Re: [pvusers] Rated output vs reality

["Robert Warren" <robertwarren@mail.com>]

Dear Michael Bearden,
 If you are only getting 1400 watts from a 2100 watt PV system, then I have to ask some basic questions. Where do you live? As you probably live in the US, you should expect pretty much full output in direct sun. However, as it is the middle of the summer, you could be losing 15% in lower production due to the high temperatures of your panels (they are a lot less efficient in hot sun, and work better in cold weather).  Check your meter at maybe 10 AM, before it gets too hot, but the sun needs to be high enough to have pretty direct rays. 
 What angle are your modules mounted at? Do they face true South? 
 Did you install it yourself or have it installed? It is possible to have a couple of panels wired backwards, in which case they canel each other out. I have seen this many times, it is an easy mistake to make. If you have a multimeter, you should see if the open circuit voltages of the parallel strings are equal to each other. The Sun Tie inverter is a 48 volt device, and so if you have 28 modules, then you will have 7 parallel strings of 4 modules in series. Each parallel string should show something like 84 to 86 volts open circuit (not hooked up to the inverter). You ought to have a central junction box where these 7 strings come together, such as the Trace T-10 box. Then you can pull fuses and test individual strings without danger of a shock.
  Michael Welsh is correct about the superior performance of the Sunnyboy grid tied inverters. I have tested and installed over 200 of these inverters and I love them!  I have had problems with them not being set up correctly, so I check all the parameters before setting them up. Occaisonally I have had to send one back, but overall, it is a great product. But I don't suggest swapping inverters, unless your dealer will take back the Sun Tie, which I doubt. So check all your modules to see that the polarity is correct, and watch to see what our maximum power is at different times of the day.  
 For this time of year, you should be getting about 10 or 11 kWhrs/day if your angle is optimum and you live below 38 lattitude.
Good luck, 
Robert Warren
Senior Engineer,
Solar Century
www.solarcentury.co.uk

  
Date: Fri, 19 Jul 2002 14:41:24 -0700
To: "pvusers@crest.org" <pvusers@crest.org>
From: michael bearden <michael.bearden@SONOMA.EDU>
Subject: Rated output vs reality
Message-id: <3D38877B.E855ECA3@sonoma.edu>

I have a relatively new grid tied system with 28 Siemens SP75 panels,
and a Sun-tie 2500 inverter.  I expected the panels to produce much
nearer their label rating than what I am seeing even at peak hours now
when I see 1400 watts from the inverter.  I was expecting something
like
16kwh a day from this system when I installed it.
Is this an acceptable power level for this installation?
Thanks-
Michael B.

----- Original Message -----
From: Michael Welch <michael.welch@homepower.com>
Date: Fri, 19 Jul 2002 14:52:24 -0700
To: pvusers@crest.org
Subject: Re: [pvusers] Rated output vs reality 

> Consider switching to an SMA Sunny Boy inverter. You will likely see 15-25% increase in total KWH production. It will mean a rewiring of your PV array, but worth it. Talk to your installer about the advantages.
> 
> Michael Welch
>         
> Michael Welch, michael.welch@homepower.com
>      Home Power magazine
>      www.homepower.com
>      To reach me: 707-822-7884
>      To reach Home Power: 800-707-6585
> 
> 

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by Robert Warren 
robertwarren@mail.com

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