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'[EE] Precautions for long run 400 VDC cabling?'
2017\08\14@030148 by James Cameron

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G'day,

When cabling DC from a solar array back to an inverter charger, with
increasing design distance, what are the precautions for the cable
design?

My previous post on 1st August;

> (Which reminds me; placing the solar array 50m away beyond trees is
> apparently quite costly, four strings at 400V each means the
> underground DC cable back to the battery inverters has to be more
> special than normal.)

Context: a 10 kW array, four strings, nominal 400 VDC, over either 10
metres or 60 metres in buried conduit.

It is a design tradeoff.  If we can do the extra distance, we get to
keep some trees for shade.

My designer is costing the extra 50 metres as a different type of
cable, with added interface gear, at around $9k, and I'm not yet sure
why.

Gut feel is "add another panel", so I must be missing something.

I'll find out more this time tomorrow, I hope.

-- James Cameron
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2017\08\14@032409 by RussellMc

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Not directly what you asked but:

400 VDC is nasty stuff if you are not an expert in dealing with it. Those
who are probably take it in their stride, but it seems bad enough to be
super careful of.
At 400 VDC  you do not want any sort of personal involvement with an arc.
I know of a friend of a friend who was hospitalised after opening a panel
to panel connector while the system was "on sun".

Somewhat to my surprise I can draw and hold a small arc from a nominal 30
VDC 300W panel.



   â€‹ Russell
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2017\08\14@071142 by Brent Brown

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Looking at AS/NZS 5033 standard (probably applies where you are) says PV main cables >50m should be either installed in earthed mettalic conduit or be shielded cable. Avoid loops. The idea seems to be in reducing inductive surge pickup (lightning?) and attenuating surge transmission. No joins allowed in cables. Nothing else seems to jump out relating to distance.

-------- Original message --------
From: James Cameron <spam_OUTquozlTakeThisOuTspamlaptop.org>
Date: 8/14/17  7:01 PM  (GMT+12:00)
To: .....piclistKILLspamspam@spam@mit.edu
Subject: [EE] Precautions for long run 400 VDC cabling?

G'day,

When cabling DC from a solar array back to an inverter charger, with
increasing design distance, what are the precautions for the cable
design?

My previous post on 1st August;

> (Which reminds me; placing the solar array 50m away beyond trees is
> apparently quite costly, four strings at 400V each means the
> underground DC cable back to the battery inverters has to be more
> special than normal.)

Context: a 10 kW array, four strings, nominal 400 VDC, over either 10
metres or 60 metres in buried conduit.

It is a design tradeoff.  If we can do the extra distance, we get to
keep some trees for shade.

My designer is costing the extra 50 metres as a different type of
cable, with added interface gear, at around $9k, and I'm not yet sure
why.

Gut feel is "add another panel", so I must be missing something.

I'll find out more this time tomorrow, I hope.

--
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2017\08\14@172205 by Dwayne Reid

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Depending on the cost of an extra panel, I'd be seriously looking at what your gut tells you and comparing price between the extra panels vs the $9k for relocating the entire array.

Keeping the trees is probably more important just because of the shade and wind protection they provide.

dwayne

At 01:01 AM 8/14/2017, James Cameron wrote:
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2017\08\14@180050 by James Cameron

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Russell, thanks.  I'm not doing it myself, I'm getting an electrician
to do it all.

Brett, thanks.  Yes, AS/NZS 5033 will apply.  I'll see if I can bring
the distance down below 50m by dropping three trees instead of nine.
AS/NZS 5033:2014 is alleged to also require maximum voltage drop of
3%, and maximum Voc of 600V unless access restriction is added.

https://www.gses.com.au/wp-content/uploads/2016/03/5033-2014-Changes.pdf

(Access to standards is an irritation for me; used to be able to get
at them through public library, but the library lost access.  My own
business isn't yet able to justify the expense of formal access;
mostly I'm doing software and firmware.)

Dwayne, thanks.  The trees are shade for garden walks in summer
(45°C), habitat for some fascinating birds, and wind protection during
the northerly (from equator) gales and dust storms.  Tallest five
trees at about 30m height.  On the other hand, removing them would
increase the winter solar thermal input of the house windows.  ;-)


I've been reading technical training and specifications of the gear,
and had a couple of theories;

1.  longer cable means larger voltage drop, that adding a panel brings
the total power above the maximum array power of the inverter charger.
But if that is the case then it should be accepted because of the
voltage drop.  And the input will be MPPT anyway.

2.  adding a panel brings Voc above 600V requiring access
restrictions.

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2017\08\14@195134 by John Gardner

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...Access to standards is an irritation for me; used to be able to get
at them through public library, but the library lost access.  My own
business isn't yet able to justify the expense of formal access;
mostly I'm doing software and firmware.

Don't those comrades work for you?   "8)


On 8/14/17, James Cameron <.....quozlKILLspamspam.....laptop.org> wrote:
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2017\08\14@201102 by James Cameron

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No, they don't.  It was outsourced to a commercial organisation which
charges fees for access.  Think it is $200 to $600 per standard.
Haven't checked lately.

On Mon, Aug 14, 2017 at 06:51:31PM -0500, John Gardner wrote:
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2017\08\14@203855 by Denny Esterline

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Any possibility of shortening the run from the other end? e.g. Move the
inverters and/or charger parts to a weatherproof box/housing/shed and then
run a more conventional AC line to the house?

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2017\08\14@204147 by John Gardner

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Such a deal!   "8)

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2017\08\14@213904 by James Cameron

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Yes, for about the same value.  With summer ambient around 45°C, and
the products not being specified for that, we end up with an insulated
equipment cabinet and an active cooling system.

On Mon, Aug 14, 2017 at 05:38:52PM -0700, Denny Esterline wrote:
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2017\08\14@215213 by Harold Hallikainen

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> ...Access to standards is an irritation for me; used to be able to get
> at them through public library, but the library lost access.  My own
> business isn't yet able to justify the expense of formal access;
> mostly I'm doing software and firmware.
>

My company pays $5k per year to access standards, some of which I help
write. To be on a standards committee, you have to be a member of the
organization (annual fee) and pay a "standards participation fee." I just
looked at their 2015 tax return. Total income of about $5.4M. Total
expenses of 4.3M. Revenue from sale of standards was abut $423k. Largest
revenue contributor was membership dues at $1M followed by conferences at
900k.

It does not look like they make a lot of money on standards...

Harold

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2017\08\14@221116 by James Cameron

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On Mon, Aug 14, 2017 at 06:51:58PM -0700, Harold Hallikainen wrote:
>
> > ...Access to standards is an irritation for me; used to be able to get
> > at them through public library, but the library lost access.  My own
> > business isn't yet able to justify the expense of formal access;
> > mostly I'm doing software and firmware.
> >
>
> My company pays $5k per year to access standards, some of which I help
> write. To be on a standards committee, you have to be a member of the
> organization (annual fee) and pay a "standards participation fee." I just
> looked at their 2015 tax return. Total income of about $5.4M. Total
> expenses of 4.3M. Revenue from sale of standards was abut $423k. Largest
> revenue contributor was membership dues at $1M followed by conferences at
> 900k.
>
> It does not look like they make a lot of money on standards...

Agreed.

I didn't know how that compares to the organisation that sells access
to Australian standards, so I went looking ...

http://www.afr.com/brand/chanticleer/baring-private-equity-asia-finally-grabs-sai-global-20160926-grobz5

earnings before tax of $AUD 131 million (USD 91 million or so), and
last year had an offer for $AUD 1 billion.  Publishing standards isn't
their only business.

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2017\08\14@230207 by Brent Brown

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On 15 Aug 2017 at 8:00, James Cameron wrote:

> Brett, thanks.  Yes, AS/NZS 5033 will apply.  I'll see if I can bring
> the distance down below 50m by dropping three trees instead of nine.
> AS/NZS 5033:2014 is alleged to also require maximum voltage drop of
> 3%, and maximum Voc of 600V unless access restriction is added.
>
> https://www.gses.com.au/wp-content/uploads/2016/03/5033-2014-Changes.pdf
>
> (Access to standards is an irritation for me; used to be able to get
> at them through public library, but the library lost access.  My own
> business isn't yet able to justify the expense of formal access;
> mostly I'm doing software and firmware.)

Access to standards is a pain here too, but being the holder of an electrical worker licence does get you on-line access to a number of standards, which is useful.

> 1.  longer cable means larger voltage drop, that adding a panel brings
> the total power above the maximum array power of the inverter charger.
> But if that is the case then it should be accepted because of the
> voltage drop. And the input will be MPPT anyway.

The complete sentence in AS/NZS 5033:2014 is "It is reccommended that under maximum load conditions the voltage drop from the most remote PV module in the array to the input of the PCE (inverter) should not exceed 3% of the Vmp voltage (at STC) for LV PV arrays".

So given the voltage drop is just a "reccomendation", I'd imagine it could be ok to exceed it, if you have a good techincal reason for doing so and providing everything else remains satisfactory, eg. for one thing, temperature rise in cable.

Also, it seems to me the difference between Vmp max load and Vmp STC would not be nearly as much as between say Vmp max load and Voc (no-load), so the 3% drop should be much easier to acheive. Or else I'm reading it wrong and confusing myself.

Also also, (sorry if you already know) it seems quite common and acceptable to use "under-sized" inverters... eg. say 6kW of panels on a 5kW inverter. Peak generation is only limited for a short time each day/some days, eg around mid-day on a fine day in mid-summer, as the inverter will (should) limit the output to 5kW so everything stays within spec. The rest of the time below 5kW you still get the advantage of the extra panels.

I don't actually have any direct experience with DC PV arrays, I only have a 5kW AC micro-inverter system myself. Over the last 18 months or so apparently I've "saved" 354 trees... living in town I have no idea where I'm going to put them ;-)


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2017\08\14@230225 by Byron Jeff

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45°C ambient? Youch that is hot!

BAJ

On Tue, Aug 15, 2017 at 11:38:52AM +1000, James Cameron wrote:
> Yes, for about the same value.  With summer ambient around 45°C, and
> the products not being specified for that, we end up with an insulated
> equipment cabinet and an active cooling system.
>
> On Mon, Aug 14, 2017 at 05:38:52PM -0700, Denny Esterline wrote:
> > Any possibility of shortening the run from the other end? e.g. Move the
> > inverters and/or charger parts to a weatherproof box/housing/shed and then
> > run a more conventional AC line to the house?
-- Byron A. Jeff
Associate Professor: Department of Computer Science and Information Technology
College of Information and Mathematical Sciences
Clayton State University
http://faculty.clayton.edu/bjeff
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2017\08\15@021747 by Sean Breheny

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I echo Russell's warning. I'd reckon that the solar array isn't as bad as a
battery bank since it cannot source the current that batteries can, but
nonetheless, DC arcs at this voltage tend to be very difficult to interrupt
and require very special fusing and switching. I've experienced the arcs
from 48V, 50 AH lead acid battery packs and even those are spectacular - in
the "spits molten copper at you" and "makes eerie
whistling/rushing/squealing noises" categories!

On Mon, Aug 14, 2017 at 3:23 AM, RussellMc <spamBeGoneapptechnzspamBeGonespamgmail.com> wrote:

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2017\08\15@032323 by xygax

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400v dc is standard for ups battries and in some transformerless designs 800v centre tapped. The cable used in uk would normally be single wire armoured 600v rated this would have a circuit breaker with multiple breaks in both legs normally a 4 pole with 2 series poles in each leg. Schneider breakers have 120v a pole rating this would need to be checked as some are only certified at 60v (abb)



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-------- Original message --------From: Sean Breheny <TakeThisOuTshb7EraseMEspamspam_OUTcornell.edu> Date: 15/08/2017  07:17  (GMT+00:00) To: "Microcontroller discussion list - Public." <RemoveMEpiclistspamTakeThisOuTmit.edu> Subject: Re: [EE] Precautions for long run 400 VDC cabling?
I echo Russell's warning. I'd reckon that the solar array isn't as bad as a
battery bank since it cannot source the current that batteries can, but
nonetheless, DC arcs at this voltage tend to be very difficult to interrupt
and require very special fusing and switching. I've experienced the arcs
from 48V, 50 AH lead acid battery packs and even those are spectacular - in
the "spits molten copper at you" and "makes eerie
whistling/rushing/squealing noises" categories!

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2017\08\15@032806 by Clint Jay

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I have a 12V 17AH SLA that's got half a terminal missing, it spat most of
it across the workshop when I accidentally dropped a socket/ratchet onto
the battery and shorted it. I can vouch for the unpleasantness of he
screeching sound it made.

On 15 Aug 2017 7:18 am, "Sean Breheny" <EraseMEshb7spamcornell.edu> wrote:

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2017\08\15@042720 by alan.b.pearce

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> (Access to standards is an irritation for me; used to be able to get at them
> through public library, but the library lost access.  My own business isn't yet
> able to justify the expense of formal access; mostly I'm doing software and
> firmware.)

Probably worth getting friendly with your local university (or are you out beyond the Black Stump?). They will often have access to all that sort of stuff.



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2017\08\15@054222 by James Cameron

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alan.b.pearce@stfc.ac.uk wrote:
> [James wrote]:
> > (Access to standards is an irritation for me; used to be able to
> > get at them through public library, but the library lost access.
> > My own business isn't yet able to justify the expense of formal
> > access; mostly I'm doing software and firmware.)
>
> Probably worth getting friendly with your local university (or are
> you out beyond the Black Stump?). They will often have access to all
> that sort of stuff.

Thanks!

Why didn't I think of that?  My university has a library outlet only
79km away, and I can register as alumni for online access.  I'll see
how they respond.

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2017\08\15@104200 by Van Horn, David

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Funniest warning sticker I have seen lately, of course on a solar panel:  "CAUTION:  Creates electric current when exposed to light"...

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2017\08\15@104438 by Van Horn, David

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You must comply with the standards, but you have to pay to know what they are...

Somehow, this is not right.


{Original Message removed}

2017\08\15@105527 by Clint Jay

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Not right for sure, but it's been that way for a very long time and seems
only to be getting worse.

On 15 Aug 2017 3:44 pm, "Van Horn, David" <
RemoveMEdavid.vanhornspam_OUTspamKILLspambackcountryaccess.com> wrote:


You must comply with the standards, but you have to pay to know what they
are...

Somehow, this is not right.


{Original Message removed}

2017\08\15@110028 by alan.b.pearce

face picon face
>
> Funniest warning sticker I have seen lately, of course on a solar panel:
> "CAUTION:  Creates electric current when exposed to light"...
>
Yeah, it's a bit like the fire department turning up to a burning building and waiting to get the hoses out until the solar panels are made safe, as has happened in the UK ...



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2017\08\15@122403 by Sean Breheny

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I'm not sure I get how the fire dept. example is related. Isn't it good
that they waited (assuming there are no people trapped inside)? Or is the
joke that they didn't realize that they could just make them safe with an
opaque tarp?

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2017\08\15@170817 by James Cameron

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An inquiry (royal commission) into bushfires in Victoria, Australia,
received submissions asserting the building standard AS3959 for
bushfire resistance was unavailable because of the cost, and this was
a contributing factor to the deaths and losses.

A submission included the standard.  Thus it became very helpfully public.
Bit of an "oh, shi*" moment when people began reading it for the first
time.

On Tue, Aug 15, 2017 at 03:55:25PM +0100, Clint Jay wrote:
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2017\08\15@173051 by Dwayne Reid

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At 12:17 AM 8/15/2017, Sean Breheny wrote:
>I echo Russell's warning. I'd reckon that the solar array isn't as bad as a
>battery bank since it cannot source the current that batteries can <SNIP>

The problem is that the output voltage of a solar array can rise significantly when the load is removed.  Your breaking voltage of 400V suddenly doubles.  Ouch!

In other words, an arc from the output of a large, high-voltage solar array can be worse than that of the battery bank, at least in terms of quenching the arc.

dwayne


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Custom Electronics Design and Manufacturing

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2017\08\15@174150 by John Gardner

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One can see some point in emergency covers for hefty panels...

...


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2017\08\15@181752 by Brent Brown

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When the fire department turn up they quickly spot the high voltage DC equipment sitting on top of your burning house, and correctly identify it as a hazard discouraging the use of water in the first instance to put out the fire.

There are regulations for signage, which, if present and accessible, will state how and where to safely disable the PV generation equipment... only if time & other factors permit.

If it's grid connected AC micro-inverters then it's fairly straight forward.... anything/everything can be turned off in no particular order quite safely. But with DC systems it's far from simple, as discussed already. Even with load/inverter shut down first then DC isolator switches turned off in the correct order the solar array itself can/will still be live and dangerous. We're asking fire fighters to have as much knowledge of solar PV systems as installers have... it's a real challenge they have to confront these days.

Trying to covering the array to make it dark, while doing this at height, on top of a burning house, sounds a bit improbable. When there is doubt, and there certainly can be in the heat of the moment - excuse the pun, the fall back position is that lives are more valuable than possessions.

On 15 Aug 2017 at 12:24, Sean Breheny wrote:

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2017\08\15@184635 by John Gardner

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Indeed - I imagine this will be addressed in the not too distant future

by Electrical codes.  At considerable cost to... someone,  one suspects...

...


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2017\08\15@191729 by James Cameron

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On Tue, Aug 15, 2017 at 05:46:30PM -0500, John Gardner wrote:
> Indeed - I imagine this will be addressed in the not too distant future
> by Electrical codes.  At considerable cost to... someone,  one
> suspects...

Yes.

Sometime in the last few months, saw investigation reports on fires
caused by faulty termination of cables to DC isolation switches in the
UK, and the photographs showed the switches mounted indoors next to
the inverter.

In Australia, we are required to have isolation switches on the roof next
to the panels, presumably so fire crews can reach them with a pole.

So we end up with two switches; one on top, one down below.

I've no idea if this is based on evidence.  ;-)

-- James Cameron
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2017\08\15@192549 by stephen.forrestn/a

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Foam?


-----Original Message-----
From: spamBeGonepiclist-bouncesspamKILLspammit.edu [.....piclist-bouncesspam_OUTspammit.edu] On Behalf Of John Gardner
Sent: Wednesday, 16 August 2017 7:42 AM
To: Microcontroller discussion list - Public. <TakeThisOuTpiclist.....spamTakeThisOuTmit.edu>
Subject: Re: [EE] Precautions for long run 400 VDC cabling?

One can see some point in emergency covers for hefty panels...

...


On 8/15/17, Dwayne Reid <TakeThisOuTdwaynerKILLspamspamspamplanet.eon.net> wrote:
{Quote hidden}

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2017\08\16@053724 by rubenjonsson

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Actually, here in Europe the European directives and their essential
requirements are the law and harmonized standards are a recommended way
to comply with them. The directives (with the essential requirements)
are available for free. Unfortunately they are not as straight forward
and easy to convert into product requirements as the standards.

I wonder how much safer products would be if EN, IEC, ISO and UL
standards where freely available. ETSI shows that standards can be free
of charge.

/Ruben

On Tue, 15 Aug 2017 14:44:36 +0000, "Van Horn, David"
<RemoveMEdavid.vanhornspamspamBeGonebackcountryaccess.com> wrote:
> You must comply with the standards, but you have to pay to know what
> they are...
>
> Somehow, this is not right.
>
>
> {Original Message removed}

2017\08\16@075442 by RussellMc

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On 16 August 2017 at 10:17, Brent Brown <spamBeGonebrent.brown@spam@spamspam_OUTclear.net.nz> wrote:

> ​....
>


> ​
> Trying to covering the array to make it dark, while doing this at height,
> on top of a
> burning house, sounds a bit improbable.


​It's even harder than it sounds.
A typical PV panel ​maintains most of it's voltage output down to about 5%
of peak insolation.
Current output falls approximately linearly with insolation down to 10% or
so.

So, to ensure that you did not get a significant percentage of operating
voltage on the system on a sunny day, the covering tarpaulins would have to
guarantee that light levels were on average only a few percent of external
light levels in sunny-day conditions.


     Russell
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2017\08\16@080455 by RussellMc

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On 16 August 2017 at 02:41, Van Horn, David <
TakeThisOuTdavid.vanhornspamspambackcountryaccess.com> wrote:

>
> Funniest warning sticker I have seen lately, of course on a solar panel:
> "CAUTION:  Creates electric current when exposed to light"...
>
> Long ago ​I (really*) saw a person,  trying to find why an amateur band
transmitter was not 'working', reach behind the transceiver, pick up the
short cable from the transceiver which was meant to connect to an external
VSWR meter but was disconnected, and say ~= "Here's the problem". ​

​The TX was idling and VOX triggered. When he spoke it obligingly
transmitted. He yelled suitably impressively.

Maybe it needed a sign "Creates RF when exposed to speech" :-).


           Russell​

* You see a zillion made up stories about similar things in life.
I actually saw this happen :-)

Auckland Unversity radio club.
Early 1970s.
??? Debraceni / Debreczeni I think.
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2017\08\16@083552 by RussellMc

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On 16 August 2017 at 09:30, Dwayne Reid <dwaynerEraseMEspamplanet.eon.net> wrote:

> At 12:17 AM 8/15/2017, Sean Breheny wrote:
> >I echo Russell's warning. I'd reckon that the solar array isn't as bad as
> a
> >battery bank since it cannot source the current that batteries can <SNIP>
>
> The problem is that the output voltage of a solar array can rise
> significantly when the load is removed.  Your breaking voltage of
> 400V suddenly doubles.  Ouch!
>
> ​Doubling very unlikely - about 25% rise max usual. Still significant.

​Voc:Vmp depends on quality of cells with higher efficiency cells having a
lower ratio.
​
Vmp/Voc is unlikely to be lower than 0.8 and 0.85 is common. 0.9 would be a
very good cell or panel.
(Vmp x Imp / (Voc x Isc ) = "fill factor" = figure of merit.
So Voc/Vmp would be unlikely to be much more than 1.25 worst case, so about
500V for a  400V Vmp system. That gives a 100V (about) lattitude for added
Voc.
Single higher wattage panels are typically about 30V - 42V Vmp although
higher are available. So say 38v - 50V Voc.

R
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2017\08\16@100431 by Van Horn, David

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The fellow I WATCHED, while he was troubleshooting a 100W PA system.  He had a single speaker connected, and he was getting some slight audio, so he almost stuck his head inside the cone of the speaker. About that time, the intermittent connection connected....  Those horns are pretty efficient.




* You see a zillion made up stories about similar things in life.
I actually saw this happen :-)

Auckland Unversity radio club.
Early 1970s.
??? Debraceni / Debreczeni I think.
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2017\08\16@123459 by Sean Breheny

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I had something similar happen when I was trying to rig up a prank. I had a
"novelty" device which made fart sounds and I was connecting it to an
external amp and speaker to make it somewhat louder as a part of a prank. I
didn't know what the output level would be so I kept increasing the gain of
the amp and was getting disappointing results. Suddenly the amp BLASTED a
fart sound so loud that the entire office heard it. The connection was
intermittent and had just resolved itself :)



On Wed, Aug 16, 2017 at 10:04 AM, Van Horn, David <
RemoveMEdavid.vanhornEraseMEspamspam_OUTbackcountryaccess.com> wrote:

{Quote hidden}

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2017\08\16@174541 by James Cameron

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Have spoken again to my very busy electrician, and he was designing
for no more than 1% loss in each cable run, because of an overall
standard that requires no more than 1% loss ... so I reminded him that
3% was allowed for the DC run from the panels, but I'm not yet
confident I've got his agreement.  He then went on to say it was
mainly about the voltage drop.

-- James Cameron
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2017\08\16@195233 by John Ferrell

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Unfortunately (at least in the US ) much of the criminal law is behind a Paywall which prevents the citizen from knowing the law until it is too late.  Since the NFPA (National Fire Protection ??) is not available to the homeowners they frequently run afoul of the building codes.  It appears that some inspectors write their own rules on the spot.


On 8/16/2017 5:37 AM, @spam@rubenjonssonRemoveMEspamEraseMEbredband.net wrote:
> I wonder how much safer products would be if EN, IEC, ISO and UL
> standards where freely available. ETSI shows that standards can be free
> of charge.

-- John Ferrell W8CCW
   Julian NC 27283
 It is better to walk alone,
than with a crowd going the wrong direction.
                  --Diane Grant


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2017\08\17@001525 by RussellMc

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On 17 August 2017 at 09:45, James Cameron <EraseMEquozlspam@spam@laptop.org> wrote:

> Have spoken again to my very busy electrician, and he was designing
> for no more than 1% loss in each cable run, because of an overall
> standard that requires no more than 1% loss ... so I reminded him that
> 3% was allowed for the DC run from the panels, but I'm not yet
> confident I've got his agreement.  He then went on to say it was
> mainly about the voltage drop.
>
> ​As Vdrop is proportional to resistance at the same current (V=IR)
and power loss is also proportional to resistance at constant current
(P=I^2.R)
tripling power loss or voltage drop decreases your copper volume by a
factor of 3 so hopefully your cable cost by a factor of 2 to 4 (as there is
no certainty which way cost scales with area).

An extra panel sounds like a good idea if you MUST maintain max_power, BUT
2% power lost at max power is rather less often and rather less in Winter
and irrelevantish in Summer, so max allowed cable loss seems sensible.

Inverter will accept voltage across a significant range. As long as Vin is
within MPPT range it's not overly important.

A nephew recently installed a 10 kW fully off-grid solar system. His panels
are permanently set at the winter maximum angle.




            Russell
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'[EE] Precautions for long run 400 VDC cabling?'
2017\09\04@220110 by James Cameron
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On Mon, Aug 14, 2017 at 05:01:38PM +1000, James Cameron wrote:
> When cabling DC from a solar array back to an inverter charger, with
> increasing design distance, what are the precautions for the cable
> design?

Some specifications have been filled in, and a quotation received from
my designer.  I'm pleased with it.

The system is to consist of;

1.  photovoltaic array, 10 kW, as 36 modules in four series strings,
each module Voc 39.9V, peak power 300W, Isc 9.64A, so each string
359.1V at 9.64A, (Trina Honey M Plus TSM-DD05A, see references),

2.  DC cabling, four runs of 400V DC cable, to a maximum of 1% loss
(not yet sure why), and any necessary array earthing cables,

3.  two inverter/chargers, each with two DC MPP inputs, one battery
connector for a 48V nominal battery, one grid interconnect, and one
emergency power output, (SolaX X-hybrid E series SK-SU5000E, see
references),

4.  two 10 kWh lithium-ion battery arrays, (LG Chem RESU10, see
references),

5.  contactors for switching loads to emergency power output of
inverter/chargers,

6.  current transformer monitored by the inverter/chargers to
minimise grid import and export.

My quick system diagram showing power limits;

http://dev.laptop.org/~quozl/solar-2017-09.png

Theory of operation; power from the photovoltaics (2.5 kW per string)
is taken by a maximum power point tracking input of an
inverter/charger, and depending on battery state of charge, policy,
and consumer loads, is delivered to either the battery (2.5 kW) or the
loads in synchronisation with the grid (4.6 kW).

When grid voltage collapse occurs, an inverter/charger will drive a
contactor to switch a set of loads to an emergency power output, which
will deliver up to 2 kW per inverter/charger.  Is specified to take up
to five seconds.


References:

Trina Solar DD05A.08 - Data Sheet
http://static.trinasolar.com/sites/default/files/Honey%20M%20Plus%20DD05A%28II%29%20Australia%20Feb2017%20A.pdf

Trina Solar DD05A.08 - Install Guide
http://static.trinasolar.com/sites/default/files/PS-M-0434%20A%20Installation%20Manual%20of%20Standard%20Module_IEC_UL_2016_A.pdf

SolaX X-hybrid E series SK-SU5000E - Data Sheet
http://www.solaxpower.com/wp-content/uploads/2017/08/Gen2-X-hybrid.pdf

SolaX X-hybrid E series SK-SU5000E - Install Guide
http://www.solaxpower.com/wp-content/uploads/2017/01/X-Hybrid-Install-Guide..pdf

SolaX X-hybrid E series SK-SU5000E - with LG Chem battery Wiring Schematic
http://www.solaxpower.com/wp-content/uploads/2017/01/SK-SUxxxxE-LG-Wiring-Schematic.pdf

LG Chem RESU10 - Data Sheet
http://www.lgchem.com/upload/file/product/ESS_LGChem_ENG[0].pdf

LG Chem RESU10 - Install Guide
http://solarjuice.com.au/wp-content/uploads/2016/11/RESU-48V_installation_manual_R2_eng_2016-10-21-1.pdf

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2017\09\05@002523 by stephen.forrestn/a

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Nice system James -
A couple of q's... (if you don't mind)

How long is the 400V run (maybe mentioned previously but??)
Are the four runs bundled or separately trenched?
How did you size your system? Was it on existing consumption with net export, coverage for outage, price break point, best within budget?
I remember you planned ground based panels - yes?
Will they all be at a level or tiered?
Same orientation or differently optimised for time/season? (I guess not tracking.)

I'll probably think of other questions after I hit send ;o)

I lived off grid for 7 years with an old late 90's - early 00's era system that came with the property, and newish 12 V 700 Ah LA cells. We were more than 2 km from the nearest mains power so no other option. Our system only had a 1200 W inverter with about the same in PV capacity. Fridge was gas, hot water solar/fuel stove and back-up of one of two generators, depending on load. We were very frugal with our power, especially in winter!

It was a beautiful place to live (central Victoria). Weeks of 40+ C weather was tough though with no A/C. We are no longer there (work) but how I miss it.

Anyway, good luck with the install. Don't forget to double the works cost ;o)

Stephen



{Original Message removed}

2017\09\05@021218 by James Cameron

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Thanks Stephen.  Your questions are interesting.  ;-)

I've measured the 400V run just now with a pole, and calculate it at
about 45.5 m.

(Half width of the array string is 4.5 m, then about 3 m to get into
trench, then 35 m of trench, then about 3 m to get out of trench to
equipment bay.  Tall trees that we are unwilling to remove are the
cause of 20 m extra trench length.)

Don't know if the four runs will be bundled or separately trenched,
but the layout of the array suggests two trenches in a V or Y shape
would maintain minimum lengths.

System was sized for extended outages; minimum loads for domestic
health; water pump, heat pumps, and cooking.  Export uninteresting,
because of high regulatory compliance costs, low price paid, and no
time of export pricing.  That may change later.  Reposit looks good.

(Grid did nearly collapse last summer; forecast demand above available
generator capacity, and I'm estimating 10% probability of a day long
collapse this summer, and 30% the year after. It is difficult to plan
when so many factors may perturb the system on a whim, and the
perturbations haven't been long term lately.  Call me the leading edge
of the death spiral.)

Array is to be ground mounted on a structural steel frame with
concrete around the verticals.

Two tiers; 18 modules on upper tier, 18 modules on lower tier; about
18 m wide, and 3.3 m from top to bottom.  Fixed orientation to solar
North, and not tracking.

You didn't ask, but I'll also mention the equipment bay is to be
inside the house envelope, to increase the life of the batteries.  We
had some 45°C 10% RH days last summer.

On Tue, Sep 05, 2017 at 04:25:19AM +0000, @spam@stephen.forrestspam_OUTspam.....agilent.com wrote:
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2017\09\05@031356 by stephen.forrestn/a

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Cheers :o)

It is amazing how quickly those zigs and zags in a run add up.
I know about those 45 C days! Hard on all gear exposed to the sun.
Ground mounted MUCH easier to clean and cleaning is important. When we arrived at our place, some of the panels had lichen growing on them - not good for efficiency.

I am jealous.

S.


{Original Message removed}

2017\09\05@033401 by RussellMc

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On 5 September 2017 at 14:01, James Cameron <spamBeGonequozlEraseMEspamlaptop.org> wrote:


> Some specifications have been filled in, and a quotation received from
> my designer.  I'm pleased with it.
>

Sounds very nice.
More questions will happen, but a few to start.

- I note you are proposing "true" Lithium Ion cells as opposed to the
LiFePO4 that you mentioned previously.

Why this choice? (Cost/lifetime/capacity/ planned use, ...)
What is the cycle life at what design DOD% and what Vmax do they use on the
cells to get rated lifetimes.
(Cell spec says 3.0V-4.2V full range which is = usual).
Other related?

- How are the PV panel cables fastened to the system?   [[Say what?  :-) ]]


*- ​Comment only: *

I note you correctly quote Isc and Voc
So combined voltages and current you quote are Vmax with no load and I with
system shorted at panels

Very impressive 18.3% panel efficiency. Nicely up on what was typical even
a few years back.
(With 18.6% from very top offering).


       Russell
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2017\09\05@043104 by James Cameron

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On Tue, Sep 05, 2017 at 07:33:18PM +1200, RussellMc wrote:
> On 5 September 2017 at 14:01, James Cameron <quozlspamBeGonespamlaptop.org> wrote:
>
>
> > Some specifications have been filled in, and a quotation received
> > from my designer.  I'm pleased with it.
> >
>
> Sounds very nice.
> More questions will happen, but a few to start.
>
> - I note you are proposing "true" Lithium Ion cells as opposed to the
> LiFePO4 that you mentioned previously.
>
> Why this choice? (Cost/lifetime/capacity/ planned use, ...)

Availability from designer and installer.  In other words, apart from
saying "not lead-acid", I've allowed them freedom.  They are terribly
busy, and I don't feel I have much choice.

> What is the cycle life at what design DOD% and what Vmax do they use
> on the cells to get rated lifetimes.  (Cell spec says 3.0V-4.2V full
> range which is = usual).  Other related?

Don't know, sorry.

> - How are the PV panel cables fastened to the system?  [[Say what?
> :-) ]]

My guess is that they'll be coated with honey, which will bring the
ants, then the spiders will hunt the ants, then the various parasitic
wasps will take out the spiders to use as stunned but living egg
nurseries, and the resulting dried muddy mess will stop any cable from
moving.  ;-)

The actual mating surfaces of the module cables will probably hide
inside a little junction box to connect to the 400V DC cable run.

> *- ​Comment only: *
>
> I note you correctly quote Isc and Voc. So combined voltages and
> current you quote are Vmax with no load and I with system shorted at
> panels

Yeah, I felt these were the most relevant points of the IV curve for
insulation and cable diameter.  The third relevant point would be Pmax.

> Very impressive 18.3% panel efficiency. Nicely up on what was
> typical even a few years back.  (With 18.6% from very top offering).

Thanks.  I hadn't noticed.

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2017\09\05@082459 by RussellMc

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>
> > - How are the PV panel cables fastened to the system?  [[Say what?
> > :-) ]]
>
> My guess is that they'll be coated with honey, which will bring the
> ants, then the spiders will hunt the ants, then the various parasitic
> wasps will take out the spiders to use as stunned but living egg
> nurseries, and the resulting dried muddy mess will stop any cable from
> moving.  ;-)
>
> The actual mating surfaces of the module cables will probably hide
> inside a little junction box to connect to the 400V DC cable run.
>

​I'd check which honey they use.
I'd expect that in Oz by now serious people 'do it right' ​- the standards
tend to proscribe things like cable ties which usually work for 'years'.
Maybe 8 or 4 or 2 or ...
Never 20. Metal ct's get used. Many systems now have wiring clips as p[art
of the panel frame or mounting frame.


       R
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2017\09\05@154449 by Denny Esterline

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Interesting...
I managed to get on a mailing list for a company named Heyco. (I use some
of their cord grips)
Their emails have been pushing their line of cable managment bits and
doo-dads for solar installations lately. Metal spring clips, stainless
steel cable ties, etc.

Probably at least vaguely interesting to at least one of you :-)
https://www.heyco.com/Solar_Power_Components/


-Denny


On Tue, Sep 5, 2017 at 5:24 AM, RussellMc <RemoveMEapptechnz@spam@spamspamBeGonegmail.com> wrote:

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2017\09\05@171552 by James Cameron

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On Tue, Sep 05, 2017 at 04:12:10PM +1000, James Cameron wrote:
> (Grid did nearly collapse last summer; forecast demand above available
> generator capacity, and I'm estimating 10% probability of a day long
> collapse this summer, and 30% the year after. It is difficult to plan
> when so many factors may perturb the system on a whim, and the
> perturbations haven't been long term lately.  Call me the leading edge
> of the death spiral.)

Further comment.

Available generator capacity is constrained by thermal coal plant
sighted within coal reserves that have now been exhausted, now moving
fuel from further away, and hanging on waiting for the plant
maintenance costs to exceed profit after transport costs.  Just
business and logistics.

None of which seems to be visible in the public political discourse
which instead fixates on policy responses.

http://www.abc.net.au/news/2017-09-06/electricity-markets-struggling-as-coal-shuts-down-aemo-says/8875874

And risk of load-shedding this summer estimated by the market operator
at up to 43% for most vulnerable state.

http://www.abc.net.au/news/2017-09-05/turnbull-in-talks-with-agl-keep-liddell-coal-power-station-open/8874874

Load-shedding typically begins with the large industrial customers
like aluminium production.

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