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'[EE]: high efficiency feed to mains'
2001\03\10@085026 by John

flavicon
face
Hello Peter & PIC.ers,

Please forgive the long post, but this covers in issue I'm sure will
resonate with many.  PICs _do_ come into it, a little.

To answer your direct question, an induction motor is an
asynchronous machine fed by the ac mains.
Usually this is 3phase 50Hz, 380volt line rms (at least in this country).
For the same grid it can be 1phase, running at 220v, this motor would
have a `start'  or auxiliary winding and a mean series cap.
to give it torque at standstill & thus get the rotor moving.

Induction motors have  stator windings that produce a magnetic field
rotating at the mains frequency, ie 50Hz or 60Hz.
For a two-pole motor this translates to a field rotating
at 50 x 60 = 3000RPM.
For a four-pole, it becomes 50/2 x 60 = 1500RPM.

Your rotor will not actually spin at these rates, when the motor is
developing torque. At synchronous speed the torque produced is exactly
zero, torque only occurs once there is a slippage between the
rotating magnetic field and the rotor speed.
This induces an alternating magnetic flux in the rotor at a frequency
equal to the slip.
*This* then generates rotor winding (cage) current and in turn torque,
so the contraption can operate like we want it, ie a motor.
As you increase the mechanical load, the torque
rises to meet demand.

The *same* machine can act as an asynchronous generator too,
(how? as the audience gasps in anticipation...)
Well, y'just overdrive the thing, beyond the synchronous speed, then
the power flow goes out the machine back to the mains.
NB Not the current as such, but the voltage and current phase
relationship changes s.t.  power flow becomes m/c >> mains.

This -now it's a generator- machine cannot be used as a genny
on its own, it *has* to be connected to an a.c. grid complete with
e.m.f. .
If it is spun on its own it produces no voltage because there is no
source of excitation. It'll just speed up if there is no control mechanism,
but produce no electrical power.
This should make it safe for a utility to have multiple home-owners
be connected at the time the grid goes out-to-lunch.

The great worry that micro-power generators will back-feed the grid
and keep the lines energised falls away.
Have I missed something in my explanation or understanding of
the issues here?  I can't think of a reason why this can't be a
practical / safe /simple /cheap generation scheme.

enough theory.

I think this is all very relevant to the community of diy-at-home
micro-power-plant enthusiasts.
They aim to suck power out of the sun or the wind, then by
masses of ingenious (not to say expensive) inverters, batteries,
controllers - to include PIC.ery of course - they can use
or store the energy, and sell any excess back to their grid operator,
or utility as our New World cousins would call it.

So, why aren't off-the-shelf-already-available cheap
mass-produced induction motors being used as the
generators in home-power schemes?
A PV array could drive a brushless dc-motor, in turn
over-driving an induction machine to reverse the cash-flow.
It can be shut down at night, to avoid motoring waste.

Am I missing something? If so, what?
Is this just too simple & would provide no profits to the
green-power equipment producers?
Perish the thought, John, they are Earth huggers just like you!



best regards,   John

>Date:    Fri, 9 Mar 2001 14:08:59 +0200
>From:    "Peter L. Peres" <spam_OUTplpTakeThisOuTspamACTCOM.CO.IL>
>Subject: Re: [EE] high efficiency feed to mains
>
>What is an 'induction motor' ?
>
>Peter

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2001\03\10@091349 by Roman Black

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John wrote:

> I think this is all very relevant to the community of diy-at-home
> micro-power-plant enthusiasts.
> They aim to suck power out of the sun or the wind, then by
> masses of ingenious (not to say expensive) inverters, batteries,
> controllers - to include PIC.ery of course - they can use
> or store the energy, and sell any excess back to their grid operator,
> or utility as our New World cousins would call it.
>
> So, why aren't off-the-shelf-already-available cheap
> mass-produced induction motors being used as the
> generators in home-power schemes?
> A PV array could drive a brushless dc-motor, in turn
> over-driving an induction machine to reverse the cash-flow.
> It can be shut down at night, to avoid motoring waste.
>
> Am I missing something? If so, what?
> Is this just too simple & would provide no profits to the
> green-power equipment producers?


No you are not missing something, it's a great idea.
However economics rule the roost (i'm sounding like
Olin??)

To run from solar panel or batteries into an MG set to
the mains requires
* pwm controller for dc motor
* dc motor
* ac generator

Note that all three components must be rated for the
worst case max power usage. Also the FETs and drive
circuit to drive full power PWM into the dc motor is
about the same amount of kit needed to just invert the
DC directly into AC and feed it into the mains.

With improvements in semiconductor prices and power
capability the shift is truly towards just doing it all
with semis and avoiding the mechanical MG side altogether.
Even larger installations are slowly upgrading from mech
to electronic DC-AC converters.

In the case of a thrifty hobbyist who wants to do this
at home, the MG solution might work if they can source
the DC and AC motors cheap enough at scrapyards. But to
get good efficiencies they really need to run the
batteries and MG set at peak efficiency which means
controlling current which is the whole semi issue all
over again. If you have 1kw of FETs why bother driving
a motor/generator? Why not just make the AC by switching
the FETs?

Having said that, I do love the hum and breeze from
a decent MG set. As a first year apprentice I used to
sneak off and spend time in the number 2 substation,
with the wind blowing my hair from the big motors (each
was car sized), watching the little dials move as the
set compensated for the 1000A DC feed to the cranes,
dreaming that all that power was mine... Geeky or
what? ;o)
-Roman

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2001\03\10@122640 by Olin Lathrop

face picon face
> Having said that, I do love the hum and breeze from
> a decent MG set. As a first year apprentice I used to
> sneak off and spend time in the number 2 substation,
> with the wind blowing my hair from the big motors (each
> was car sized), watching the little dials move as the
> set compensated for the 1000A DC feed to the cranes,
> dreaming that all that power was mine... Geeky or
> what? ;o)

Kinda reminds me of "I'm a lumberjack and I'm OK ..."


*****************************************************************
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(978) 772-3129, olinspamKILLspamembedinc.com, http://www.embedinc.com

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2001\03\10@142258 by Chris Carr

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> > Having said that, I do love the hum and breeze from
> > a decent MG set. As a first year apprentice I used to
> > sneak off and spend time in the number 2 substation,
> > with the wind blowing my hair from the big motors (each
> > was car sized), watching the little dials move as the
> > set compensated for the 1000A DC feed to the cranes,
> > dreaming that all that power was mine... Geeky or
> > what? ;o)
>
> Kinda reminds me of "I'm a lumberjack and I'm OK ..."
>
I put on women's clothing and let the breeze blow up my dress

Nah, not as good as the original, and it doesn't rhyme  :-)

Chris

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2001\03\10@145033 by Chris Carr

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> > Having said that, I do love the hum and breeze from
> > a decent MG set. As a first year apprentice I used to
> > sneak off and spend time in the number 2 substation,
> > with the wind blowing my hair from the big motors (each
> > was car sized), watching the little dials move as the
> > set compensated for the 1000A DC feed to the cranes,
> > dreaming that all that power was mine... Geeky or
> > what? ;o)
>
It reminds me of when I used to maintain a Microwave Relay Station. This had
what we called a Continuity Set. The incoming Utility Supply powered an AC
Motor whose shaft extended out to an Alternator. This powered the  Station
Electric's. However, between the AC Motor and the Alternator was a DC Motor
which was powered from a battery bank.

Under normal operation the AC Motor powered the Alternator which powered the
station. In the event of a incoming mains failure the DC Motor took over the
driving of the Alternator until the Diesel Generator started up and
stabilised and this was then connected to the AC Motor and the DC Motor
switched Off. As far as I can remember, the regulation of the DC motor was
by the field winding, this is in the days of Relay Logic after all.

One day we had a failure of the Utility Supply. All relays clicked in and
out as they should have except the one that started the Diesel Generator. We
were alerted when the continual background low pitched whine started to go
lower in pitch. The problem was solved by dashing to the Power Room and
applying a well placed kick to the control unit front panel.

The following month was spent filling out reports on why we needed to
replace every Klystron and TWT in the Station.

Happy Days, It was pre Monty Python and I don't believe William Gates III
had even been born then, Life was so much simpler :-)

Chris

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2001\03\11@012839 by Harold M Hallikainen

picon face
       Though they take a certain minimum amount of space (I can't put a
windmill on my calculator), it seems that windmills take less space per
kw out and cost less per kw out than PV arrays. So, perhaps we should
just build wind mills. The "match the source to the load" problem (which
required a maximum power point controller between the PV panel and the
motor/generator below) can be handled using a variable pitch prop on the
windmill. We'd just watch the watts out of the windmill generator and
tweak the prop pitch to maximize it. If the power goes negative (we have
a big fan instead of a windmill), drop it off the line. When the open
circuit speed of the windmill is increases and reaches line synchronous
speed, drop it on the line.
       Now if I could get my apartment manager to let me put a windmill on the
roof...


Harold



On Sun, 11 Mar 2001 01:14:21 +1100 Roman Black <.....fastvidKILLspamspam.....EZY.NET.AU>
writes:
{Quote hidden}

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2001\03\11@021054 by Roman Black

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Harold M Hallikainen wrote:
>
>         Though they take a certain minimum amount of space (I can't put a
> windmill on my calculator), it seems that windmills take less space per
> kw out and cost less per kw out than PV arrays. So, perhaps we should
> just build wind mills. The "match the source to the load" problem (which
> required a maximum power point controller between the PV panel and the
> motor/generator below) can be handled using a variable pitch prop on the
> windmill. We'd just watch the watts out of the windmill generator and
> tweak the prop pitch to maximize it. If the power goes negative (we have
> a big fan instead of a windmill), drop it off the line. When the open
> circuit speed of the windmill is increases and reaches line synchronous
> speed, drop it on the line.
>         Now if I could get my apartment manager to let me put a windmill on the
> roof...


Yep, windmills are great! I think they are peaceful
and relaxing to watch too, if you have ever had the
chance to watch a REAL big one, like a 300kw+ size.
Magnificent.:o)

I also agree with running the mill on-line directly,
in the past this was only really used with very large
mills. Now with PICs to sync the mill speed to mains
freq and control blade pitch etc this is becoming
practical for smaller installations. That really affects
the economic viability of wind power as a business.

There are two economies of scale with alternative
energy, macro and micro. Everybody "knows" that it is
only economically viable to make BIG power stations.
But is is also possible to make money from very small
stations, through economies of personal labour and
clever sourcing of parts. Like salvaging small
generators from scrapyards and auctions etc.

With semiconductor prices dropping it is also becoming
more attractive to use electronics rather than
mechanical solutions. Although variable pitch blades
are nice you can get good results with a simpler,
cheaper turbine and use electronics to adjust the
power tracking for max efficiency. If this is done
at the same time it is fed into the mains you kill
two birds with one inverter. :o)
-Roman

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2001\03\11@082434 by John

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Hello Roman & PIC.ers,

{Quote hidden}

..

mmm...   buttt....  why is it necessary to provide PWM control
to the DC motor at all?
The sun's power is priceless (think about it) so you don't have
a reason to limit whatever the PV array gives you.
Take the lot. Run the DC motor direct-on-line from the PV
and put cheapo thermal cut-outs within the windings.

The RPM is regulated within a tight range by the grid frequency,
and the quadrant of loading that the ac machine is in.

If power flow ever reverses, which it will in dark periods, the
ac machine starts to motor.  Detect that  -no sweat for a
hard-core PIC.er of course-  & shut the set down.

No batteries. No back-feed when the grid dies.
No FETs. No PWM. No inverters.
A PIC, but a wee one will do.

MG sets just turn me on.....


   best regards,   John



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2001\03\11@111245 by Roman Black

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John wrote:

> mmm...   buttt....  why is it necessary to provide PWM control
> to the DC motor at all?
> The sun's power is priceless (think about it) so you don't have
> a reason to limit whatever the PV array gives you.
> Take the lot. Run the DC motor direct-on-line from the PV
> and put cheapo thermal cut-outs within the windings.
>
> The RPM is regulated within a tight range by the grid frequency,
> and the quadrant of loading that the ac machine is in.
>
> If power flow ever reverses, which it will in dark periods, the
> ac machine starts to motor.  Detect that  -no sweat for a
> hard-core PIC.er of course-  & shut the set down.
>
> No batteries. No back-feed when the grid dies.
> No FETs. No PWM. No inverters.
> A PIC, but a wee one will do.


Hi John, actually the cost of solar power is
quite high. When you have paid $600 for a 100w
solar panel you want to make sure the most energy
possible is utilised.

If you just connected the solar panel to a DC motor
the efficiency is very low. Solar panels change
output volts and amps depending on sunlight, and
to get max power you need to draw the right amount
of amps. Too much and the volts drop, efficiency
drops, also too little amps and the power is wasted.
This is called MPT; max power tracking and requires
the ability to use PWM for adjusting the amount of
amps drawn from the panel in real time.

Consider you could get a 1hp (750w) DC motor from
a scrapyard for $100, but 750w of solar panels
will cost you close to $4500. You will want to run
those solar panels as efficiently as you can, even
if it means getting some pwm fets! :o)
-Roman

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2001\03\11@150156 by Sean H. Breheny

face picon face
What are the limiting factors to solar cells? Is this 100w panel limited by
the amount of sun that reaches it, or is it that the cells just can't
handle more than 100w? Is it a thermal problem?

The reason I ask is that it seems to me that one could put a small number
of cells close to the focal point of a huge parabolic reflector, use motors
to track the sun, and get a lot higher output per cell than if you just
used a flat panel. The fact that I have never seen this, though, makes me
suspect that the amount of light reaching the cells is not the key limiting
factor. Is that the case?

Sean

At 03:11 AM 3/12/01 +1100, you wrote:

>Hi John, actually the cost of solar power is
>quite high. When you have paid $600 for a 100w
>solar panel you want to make sure the most energy
>possible is utilised.

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2001\03\11@151620 by hard Prosser

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I think that there is a temperature limit. By focusing like this, and given
the lowish efficiency of the cells, the temperature rise is unacceptable, I
have seen systems using some reflection improvement but not to a large
extent.
Incidentally, the daily power output from a solar array can be
significantly improved by tracking the sun - but the complexity involve,
along with the maintainance aspect appear to make this enhancement
uncommon. Come up with a cheap and reliable way of doing it and there could
be a significant market.

Richard P





What are the limiting factors to solar cells? Is this 100w panel limited by
the amount of sun that reaches it, or is it that the cells just can't
handle more than 100w? Is it a thermal problem?

The reason I ask is that it seems to me that one could put a small number
of cells close to the focal point of a huge parabolic reflector, use motors
to track the sun, and get a lot higher output per cell than if you just
used a flat panel. The fact that I have never seen this, though, makes me
suspect that the amount of light reaching the cells is not the key limiting
factor. Is that the case?

Sean

At 03:11 AM 3/12/01 +1100, you wrote:

>Hi John, actually the cost of solar power is
>quite high. When you have paid $600 for a 100w
>solar panel you want to make sure the most energy
>possible is utilised.

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2001\03\11@153524 by D. Schouten

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> What are the limiting factors to solar cells? Is this 100w panel
limited by
> the amount of sun that reaches it, or is it that the cells just
can't
> handle more than 100w? Is it a thermal problem?

A 100W panel can deliver 100W max usually under the conditions that
1000W per square meters of solar power reaches the panel. Here in the
Netherlands this level of radiation is only reached a few days per
year. But in a more sunny climate it can be reached quite often a
couple of hours per day.
The maximum output power of the PV panel is limited by it's own
impedance (it's a current source). The 100W panels I know have a short
circuit current of approx. 3.2A. When you multiply this with the
maximum power point voltage of approx. 31VDC, you see where the power
rating comes from. Of course there is a thermal problem too, since the
panel impedance will rise with temperature.

> The reason I ask is that it seems to me that one could put a small
number
> of cells close to the focal point of a huge parabolic reflector, use
motors
> to track the sun, and get a lot higher output per cell than if you
just
> used a flat panel. The fact that I have never seen this, though,
makes me
> suspect that the amount of light reaching the cells is not the key
limiting
> factor. Is that the case?

Well, the amount of light reaching the cells is definately important,
but it is also the size of the total PV array surface which makes the
power (lot's of series/parallel connected cells collecting light).
Unfortunately I can't give you an exact answer to your question. I'm
more into the electronics rather than the physical aspects of solar
cells.

Daniel...

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2001\03\11@154808 by Thomas C. Sefranek

face picon face
"Sean H. Breheny" wrote:

> What are the limiting factors to solar cells? Is this 100w panel limited by
> the amount of sun that reaches it, or is it that the cells just can't
> handle more than 100w?

Connections may be lossy, I squared R.

> Is it a thermal problem?
>
> The reason I ask is that it seems to me that one could put a small number
> of cells close to the focal point of a huge parabolic reflector, use motors
> to track the sun, and get a lot higher output per cell than if you just
> used a flat panel. The fact that I have never seen this, though, makes me
> suspect that the amount of light reaching the cells is not the key limiting
> factor. Is that the case?

True enough, remember the heat is also concentrated.
PV systems work best in VERY cold places.
(Heat makes them lossy.)
The life of the cell is directly influenced by how much heat they are subjected
to.
Manufacturers actually add cells to a panel for operation in hot places to make

up for voltage losses with heat.

{Quote hidden}

I'm trying to squeeze every milliamp from my 450 watts of panels!


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2001\03\12@042247 by Alan B. Pearce

face picon face
>Incidentally, the daily power output from a solar array can be
>significantly improved by tracking the sun - but the complexity involve,
>along with the maintainance aspect appear to make this enhancement
>uncommon. Come up with a cheap and reliable way of doing it and there could
>be a significant market.

One low tech way of doing this is to have a double acting piston to push the
array back and forth. Then down each side of the array have a pipe suitably
painted black to be heat absorbing. One pipe connects to one end of the piston,
and the other pipe connects to the other end of the piston. The theory is the
sun will heat the two pipes, and whatever liquid is in there will get heated.
The array will move until the two pipes are receiving equal heat energy from the
sun, at which point the liquid pressures on both sides of the piston will be
equal.

I originally came across this suggestion in a Mother Earth News magazine, but
have never actually tried it. It was suggested for moving a solar water heating
array. It would need some thought put into the type of bearings that the array
rotates on to get suitably low friction as the only source of energy to move it
is the liquid pressure from the sun heat, but even with large errors at the
extremes of movement would probably give a useful addition to the array
efficiency.

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2001\03\13@014119 by Roman Black

flavicon
face
Alan B. Pearce wrote:
>
> >Incidentally, the daily power output from a solar array can be
> >significantly improved by tracking the sun - but the complexity involve,
> >along with the maintainance aspect appear to make this enhancement
> >uncommon. Come up with a cheap and reliable way of doing it and there could
> >be a significant market.
>
> One low tech way of doing this is to have a double acting piston to push the
> array back and forth. Then down each side of the array have a pipe suitably
> painted black to be heat absorbing. One pipe connects to one end of the piston,
> and the other pipe connects to the other end of the piston. The theory is the
> sun will heat the two pipes, and whatever liquid is in there will get heated.
> The array will move until the two pipes are receiving equal heat energy from the
> sun, at which point the liquid pressures on both sides of the piston will be
> equal.


Hi Alan, that's clever and I can see why it
appeals to the alternative energy people. :o)

But really, since you only need to scan the
panel through 120 degrees rotation over maybe
12 hours, how much power would this take? I
would not expect it to use more than 1% of panel
output power, probably 1/10th of 1%. Assuming
a decent quality small motor run for one second
every few minutes.
-Roman

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2001\03\13@035512 by Alan B. Pearce

face picon face
>But really, since you only need to scan the
>panel through 120 degrees rotation over maybe
>12 hours, how much power would this take? I
>would not expect it to use more than 1% of panel
>output power, probably 1/10th of 1%. Assuming
>a decent quality small motor run for one second
>every few minutes.

But it has the advantage that it does not take any power from the solar cells,
but may reduce the efficiency at each end of the travel.

What I would want to do is be up at sun up to watch it swing back in the
morning... :)

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2001\03\13@125403 by goflo

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face
How about using LPG as a working fluid?  Large
pressure differential for small temp difference
in the 0-50 C range...

Jack

{Quote hidden}

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2001\03\13@133243 by Alan B. Pearce

face picon face
>How about using LPG as a working fluid?  Large
>pressure differential for small temp difference
>in the 0-50 C range...

I wonder what the local fire department would say...

I guess the biggest problem would be filling it.

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2001\03\13@183427 by goflo

flavicon
face
Alan B. Pearce wrote:
>
> >How about using LPG as a working fluid?  Large
> >pressure differential for small temp difference
> >in the 0-50 C range...
>
> I wonder what the local fire department would say...

Don't tell 'em :)

> I guess the biggest problem would be filling it.

Use a couple of small disposable cylinders - Screw-on
fittings, pressure relief valves, ~$2 USD, painted black
and arranged behind the panel so that as the sun moves the
appropriate bottle is exposed...

Jack

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2001\03\14@035538 by Alan B. Pearce

face picon face
>Use a couple of small disposable cylinders - Screw-on
>fittings, pressure relief valves, ~$2 USD, painted black
>and arranged behind the panel so that as the sun moves the
>appropriate bottle is exposed...

The original article IIRC had a long thin pipe up the side of the panel so that
a small change in the angle of the sun made a large change in the percentage of
the pipe in sunlight/shadow. I guess this could still be done by having the
disposable cylinders hidden and acting as a reservoir for the rest of the
piping.

I had been envisaging filling the system from an LPG cylinder recharged at the
local filling centre, but the difficulty with this is these cylinders are
designed to draw off gas, and one would really need a cylinder with a tube into
the liquid to draw off liquid to fill the piping. I guess one could always mount
the cylinder upside down while doing the fill. :))

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2001\03\14@131757 by Peter L. Peres

picon face
Instead of LPG use safe freon. Electronic freeze spray may be a good
start. I have seen such a thing a long time ago. Since it uses no
electricity it was good for systemas that make hot water (the parabolical
or cylindical long mirror kind with a black pipe in the focal point).

Peter

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2001\03\14@153424 by John

flavicon
face
Hello Roman & PIC.ers,

Looks like I coulda done more homework before coming
along with my cockamamy ideas...

{Quote hidden}

Maximum Power Transfer..   mmm..  OK
Explains the need for PWM.

I guess the effective source impedance of a PV
panel has about 3 or 4 degrees of
freedom.


<snipd>

>a scrapyard for $100, but 750w of solar panels
>will cost you close to $4500. You will want to run
>those solar panels as efficiently as you can, even
>if it means getting some pwm fets! :o)
>-Roman
>

Those panels look a lot co$tlier than I imagined.
Changes the economic recipe a tad.

FWIW, grid energy in this country is still dirt-cheap
in world terms.
My latest bill, open in front of me, reflects a price
equivalent to US$ 0.036 / kWh ( 3.6 US cents).
I think Californian juice sells ~22 US cents.

Even if we have lots of sunshine here (and we do),
it'll not be worth using PV solar power except for
remote sites, etc.


   best regards,   John


e-mail from the desk of John Sanderson, JS Controls.
Snailmail:          PO Box 1887, Boksburg 1460, Rep. of South Africa.
Tel/fax:            Johannesburg  893 4154
Cellphone no:   082 741 6275
email:                EraseMEjsandspamspamspamBeGonepixie.co.za
Manufacturer & purveyor of laboratory force testing apparatus, and related
products and services.

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2001\03\14@184555 by goflo

flavicon
face
Don't know what's std in the UK, but small cylinders designed to
supply vapor CAN be inverted to draw off liquid - I fill portable
bottles this way.

    Caveat - Imperative that bottles not be over-filled.

For those unacquainted with LPG, it is stored as a liquid under
pressure. While the fire danger is nominal, dangerous pressures
can evolve in an improperly designed, constructed, or OVER-FILLED
system. Nothing to fool around with if you don't know what you're
about, so make sure you do...

Jack

Alan B. Pearce wrote:
{Quote hidden}

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2001\03\15@060208 by Roman Black

flavicon
face
Peter L. Peres wrote:
>
> Instead of LPG use safe freon. Electronic freeze spray may be a good
> start. I have seen such a thing a long time ago. Since it uses no
> electricity it was good for systemas that make hot water (the parabolical
> or cylindical long mirror kind with a black pipe in the focal point).
>
> Peter


Here's an idea, and it uses a PIC! :o)
Use an electric motor for solar panel scanning. Ok,
so that's not amazing. But you could also use a
simple reflective sheet, so that  you can get twice
the solar energy onto the panel.

Ok, smarties will comment that you can't do that as
you exceed the thermal limits of the panel when the
sun is overhead, whcih is the reason reflectors are
not advised.

Here's the clever bit, when the sun is lower in the
sky or clouds are present the device turns to give
panel+reflector= twice the energy. But when the sun
is too strong the panel can be rotated just enough
to disable the reflector, giving just the panel in
full sun. I checked around the net but no one is
doing this... It's very easy too.

The PIC could control the process, checking the
sun's intensity and position, and adjusting the
panel tracking motor for the best total power produced.
:o)
-Roman

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2001\03\15@061447 by Roman Black

flavicon
face
John wrote:

> Maximum Power Transfer..   mmm..  OK
> Explains the need for PWM.
>
> I guess the effective source impedance of a PV
> panel has about 3 or 4 degrees of
> freedom.


You got that right! Affected by heat, light, current
and the worst thing is they are series device, so if
a leaf falls and covers one CELL the whole panel goes
high impedance, not good for power transfer at all. :o)


{Quote hidden}

Remote sites are where it's happening. The cost of
getting power to these places is very high, and can be
20 times what you are paying. These are the areas
where the power company is much more likely to do
net-metering or buy-back schemes. Because of Australia's
size and small population there are a lot of places
like that here. Some townships buy diesel fuel and
generate their own electricity in small local power
stations, others with natural gas.
-Roman

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2001\03\15@074934 by Alan B. Pearce

face picon face
>The PIC could control the process, checking the
>sun's intensity and position, and adjusting the
>panel tracking motor for the best total power produced.
>:o)

Of course you will run the PIC off its own solar panel so it is not pinching
power produced by the main panels... :o)

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2001\03\15@093336 by Roman Black

flavicon
face
Alan B. Pearce wrote:
>
> >The PIC could control the process, checking the
> >sun's intensity and position, and adjusting the
> >panel tracking motor for the best total power produced.
> >:o)
>
> Of course you will run the PIC off its own solar panel so it is not pinching
> power produced by the main panels... :o)


Ha ha! Has anyone done a solar PIC?? Heck, the
thing could sleep for 99.9% of the time, it's
not like the sun moves really quickly or changes
brightness really quickly. :o)
-Roman

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2001\03\15@095046 by Bond Peter S-petbond1

flavicon
face
> Ha ha! Has anyone done a solar PIC?? Heck, the
> thing could sleep for 99.9% of the time, it's
> not like the sun moves really quickly or changes
> brightness really quickly. :o)

There was a road stud developed in the UK a couple of years ago using PICs -
solar cell + LEDs to illuminate lane markings.  Spent the day charging, and
then as much time as possible asleep.  There were plans for all the
different things that could be done with them - get them to strobe to
indicate accidents, stay on for a couple of seconds after a car passed them
etc. etc.

They were trialled in an accident blackspot area, and I've heard nothing
about them since.  Unfortunately, they ended up more expensive than the
standard reflective type.

Peter

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2001\03\15@113727 by goflo

flavicon
face
Peter L. Peres wrote:

> Instead of LPG use safe freon. Electronic freeze spray may be a good
> start. I have seen such a thing a long time ago. Since it uses no
> electricity it was good for systemas that make hot water (the parabolical
> or cylindical long mirror kind with a black pipe in the focal point).

Freon? You must live in a free country - Here a kilo of freon
will probably get you more time than a kilo of pot :) Anyway,
similar safety considerations apply - Freon is relatively inert
and non-toxic, of course, with a lower vapor pressure than LPG,
but - ANY confined substance which can undergo a phase change in
the ambient temp range is a potential bomb under the right cir-
cumstance.

In the case we're discussing, a lower vapor pressure means more
working fluid for a given amount of force, so I'm not sure I see
the advantage.

regards, Jack

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2001\03\15@135316 by Robert Rolf

picon face
If heat is such a problem, why not use 'cold mirror' technology as
is found on projector lamps? Basically a thin film filter applied to the
panel to reflect the damaging IR while allowing the appropriate part
of the spectrum to reach the panel. The reflectors could also be
made of complemenatary filtering glass, reflecting the 'good'
wavelengths,
while allowing the damaging ones to pass through.
The small loss in raw efficiency would be made up by the higher
collection efficiency the extra reflectors bring, and this thin
film technolgy is well developed so it can't be that expensive.

If leaves or other debris are really such a problem, would it be worth
having a compressed air jet on each panel, controlled by a PIC that
could sense a loss of panel output relative to the others, and activate
an air valve to blast off the debris?

Hummmm, time for me to apply for that patent...

Robert

Roman Black wrote:
{Quote hidden}

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2001\03\15@145151 by Sean Breheny

face picon face
Hi Robert,

I'm sure that would help, but IR is not the only reason why the cells get
hot. Radiation at any wavelength (visible included) heats something up
when it is absorbed. Also, the current flowing through the cells causes
I2R and IV losses.

Sean


On Thu, 15 Mar 2001, Robert Rolf wrote:

{Quote hidden}

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2001\03\16@043333 by Roman Black

flavicon
face
Robert Rolf wrote:
>
> If heat is such a problem, why not use 'cold mirror' technology as
> is found on projector lamps? Basically a thin film filter applied to the
> panel to reflect the damaging IR while allowing the appropriate part
> of the spectrum to reach the panel. The reflectors could also be
> made of complemenatary filtering glass, reflecting the 'good'
> wavelengths,
> while allowing the damaging ones to pass through.
> The small loss in raw efficiency would be made up by the higher
> collection efficiency the extra reflectors bring, and this thin
> film technolgy is well developed so it can't be that expensive.


Quite a few universities are studying using reflectors
and specialised cooling for the solar cells. I think my
suggestion has advantages being very cheap and easy to
produce.


> If leaves or other debris are really such a problem, would it be worth
> having a compressed air jet on each panel, controlled by a PIC that
> could sense a loss of panel output relative to the others, and activate
> an air valve to blast off the debris?
>
> Hummmm, time for me to apply for that patent...

Ha ha! Go for it! I'm sure the patent lawyers need
some more money. Since there are already thousands of
solar system patents it might not be worth much,
especially if it's a US patent. Now if you can get
a Chinese patent you might make something! ;o)
-Roman

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2001\03\16@163305 by Peter L. Peres

picon face
> Ha ha! Has anyone done a solar PIC?? Heck, the
> thing could sleep for 99.9% of the time, it's
> not like the sun moves really quickly or changes
> brightness really quickly. :o)

I have run a 16F84 at 32kHz off two amorphous solar panels (about 2.4V at
5mA at 200 lux each). The panels (together) were smaller than a cigarette
pack. All the problems with brownout/etc exist, plus unless you seriously
overrate the panel specs it will only work in really bright places. I
don't think that this applies to solar panel drivers.

The freon cylinders for solar panel moving I saw were actually some kind
of bellows in a cylinder with a loose piston afair. Perhaps you could use
rubber balloons filled to 5-10% of the inflated volume with etylic ether.
No pics though. ;-)

Of course the ultimate solar panel mover is an electric clock with 24 hour
dial and a cam ;-) Think 10W synchronous motor and gearing to suit panel
weight etc.

Peter

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2001\03\16@171304 by Peter L. Peres

picon face
> Freon? You must live in a free country - Here a kilo of freon
> will probably get you more time than a kilo of pot :) Anyway,
> similar safety considerations apply - Freon is relatively inert
> and non-toxic, of course, with a lower vapor pressure than LPG,
> but - ANY confined substance which can undergo a phase change in
> the ambient temp range is a potential bomb under the right cir-
> cumstance.

I think that there are safe freons and I did say safe. Anyway I was
referring to LPG forming combustible mixtures with air starting at 2% by
volume, which is bad news for DIY (ever seen how tiny the hole in a
lighter or LPG burner is ?).

Ether has been used before to actuate such things. It boils at a few tens
of degrees C (30-40 ?) depending on ambient pressure (I don't have the
data here).

Peter

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2001\03\16@175345 by Peter L. Peres

picon face
> In the case we're discussing, a lower vapor pressure means more
> working fluid for a given amount of force, so I'm not sure I see
> the advantage.

HCFCs with boiling points up to 10-15 degrees C and more are available.

Peter

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2001\03\16@200201 by Peter L. Peres

picon face
Here are some guys who did it with many small mirrors:

http://www.eskimo.com/~billb/amateur/mirror.html

Peter

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