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

[Bill Brooks]

Peter and Darryl,

The right way to do this is using a computer program PVSYST ($800). It will
calculate the operating voltage of each string and the overall performance.
Not much else out there can calculate it. That being said, the loss of these
two orientations will be less than 2% based on the different orientations
(orientation issues aside). The other wildcard is differential shading.
Shading one or two modules in one of the two strings will cause large losses
in the shaded string. Under no shading, the losses will be too small to
notice.

Array voltage is a function of temperature, no irradiance. High irradiance
causes higher operating temperatures, but the inverter will be dominated by
the higher producing string in nearly all cases. A good power tracking
inverter like the SMA or Fronius would be the best call for such an array.

Bill.



-----Original Message-----
From: re-wrenches-bounces at lists.re-wrenches.org
[mailto:re-wrenches-bounces at lists.re-wrenches.org] On Behalf Of Peter
Parrish
Sent: Thursday, December 25, 2008 11:04 AM
To: daryl_solar at yahoo.com; 'RE-wrenches'
Subject: Re: [RE-wrenches] Inverter with two strings of different
orientation

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 
> 
> _______________________________________________
> List sponsored by Home Power magazine
> 
> List Address: RE-wrenches at lists.re-wrenches.org
> 
> Options & settings:
> http://lists.re-wrenches.org/options.cgi/re-wrenches-re-wrenches.org
> 
> List-Archive:
> http://lists.re-wrenches.org/pipermail/re-wrenches-re-wrenches.org
> 
> List rules & etiquette:
> www.re-wrenches.org/etiquette.htm
> 
> Check out participant bios:
> www.members.re-wrenches.org


      
_______________________________________________
List sponsored by Home Power magazine

List Address: RE-wrenches at lists.re-wrenches.org

Options & settings:
http://lists.re-wrenches.org/options.cgi/re-wrenches-re-wrenches.org

List-Archive:
http://lists.re-wrenches.org/pipermail/re-wrenches-re-wrenches.org

List rules & etiquette:
www.re-wrenches.org/etiquette.htm

Check out participant bios:
www.members.re-wrenches.org




_______________________________________________
List sponsored by Home Power magazine

List Address: RE-wrenches at lists.re-wrenches.org

Options & settings:
http://lists.re-wrenches.org/options.cgi/re-wrenches-re-wrenches.org

List-Archive:
http://lists.re-wrenches.org/pipermail/re-wrenches-re-wrenches.org

List rules & etiquette:
www.re-wrenches.org/etiquette.htm

Check out participant bios:
www.members.re-wrenches.org