ST poor-formance [RE-wrenches]

[Bill Brooks]

Travis,

The best irradiance meter (other than a pyranometer) is a shorted PV module.
If you have a module that you are confident is in good condition, the
short-circuit current will be proportional to irradiance. The module must be
in the exact same orientation as the array you are comparing it to.

Example:

Isc = 5.0 amps @ 1000 W/m2

measured Isc = 4.0 amps

Calculation:  4.0/5.0 * 1000 = 800 W/m2

A more detailed version of this method is in my installation guide. This is
usually within 5%-10% accuracy for a good PV module. The eye is almost
useless to detect irradiance--it can adjust to different light levels too
well.

Bill.

> -----Original Message-----
> From: Travis Creswell, Ozark Solar [mailto:ozsolar at ipa.net]
> Sent: Tuesday, July 24, 2001 4:23 AM
> To: RE-wrenches at topica.com
> Subject: Re: ST poor-formance [RE-wrenches]
>
>
> William,
>
> Are using an insolation meter?  My experience is that even a trained eye
> (mine) can easily be off 15% when estimating insolation.  A
> perfectly clear
> sky rarely is anywhere near 1000w/m2.
>
> Travis
> ----- Original Message -----
> From: "William Miller" <wrmiller at slonet.org>
> To: <RE-wrenches at topica.com>
> Sent: Tuesday, July 24, 2001 1:14 AM
> Subject: ST poor-formance [RE-wrenches]
>
>
> > Friends:
> >
> > A few weeks ago I posted a question about apparent poor performance of
> > ST2500 inverters as witnessed by myself.  Trace offered a replacement
> chip.
> >  I received the chips and have upgraded 1 of the 3 inverters.  There was
> no
> > improvement seen.
> >
> > These inverters are all running at about 60% of nominal rating.  The
> panels
> > are new, clean and oriented directly towards the sun, within 5 degrees,
> > during our tests.  The ambient temperatures have been in the 70 to 80
> > degree F range.
> >
> > Calculations suggest that we should see in the neighborhood of 80%
> efficiency.
> >
> > The dealer who sold these inverters has contacted Trace and we
> are waiting
> > to hear from them what explanation they can offer for this
> reduced output.
> > In the meantime, we are checking our work and readings.  We
> will keep you
> > posted.  If anyone else has any new experience with the ST inverters, I
> > would love to hear about it.
> >
> > William Miller
> >
> > __________________________________________________________________
> > William Miller
> > SLO Communications: Communications and Power Systems Consulting
> > PO Box 50, Santa Margarita, CA 93453
> > Voice :805-438-5600 Fax: 805-438-4607 VMail: 805-546-4875
> > email: wrmiller at slonet.org
> > License No. C-10-773985
> > _____________________________________________________________
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> > _____________________________________________________________
> > "I stand by all the misstatements that I've made." Dan Quayle
> > __________________________________________________________________
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