William,
In a series string, the one-cell shading in the long dimension will reduce the voltage of the string by 1/3 of one module. This is often a small amount of voltage since 12 or 13 modules are in string. In lower voltage systems, the loss will be much more pronounced. No shading is good and shading on a portion of a single module in a string will not effect performance substantially. The problem comes with interrow shading where each module looses 1/3. Now the overall loss is much more than 1/3 of the string because the other strings will dominate the inverter voltage (assuming you have multiple strings-that is why you have multiple rows). If only one row is shaded, then the output of that string will be reduced to operating at the shade light level. If all strings except the first row are shaded, then a sophisticated inverter will try to powertrack the array at 2/3 voltage-and therefore 2/3 power. This only works if the inverter can operate at 2/3 voltage. If not, then the whole array will likely work off of the first row output and ALL the subsequent rows will produce power at whatever light level the shade delivers. Bill. From: [email protected] [mailto:[email protected]] On Behalf Of William Miller Sent: Friday, April 23, 2010 11:26 PM To: RE-wrenches Subject: [RE-wrenches] Inter-row shading, additional information Friends: I was incorrect on one point in my previous post on the subject. The SolarWorld SW230 is comprised of one series string of cells. It acts somewhat like there are three strings because of the bypass diodes. If you shade one cell of one group, the bypass diodes kick in and allow the module to continue to produce power but at a reduced level. Our test showed that if the short edge is shaded for more than half of a cell width on the narrow edge, the total output caved. The same shading on the long edge reduced output minimally. William Miller Please note new e-mail address and domain: William Miller Miller Solar Voice :805-438-5600 email: [email protected] http://millersolar.com <http://millersolar.com/> License No. C-10-773985
_______________________________________________ List sponsored by Home Power magazine List Address: [email protected] 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
