little help needed with a SB1800 [RE-wrenches]

[Bill Brooks]

Pat,

How about--it's winter--so the irradiance is low (system has been installed
for less than 4 months). This is a performance estimation mistake on your
part.

You could have a wiring mistake. Although Alan has a point about high
temperatures, I don't think that is the problem here. This system should do
fine at high temperatures.

One of your series/parallel strings could be wired backwards or wrong or you
could have a miswired or bad module. With that crazy of a wiring setup,
getting it right is very difficult and getting it wrong is easy and causes
big performance losses. Finding it is even more difficult.

All that being said--whatever your performance estimate was is too high.
It's winter and I calculate that your array is getting the equivalent of 2.9
sun hours per day. That is very much in line with what is normal for this
time of year.

Not to pick on you too much but where is your irradiance measurement to
coincide with your reading of 990 Watts? 990 Watts would be bad if the
irradiance was 1000 W/m^2; it would be normal if the irradiance was 800
W/m^2 and would be excellent if the irradiance were 600 W/m^2. Pull out your
$130 Daystar meter and measure the irradiance in the plane of the array and
compare that to your output. I think you will find everything is okay.

If you want to know how to calculate performance against a handheld meter,
check out page 23 the Installation Guide on the CEC website
http://www.energy.ca.gov/reports/2001-09-04_500-01-020.PDF. Every installer
should know how to do that estimate as a part of their everyday job.

Bill.

-----Original Message-----
From: Allan Sindelar [mailto:allan at positiveenergysolar.com]
Sent: Monday, February 09, 2004 3:07 PM
To: RE-wrenches at topica.com
Subject: Re: little help needed with a SB1800 [RE-wrenches]


Brian,
Assuming 4.4A Imp at 17.0 Vmp, your array should be producing 8.8A at 204
VDC. Are you getting that?

Also, the minimum operational voltage for the SB1800 is 156VDC. Are you
exceeding that during hot weather? My guess is that you are, as it's hard to
drop below 13.0 Vmp on a 12V module. But a single wiring mistake could drop
you below that threshold during certain conditions, such as hot weather.

BtW, anybody need a working GC1000? How about a dead one?

Allan @+E

----- Original Message -----
From: "brian" <brian at paloaltohardware.com>
>
> A customer of mine had a small grid-tied PV system with 16 Siemens SP-75
> and an AEI GC1000.
>
> Anyway... I added 8 more modules, and installed an SMA SB1800.  To avoid
> having to rewire a lot of the existing array, I came up with a somewhat
> odd wiring schematic;  but the voltage string sizing work out fine on
> paper, and even SMA saw no problem with it.  Here is a simple version of
it:
>
> http://www.paloaltohardware.com/temp/
>
> So the problem... is that in 1424 hours of operation, the SB1800 has
> only produced 440 kWH.  The most I've ever seen the thing put out is
> about 990 watts AC.  (the array faces just about due south, no shade at
> all, about 25degree slope.
>
> Any ideas?

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