[RE-wrenches] PV voltage at Isc

Sat Feb 5 12:01:07 PST 2011

Greg,

Great question.

All power generators and energy storage devices (batteries, capacitors, etc.) have what's termed "internal resistance", also termed "internal impedance" when frequency greater than DC is involved.  This resistance/impedance is what limits the output current of these devices.

When you short-circuit PV, you'll measure amperage flowing through the leads commensurate with whatever that internal resistance happens to be at that moment (dependent on irradiance, temperature, and other variables).  With a theoretically perfect zero-ohm load, 100% of the voltage being generated by the PV at that moment will be drpped across its internal resistance.  The load (being "perfect") will have zero volts across it (E = I * R).  If R = 0, so does E.

In real life, there will always be a voltage greater than zero across your load, no matter how infinitesimal, because no matter how large a conductor you use, it will have some value of R greater than zero.  The voltage across the "short" may be on the order of a few millivolts (thousandths of a volt) .. down to a few hundred microvolts (millionths of a volt) for very large conductors.  However, the value of this voltage is so low compared to normal PV operating voltages as to be considered zero for all intents and purposes.

Dan

--- On Sat, 2/5/11, Greg Egan <greg at remotepowerinc.com> wrote:

From: Greg Egan <greg at remotepowerinc.com>
Subject: [RE-wrenches] PV voltage at Isc
To: re-wrenches at lists.re-wrenches.org
Date: Saturday, February 5, 2011, 1:30 PM

Fellow Scientists,

I got in a discussion with a wrench the other day.  He is under the
impression that when a PV module is at short circuit current there is
no voltage.  My understanding of electricity is that if there's no
voltage there's no current because current needs voltage in order to
flow.  I'm seeing it as a difference in potential, voltage that is.  If
there's no difference in potential I don't understand why current would
flow.  

I googled it and the few links I checked out were on his side - zero
voltage at Isc.  All this is of course irrelevant to the business of
installing PV so if you don't care I don't blame you.  

So I still think that if you a precise enough meter that if you stuck
the test leads into the cables sticking out of the back of a shorted PV
module that you'd read some small voltage that was approaching zero. 
Any explanation of why I am right or wrong in plain English (I'm not
really a scientist) would be welcome.

All the best,

Greg Egan

Remote Power Inc.

Fairbanks, AK

re-wrenches-request at lists.re-wrenches.org wrote:

  Send RE-wrenches mailing list submissions to
	re-wrenches at lists.re-wrenches.org

To subscribe or unsubscribe via the World Wide Web, visit
	http://lists.re-wrenches.org/listinfo.cgi/re-wrenches-re-wrenches.org
or, via email, send a message with subject or body 'help' to
	re-wrenches-request at lists.re-wrenches.org

You can reach the person managing the list at
	re-wrenches-owner at lists.re-wrenches.org

When replying, please edit your Subject line so it is more specific
than "Re: Contents of RE-wrenches digest..."

When responding to posts within the Digest, be sure to restore the Subject: line to the original, and please edit out any extraneous lines from the quoted message.

Today's Topics:

   1. Re: PV Encapsulant Quality (Eric Thomas)
   2. I Need a Sharp SunVista Manual (Brian Sipp)
   3. Re: I Need a Sharp SunVista Manual (Jeff Irish)
   4. Re: I Need a Sharp SunVista Manual (Brian Sipp)
   5. Re: PV Encapsulant Quality (Jesse Dahl)
   6. Re: Matching modules into Xantrex GT (Allan Sindelar)

----------------------------------------------------------------------

Message: 1
Date: Fri, 4 Feb 2011 10:33:27 -0800
From: Eric Thomas <solarepiphany at gmail.com>
To: re-wrenches at lists.re-wrenches.org
Subject: Re: [RE-wrenches] PV Encapsulant Quality
Message-ID:
	<AANLkTi=fAxBTRHLxoR9WQaLEJn8e7v_gygpdYepusjb6 at mail.gmail.com>
Content-Type: text/plain; charset="iso-8859-1"

Here is a great report that goes over advanced life cycle
testing of modules and their reasons for failure.
http://www.nrel.gov/docs/fy11osti/47755.pdf . It is a recent study and there
is some good info regarding encapsulents. I can tell you that the high
ranker on the results chart is the Silicon Energy Cascade module. With its
glass on glass encapsulent and integrated wireway, its the most robust
module I've ever seen. We installed the largest WA residential system
utilizing these modules in Dec of last year. They are nice to work
with...not without their challenges of course, but as far as warranty..I
think they will last the test of time.

Eric Thomas
Solar Epiphany
(206)919-3014
www.solarepiphany.com
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.re-wrenches.org/pipermail/re-wrenches-re-wrenches.org/attachments/20110204/799c5d79/attachment.html>

------------------------------

Message: 2
Date: Fri, 4 Feb 2011 13:21:09 -0800
From: "Brian Sipp" <Brian.Sipp at FirstSourceSolar.com>
To: "'RE-wrenches'" <re-wrenches at lists.re-wrenches.org>
Subject: [RE-wrenches] I Need a Sharp SunVista Manual
Message-ID: <8B7DB7ABA13B4A05A1E69FCEA166F07B at FirstSource>
Content-Type: text/plain; charset="us-ascii"

I just got off the phone with the worlds worst customer (dis)service rep. at
Sharp.  It really calls into question whether I want to sell any more of
Sharp modules, if this is how they treat their past customers.  

Does anyone have a PDF of the Sharp SunVista manual?  The only thing I find
online, or Sharp would provide, is a 2 page cut sheet.     

Brian M. Sipp
First Source Solar Systems
 <http://www.firstsourcesolar.com/> www.FirstSourceSolar.com 

-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.re-wrenches.org/pipermail/re-wrenches-re-wrenches.org/attachments/20110204/5c558a63/attachment-0001.htm>

------------------------------

Message: 3
Date: Fri, 4 Feb 2011 16:31:41 -0500
From: "Jeff Irish" <jeff at hvce.com>
To: "RE-wrenches" <re-wrenches at lists.re-wrenches.org>
Subject: Re: [RE-wrenches] I Need a Sharp SunVista Manual
Message-ID:
	<86FA2C8AA80F3C49AE21B7EC7BD559B8798995 at HVCE-SERVER.hvcegroup.local>
Content-Type: text/plain; charset="us-ascii"

Brian,

I have one but it's a big file and I don't want to overload everyone's
mailboxes.  Email me off-line at jeff at hvce.com

Jeff Irish

Hudson Valley Clean Energy

and Adirondack Solar

________________________________

From: re-wrenches-bounces at lists.re-wrenches.org
[mailto:re-wrenches-bounces at lists.re-wrenches.org] On Behalf Of Brian
Sipp
Sent: Friday, February 04, 2011 4:21 PM
To: 'RE-wrenches'
Subject: [RE-wrenches] I Need a Sharp SunVista Manual

I just got off the phone with the worlds worst customer (dis)service
rep. at Sharp.  It really calls into question whether I want to sell any
more of Sharp modules, if this is how they treat their past customers.  

Does anyone have a PDF of the Sharp SunVista manual?  The only thing I
find online, or Sharp would provide, is a 2 page cut sheet.     

Brian M. Sipp
First Source Solar Systems
www.FirstSourceSolar.com <http://www.firstsourcesolar.com/>  

-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.re-wrenches.org/pipermail/re-wrenches-re-wrenches.org/attachments/20110204/6a2faf4d/attachment-0001.htm>

------------------------------

Message: 4
Date: Fri, 4 Feb 2011 14:05:03 -0800
From: "Brian Sipp" <Brian.Sipp at FirstSourceSolar.com>
To: "'RE-wrenches'" <re-wrenches at lists.re-wrenches.org>
Subject: Re: [RE-wrenches] I Need a Sharp SunVista Manual
Message-ID: <F23DB5CB2F37496092CD7CCC9A263EC8 at FirstSource>
Content-Type: text/plain; charset="us-ascii"

Wow, that was fast!  Thank you to everyone who replied on and off line.  As
always the wealth of knowledge on the forum, and folks openness to share
always impresses me!  

This made my day!

PS:  Sharp - Start taking notes...

Brian M. Sipp
First Source Solar Systems
 <http://www.firstsourcesolar.com/> www.FirstSourceSolar.com 
Office: 530-554-1925
Mobile: 916-342-2630

  _____  

From: re-wrenches-bounces at lists.re-wrenches.org
[mailto:re-wrenches-bounces at lists.re-wrenches.org] On Behalf Of Jeff Irish
Sent: Friday, February 04, 2011 1:32 PM
To: RE-wrenches
Subject: Re: [RE-wrenches] I Need a Sharp SunVista Manual

Brian,

I have one but it's a big file and I don't want to overload everyone's
mailboxes.  Email me off-line at jeff at hvce.com

Jeff Irish

Hudson Valley Clean Energy

and Adirondack Solar

  _____  

From: re-wrenches-bounces at lists.re-wrenches.org
[mailto:re-wrenches-bounces at lists.re-wrenches.org] On Behalf Of Brian Sipp
Sent: Friday, February 04, 2011 4:21 PM
To: 'RE-wrenches'
Subject: [RE-wrenches] I Need a Sharp SunVista Manual

I just got off the phone with the worlds worst customer (dis)service rep. at
Sharp.  It really calls into question whether I want to sell any more of
Sharp modules, if this is how they treat their past customers.  

Does anyone have a PDF of the Sharp SunVista manual?  The only thing I find
online, or Sharp would provide, is a 2 page cut sheet.     

Brian M. Sipp
First Source Solar Systems
www.FirstSourceSolar.com <http://www.firstsourcesolar.com/>  

-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.re-wrenches.org/pipermail/re-wrenches-re-wrenches.org/attachments/20110204/43b16ce8/attachment-0001.htm>
-------------- next part --------------
A non-text attachment was scrubbed...
Name: not available
Type: image/gif
Size: 3648 bytes
Desc: not available
URL: <http://lists.re-wrenches.org/pipermail/re-wrenches-re-wrenches.org/attachments/20110204/43b16ce8/attachment-0001.gif>

------------------------------

Message: 5
Date: Fri, 4 Feb 2011 16:05:45 -0600
From: Jesse Dahl <dahlsolar at gmail.com>
To: RE-wrenches <re-wrenches at lists.re-wrenches.org>
Subject: Re: [RE-wrenches] PV Encapsulant Quality
Message-ID: <69420D91-5072-41E1-AF12-4A9FE7D1B492 at gmail.com>
Content-Type: text/plain; charset="us-ascii"

Wrenches,

I live in northern MN where Silicon Energy is building a new manufacturing plant. I also teach at the local community college.  I have met with silicon energy and have seen the tests.  Great module. Looks nice installed too.  Mounting options are limited but the glass on glass is a really good idea. 

Jesse

Sent from my iPhone

On Feb 4, 2011, at 12:33 PM, Eric Thomas <solarepiphany at gmail.com> wrote:

    Here is a great report that goes over advanced life cycle
testing of modules and their reasons for failure.
http://www.nrel.gov/docs/fy11osti/47755.pdf . It is a recent study and there is some good info regarding encapsulents. I can tell you that the high ranker on the results chart is the Silicon Energy Cascade module. With its glass on glass encapsulent and integrated wireway, its the most robust module I've ever seen. We installed the largest WA residential system utilizing these modules in Dec of last year. They are nice to work with...not without their challenges of course, but as far as warranty..I think they will last the test of time.

Eric Thomas
Solar Epiphany
(206)919-3014
www.solarepiphany.com

_______________________________________________
List sponsored by Home Power magazine

List Address: RE-wrenches at lists.re-wrenches.org

Options & settings:
http://lists.re-wrenches.org/options.cgi/re-wrenches-re-wrenches.org

List-Archive: http://lists.re-wrenches.org/pipermail/re-wrenches-re-wrenches.org

List rules & etiquette:
www.re-wrenches.org/etiquette.htm

Check out participant bios:
www.members.re-wrenches.org

  -------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.re-wrenches.org/pipermail/re-wrenches-re-wrenches.org/attachments/20110204/7214d211/attachment-0001.htm>

------------------------------

Message: 6
Date: Fri, 04 Feb 2011 23:22:56 -0700
From: Allan Sindelar <allan at positiveenergysolar.com>
To: Kent Osterberg <kent at coveoregon.com>
Cc: RE-wrenches <re-wrenches at lists.re-wrenches.org>
Subject: Re: [RE-wrenches] Matching modules into Xantrex GT
Message-ID: <4D4CECC0.8000901 at positiveenergysolar.com>
Content-Type: text/plain; charset="us-ascii"

An HTML attachment was scrubbed...
URL: <http://lists.re-wrenches.org/pipermail/re-wrenches-re-wrenches.org/attachments/20110204/a351e6c6/attachment-0001.htm>

------------------------------

_______________________________________________
List sponsored by Home Power magazine

List Address: RE-wrenches at lists.re-wrenches.org

Options & settings:
http://lists.re-wrenches.org/options.cgi/re-wrenches-re-wrenches.org

List-Archive: http://lists.re-wrenches.org/pipermail/re-wrenches-re-wrenches.org

List rules & etiquette:
www.re-wrenches.org/etiquette.htm

Check out participant bios:
www.members.re-wrenches.org

End of RE-wrenches Digest, Vol 4, Issue 49
******************************************

-----Inline Attachment Follows-----

_______________________________________________
List sponsored by Home Power magazine

List Address: RE-wrenches at lists.re-wrenches.org

Options & settings:
http://lists.re-wrenches.org/options.cgi/re-wrenches-re-wrenches.org

List-Archive: http://lists.re-wrenches.org/pipermail/re-wrenches-re-wrenches.org

List rules & etiquette:
www.re-wrenches.org/etiquette.htm

Check out participant bios:
www.members.re-wrenches.org

-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.re-wrenches.org/pipermail/re-wrenches-re-wrenches.org/attachments/20110205/1614146c/attachment-0004.html>