moving linear array is subject to cos
phi/2 losses and that the mirrors shade each other beyond a relatively
small sun angle (say 45 degrees). But the time of useful sun is only
about 6-8 hours per day and at that angle cos phi/2 loss is <15%.

Peter

2005\09\24@053647 by Tim ODriscoll

flavicon
face
On Fri, 2005-09-23 at 20:12 -0400, Byron A Jeff wrote:
> Any solar electrical supplement would help. I'm wondering about concentrated solar
> onto a PV panel now.

If you took a 1m^2 PV panel and used 2x 1m^2 sun-tracking mirrors to
focus the sun onto it, would that not be a cheaper way to double the
output of the PV panel than just buying another PV panel?

I suppose the PV panel's aren't designed for that much sunlight, and
might not like the heat..

2005\09\24@054541 by Peter

picon face

Apropos Stirling (small), how about this set up in the focal point of a
solar collector ? :

http://www.bekkoame.ne.jp/~khirata/gallery/special1.gif

from:

http://www.bekkoame.ne.jp/~khirata/english/gallery.htm

If it's not obvious, it is a one-cylinder displacer-less Stirling (or
Newcomen) engine. The 'displacer' is the shutter that can shield the
burner flame from the hot part.

Then there are NASA closed oscillating Stirlings (I think that one could
try to build a low tech version using pistons and cylinders from a car
engine):

http://www.grc.nasa.gov/WWW/tmsb/stirling.html

(click on the drawing to see the animation)

(off topic: now, who was hating the grassmowing chore ? ;-)

http://www.evatech.net/

Peter

2005\09\24@071908 by Russell McMahon

face
flavicon
face
****
A very useful rule of thumb is that a well designed and built air
based Stirling engine using typical burner temperatures can deliver
around 0.5 watt/ atmosphere/cc. ie a 1 litre engine running at 10
atmospheres could be expected to produce 0.5 x 1000 x 10 = 5 kW.
5 kW/litre is "modest" by most IC engine standards but the 1 litre
cylinder is far less challenging than a 1 litre IC engine.
****

{Quote hidden}

All such designs are fun but of very low specific power output and low
efficiency. To get good efficiency and power from a Stirling engine
you have to work hard and smart. For high Carnot efficiency you need
high temperature. For high delivered  % of Carnot efficiency but not
necessarily high power density attention to all aspects of the
regenerator and all the other obvious things is required. For power
density you need suitable gas (essentially Hydrogen or Helium) and
high pressures. Air Stirling at modest pressures is entirely doable
BUT the engine will be very low lowered for its size compared to
typical internal combustion engines.



> Then there are NASA closed oscillating Stirlings (I think that one
> could try to build a low tech version using pistons and cylinders
> from a car engine):
>
> http://www.grc.nasa.gov/WWW/tmsb/stirling.html

More

       http://www.grc.nasa.gov/WWW/tmsb/stirling/doc/lrgfp.html

12.5 kW. Helium. 1050K hot. 15 MPa operating (about 2000 psi).
Non contact seals (important).

20% overall efficiency.
(Carnot efficiency is 50% so tghis is 40% of Carnot which is good).


10 watt radioisotope powered Stirling with 14,000 hours running time.
James would be right at home with this one :-)

       http://www.grc.nasa.gov/WWW/tmsb/stirling/doc/smlrsg.html

Some of this material may be a little dated ;-)

       http://www.grc.nasa.gov/WWW/tmsb/stirling/doc/codes.html

   HFAST is written in Microsoft FORTRAN. For engine performance
calculations it requires several seconds on an IBM 286 type desk-top
computer that has 1 MB of RAM. For engine design optimization, which
could require several hundred performance calculations, a 386 or 486
type desk top computer would be more convenient.




       RM

2005\09\24@080034 by Peter

picon face

According to this article:

http://solstice.crest.org/renewables/dish-stirling/chapter1/concentrators.html

"With current technologies, a 5-kWe dish/Stirling system requires a dish
of approximately 5.5 meters (18 feet) in diameter, and a 25-kWe system
requires a dish approximately 10 meters (33Jfeet) in diameter."

Assuming a garage built amateur system would be 1/10th as efficient it
means ~0.5kWe from a 6 meter dish at probably 1/100 of the cost of a
commercial system (which is in the $300k range for this size as I can
see ?).

Aside: One can buy a ready built and tested ready to go Stirling motor
that generates 500We for EUR5000 right now. At 19 cents per kW (~EUR
0.15) it would break even after less than 72k hours ? I think that it
would be realistic for a garage built one of the same size to make
250We, and cost less than EUR1000 to make (hours of work not counted).
Then it would have to run for 25k hours (~3 years) to break even with
electricity at $0.19/kWh ? (again the calculation above does not account
for the mirrors and maintenance and installation cost).

Peter

2005\09\24@081810 by Howard Winter

face
flavicon
picon face
Russell,

On Sat, 24 Sep 2005 19:01:16 +1200, Russell McMahon wrote:

>...<
> Extracted from various place in my "energy" file with no attempt to
> give them context.
>
> There are a few contradictory figures here but overall it gives a
> reasonable indication.
>
> Hydrogen is king :-)

And completely pollution free!

> Ethanol has over 25% more energy per than Methanol but is well down on
> liquid hydrocarbon fuels.
> Anthracite is better than alcohols (but really hard on the injectors).

LOL!  When I was a kid we had an anthracite boiler in the kitchen - it used bean-sized pieces that fed down
from a hopper "automatically".  The main maintenance item was removing the clinker, which formed a
pancake-sized mass, every coupld of days.  Otherwise just topping up the hopper was all that was needed.

> Interestingly, diesel is notably higher in energy content than petrol
> (depending which of my 'data' you believe :-( ) -  and is far cheaper
> per volume in this country than petrol

Sadly not everywhere - it used to be a lot cheaper here, but it's now a few pence a litre more expensive than
ordinary petrol.

> - and "super" petrol is  slightly lower in energy content than standard grade ie octane rating,
> which relates to resistance to compression ignition, and energy
> content are not well correlated,

A lot of people don't realise that - the octane rating is nothing to do with the power produced.  In the days
when we had four "star" ratings of petrol, from about 91 to 101 octane, some people would use higher grades
then they needed because they thought it was more powerful, or did the car good in some way!  In fact you
should use the lowest grade that will run happily (without "pinking" or detonation).

Cheers,



Howard Winter
St.Albans, England


2005\09\24@091425 by Byron A Jeff

face picon face
On Sat, Sep 24, 2005 at 10:36:46AM +0100, Tim ODriscoll wrote:
> On Fri, 2005-09-23 at 20:12 -0400, Byron A Jeff wrote:
> > Any solar electrical supplement would help. I'm wondering about concentrated solar
> > onto a PV panel now.
>
> If you took a 1m^2 PV panel and used 2x 1m^2 sun-tracking mirrors to
> focus the sun onto it, would that not be a cheaper way to double the
> output of the PV panel than just buying another PV panel?

Yes. The only problems are...

> I suppose the PV panel's aren't designed for that much sunlight,

Actually they will produce more power with more light. However,

> and  might not like the heat..

And this is big time. The efficiency of PV panels drop precipitously
when heated. They need to be cooled to be effective.

The more I think about it, I believe that every house needs to have
a couple of watertight cisterns built below them. There's so so much
you can do with huge tanks of water. For example with the PV panels
you could heat exchange with cool water during the day heating up a
tank, then at night when the ambient temp cools, you could radiate the
heat back into the night air cooling the water for the next day.
Of course you could get all of the hot water you ever wanted from such
a system and possible even get water based radiant heat in the winter.

But you need a huge tank of water to do it.

BAJ

2005\09\24@093153 by Russell McMahon

face
flavicon
face
> Then it would have to run for 25k hours (~3 years) to break even
> with electricity at $0.19/kWh ? (again the calculation above does
> not account for the mirrors and maintenance and installation cost).


Or night time :-)
Make that more like 12 years :-(.


       RM

2005\09\24@094647 by Byron A Jeff

face picon face
On Sat, Sep 24, 2005 at 10:41:28AM +0300, Peter wrote:
>
> Sorry for replying out of thread, I do not use a threaded mail reader
> and I get digests in the evening normally.

No worries.

> Re: fuel heat value I used in calculation: I used gasoline which is
> rated at 45 MJ/kg and priced as of yesterday in Texas (average about
> $2.6/gal), according to the web. I assumed that the cost of other fuels
> would be cheaper since gas is considered very expensive now.

Weight of a gallon? Let me see if I can find it...

5.8 to 6.5 lbs. Let's take the average of 6.1 lbs.

2.2 lbs/kg so 6.1 lbs is 2.77 kg
2.77 kg *45 MJ/kg is 125 MJ rounded up.

So gas is in the same ballpark as natural gas in terms of both MJ (125 MJ vs.
105.5 MJ) and cost ($2.60 USD/gallon vs $2.50 USD/therm)

A "therm" worth of electricity is a shade over 29 kWh. And the burning efficiency
of a kWh is virtually 100 percent, whereas the extremely high efficiency gas
only approaches 90% (with the rest going up the flue). So it actually takes 11%
more gas to produce the same amount of heat energy as an equivalent amount of
electricity. So the corresponding "therm" for electricity is actually only 26.1 kWh
as comparated to a high efficiency gas furnace.

So compare the cost of a gallon of gas, a therm of natural gas, and a "therm"
of electricity costwise:

gas: $2.60
NG:  $2.50
electricity: 26.1 kWh * $0.051/khW = $1.33

It's a no brainer!

> Re: cost of heating $150/month: this is a figure I got from several
> discussions wrt heating costs on the web, for the last year (2004), for
> somewhere in the central US afair, using kerosene I think. It may be
> double now. I was just trying to get some numbers.

Probably triple from last year. So take that $150/month and make it $450/month and
you're in the right ballpark.

> Re: mylar mirror: The vacuum formed mirror is not really new but its
> efficiency is only 0.8 or so afaik.

I'm going to invoke James here: I'm willing to sacrifice some efficiency for low
cost and ease of setup.

> You can make a better mirror using
> the spun cast method or by using a dish as a former for a fiberglass or
> composite concrete copy.

Cost? Complexity?

> The mirror you make need not be round (pita to
> handle), it can be a rectangle inscribed in the mold or a petal
> (triangle as above). That way you lose some surface but the thing is
> much easier to make, handle and array.

No doubt.

> The problem with the parabolic shape proposed is, you cannot make an
> array from them (the focal point is way too close). So it turns out that
> just taking plain glass mirrors (at $6 / sq. meter if what I read was
> true) and warping them slightly in a frame (they will warp anyway) will
> yield something closer to the 10 meter focal distance needed for an
> array.

Why 10m?! I actually wanted a much closer focal point. That simplifies
tracking everything. Coordinating a mirror array and then a target that's
30 ft away is a daunting task. An ideal focal box would be 2-3m from the
center of the array.

> Then the secondary mirror can be on a pole, and IT can be
> hyperbolic (using a parabolic dish as casting form and mirroring the
> 'wrong' side), and the target on the ground and fixed, where you can get
> at it.

Again I was planning on tracking the target too, moving the whole assembly from
east to west during the day. I agree with James that tracking individual
mirror elements is way more complex than having a fixed mirror array that
tracks as a single unit.

> Imho the bad news with the array is, the mirrors need to move.

Bingo!

>The good  news is that arrays scale.

But the complexity scales too because the mirrors must track individually
right? Or can each mirror be fixed in such a way that you can track an
entire linear row with a single motor? Or am I missing something?

> You can start with 2 mirrors and increase to
> 50 later.

That's why I wanted to go with the mylar. You build the whole assembly
once as a single unit.

>The bad news is that a moving linear array is subject to cos
> phi/2 losses and that the mirrors shade each other beyond a relatively
> small sun angle (say 45 degrees). But the time of useful sun is only
> about 6-8 hours per day and at that angle cos phi/2 loss is <15%.

Complexity is a killer here. A backyard setup has to be simple to be
effective, even if that simplicity causes some losses.

Tracking a single big mirror along with a target that tracks with the
mirror is much less complex than tracking a wide array of individual
mirrors. That's why Curnutt style furnances are a fixed array of mirrors
with the whole assembly tracking the sun. The current Sunflower technology
uses some type of gimbal arrangement where all 25 mirrors of the array are
individually tracked using only a couple of motors. But it's complex.
And complex leads to breakdowns.

BAJ

2005\09\24@112338 by Peter

picon face

Dr. BAJ said:

>> I (Peter) said:
>>
>> The problem with the parabolic shape proposed is, you cannot make an
>> array from them (the focal point is way too close). So it turns out
>> that just taking plain glass mirrors (at $6 / sq. meter if what I
>> read was true) and warping them slightly in a frame (they will warp
>> anyway) will yield something closer to the 10 meter focal distance
>> needed for an array.
>
>Why 10m?! I actually wanted a much closer focal point. That simplifies
>tracking everything. Coordinating a mirror array and then a target
>that's 30 ft away is a daunting task. An ideal focal box would be 2-3m
>from the center of the array.

If you use the fixed mirror on a pole and target below it scheme then
you need that kind of focal distance.

Because of the distance from the pole required, the moving mirrors will
need to have a large focal distance (10 meters or more). This is easily
done by taking a plain glass flat mirror and simply attaching a suction
cup on the back and pulling it out with one or a few kgf. The equivalent
glued (epoxied) assembly would be your individual moving mirror. The
mirror will not be parabolic but it will likely be much better than
mylar experiments (my limited experience with mylar is not goot. It has
to be fixed on something very rigid which tends to be heavy).

>> Then the secondary mirror can be on a pole, and IT can be hyperbolic
>> (using a parabolic dish as casting form and mirroring the 'wrong'
>> side), and the target on the ground and fixed, where you can get at
>> it.
>
>Again I was planning on tracking the target too, moving the whole
>assembly from east to west during the day. I agree with James that
>tracking individual mirror elements is way more complex than having a
>fixed mirror array that tracks as a single unit.

In your opinion, what is easier to build, 10 or 100 or 1000 individual
identical mirrors weighing less than 50kg each freestanding or attached
to a simple pole driven into the ground, which can be individually made,
one at a time (one per weekend ?), or a third of a ton of parabolic
mirror with attached assorted hardware such as a generator, a condenser,
wiring and whatnot, which needs to be pointed to 2 degrees precision in
2 dof in despite of wind and structure bending, and requires a small
construction crew and good weather to put up and get down.

>The good  news is that arrays scale.
>
>But the complexity scales too because the mirrors must track
>individually right? Or can each mirror be fixed in such a way that you
>can track an entire linear row with a single motor? Or am I missing
>something?

You can track the entire row with 1 motor but you probably do not want
to. A small ~2W servo per mirror would do the job fine imho. Maybe even
a usual model servo with the pot removed and attached to a sector gear
made @home.

A model servo produces about 42 oz*in. If geared down to 1:100 with a
simple worm gear (threaded rod + rough cut gear in mild steel sheet) it
would make 3 kg*m which is likely enough to point an aerodynamically
balanced 1 meter square mirror in calm weather (assuming a nice bearing
such as hollow-axle-and-steel-ball). The sector gear would be about 200
mm radius half circle, easily made even by hand. Of course it would have
to be able to take 300kgf at the rim (and so would the worm gear and its
bearings) but this is not impossible.

>> You can start with 2 mirrors and increase to
>> 50 later.
>
>That's why I wanted to go with the mylar. You build the whole assembly
>once as a single unit.

And limit its power for good.

{Quote hidden}

Talking of breakdowns, what happens if you want to modify something on a
big rig ? Call in construction crews ? Crane truck ?

The small-moving-mirror system seems to be favored by all the systems
that are in current use or experimentation. Even if several mirrors are
removed or faulty the array continues to work.

Peter

2005\09\24@124407 by Peter

picon face

Here is a new twist on the Rankine cycle that may change things to the
better:

http://www.dself.dsl.pipex.com/MUSEUM/POWER/ammonia/ammonia.htm

look up 'Kalina cycle'.

Peter

2005\09\24@133452 by Peter

picon face


> And completely pollution free!

Afaik burning hydrogen in air is not good. You get ammonia, nitric
oxides, hno3 ...

Peter

2005\09\24@133735 by Peter

picon face


On Sat, 24 Sep 2005, Byron A Jeff wrote:

>> You can make a better mirror using
>> the spun cast method or by using a dish as a former for a fiberglass or
>> composite concrete copy.
>
> Cost? Complexity?

Making a large fiberglass mirror (or antenna) is no harder than making a
boat. In fact it is easier. Once you have the form (the satelitte dish)
it's easy.

Peter

2005\09\24@154122 by Byron A Jeff

face picon face
On Sat, Sep 24, 2005 at 06:23:35PM +0300, Peter wrote:
>
> Dr. BAJ said:
>
> >>I (Peter) said:
> >>
> >>The problem with the parabolic shape proposed is, you cannot make an
> >>array from them (the focal point is way too close). So it turns out
> >>that just taking plain glass mirrors (at $6 / sq. meter if what I
> >>read was true) and warping them slightly in a frame (they will warp
> >>anyway) will yield something closer to the 10 meter focal distance
> >>needed for an array.
> >
> >Why 10m?! I actually wanted a much closer focal point. That simplifies
> >tracking everything. Coordinating a mirror array and then a target
> >that's 30 ft away is a daunting task. An ideal focal box would be 2-3m
> >from the center of the array.
>
> If you use the fixed mirror on a pole and target below it scheme then
> you need that kind of focal distance.

Which kind of focal distance? 2-3m or 10m?

>
> Because of the distance from the pole required, the moving mirrors will
> need to have a large focal distance (10 meters or more). This is easily
> done by taking a plain glass flat mirror and simply attaching a suction
> cup on the back and pulling it out with one or a few kgf. The equivalent
> glued (epoxied) assembly would be your individual moving mirror. The
> mirror will not be parabolic but it will likely be much better than
> mylar experiments (my limited experience with mylar is not goot. It has
> to be fixed on something very rigid which tends to be heavy).

The mylar pulled by a vacuum isn't fixed on anything. That's exactly why
it's lightweight.

{Quote hidden}

Alex, I'll take door number three: An easily and cheaply constructed mylar
vacuum mirror housed in a transparent polycarbonate structure. View this image
to get an idea: http://www.suntuf.com/images/Suntufgreenhousehobby.jpg

The structure handles the wind deflection while allowing the vast majority of
the sunlight in to the mirror.

Also tracking doesn't have to be perfect. I'll bet a perfectly fine job could be
done open loop simply by knowing the day of year, time of day, and latitude
of the location.

Also there's nothing to say that you cannot have multiple smaller mylar/vacuum
mirrors tracking to a single target. Or even better each tracking with it's
own PV panel or generator, all housed in a single building.

I understand why you would want to componetize the project. But there's
much more complexity in synchronizing a bucketful on individual small
elements than 1 larger element.

[Servo tracking snipped]

> >>You can start with 2 mirrors and increase to
> >>50 later.
> >
> >That's why I wanted to go with the mylar. You build the whole assembly
> >once as a single unit.
>
> And limit its power for good.

There are still options. Build a bigger mirror unit. Add a second mirror.
It's scalable in larger chunks.

{Quote hidden}

I can handle a 4'x8' sheet of plywood by myself. So an 8'x8' which can collect
nearly 5 m^2 of sunlight wouldn't require a crane. And it would concentrate
about 4500W of power onto the target.

> The small-moving-mirror system seems to be favored by all the systems
> that are in current use or experimentation. Even if several mirrors are
> removed or faulty the array continues to work.

I'm clear on that. but I take issue with the complexity.

The Phoenix Turbine builder guys took on the parabolic form project. They
describe how to build a 9 ft parabola using fiberglass
reinforced plastic. It takes a couple of weeks and weighs less than 200 lbs
when done. The pages are here:

phoenixnavigation.com/ptbc/articles/ptbc37.htm
phoenixnavigation.com/ptbc/articles/ptbc39.htm
phoenixnavigation.com/ptbc/articles/ptbc40.htm
http://phoenixnavigation.com/ptbc/articles/ptbc41.htm

Here is the numbers for their example dish:

"For our 108" dish, with an FD of 0.357 and a radius of 54 inches, the Focal Point
will be 38.51 inches, and dish depth is 18.91 inches."

As far as I'm concerned, that's perfect.

Once the concrete form is developed, one can make up an extra dish in a week
or so. While a difficult task to be sure, it isn't impossible. Nor does it have
to be perfect. Two or three of these bad boys could make a serious dent in
the electrical budget for a house. And unless I miss my guess, electricity is
going to go up in price just like every other form of energy that petrol
based.

BAJ

2005\09\24@174531 by Byron A Jeff

face picon face
On Sat, Sep 24, 2005 at 07:44:00PM +0300, Peter wrote:
>
> Here is a new twist on the Rankine cycle that may change things to the
> better:
>
> www.dself.dsl.pipex.com/MUSEUM/POWER/ammonia/ammonia.htm
>
> look up 'Kalina cycle'.

This post got me to wandering all day. I ended up at a Yahoo group on
solar AC. Had an interesting article that ties up everything we've
been talking about:

http://groups.yahoo.com/group/solar-ac/message/44

In short a turbine that is powered by lower temp ammonia steam that
turns ice cold as is spins the turbine. Medium level solar heat
steams the ammonia, and the residual cold can be used to cool
a space. Electricity and cold air! What a combo!

BAJ

2005\09\24@175510 by Denny Esterline

picon face
> > And completely pollution free!
>
> Afaik burning hydrogen in air is not good. You get ammonia, nitric
> oxides, hno3 ...

And let's not forget about the _production_ of the hydrogen, it's not like
we can just suck it out of the air.

The only current LARGE scale production method is to reform natural gas -
this process not only takes energy (high temp operation) but also produces
more CO2 than burning the natural gas directly. (all of the carbon is
converted to CO2 plus the energy needed to heat the reaction)

Electrolysis is fine, until you consider where the electricity comes from.
Sure PV panels can make electricity without emitting unpleasant byproducts,
until you consider the processes used to make them. It's been a while since
I've done the research, but the last numbers I seen indicated that a PV cell
would have to operate for something like 100 years to recoup 'real' costs
competing with current utility rates. ('real' costs remove the effect of
various tax incentives and industry subsidies) Sure utility rates are going
to rise during that time, which does alter those calculations. But if
utility rates do rise, so will the cost to manufacture PV cells.

Of course you could use Nuke, but we know how much everybody loves that
idea. <grin>

And recall that Hydrogen is the smallest of all the elements, when
compressed it leaks right through the sides of the tank. The best tanks
currently available have about a thirty day half life. Yes Hydrogen does
have more energy per unit mass, but compressed Hydrogen has about 1/4 the
energy per volume of liquid hydrocarbon fuels. So to maintain a comparable
range, a Hydrogen automobile will need a fuel tank four times as large as
they currently have, plus it needs to be a stronger tank because it has to
hold compressed gas- so it'll be heavier. And yes, you can store Hydrogen as
a cryogenically cooled liquid, but maintaining those temperatures takes some
energy too.

And what about safety? Since hydrogen is odorless and colorless, it'd be
necessary to add an artificial scenting agent so people can detect leaks,
right? (they already add methyl mercaptan (CH3SH) to natural gas and
propane) Problem is even in _extremely_ small concentrations sulfur will
destroy the proton exchange membrane in a fuel cell in a matter of hours. In
fact at this point there are NO suitable odorants to use in hydrogen
systems.

There are _serious_ flaws in the proposed "Hydrogen Future", and nobody
seems to be talking about them. They might be solvable, but I'm not holding
my breath.

<end unscheduled rant, I now return you to your previously scheduled
PICLIST>

-Denny

2005\09\24@185409 by Dave Tweed

face
flavicon
face
On Sat, Sep 24, 2005 at 06:23:35PM +0300, Peter wrote:
> Dr. BAJ said:
> > >I (Peter) said:
> > >
> > >The problem with the parabolic shape proposed is, you cannot make an
> > >array from them (the focal point is way too close). So it turns out
> > >that just taking plain glass mirrors (at $6 / sq. meter if what I
> > >read was true) and warping them slightly in a frame (they will warp
> > >anyway) will yield something closer to the 10 meter focal distance
> > >needed for an array.
> >
> > Why 10m?! I actually wanted a much closer focal point. That simplifies
> > tracking everything. Coordinating a mirror array and then a target
> > that's 30 ft away is a daunting task. An ideal focal box would be 2-3m
> > from the center of the array.
>
> If you use the fixed mirror on a pole and target below it scheme then
> you need that kind of focal distance.

There's no need to warp individual mirrors; in fact, in some ways it's
counterproductive.

As long as the heat-collecting area on the engine is about the same size
as any individual mirror, just have the flat mirror reflect its particular
patch of sunlight onto the collector without focusing it. The light
intensity at the collector will still be multiplied by the number of
mirrors.

If the mirror itself has a particular focus, then the axis alignment
between the mirror and the collector must be maintained as the mirror
tracks the sun. With a flat mirror, this becomes a don't-care, and each
mirror can be independently steered by a simple heliostat.

-- Dave Tweed

2005\09\24@193816 by Jinx

face picon face
> tracks the sun. With a flat mirror, this becomes a don't-care,
> and each mirror can be independently steered by a simple
> heliostat

Like a solar furnace ?

http://www.amasci.com/amateur/mirror.html

I've seen the one in New Mexico. A large array of flat mirrors
reflect sunlight onto a collector up a tower. Very very hot

I remember seeing a sewage treatment method using something
similar. The sewage or other waste water is loaded with titanium
dioxide (the pigment in white paint) and run through a transparent
pipe. Solar reflectors heat the water and also bombard it with a
very high dose of UV. At the end of the pipe-line the TiO2 is
filtered out, leaving potable water

2005\09\25@070340 by Jinx

face picon face
> And recall that Hydrogen is the smallest of all the elements,
> when compressed it leaks right through the sides of the tank

Isn't it stored as metal hydride ? I'm sure I saw an alpine train
that ran in, of all places, remote parts of Peru (it was in one of
the BBC series Great Train Journeys)

2005\09\25@074842 by Dave Tweed

face
flavicon
face
Jinx <.....joecolquittKILLspamspam@spam@clear.net.nz> wrote:
> I wrote:
> > tracks the sun. With a flat mirror, this becomes a don't-care,
> > and each mirror can be independently steered by a simple
> > heliostat
>
> Like a solar furnace ?
>
> http://www.amasci.com/amateur/mirror.html

Actually, I was thinking more along the lines of Solar One/Solar Two
near Barstow, CA, scaled down a bit.

  http://www.nrel.gov/docs/fy01osti/28751.pdf

I also remember the high temperature solar furnaces you're thinking of,
in particular, the one in Odeillo, France:

  http://www.imp.cnrs.fr/foursol/1000_en.shtml

But those are two-stage systems -- a sea of flat heliostats are used to
feed parallel rays to a true (fixed) parabolic reflector in order to
achieve the very highest temperatures. Way overkill for simple power
conversion.

-- Dave Tweed

2005\09\25@075401 by Denny Esterline

picon face
> > And recall that Hydrogen is the smallest of all the elements,
> > when compressed it leaks right through the sides of the tank
>
> Isn't it stored as metal hydride ? I'm sure I saw an alpine train
> that ran in, of all places, remote parts of Peru (it was in one of
> the BBC series Great Train Journeys)

Yes, it can be stored as a hydride. But that's less than ideal too. You
still have volumetric density issues, added mass of the metal, energy
required to seperate the hydride, etc. Research contiues on all fronts, but
we're far from there yet.

-Denny

2005\09\25@081947 by Jake Anderson

flavicon
face
actually as i understand it the hydride basically acts as a sponge.
eg NIMH batteries.
the hydride is "brewed" to a certain pressure and when the pressure of H is
above that point it will absorb gas, and when its below that level it will
release gas. Whats more it will do it slowly so in the event of a case burst
you will still only wind up with a stream of H rather than a bang.

if you believe the manufacturers you can get about the same volumetric
efficency as liquid hydrogen with the hydrides, however that isnt saying
much ;->.

> {Original Message removed}

2005\09\25@143004 by Peter

picon face

On Sat, 24 Sep 2005, Dave Tweed wrote:

{Quote hidden}

Yes but flat mirrors are not flat in the context of 10+ meter target
distances. They always warp. So it is better to warp them in the
concentrating direction. I have some experience with this.

> If the mirror itself has a particular focus, then the axis alignment
> between the mirror and the collector must be maintained as the mirror
> tracks the sun. With a flat mirror, this becomes a don't-care, and each
> mirror can be independently steered by a simple heliostat.

It is more economical to use a polar mount and just rotate the mirrors
on an axis. The other axis needs to move only once every two weeks for a
parabolic mirror (much less often for flat mirrors).

Maybe BAJ is right and the mylar foil device is the way to go for a
start.

Peter

2005\09\25@143008 by Peter

picon face

On Sat, 24 Sep 2005, Byron A Jeff wrote:

>> If you use the fixed mirror on a pole and target below it scheme then
>> you need that kind of focal distance.
>
> Which kind of focal distance? 2-3m or 10m?

10+m

> The mylar pulled by a vacuum isn't fixed on anything. That's exactly why
> it's lightweight.

I know. You can make a small one using a large aluminium wok fitted with
a bicycle valve (backwards) and a regular survival blanket. Without a
bicycle valve you poke a tiny hole in the mylar, suck and then quickly
tape the hole over. The mirror will double as a thermometer, barometer,
and microphone, but it will work in a way.

> Alex, I'll take door number three: An easily and cheaply constructed mylar
> vacuum mirror housed in a transparent polycarbonate structure. View this image
> to get an idea: http://www.suntuf.com/images/Suntufgreenhousehobby.jpg

Ok, you win. Anyway you will build this ;-)

> Also tracking doesn't have to be perfect. I'll bet a perfectly fine job could be
> done open loop simply by knowing the day of year, time of day, and latitude
> of the location.

Depending on the mirror gain and imprefection that won't work. The
higher the gain of the mirror, the more accurate the tracking needs to
be.

I think that you have to work backwards. Find the energy density and
temperature you can afford on your target thing and work backwards to
the number of 'suns' you can put on it without melting something
important.

It may be that you will be able to work with only 2-3 suns. For example
consider a normal electric heater plate, often rated 2kW, about 30cm
diameter. It would be equivalent with a 2m^2 mirror but with a
concentration factor of about 28x by surface (1.6 meter diameter
mirror). A 1.6 meter mirror that makes a 30cm diameter spot is very
rough as mirrors go.

Since you need to test the generator anyway, why not take such a heater
plate, and put your generator on it. Since you know the electrical input
to the plate you will be able to estimate the efficiency of the
generator without building any mirrors and without going outside. How
does this sound ?

> I understand why you would want to componetize the project. But there's
> much more complexity in synchronizing a bucketful on individual small
> elements than 1 larger element.

> The Phoenix Turbine builder guys took on the parabolic form project. They
> describe how to build a 9 ft parabola using fiberglass
> reinforced plastic. It takes a couple of weeks and weighs less than 200 lbs
> when done. The pages are here:

...

> "For our 108" dish, with an FD of 0.357 and a radius of 54 inches, the Focal Point
> will be 38.51 inches, and dish depth is 18.91 inches."
>
> As far as I'm concerned, that's perfect.

Ok. But you can start today if you have a wok or a hotplate. See above.
The hotplate will be only 1/3 of your 108" output but it may be a good
start to find out what the generator can do (not a lot if you do not go
very very hot).

If yo can do with a longer focal distance you can use a large saucepan
instead of the wok ;-)

Peter

2005\09\25@143013 by Peter

picon face

On Sun, 25 Sep 2005, Jake Anderson wrote:

> actually as i understand it the hydride basically acts as a sponge.
> eg NIMH batteries.
> the hydride is "brewed" to a certain pressure and when the pressure of H is
> above that point it will absorb gas, and when its below that level it will
> release gas. Whats more it will do it slowly so in the event of a case burst
> you will still only wind up with a stream of H rather than a bang.

If you ever worked with H2 in a flame/burner context you will know that
there is no such thing as a 'very small hydrogen leak' and that each and
every ignition comes with a bang unless you are using a feather touch on
the tap. The flammability limits are between 1% and 95% or such (I do
not remember the exact numbers) and it ignites at ~200 degrees C.
Acetylene comes second best on this scale, and it is *much* more
forgiving than H2 with handling. A hot lightbulb or a soldering iron is
enough to set off H2 even without catalysts which occur naturally (f.ex.
in paint and cigarette ashes) and static electricity.

People who work with lead acid and NiCd liquid electrolyte batteries can
probably tell you horror stories about 'small hydrogen accumulations'
in enclosed spaces (even ventilated).

Peter

2005\09\25@152108 by Wouter van Ooijen

face picon face
>> Hydrogen is king :-)
> And completely pollution free!

Is that true? When any fuel is burned with air NOx is produced. I don't
know whether the amount produced when burning H2 is significant, but
unless you use O2 it won't be zero.

Wouter van Ooijen

-- -------------------------------------------
Van Ooijen Technische Informatica: http://www.voti.nl
consultancy, development, PICmicro products
docent Hogeschool van Utrecht: http://www.voti.nl/hvu


2005\09\25@231419 by Peter

picon face

On Sat, 24 Sep 2005, Byron A Jeff wrote:

> On Sat, Sep 24, 2005 at 07:44:00PM +0300, Peter wrote:
>>
>> Here is a new twist on the Rankine cycle that may change things to the
>> better:
>>
>> www.dself.dsl.pipex.com/MUSEUM/POWER/ammonia/ammonia.htm
>>
>> look up 'Kalina cycle'.
>
> This post got me to wandering all day. I ended up at a Yahoo group on
> solar AC. Had an interesting article that ties up everything we've
> been talking about:
>
> http://groups.yahoo.com/group/solar-ac/message/44
>
> In short a turbine that is powered by lower temp ammonia steam that
> turns ice cold as is spins the turbine. Medium level solar heat
> steams the ammonia, and the residual cold can be used to cool
> a space. Electricity and cold air! What a combo!

There is no magic involved. First when you input heat at the mirror, you
get no heat output or input at the turbine if correctly designed (the
best expansion for power output is adiabatic) and heat output at the
condenser. If the turbine overexpands then it will cool down at the
expense of output power. What you can do, is to arrange for the turbine
to drive a blower that will create suction and evaporate more ammonia
from a *different* evaporator than the one heated by the mirror and do
some real cooling. This will probably work much better than generating
electricity. I think that the suction of the compressor can be used for
this too. Maybe an old automotive turbocompressor will start something
wonderful in a propane dual circuit ?

I think that an automotive turbo has almost the right proportions for
use in a solar powered Brayton cycle. It is designed to work with hot
air, the volumetric and pressure ratio is about right for a reasonably
efficient homemade parabolic sun collector (i.e. Tturbine inlet~=500+
deg C and Tcompressor inlet=ambient).

A small turbo from a ~65hp engine, preferrably from a Diesel, will
probably handle 10kW without problems using just air as working fluid.

I just looked here:

www.turbocalculator.com/compressor-maps/t3-40.jpg
(parent: http://www.turbocalculator.com/map-t3.php?img=t3-40&turbo=Garett%20T3%2040%20Trim)

That's a ~20kW thermal engine that could be up to ~30% efficient for
under $300 if used with T1=~270 degC air, T2=~30 degC air (water cooled)
at ~0.08 kg/sec mass flow, 1:1.8 pressure ratio (I assume that the input
and output pressure ratios are almost identical), and about 100,000 rpm.
20kW comes from mass flow times 1005J/kg*K times delta-T. Removing the
heat from the cooler would require less than 0.5l/sec of water with 10
degrees C across the cooler. 20kW from the sun would probably be a
single 5 x 5 meter parabolic reflector (requiring at least 10 meters of
focal distance - hehehe - this number keeps coming back). I am pretty
sure that 1kW or more electrical could be extracted from this without
trouble. Some work required [tm]. I really want to see the steam engine
that competes with this even on paper. I think that it's more realistic
to run it with a higher pressure and temperature ratio for more power
(e.g. 400 degrees C and 1:2.2 at ~25kW). It's 5AM here, I am going to
sleep.

Other:

1. You can model your thermodynamic cycle using suitable software.
F.ex.:

       http://www.qrg.northwestern.edu/software/software.htm

worth reading:

       http://www.qrg.northwestern.edu/thermo/design-library/airstd/brayton.html

2. The French engineer who first used Ammonia pressure from ammonia
boiled in large flat sun collectors on this roof, more than 100 years
ago, to run a water pump did not use a concentrator at all. If you say
that you do not care about efficiency then you have to use a large
surface anyway. So no mirrors, just conventional sun collectors (as used
for hot water) and a low boiling point liquid to transport the heat and
run it through a small engine or turbine, and go for low cost (and
flammable or toxic roof, depending on whether you use ammonia or
propane as working fluid - oops).

3. What would happen if you would use a Rankine cycle that would use a
power turbine and sun collectors to boil a suitable temp. liquid in the
daytime to make power & cooling and an electric compressor to liquefy it
back in the nighttime (at 9 cents/kW). How big would it have to be to
run for 8 hours and what fluid would work best.

Peter


2005\09\26@021018 by James Newtons Massmind

face picon face
> Making a large fiberglass mirror (or antenna) is no harder
> than making a boat. In fact it is easier. Once you have the
> form (the satellite dish) it's easy.


Actually...

That is sort of interesting....

What if you could get a hold of a nice big satellite dish? With the mount
and all....


Hummm....

Those things can't flex much and still get a good signal to the feed horn.


---
James.

2005\09\26@022050 by James Newtons Massmind

face picon face
> If you ever worked with H2 in a flame/burner context you will
> know that there is no such thing as a 'very small hydrogen
> leak' and that each and every ignition comes with a bang
> unless you are using a feather touch on the tap. The
> flammability limits are between 1% and 95% or such (I do not
> remember the exact numbers) and it ignites at ~200 degrees C.
> Acetylene comes second best on this scale, and it is *much*
> more forgiving than H2 with handling. A hot lightbulb or a
> soldering iron is enough to set off H2 even without catalysts
> which occur naturally (f.ex.
> in paint and cigarette ashes) and static electricity.

This is worth quoting and repeating. The hydrogen future is a freaking JOKE.

It is being used to kill off reasonable solutions with current technology.

Nuke plants would be a safer option if only because the people at the plant
have some respect for the danger of the system. Handing each of the people
on he freeway a bottle of hydrogen is my worst nightmare. Honestly, gasoline
is much safer than Hollywood has convinced most people.

---
James.


2005\09\26@023620 by James Newtons Massmind

face picon face
> I think that an automotive turbo has almost the right
> proportions for use in a solar powered Brayton cycle. It is
> designed to work with hot air, the volumetric and pressure
> ratio is about right for a reasonably efficient homemade
> parabolic sun collector (i.e. Tturbine inlet~=500+ deg C and
> Tcompressor inlet=ambient).

A solar collector could defiantly generate those sorts of temp in air. The
trick might be finding a good way of contain the air and still allowing the
heat to transfer... I don't know much about super high temp heat exchange.

> A small turbo from a ~65hp engine, preferably from a Diesel,
> will probably handle 10kW without problems using just air as
> working fluid.

Easy to find in a junkyard.

> I just looked here:
>
> www.turbocalculator.com/compressor-maps/t3-40.jpg
> (parent:
www.turbocalculator.com/map-t3.php?img=t3-40&turbo=Garett%20T3%2040%2
0Trim)
>
> That's a ~20kW thermal engine that could be up to ~30%
> efficient for under $300 if used with T1=~270 degC air,
> T2=~30 degC air (water cooled) at ~0.08 kg/sec mass flow,
> 1:1.8 pressure ratio (I assume that the input and output
> pressure ratios are almost identical), and about 100,000 rpm.

So two heat exchangers (one high temp and one low), a source of water, a
nice fat mirror, the turbo and an air compressor?

> 20kW comes from mass flow times 1005J/kg*K times delta-T.
> Removing the heat from the cooler would require less than
> 0.5l/sec of water with 10 degrees C across the cooler.

Easy.

{Quote hidden}

Wait! No! Think about this one some more...

>          
> www.qrg.northwestern.edu/thermo/design-library/airstd/brayton.html
>

That is REALLY interesting... I wonder if anyone has built something like
this...

<SNIP>


> 3. What would happen if you would use a Rankine cycle that
> would use a power turbine and sun collectors to boil a
> suitable temp. liquid in the daytime to make power & cooling
> and an electric compressor to liquefy it back in the
> nighttime (at 9 cents/kW). How big would it have to be to run
> for 8 hours and what fluid would work best.

You mean like boil water all day and keep it in an insulated tank, then
release the pressure at night to turn the generator?

---
James.


2005\09\26@060057 by Alan B. Pearce

face picon face
>> If you use the fixed mirror on a pole and target below
>> it scheme then you need that kind of focal distance.
>
>There's no need to warp individual mirrors; in fact, in
>some ways it's counterproductive.
>
>As long as the heat-collecting area on the engine is about
>the same size as any individual mirror, just have the flat
>mirror reflect its particular patch of sunlight onto the
>collector without focusing it. The light intensity at the
>collector will still be multiplied by the number of mirrors.
>
>If the mirror itself has a particular focus, then the axis
>alignment between the mirror and the collector must be
>maintained as the mirror tracks the sun. With a flat mirror,
>this becomes a don't-care, and each mirror can be
>independently steered by a simple heliostat.

How about an idea on a possible increase in efficiency?

While reading this I pondered on the efficiency loss of having the parabolic
mirror heating the engine directly. However this also means that the far
side - the side in shadow - will have to be heated by thermal conduction
around the cylinder head, and in the process be robbing some of the
temperature increase the lit side has, and actually radiating the heat.

Now if the engine can be moved a touch closer to the mirror than the focus
point, so that some of the energy input is shone over the top onto another
mirror that reflects it onto the side otherwise in shade, then surely the
overall conversion efficiency will rise.

2005\09\26@062430 by Peter

picon face

It is really necessary to read most of what is out there wrt mirrors and
sun power (himemade):

http://www.redrok.com/electron.htm#led3x

sun trackers, parabolic and not, with water boiler, stirling in focal
point and all that. No turbocharger though ;-)

The 'high temperature' assembly for the hot air exchanger of a
turbocharger sun-fired device should be possible to assemble by brazing
if the device will not become hotter than 700 degrees C (at least not at
the welds). It only needs to keep 2 to 3 bars of pressure, less than in
a car tyre. I am fairly sure it can be done.

Peter

2005\09\26@072431 by Byron A Jeff

face picon face
On Mon, Sep 26, 2005 at 06:14:10AM +0300, Peter wrote:
{Quote hidden}

I think I need to be wapped with a clue stick. I just took a look at the
Brayton cycle engine at this NASA site:

http://www.grc.nasa.gov/WWW/K-12/airplane/brayton.html

There's a combustor in the middle of it. What exactly are we proposing
to burn? Or are we simply leaving that stage out and turning the
turbine by expanded hot air?

{Quote hidden}

Now that looks like a winner!

> It's 5AM here, I am going to sleep.

You deserve it!

BAJ

2005\09\26@080211 by Russell McMahon

face
flavicon
face
>> That's a ~20kW thermal engine that could be up to ~30% efficient
>> for
>> under $300 if used with T1=~270 degC air, T2=~30 degC air (water
>> cooled)

That's about 68% of Carnot efficiency.
   Carnot = (270-30)/(270+273) = 44%
   30/44 = 68.2%

Murphy tends to have bad things to say about people trying to achieve
such high efficiencies :-(

Also, effective cold temperature is usually rather higher than the
cooling source. 30 C cold air is achievable but only with close
attention to cold side heat exchanger design.


       RM

2005\09\26@095419 by Peter

picon face

Must read study:

http://www.eng.tau.ac.il/~kribus/Publications/STIMGen-JSEE-02.pdf

Peter

2005\09\26@130039 by Peter

picon face

On Sun, 25 Sep 2005, James Newtons Massmind wrote:

>> 1:1.8 pressure ratio (I assume that the input and output
>> pressure ratios are almost identical), and about 100,000 rpm.
>
> So two heat exchangers (one high temp and one low), a source of water, a
> nice fat mirror, the turbo and an air compressor?

What air compressor ? The turbo has a turbine and an air compressor, yes
? And they are setup at almost the right ratio for this kind of work,
excepting for the different density of exhaust vs. intake air in a
normal IC engine (exhaust is about 20-30% denser if complete combustion
occurs afaik).

> Wait! No! Think about this one some more...

I love support. Next time get closer and keep the coffee IV going ...

{Quote hidden}

Yes but NOT water. Something else that can be heated more with better
efficiency at low temperature. And you extract the power in the daytime
when the temperature difference is large. Exmaple:

You have a pool. You have an unused roof space (shaded, insulated). You
put pressure vessels (gas cylinders) in the roof space and in the pool
(under water, at the bottom). You set up an electric pump that can pump
cold high pressure vapor or liquid from the cylinders in the pool to
even higher pressure liquid (cooled after it exits the compressor) in
the roof space. The pump will run at night when electricity is cheap and
turn most of the vapor and liquid from the tanks in the pool into cold
liquid at high pressure under the roof. You set up a solar collector and
furnace and a turbine (or piston engine) with a generator to take high
pressure cold liquid from the roof cylinders during sun time, boil it,
and expand generating power (and overexpand generating cold for cooling
the house) during the daytime. The exhaust from the turbine/engine goes
to the cold cylinders in the pool and stays there until night comes and
then the cycle repeats.

It is a closed circuit system that extracts heat from the sun sinking it
into the pool, and uses regeneration powered by cheap electricity. Since
it provides cold and power it can probably replace the airconditioner
and run most house appliances during the daytime.

On cold days some of the cold liquid (likely propane) would be burned in
a heater where the solar furnace is and run the turbine in the daytime.
Or the cycle could be reversed to extract heat from the water in the
pool by just changing the pressure in the system (low pressure in the
pool cylinders = heat absorbtion from the pool water).

In fact if you have two pools you could put all the cylinders in the
pools. Or bury one set. Etc etc. It's all about using the available
energy to the maximum $/J efficiency.

Peter

2005\09\26@131655 by Peter

picon face

On Mon, 26 Sep 2005, Byron A Jeff wrote:

>> I (Peter) wrote:
>>
>> There is no magic involved. First when you input heat at the mirror, you
>> get no heat output or input at the turbine if correctly designed (the
>> best expansion for power output is adiabatic) and heat output at the

Correction: The best cycle for mechanical output seems to be Ericsson
(isothermal expansion or Brayton + extra heat exchanger, aka
regenerator).

> I think I need to be wapped with a clue stick. I just took a look at the
> Brayton cycle engine at this NASA site:
>
> http://www.grc.nasa.gov/WWW/K-12/airplane/brayton.html
>
> There's a combustor in the middle of it. What exactly are we proposing
> to burn? Or are we simply leaving that stage out and turning the
> turbine by expanded hot air?

We are talking about a closed circuit Brayton cycle using air (maybe
with the oxygen removed by running it over hot charcoal somewhere in the
circuit) where an automotive turbogenerator's turbine is used to extract
power and the compressor to push the fluid back, through a solar heated
furnace on the hot side, and a water cooled radiator on the cold side.
Maybe converted to Ericsson by adding another heat exchanger between
turbine output and compressor output (If I got it right).

>> that competes with this even on paper. I think that it's more realistic
>> to run it with a higher pressure and temperature ratio for more power
>> (e.g. 400 degrees C and 1:2.2 at ~25kW).
>
> Now that looks like a winner!

Only if it works. Anyway it would cost less than half to build, compared
to what a 500 Watt Stirling costs (5000 EUR).

I have been thinking some more about it. I think that a normal
automotive exhaust manifold could be used as the hot part heat exchanger
somehow. It would mate perfectly with the turbine inlet. That could take
care of the high temp. seal which is a problem anyway.

Peter

2005\09\26@133558 by Peter

picon face

On Mon, 26 Sep 2005, Russell McMahon wrote:

>>> That's a ~20kW thermal engine that could be up to ~30% efficient for
>>> under $300 if used with T1=~270 degC air, T2=~30 degC air (water cooled)
>
> That's about 68% of Carnot efficiency.
>   Carnot = (270-30)/(270+273) = 44%
>   30/44 = 68.2%
>
> Murphy tends to have bad things to say about people trying to achieve such
> high efficiencies :-(

Yes but going for 30% thermal is reasonable imho. I referred to 30%
thermal and 1kWe out from 25kW thermal (= 4% thermal input to electrical
out). For rough comparison a 3.5hp motor generator has about 1.5-2kWe
out but will consume more than 0.5kg of fuel per hour (at 45MJ/kg =
25MJ, and about 12% efficient). The 20kW sun thing would input 72MJ/hour
so the generator set is probably 3x more efficient than the sun turbine.
I don't think that there is anything majorly wrong with my calculations.
Literature quotes small turbines in similar conditions (with T1=1100K)
at 15% efficiency (thermal in to electrical out). Claiming one third of
that is probably not exaggerated.

> Also, effective cold temperature is usually rather higher than the cooling
> source. 30 C cold air is achievable but only with close attention to cold
> side heat exchanger design.

There is no limit to its size though, and it is water cooled. You'd use
an automotive radiator or an air conditioner heat exchanger in a box
probably, with water in the pipe and turbine exhaust in the air circuit,
mounted inside a 200l drum. It need not be airtight, the low pressure
part would run at slightly above atomsphere and the intake of the
compressor slightly below. That would put the turbine where it 'feels'
best.

Peter

2005\09\26@155917 by James Newtons Massmind

face picon face
> Only if it works. Anyway it would cost less than half to
> build, compared to what a 500 Watt Stirling costs (5000 EUR).

I would be willing to help defer the cost of a test Brayton cycle system.

> I have been thinking some more about it. I think that a
> normal automotive exhaust manifold could be used as the hot
> part heat exchanger somehow. It would mate perfectly with the
> turbine inlet. That could take care of the high temp. seal
> which is a problem anyway.

Could you use the radiator as the cold side heat exchanger? Pour water over
it as the air is pushed through the inside where the water usually goes.

Think about how cool it would be to make this entire rig from the remains of
a turbo charged car or truck with a blown engine.

---
James.


2005\09\26@231644 by Byron A Jeff

face picon face
On Mon, Sep 26, 2005 at 08:16:53PM +0300, Peter wrote:
{Quote hidden}

The only problem I see is that an exhaust manifold isn't designed to heat gas
though hot gas goes through it. For this project to work there would need to
be an efficient "air burner" that's the target for the solar collector. A high
temp evaporated tube passing air through it is something along the right lines.
Or using a flat steel plate (18in x 18in x 1in) with tubes drilled through it.

I think I see the cycle now. Starting at the solar collector transfer plate:

1) Air is heated at the solar collector transfer plate.
2) Hot air is blown through the turbine.
3) The turbine exhaust is coupled to the compressor intake.
4) The compressor compresses the air and creates positive air pressur through the
  system.
5) The exhaust from the compressor is passed through a radiator circulating cold
  water. Or using a car intercooler that's dipped in a cold water bath.
  This is the waste heat transfer giving us useful hot water out while cooling the
  air out of the turbocharger.
6) The cool air cycles back around to step #1.

Close to the mark?

Any idea of the temp and pressure that the turbine inlet is expecting?

Also I gotta ask again: are you sure that steam is out of reach? The conversion from
water to steam will give a huge expansion giving a lot of pressure to drive the
turbine.

BAJ

2005\09\27@065024 by Michael Rigby-Jones

picon face


>-----Original Message-----
>From: piclist-bouncesspamKILLspammit.edu [.....piclist-bouncesKILLspamspam.....mit.edu]
>Sent: 27 September 2005 04:17
>To: Microcontroller discussion list - Public.
>Subject: Re: [OT] Solar Steam Engines...
>
>
>Also I gotta ask again: are you sure that steam is out of
>reach? The conversion from water to steam will give a huge
>expansion giving a lot of pressure to drive the turbine.

But you have to put in a huge amount of energy to start with!

Mike

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2005\09\27@074916 by Russell McMahon

face
flavicon
face
> ... Anyway it would cost less than half to build, compared to what a
> 500 Watt Stirling costs (5000 EUR).

Why?
People seem to want to dismiss Stirling engines for all sorts of
reasons but most seem to be based on false impressions or uncertain
assumptions. What it costs to BUILD a 500 watt Stirling engine is
quite different from what it presently costs to buy one. The
difference between cost and selling prices includes such factors as
marketing, suitability for niche markets which will tolerate higher
profit margins and the consequent "what the market will bear"
costings. If you are making say 10% profit then if you double the
selling price you can afford to sell somewhere around only 10% as much
before you lose money. Fixed costs, volume sensitive costs, size of
plant and many other factors apply but as a general rule, for a niche
market product the true cost of production is quite different from the
selling cost. It's only when you get a highly competitive commodity
market that the two approach each other closely. (The invisible hand
at work :-) ).

So: The same would apply to any other engine you built. The Whispergen
may be the basis for that statement about cost. I greatly doubt that
it *costs* E5000 to build a Whispergen. There is nothing overly magic
about Stirlings or arcane in their engineering, as long as you don't
want high volumetric power density. In the applications being
discussed here that's not a requirement.


       RM

2005\09\27@080154 by Byron A Jeff

face picon face
On Tue, Sep 27, 2005 at 11:43:17PM +1200, Russell McMahon wrote:
> >... Anyway it would cost less than half to build, compared to what a
> >500 Watt Stirling costs (5000 EUR).
>
[Snipped to the chase]

> There is nothing overly magic
> about Stirlings or arcane in their engineering, as long as you don't
> want high volumetric power density. In the applications being
> discussed here that's not a requirement.

Russell,

Do you have any pointers to real Stirling designs? Almost everything I have
seen is a toy, or an ad. The one real engine that I saw, using a Briggs and
Stratton mower engine, only had pictures. There were no design specs or
power output descriptions.

The theory makes sense: have a hot and cold side. Heat fluid to the hot side
pushing a power piston. The displacer moves the hot air to the cold side
pulling the piston back in.

What I need to some design that I can point concentrated sunlight to and
get some results. I can finally see that using a car turbocharger and
intercooler. The only missing number is the turbine inlet pressure.

Ideas?

BAJ

2005\09\27@080537 by Byron A Jeff

face picon face
On Tue, Sep 27, 2005 at 11:50:14AM +0100, Michael Rigby-Jones wrote:
>
>
> >-----Original Message-----
> >From: EraseMEpiclist-bouncesspam_OUTspamTakeThisOuTmit.edu [piclist-bouncesspamspam_OUTmit.edu]
> >Sent: 27 September 2005 04:17
> >To: Microcontroller discussion list - Public.
> >Subject: Re: [OT] Solar Steam Engines...
> >
> >
> >Also I gotta ask again: are you sure that steam is out of
> >reach? The conversion from water to steam will give a huge
> >expansion giving a lot of pressure to drive the turbine.
>
> But you have to put in a huge amount of energy to start with!

I understand that. But a 1500 to 1 expansion you can extract some
real power from that energy.

With a 3m diameter mirror it's possible to get over 1000C of
sunlight concentrated into a relatively small spot. It is possible
to create enough steam to drive a TC from it? What if we preheated
the inlet water?

The energy is cheap. The question is can we gather enough of it
to generate enough steam to drive a TC?

BAJ

2005\09\27@082321 by Michael Rigby-Jones

picon face


{Quote hidden}

You can't measure energy input in degrees C though.  I'm sure it has probably been covered at least once in this thread, though I haven't read it all, but how much energy can you realisticly expect from a 3m mirror on a sunny day?

Heating the inlet water will help a tiny bit, but the vast majority of the energy is taken in converting water in steam(i.e. the latent heat of vaporization), especialy if it's under pressure (which of course it will have to be to do any usefull work).

Regards

Mike

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2005\09\27@103151 by Dave Tweed

face
flavicon
face
Byron A Jeff <TakeThisOuTbyronEraseMEspamspam_OUTcc.gatech.edu> wrote:
> Do you have any pointers to real Stirling designs? Almost everything I
> have seen is a toy, or an ad. The one real engine that I saw, using a
> Briggs and Stratton mower engine, only had pictures. There were no design
> specs or power output descriptions.

Have you ever seen the WhisperGen, from Christchurch, NZ? Seems real
enough.

  http://www.whispergen.com/

4-cylinder Sterling engine producing 1200W of AC power on natural gas,
or 800W of DC power on diesel/kerosene. Up to 8000W of waste heat
available for domestic hot water or general heating needs.

-- Dave Tweed

2005\09\27@144331 by Peter

picon face

On Mon, 26 Sep 2005, James Newtons Massmind wrote:

>> Only if it works. Anyway it would cost less than half to
>> build, compared to what a 500 Watt Stirling costs (5000 EUR).
>
> I would be willing to help defer the cost of a test Brayton cycle system.
>
>> I have been thinking some more about it. I think that a
>> normal automotive exhaust manifold could be used as the hot
>> part heat exchanger somehow. It would mate perfectly with the
>> turbine inlet. That could take care of the high temp. seal
>> which is a problem anyway.
>
> Could you use the radiator as the cold side heat exchanger? Pour water over
> it as the air is pushed through the inside where the water usually goes.

That is not good for flow resistance reasons. The radiator was optimised
to work in a certin way. It is best to use it like that.

> Think about how cool it would be to make this entire rig from the remains of
> a turbo charged car or truck with a blown engine.

If you manage to refurbish the bearings on the turbo it should be
doable. The exhaust manifold and the turbo with the respective piece of
exhaust tubing will likely be the most important parts to salvage,
together with the water pump (if it comes off the block), and maybe the
oil pump (messy). If the turbo has an intercooler then take that too,
together with all the air and oil tubing that connects to it. Finding
hoses and clamps that fit fittings on equipment manufactured in a far
away country is a big pita ime.

Peter

2005\09\27@150712 by Peter

picon face

On Mon, 26 Sep 2005, Byron A Jeff wrote:

>> Only if it works. Anyway it would cost less than half to build, compared
>> to what a 500 Watt Stirling costs (5000 EUR).
>>
>> I have been thinking some more about it. I think that a normal
>> automotive exhaust manifold could be used as the hot part heat exchanger
>> somehow. It would mate perfectly with the turbine inlet. That could take
>> care of the high temp. seal which is a problem anyway.
>
> The only problem I see is that an exhaust manifold isn't designed to heat gas
> though hot gas goes through it. For this project to work there would need to
> be an efficient "air burner" that's the target for the solar collector. A high
> temp evaporated tube passing air through it is something along the right lines.
> Or using a flat steel plate (18in x 18in x 1in) with tubes drilled through it.

I made a drawing and you can see it here (thanks to James for putting it
up - I have yet to learn how to use the piclist system):

http://www.piclist.com/techref/member/plp-actcom-f00/sun-turbo-1.htm

The manifold is optimised in many ways and perfectly mates with the
turbo inlet. I would suggest most of its branches to be capped off with
lids, glass wool insulation of 1-2 inches wrapped around it, and an
inset tube welded to a holed flange put in. The inset tube would be the
blackbody of the sun target, through a hole in the flange that bolts it
on the manifold. The air from the compressor would enter through another
of the flanges and run between the inside tube and the wall of the
manifold to heat up, with several circuits until it would exit towards
the turbine. It will pass something like 0.08 m^3/second on the cold
side and 2-3 times as much on the hot side.

> Any idea of the temp and pressure that the turbine inlet is expecting?

> Also I gotta ask again: are you sure that steam is out of reach? The conversion from
> water to steam will give a huge expansion giving a lot of pressure to drive the
> turbine.

Conversion of water to steam gives not 'a lot' of expansion but exactly
as predicted by steam tables. To get out power you have to use high
temperature. The characteristics of steam are such that at the same
700-800K where the automotive turbo will work with 2-3bar, steam needs
210+ bar. This means that the boiler, the turbine, and the feed pump
must take 210bars continuous. Nobody I know has the technology to work
with 210bar steam in the garage, even if not at 700K. Even 40 bars is
too much for most 'home use' equipent. If you feel courageous obtain a
scuba tank and use it to power your turbine or generator (very
dangerous - you cannot blame me if you get hurt).

Steam is good to use for a certain range of combustion temperatures
where the pressure does not become excessive and where it can do a good
job (at low efficiency).

Power stations that use steam at high temperature have complicated and
dangerous installations constantly purifying the water in the circuit,
adding chemicals like Hydrazine (poison!) to remove oxygen. Any oxygen
in the circuit will instantly convert the innards of the equipment into
high quality rust, when combined with steam at 700+K.

Peter

2005\09\27@152019 by Peter

picon face

On Tue, 27 Sep 2005, Russell McMahon wrote:

>> ... Anyway it would cost less than half to build, compared to what a 500
>> Watt Stirling costs (5000 EUR).
>
> Why? People seem to want to dismiss Stirling engines for all sorts of
> reasons but most seem to be based on false impressions or uncertain
> assumptions. What it costs to BUILD a 500 watt Stirling engine is
> quite different from what it presently costs to buy one. The
> difference between cost and selling prices

I don't want to dismiss anything but the turbo has a potential of 20:1
Watts/$. My reference price and power was from here:

http://www.geocities.com/Viebachstirling/

Pages are in German.

> includes such factors as marketing, suitability for niche markets which will
> tolerate higher profit margins and the consequent "what the market will bear"
> costings. If you are making say 10% profit then if you double the selling
> price you can afford to sell somewhere around only 10% as much before you
> lose money. Fixed costs, volume sensitive costs, size of plant and many other
> factors apply but as a general rule, for a niche market product the true cost
> of production is quite different from the selling cost. It's only when you
> get a highly competitive commodity market that the two approach each other
> closely. (The invisible hand at work :-) ).

I agree 100% but getting things done implies not disregarding the W/$
ratio. I was unable to find a better deal for a Stirling on the Internet
(better than $10/W, as in the Vierbach linked to above). It may well
turn out that the turbine will cost more. A better figure of merit would
be Wh/$ considering engine life. E.g. a new Vierback will be EUR5000 but
a new turbine once everything else is in place will be $300.

It is clear to me that at this time this is a wasteful experiment. But
someone has to start somewhere and who knows where it will lead.

Peter

2005\09\27@153101 by Peter

picon face

Russell, all:

The correct spelling is of course Viebach and not Vierbach. The 5000EUR
price is for completed Viebach motors (built from kits):

http://www.uwemoch.de/

Peter

2005\09\27@154337 by James Newtons Massmind

face picon face
Try and purchase one.

What is the mean time between failure?

Sterlings are a pipe dream.


Solar steam or hot air turbine engines are at least accessable NOW.


---
James.



> {Original Message removed}

2005\09\27@154709 by James Newtons Massmind

face picon face
> 210+ bar. This means that the boiler, the turbine, and the feed pump
> must take 210bars continuous. Nobody I know has the
> technology to work with 210bar steam in the garage, even if
> not at 700K. Even 40 bars is too much for most 'home use'
> equipent. If you feel courageous obtain a scuba tank and use
> it to power your turbine or generator (very dangerous - you
> cannot blame me if you get hurt).

I totally agree with Peter here. EXTERNAL, high pressure, steam is
dangerous.

That is the point of the internal flash boiler idea I was presenting: That
it only has a LITTLE steam and it is all INSIDE the cylinder of the engine.
The high pressure is contained and exists only for the power stroke, just as
in a standard gasoline engine.
http://www.massmind.org/idea/mc-heat-inject.htm

This hot air turbo generator is much nicer. Low(er) pressures all around,
nothing but hot air to vent (although that may be somewhat dangerous) and
commonly available engine parts in all cases.
http://www.piclist.com/techref/member/plp-actcom-f00/sun-turbo-1.htm

This is NOT a pipe dream: Although it might not work, both of these ideas
are such that any fairly well equipped home garage with some time and money
can test them and report what the problems or promise of the ideas actually
are.

I presented a series of steps that I would follow to test the internal flash
engine idea:

If I had a spare unit like that, I would just vice it, take the spark plug
out, put a torch to the head and spray water from a bottle into the spark
plug hole to see what happens. Err... Wearing a heavy glove of course. If it
makes a nice puff of steam, I'd move on.

Then I might go and buy a fuel injector from the local auto parts place and
see about finding a way to screw it in place of the plug and feed it with
some water from a tank and hose. Then disable the intake valve, move the
engine to just past TDC, heat the head up and spark the injector.

If it turned the crank, even a little, I would work on changing the exhaust
valve timing so that it prevented any compression. And figure out a trigger
for the injector based on TDC.

Somewhere in there, if I had a mill, I would try to increase the surface
area inside the head. Maybe build a shroud to keep more of the torch heat
focused on the head.

It might actually start to run... Or not... Either way, it would be good to
know.

Notice that this totally ignores the solar collector which is a separate
problem with many different possible solutions.

What sort of "baby steps" could be used to test the hot air turbo system?
Could a turbo be connected with tubing and a propane torch on the hot side
and an ice pack on the cold side? What is the minimum requires to see ANY
movement even without real power generation?

---
James Newton, massmind.org Knowledge Archiver
RemoveMEjamesspamTakeThisOuTmassmind.org 1-619-652-0593 fax:1-208-279-8767
All the engineering secrets worth knowing:
http://techref.massmind.org What do YOU know?


2005\09\27@171211 by Byron A Jeff

face picon face
On Tue, Sep 27, 2005 at 10:07:14PM +0300, Peter wrote:
{Quote hidden}

WOW!

One element you are missing is the turbocharger lubrication system. You'll
need an oil pump setup too.

{Quote hidden}

Can you describe where these items would fit using an example manifold?
Here's a large image here:

http://www.brit.ca/~tboicey/mgparts/pics/exhaust_manifold-1.jpg

{Quote hidden}

That's not possible. I understand.

> Nobody I know has the technology to work
> with 210bar steam in the garage, even if not at 700K. Even 40 bars is
> too much for most 'home use' equipent. If you feel courageous obtain a
> scuba tank and use it to power your turbine or generator (very
> dangerous - you cannot blame me if you get hurt).

I'll pass. The pressure is way too high for any perceived benefit.

> Steam is good to use for a certain range of combustion temperatures
> where the pressure does not become excessive and where it can do a good
> job (at low efficiency).
>
> Power stations that use steam at high temperature have complicated and
> dangerous installations constantly purifying the water in the circuit,
> adding chemicals like Hydrazine (poison!) to remove oxygen. Any oxygen
> in the circuit will instantly convert the innards of the equipment into
> high quality rust, when combined with steam at 700+K.

Ouch.

So back to the all air installation... why is R a water radiator instead of
another intercooler? Would it not be possible to simply immerse both
intercoolers in a water bath?

Will the generator also be the starter? So you supply electricity to get
the setup going in the morning then extract power once it comes up to speed?
There seems to be great symmetry in that.

BAJ

2005\09\27@172559 by James Humes

picon face
Here is an idea i had when in school after seeing a small stirling engine
that operated by placing it on top of a mug of hot coffee... after you
helped the engine overcome starting torque, it kept itself quite nicely.
Ignoring feasibility (I did major in math, we're allowed to do that), my
idea was to build quite a few stirling engines along those lines but upside
down.. (ie, the cooling section is on the bottom). Now, bury the cooling
section and leave the part you must heat above ground in a sunny place. Once
the temperature differential is in the right place, give them a start. So,
on each engine we put a small generator and trickle charge our batteries.
Go ahead, I'm ready for all the many things I haven't thought of that make
this a bad idea:p
James

2005\09\27@175347 by Howard Winter

face
flavicon
picon face
James,

On Tue, 27 Sep 2005 15:25:59 -0600, James Humes wrote:

{Quote hidden}

Well you've just described a solar powered Stirling engine - or an array of them.  Nothing wrong with that,
but you have to get rid of the heat from the cold side - just burying it would heat up the ground underneath
and it would stop.  Set up convection cooling, using a chamber underneath leading to a chimney, say, and you'd
have a better chance.  The feasibility problem comes from the efficiency - low temperature-differential
Stirlings aren't very good, so you may not find much usable power.  They'd go round, but they might not have
enough power to turn anything useful like a generator!

Cheers,

Howard Winter
St.Albans, England


2005\09\27@191842 by James Newtons Massmind

face picon face
Nothing wrong with that idea... Just that the cost of the stirling engines
do make it unfeasible. I'm an engineer, we aren't allowed to ignore that.

---
James.



> {Original Message removed}

2005\09\28@090155 by Russell McMahon

face
flavicon
face
James appears to be seeking a conversion experience :-)
Ridicule something for too long and you run the severe risk of
becoming its acolyte for life.

> Try and purchase one.

Evidently you haven't followed any of the Stirling Engine links I have
provided recently and on past occasions.
Google on Whispergen and examine some of the 22,000 hits and decide if
it is indeed a real product or a phantasm.

Look at    http://www.whispergen.com
While this may look like any number of shonky sites that do not have
real product to back up the pictures, in this case it is not the case.
Google on Whispergen and you will find they have been around for some
years and are available for money. I have seen one in the flesh. As I
discussed recently, they are expensive compared to IC units of similar
capabilities and for good reason. But the reasons are not principally
related to the cost of production.

The Whispergen was developed from scratch by a Stirling engine
enthusiast who acquired a number of prior devices, including Philips
Stirling Engines made in the 1950's, did his PhD on Stirling engines,
and then developed his own patented coupling for a 4 piston unit and
THEN commercialised it. He is Dr Donald Klucas. The parent company is
based in Christchurch New Zealand. It is owned mainly by two of NZ's
electricity/energy supply companies as they provided the startup funds
and/or bought the shares of those who did. They have a contract to
supply a goodish number (10,000? 30,000? to a UK energy supply company
to act as load distribution units by installing them as CHP units in
homes. Selling gas and electricity makes this attractive to a
supplier. Whether this order comes to fruition remainds to be seen.

> What is the mean time between failure?

See above site.
Good.
Doesn't use exotica as high volumetric energy density is not required.
Has a standard maintenance arrangement, as do all engine sused in
serious applications.

BUT - this will be of interest
www.mech.canterbury.ac.nz/MEFinalYear/Projects%202004/LubricationSealingSolutionsForWhisperGen.shtml
Note, you have to havea real product before you can improve it.


> Sterlings are a pipe dream.

Sterlings may well be.
But Stirlings aren't ;-)

Google on "dean kamen" and "stirling engine".
If you don't know who DK is Google him up and then the above.
DK does indeed dream some major dreams - but many of them end up
clothed in steel and plastic and electronics.

A Sterling engine is a metal expansion engine that uses metal rods
heated and cooled to provide motive power. Stroke is understandably
small:-)

There have been many small Stirling engines made and a few large ones.
The major barrier to the widespread introduction of Stirling engines
is greed and stupidity - ie cheap petroleum and tolerance of the vast
waste of resources. As long as people would rather waste resources at
artificially low prices rather than acheive energy efficiency we will
continue as we have in the past. A useful albeit incomplete analogy is
someone with a bedroom stacked full of 100 dollar bills. As long as
they last it's easy and "cheap" to shovel them into the fire to heat
the house. That other people may put them to other uses and find other
ways of heating the house does not enter the equation. Our children's
children's children, should they get to exist, would curse us chapter
and verse over our wastrel ways were it not for the pletious supply of
lunar He3 that they will have to fuel their fusion reactors :-).

> Solar steam or hot air turbine engines are at least accessable NOW.

Nothing is accessible now unless you do it.
Just as vanishingly few amateurs produce significant sized IC engines
you find few people building larger serious Stirlings.
How many amateurs do you know who have built their own eg 12 HP twin
cylinder engine starting from scratch, apart from Orville and Wilbur?

Compared with making your own IC engine a say 1 HP Stirling should be
reasonably easy. Using air at about 150 psi you'd need about a 250cc
swept piston area. Large if you think in IC terms. Not at all large if
you think in bits of metal terms. More could be said, but if the above
does not dissuade people from making unsupported comments like "try
and purchase one" then no amount of technical comment will help :-(

A 5 litre stainless steel soup pot run at about 15 psi should make
about 3 horsepower when sorted :-).


       RM










2005\09\28@091204 by Russell McMahon

face
flavicon
face
> The correct spelling is of course Viebach and not Vierbach. The
> 5000EUR price is for completed Viebach motors (built from kits):
>
> http://www.uwemoch.de/

Very pretty.
But, look at that engine and the drawings and suggest a more realistic
price if it was built in any volume. The 5000 Euro buys you a
handcrafted (rough) gem. One would not normally expect to pay more
than a small fraction of that for something of that nature if it was
mass produced.


       RM

2005\09\28@094932 by Russell McMahon

face
flavicon
face
For an excellent, brutally honest discussion of the long hard
expensive path to market for the Whispergen Stirling combined heat &
power unit see

       www.unlimited.co.nz/unlimited.nsf/default/A59ACC6CAB5E4050CC256F50007B1760
&
       http://www.unlimited.co.nz/unlimited.nsf/UNID/720112B6E0104AD3CC256F560010EF4C

They have a $300 million order for 80,000 over 5 years from Powergen
in the UK (is that real enough?) BUT that could yet not happen.
Investment so far is apparently about $NZ 20 million, so it's not an
easy path.

The UK dometic market prices gas energy at 25% of equivalent
electricity so it's much easier to cost justify a domestic heat and
power generator than in say NZ. With excess power being delivered to
the grid consumers can effectively "store" power made for subsequent
use.



       RM


2005\09\28@150721 by Hopkins

flavicon
face
Hi Russell,

I know you have an interest in Stirling engines.

Are there sites that give plans that an amateur can follow to build a
Stirling engine of say 2 or 3 hp?

I have also been thinking in terms of a solar heated Stirling engine to
drive a 1 or 2 kw generator.

One idea put to me is to use power generated by the generator rectified
to DC in parallel to Rectified mains AC to power a hot water cylinder,
possibly with a PIC controlled load sharing.

_______________________________________

Roy
Tauranga
New Zealand
_______________________________________



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28/09/2005


2005\09\28@165018 by Peter

picon face

On Tue, 27 Sep 2005, Byron A Jeff wrote:

> On Tue, Sep 27, 2005 at 10:07:14PM +0300, Peter wrote:
>>
>> I made a drawing and you can see it here (thanks to James for putting it
>> up - I have yet to learn how to use the piclist system):
>>
>> http://www.piclist.com/techref/member/plp-actcom-f00/sun-turbo-1.htm
>
> WOW!
>
> One element you are missing is the turbocharger lubrication system. You'll
> need an oil pump setup too.

You can think of it as being driven by the water pump.

> Can you describe where these items would fit using an example manifold?
> Here's a large image here:
>
> http://www.brit.ca/~tboicey/mgparts/pics/exhaust_manifold-1.jpg

That's a V6's manifold (one of the two). I will have to make a drawing
and post it and then it might become clearer.

> So back to the all air installation... why is R a water radiator instead of
> another intercooler? Would it not be possible to simply immerse both
> intercoolers in a water bath?

The radiator has to remove a lot of heat from the turbine output. It may
happen that a second turbine can be mounted at the output of the first
to extract power. I do not know the exact data for this and it is hard
work for me to predict what the thing will do anyway. I am just
expanding an idea that does not seem to be more harebrained than other
ideas that exist on this theme.

The radiator R would have to handle low pressure, low density air so it
would have to be large anyway. Much larger than an intercooler.

I know that amateurs have built 'demo' gas turbines using such
turbochargers, but in open circuit and with internal burners. I have
looked at their figures and 'my' idea seems to be in the right order of
magnitude.

>From my calculations (which are most likely incorrect) a smaller home
type air conditioner heat exchanger (the kind mounted in a duct in the
basement) is about the right size for this job.

> Will the generator also be the starter? So you supply electricity to get
> the setup going in the morning then extract power once it comes up to speed?
> There seems to be great symmetry in that.

There has to be something to start the turbine because the device will
not start operating by itself. Using a motor-generator seems to be
standard from what I read but not at 100k rpm. I have some experience
over-revving home vacuum type motors in vacuum (2 in series + variac to
raise voltage) and I did not like the end result (exploded/bent/welded
motor rotor). That may be the hardest part to get by. But for a start
jut making the whole thing work without extracting power would be nice
imho. You get hot water anyway.

Peter

2005\09\28@173950 by Howard Winter

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Russell,

I just knew you'd get to rebuff James' scepticism before I had a chance to!  :-)

Whispergen...

On Thu, 29 Sep 2005 01:01:50 +1200, Russell McMahon wrote:

>...<
> They have a contract to
> supply a goodish number (10,000? 30,000? to a UK energy supply company
> to act as load distribution units by installing them as CHP units in
> homes. Selling gas and electricity makes this attractive to a
> supplier. Whether this order comes to fruition remainds to be seen.

They have had a trial going for some time of a few hundred home installations - they asked for volunteers to
try them, and I leaped at it and applied.  Unfortunately I wasn't within the profile they were looking for, so
that was that.  It's been running a couple of years, I think.

One of the annoying things is that they say that surplus electricity will be bought-back by the supplier
(PowerGen), but what they don't mention is that it will be paid for at the "generated" wholesale rate, which
is about 0.5p / kWh, rather than the retail price of about 10p.  I think that's wrong, because the electricity
I'd pump into the grid would be used by my neighbours, so there's no distribution cost involved - they'd pay
me 0.5p and my neigbour would pay them 10p for it - 1900% profit for doing nothing!  If they allowed net
metering (I pay for what I've used less what I've supplied, kWh for kWh), it would be a lot fairer and a lot
more financially viable.  Especially as I'd be paying them for the gas to generate it!

Cheers,


Howard Winter
St.Albans, England


2005\09\28@185137 by Jinx

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> One of the annoying things is that they say that surplus
> electricity will be bought-back by the supplier (PowerGen),
> but what they don't mention is that it will be paid for at the
> "generated" wholesale rate, which is about 0.5p / kWh,
> rather than the retail price of about 10p

A man self-sufficient using solar panels recently did a deal with
a NZ power company to sell the excess back at domestic retail.
He was pleased of course, but you could tell that the power
company exec interviewed was not too happy and had a "hmmm,
we'll see how it goes and this is not really a precedent" attitude

http://www.tvnz.co.nz/view/page/554440/613854

The power companies are not having much good press lately.
Weak dams, low lakes, where to put pylons, protests about
station upgrades, prices in general etc. Compared with all, this
the story above isn't much of a redress on the PR front, but
maybe it will encourage others to use alternative generation

2005\09\28@233214 by andrew kelley

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I dont know if this has occurred to anyone, but it would seem to me that if
you can generate a heat differential use a large Peltier junction with the
water flowing across the bottom and the sun beating down on the top... Why
not? No moving parts.. But thats probably aside from the matter.
andrew

2005\09\28@234038 by Spehro Pefhany

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At 11:32 PM 9/28/2005 -0400, you wrote:
>I dont know if this has occurred to anyone, but it would seem to me that if
>you can generate a heat differential use a large Peltier junction with the
>water flowing across the bottom and the sun beating down on the top... Why
>not? No moving parts.. But thats probably aside from the matter.
>  andrew

I have seen electric fans that fit in a chimney pipe that operate by this
principle.

Horrible efficiency, AFAIUI, but it works.

>Best regards,

Spehro Pefhany --"it's the network..."            "The Journey is the reward"
speffEraseMEspam.....interlog.com             Info for manufacturers: http://www.trexon.com
Embedded software/hardware/analog  Info for designers:  http://www.speff.com
->> Inexpensive test equipment & parts http://search.ebay.com/_W0QQsassZspeff


2005\09\29@012129 by Russell McMahon

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> Are there sites that give plans that an amateur can follow to build
> a
> Stirling engine of say 2 or 3 hp?

No :-) :-(
There is lots of discussion but not much doing at a shareable level.
At the amateur level James comments about Stirlings being a pipe dream
are closer to the mark than at a commercial level.
People build any number of low power toys but there is little serious
that doesn'tr cost an arm and two legs.

That said, I can really see no reason why a group of enthusiasts
couldn't design a modest output high capacity low cost unit and build
a trial unit.
I'd be happy to participate in such a project as time allows.
Something using something like a  stainless steel soup pot as the
pressure vessel and working at ridiculously low pressures and with an
actively driven displacer should be quite reasonably doable. It would
be largte for it's output but have a number of advantages.

> I have also been thinking in terms of a solar heated Stirling engine
> to
> drive a 1 or 2 kw generator.

If you achieve say 10% end to end that's 10 or 20 kW in - a very
signifcant device!
Even at 30% end to end its very substantial.

> One idea put to me is to use power generated by the generator
> rectified
> to DC in parallel to Rectified mains AC to power a hot water
> cylinder,
> possibly with a PIC controlled load sharing.

The only sensible outputs are mechanical power in one form or another
or electricity. Anything that produces heat is better off using the
heating inmput directly. The Whispergen achieves its marginal
financial viability at its present price by producing electricity and
then using the wate heat to heat water. It is viable in niche
applications (on boats was the initial market) and where alternative
energy costs are dear. Produced in true volume it would probably be
viable in many more domestic situations.


       Russell McMahon


2005\09\29@013048 by Russell McMahon

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> I dont know if this has occurred to anyone, but it would seem to me
> that if
you can generate a heat differential use a large Peltier junction with
the
water flowing across the bottom and the sun beating down on the top...
Why
not? No moving parts.. But thats probably aside from the matter.
/>

Entirely doable.
Efficiency and cost considerations usually limit use to specialist
applications.

_________

Excellent  - Tutorial, basic maths and online calculator

       http://www.ferrotec.com/usa/thermoelectric/ref/3ref13.htm

Thermoelectric reference guide for all things Peltier

       http://www.ferrotec.com/usa/thermoelectric/ref/index.htm

________________________________________

Products

   http://kryotherm.com/

Suppliers

       http://www.peltier-info.com/generators.html


       RM

2005\09\29@013108 by Bob Ammerman

picon face
> A man self-sufficient using solar panels recently did a deal with
> a NZ power company to sell the excess back at domestic retail.
> He was pleased of course, but you could tell that the power
> company exec interviewed was not too happy and had a "hmmm,
> we'll see how it goes and this is not really a precedent" attitude
>

A significant number of regulatory jurisdictions here stateside require
power companies to accept power back on the grid from co-gens at a net
basis. IE: You get the same rate you pay.

Bob Ammerman

2005\09\29@041645 by Hopkins

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Interesting site with animated sterling engine

http://www.keveney.com/Vstirling.html

This has to be one of the better descriptions on how a Stirling engine
works.

Parent site with different animated engines

http://www.keveney.com/


_______________________________________

Roy
Tauranga
New Zealand
_______________________________________



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28/09/2005


2005\09\29@062216 by Byron A Jeff

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On Wed, Sep 28, 2005 at 11:32:13PM -0400, andrew kelley wrote:
> I dont know if this has occurred to anyone, but it would seem to me that if
> you can generate a heat differential use a large Peltier junction with the
> water flowing across the bottom and the sun beating down on the top... Why
> not? No moving parts.. But thats probably aside from the matter.

It did occur to me. But in standard form it's cost prohibitive.
A thermoelectric generator is little more than two dissimilar metals
twisted together with one end heated and the other end cooled.

The question is how to do it in such a way that useful power can be
extracted.

BAJ

2005\09\29@063225 by Byron A Jeff

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On Thu, Sep 29, 2005 at 01:20:26AM -0400, Bob Ammerman wrote:
> >A man self-sufficient using solar panels recently did a deal with
> >a NZ power company to sell the excess back at domestic retail.
> >He was pleased of course, but you could tell that the power
> >company exec interviewed was not too happy and had a "hmmm,
> >we'll see how it goes and this is not really a precedent" attitude
> >
>
> A significant number of regulatory jurisdictions here stateside require
> power companies to accept power back on the grid from co-gens at a net
> basis. IE: You get the same rate you pay.

I'd be interested in seeing if Georgia Power will do this on their
Time of Use plan. With this plan the rate is set based on the time of day.
In the peak summer months they charge 4.9 cents a kWh for off peak time
but charge 16 cents a kWh for peak time! (M-F 2-7PM)

So what would they pay if you charged up a battery bank in the morning and
then turned that power around to the grid at peak time. If it's the 11 cents
a kWh difference, there may actually be a profit model there.

Of course the obvious problem is what to do about your own power needs during
peak time? From my research an absorption AC system would be the ticket.
Absorption AC generally uses either ammonia/hydrogen or Lithium Bromide/Water
as the refrigerant. It's heat powered so the hotter the sun blazes, the better
they cool!

So one could run on solar/battery power during peak hours, selling the excess
to the grid, and use the grid in offpeak hours, charging the battery bank. You
even get the advantage that the 4.9 cents/kWh off peak is 2.5 cents/kWh cheaper
than the standard rate.

BAJ

2005\09\29@064231 by Russell McMahon

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> Interesting site with animated sterling engine
>
> http://www.keveney.com/Vstirling.html
>
> This has to be one of the better descriptions on how a Stirling
> engine
> works.

It's good. But may be misleading as that is only one Stirling
configuration - most have one power piston and one "displacer" which
is NOT acted on by the gas but instead is used solely  move gas
between hot and cold spaces at appropriate times.

Arguably *THE* most important feature of a  Stirling engine is the
regenerator. This is a through flow heat exchanger. When cold gas
flows into it from the cold side it picks up heat left from prior hot
gas which has flowed through it in the reverse direction and leaves
behind coolth. When hot gas subsequently returns in  the opposite
direction it leaves behind heat energy and picks up coolth. The
performance and efficiency of a Stirling engine live and die with the
regenerator quality. It ideally has infinite thermal capacity,. zero
dead volume and no pneumatic resistance. It has zero thermal
resistance at right angles to the gas flow and infinite thermal
resistance in the direction of the gas flow. Clearly in practice
compromises must be made.

Brief operation summary:

- Cold gas flows from cold to hot space picking up heat left in
regenerator and then being further heated by hot side heater. Gas in
hot side expands and pressure of the whole system rises equally.

- Piston is driven by expanded gas.

- Hot gas flows from hot side to cold side via regenerator, leaving
heat in regenerator and being cooled by cold side cooling. Gas in cool
side contracts and pressure in whole system drops.

- Piston is driven by the contracted gas.

Cycle repeats.
All Stirling  engines work like this.


       RM



2005\09\29@071622 by Russell McMahon

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> http://www.keveney.com/Vstirling.html
> This has to be one of the better descriptions on how a Stirling
> engine
> works.

More generic diagram from same site. Topology varies but all use the
same basic cycles. The engine "chases its tail" forever. gas is moved
hot-cold-hot, piston goes in and out, displacer moves gas in such a
way that piston is never where it wants to be for equilibrium. Some
similarity to a 1 gate Schmitt oscillator.

       RM


2005\09\29@071752 by Russell McMahon

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> A thermoelectric generator is little more than two dissimilar metals
> twisted together with one end heated and the other end cooled.

> The question is how to do it in such a way that useful power can be
> extracted.

There is a superb online tutorial and calculator on this - possibly on
the site I referenced within the last day.
Ah

   http://www.ferrotec.com/usa/thermoelectric/ref/3ref13.htm

There's no magic, but the engineering gets hard.

Basically you "simply" have to provide a suitably low resistance path
through the TE cell elements to give it an adequately low internal
resistance.
TEG = thermoelectric generator = N cells in series or series parallel.

Voltage is calculated from Seebeck effect coefficients for the
substances used.
TEG resistance is the sum of N cells in series used to get realistic
voltages.
Resistance is N x cell resistances plus n-1 bridges between them plus
connecting wires.
voltage increases with temperature differential but the substances
with best Seebeck coefficient tend to melt /die at lower temperatures.

___________

Optimal design of a multi-couple thermoelectric generator
Heavyish. But useful and interesting.
Answers Byron's question - albeit not as he would have wished it
answered :-)

       http://www.paper.edu.cn/scholar/download.jsp?file=chenjincan-6

Just to annoy
The thermoelectric generator as an endoreversible Carnot engine

       http://www.iop.org/EJ/abstract/0022-3727/30/3/007


       RM

2005\09\29@071943 by Russell McMahon

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Ken Mardle said:


> The idea of solar steam engines is far from new as this website
> (among
> others) shows:
>
> http://www.jc-solarhomes.com/fair/solar_engine18.htm

AND

Forgot to mention this site which could be of interest...

http://www.dself.dsl.pipex.com/MUSEUM/POWER/oddfluid/oddfluid.htm



       RM

2005\09\29@080617 by olin piclist

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Russell McMahon wrote:
> Voltage is calculated from Seebeck effect coefficients for the
> substances used.
> TEG resistance is the sum of N cells in series used to get realistic
> voltages.
> Resistance is N x cell resistances plus n-1 bridges between them plus
> connecting wires.
> voltage increases with temperature differential but the substances
> with best Seebeck coefficient tend to melt /die at lower temperatures.

OK, so what about a thermionic generator instead?  Sufficiently high
temperatures on a small area are within reach of the backyard mechanic.  A
parabolic dish and a stack of razor blades should be good enough.  Creating
a good vacuum and cathode coating is more difficult but no beyond reach.
This should also be light weight enough to put at the focus of a small
parabolic dish and move the whole assembly to track the sun.


*****************************************************************
Embed Inc, embedded system specialists in Littleton Massachusetts
(978) 742-9014, http://www.embedinc.com

2005\09\29@080926 by Russell McMahon

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