[RE-wrenches] Mixing and Matching PV modules--Error Corrected

Darryl Thayer daryl_solar at yahoo.com
Tue Mar 31 05:47:57 PDT 2009


hi peter
I would put 7 type A in a series and 6 type B with one type A This way the extra performance of the type A would not be lost except for the one module.
Darryl.  


--- On Mon, 3/30/09, Peter Parrish <peter.parrish at calsolareng.com> wrote:

> From: Peter Parrish <peter.parrish at calsolareng.com>
> Subject: Re: [RE-wrenches] Mixing and Matching PV modules--Error Corrected
> To: "'Peter Parrish'" <peter.parrish at calsolareng.com>, "'RE-wrenches'" <re-wrenches at lists.re-wrenches.org>
> Date: Monday, March 30, 2009, 5:50 PM
> I think I understand all the dictums about single-strings of
> PV modules: all
> the same modules, all the same azimuth and tilt, but I have
> a "special
> situation".
> 
> We are starting to accumulate a number of "second
> hand" PV modules. Some
> have frames slightly damaged by the shipper; some have come
> from warranty
> replacements; and some are odd lots that we haven't
> been able to sell.
> 
> What I want to do is to set up a demo system composed of
> two different types
> of modules. This is my initial design:
> 
> Total of fourteen modules. Two strings of seven modules
> each. Each string
> consisting of four modules of one type (type A) and three
> modules of a
> second type (type B).
> 
> Both module types have 50 cells and the type A module has
> 155mm-sq cells and
> the type B module has 150mm-sq cells. So you would think
> that the
> performance specs would match pretty well. However, since
> the type B modules
> are an earlier vintage, they probably don't have the
> latest and greatest
> surface treatment, etc., so the current specs are lower
> than one might
> expect.
> 
> Specs on type A: Voc = 30.8V, Vmp = 24.5V, Isc = 8.70A, Imp
> = 8.16A. Specs
> on type B: Voc = 30.6V, Vmp = 24.6V, Isc = 7.38A, Imp =
> 6.93A. 
> 
> So here's my question: would putting together the
> strings of four type A and
> three type B cause any problems? I know the string current
> would be limited
> by the type B modules, but above and beyond that, what
> would be the
> operating point of the type A modules and what would be the
> stress if any on
> the type B modules? I'd like this demo system to last a
> while and I
> certainly don't want to see scorch marks on the type B
> modules after a few
> months of use. 
> 
> Any thoughts?
> 
> - Peter
> 
> Peter T. Parrish, President
> California Solar Engineering, Inc.
> 820 Cynthia Ave., Los Angeles, CA 90065
> Ph 323-258-8883, Mobile 323-839-6108, Fax 323-258-8885
> CA Lic. 854779, NABCEP Cert. 031806-26
> peter.parrish at calsolareng.com 
> 
> 
> 
> 
> 
> 
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