I thought we thoroughly thrashed this one out. A no less an authority than Bill Brooks assures us that we can orient two (or more) strings differently, wire them in parallel and the MPPT algorithms in modern inverters will sort things out, essentially extracting the maximum (or nearly maximum) power available from each module.
I remain skeptical, and I won't become a believer until I can run a "first-principles" calculation on a simulator like PVSyst. Nonetheless, we do design and have installed systems consisting of two strings each with different orientations. Typically, the elevations match but the azimuths are different (e.g. 160 deg and 200 degrees). Do we get as much total energy in one day as we would with two inverters being fed by one string each and with each inverter operating with the same efficiency? We don't know for sure, but it would appear so within 10%. Here's the real reason for my post. The customer is so happy with his system he wants to max out (his PV energy production now covers only about 80% of his usage). Currently he has two strings of 8 each BP3220T modules on a Fronius IG4000. Based on Voc (at 14 deg F) for the BP3220T, we can put 14 ea modules on a string. Based on conventional Pac limits, we can put only 10 ea modules on the two strings. But taking into consideration that we have strings with different azimuths, we should be able to safely exceed this limit of 10 ea. Has anyone tried to figure out what the practical string limit is based on differing orientations? Let's assume El=25 deg, AZI=160 deg and 200 deg. - Peter Peter T. Parrish, Ph.D., President California Solar Engineering, Inc. 820 Cynthia Ave., Los Angeles, CA 90065 CA Lic. 854779, NABCEP Cert. 031806-26 peter.parr...@calsolareng.com Ph 323-258-8883, Mobile 323-839-6108, Fax 323-258-8885 _______________________________________________ List sponsored by Home Power magazine List Address: RE-wrenches@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
