[RE-wrenches] Multiple angle conundrum

Thu Apr 5 19:12:52 PDT 2012

Howie is absolutely right. Strings with different orientations on the same
MPPT are not a problem. Modules with different orientations on the same
string is a big problem. Search the archives here and you'll find a good
discussion on this. The short version is that voltage is a function of
temp, which won't change much based on orientation and the MPPT will favor
the strings with better orientation at any given time because they're
making more power.

We have a system with 6 strings on each of two opposite facing roofs. One
Sunny Boy has four strings from one side, one has four from the other and a
third has two from each side. The one with two from each side produces the
exact average of the other two. The theory works!

Dana

Dana Brandt
Ecotech Energy Systems, LLC
www.ecotechenergy.com
dana at ecotechenergy.com
360.510.0433

On Wed, Apr 4, 2012 at 11:39 AM, Howie Michaelson <howie at suncatchervt.com>wrote:

> My understanding is that if all the modules in a string have the same tilt
> and azimuth, the MPPT "hit" is nominal with 2 strings of differing angles.
>  Particularly, if they have the same azimuth, their voltages will be close
> to identical almost regardless of pitch, and therefore the current from
> the different strings will be virtually cumulative and therefore not a
> problem.  However if there is differential shading on strings functionally
> being combined, then you have a cumulative problem.  In that case, that is
> where separate MPPT algorithms (via multiple MPPT inputs in a single
> inverter, or separate string inverters, or micro inverters/optimizers)
> become useful and appropriate.
>
>
> Others please chime in to correct me if needed.
>
> Howie
> --
> Howie Michaelson
> NABCEP Certified Solar PV Installer™
>
> Catamount Solar, LLC
> Renewable Energy Systems Sales and Service
> VT Solar Electric & Hot Water Incentive Partner
> http://www.CatamountSolar.com
> 802-272-0004
>
>
> On Wed, April 4, 2012 12:38 pm, Kirpal Khalsa wrote:
> > Hilton....there are a couple ways to approach this.....There are some
> > string inverters with multiple MPPT inputs....each different slope of
> roof
> > would be installed into its own input.....the other way is to use micro
> > inverters or other individual module optimizers....in which case you are
> > completely free from mismatched orientation and slope constraints.....
> > If you are looking to use a single MPPT channel string inverter you may
> > consider splitting the arrays and having two single string inverters one
> > for each tilt angle....That said the tilt angle difference feeding the
> > same
> > inverter does not have as big of a negative impact as if the sub arrays
> > are
> > facing different directions....
> > good luck,
> > Kirpal Khalsa
> >
> > On Wed, Apr 4, 2012 at 9:14 AM, Hilton Dier III
> > <hiltondier at gmail.com>wrote:
> >
> >>  Wrenches,
> >>
> >> I am talking with a potential client about a roof mounted PV array. The
> >> client has a reasonably large south facing roof, but it is broken up by
> >> a
> >> large (18' W x 16' H) shed dormer. The roof is 10:12 and the dormer is
> >> 6:12.
> >> I designed a layout that gave the dormer some room to avoid shading. The
> >> client was disappointed by how much wattage I could get on his roof. I
> >> pointed out that installing modules in the shade of the dormer was a bad
> >> idea.
> >>
> >> He is also talking to another installer. The other installer proposed
> >> installing part of the array on the 10:12 roof and part on the 6:12
> >> dormer.
> >> The client had already asked me about that and I gave him a rudimentary
> >> explanation of maximum power point tracking and the inefficiency of such
> >> an
> >> arrangement. He asked them about that and their guy said "No big deal."
> >> He
> >> is still considering the two-angle scenario.
> >>
> >> So, how much efficiency will he lose by going with two angles? It seems
> >> like the ultimate MPPT design error to me, but I don't have a number for
> >> him to make my case. I suppose it all comes down to cents per delivered
> >> kWh
> >> in the end, but two different roof angles seems the the wrong way to go.
> >> I'd like to be able to give him a definitive idea of what he would be
> >> sacrificing with that scenario.
> >>
> >> Side note: The other installer is using the new Sunpower E20 modules.
> >> They
> >> seem to be available only from the manufacturer. Anybody have a source?
> >> Has
> >> anybody used them yet? Do they live up to the hype?
> >>
> >> Many thanks,
> >>
> >> Hilton
> >>
> >> --
> >> Hilton Dier III
> >> Renewable Energy Design
> >> Partner, Solar Gain LLC
> >> 453 East Hill Rd.
> >> Middlesex, VT 05602
> >>
> >>
> >> _______________________________________________
> >> 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
>
>
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.re-wrenches.org/pipermail/re-wrenches-re-wrenches.org/attachments/20120405/f4a45230/attachment-0004.html>