[RE-wrenches] Inverter with two strings of different orientation

[Peter Parrish]

Thanks, Daryl. That is what I understand, but mine is a superficial
understanding right now. For better or worse, I'm one of those guys who want
to see the technical details. Does anyone have a reference to the articles
Daryl is talking about?
- Peter

Peter T. Parrish, Ph.D., 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 

-----Original Message-----
From: re-wrenches-bounces at lists.re-wrenches.org
[mailto:re-wrenches-bounces at lists.re-wrenches.org] On Behalf Of Darryl
Thayer
Sent: Thursday, December 25, 2008 7:39 AM
To: RE-wrenches
Subject: Re: [RE-wrenches] Inverter with two strings of different
orientation

If each string is composed of only one orientation then there would be
little loss.  There have been a couple of papers on this at different
conferences.  I also think John Berdner wrote a paper on it for SMA.  (I
think the annual losses are in the nature of 2 to 5 %)  If however a single
string has two orientations then much larger losses occur.   
Daryl


--- On Wed, 12/24/08, Peter Parrish <peter.parrish at calsolareng.com> wrote:

> From: Peter Parrish <peter.parrish at calsolareng.com>
> Subject: [RE-wrenches] Inverter with two strings of different orientation
> To: "'RE-wrenches'" <re-wrenches at lists.re-wrenches.org>
> Date: Wednesday, December 24, 2008, 1:41 PM
> I don't think this topic has been dealt with in this
> forum. Ocassionally we
> want to use a single inverter with two or more strings,
> each string being
> loaded by a single sub-array. A sub-array being defined as
> having a single
> uniform tilt angle and azimuth. All modules are identical.
> And each
> string/sub-array contains the same number of modules.
> 
>  
> 
> The question is: "How different can the orientation be
> for the different
> sub-arrays?
> 
>  
> 
> Let me pose a concrete example: Xantrex GT5.0, two strings
> of BP Solar
> SX3190s. One string has an orientation of 15 deg tilt and
> 188 degrees
> azimuth; the other has 23 degrees tilt and 139 degrees
> azimuth. For reasons
> that are difficult to explain, none of the orientation
> angles can be
> changed, at least for the purposes of this discussion. To
> visualize what I
> am talking about: the tilts are fairly close (8 degrees)
> and the azimuths
> differ by about 45 degrees.
> 
>  
> 
> How do I calculate the combined performance? How much power
> does one give up
> compared to using separate inverters for each
> sub-array/string? Are there
> rules of thumb as to what works and doesn't? Do
> conventional inverters have
> algorithms that can navigate the non-ideal I-V
> characteristic under load? I
> know there was a tech bulletin from Fronius a while ago: I
> read it but
> didn't come away with any definitive answer. I also had
> first hand knowledge
> with MPPT algorithm problems with the Fronius inverters
> during that time
> period, which caused me to discount the tech bulletin.
> 
>  
> 
> I am quoting a system as we speak, so my inquiry is not
> hypothetical in
> nature. Any help would be appreciated.
> 
>  
> 
> - Peter
> 
> Peter T. Parrish, Ph.D., 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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