little help needed with a SB1800 [RE-wrenches]

brian brian at paloaltohardware.com
Mon Feb 9 17:27:27 PST 2004


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OK, i will go do some homework and let you guys know what I find. 

-Brian

Bill Brooks wrote:

>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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-- 
Brian Sullivan
Palo Alto Hardware
Solar Program Director
875 Alma Street
Palo Alto, CA  94301
650-327-7220 phone
650-327-7244 fax
www.paloaltohardware.com

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