Home Power measures PV Performance Richard Perez and BobÐO Schultze Ever wonder exactly how much power a PV module makes? We have. We placed just about every make module widely available on the same rack, out in the sun. Then we measured their electrical output, temperature, and solar insolation. Here is what we found. The Test Jig & Procedure See Home Power #23, page 20 for a complete rundown of our PV module test jig and procedure. Here's what we do in a nutshell. We wire the module into the jig using the instruments shown below. INSERT JIG Schematic This test jig allows us to take actual data from each module. With four Fluke 87 DMMs we measure the following data: module voltage, module current, module temperature, air temperature, and solar insolation. The DMM measuring voltage is connected directly to the module's terminals. The DMM measuring module current uses a shunt (10 Amperes, 10 milliVolt, 0.1% accuracy). A Fluke 80T-150U temperature probe is used to measure both module temperature and air temperature. A Li-Cor 200SB pyranometer measures insolation. This data was taken at Agate Flat, Oregon (42¡ 01' 02" N. 122¡ 23' 19" W.) at an altitude of 3,300 feet. All modules are mounted on the same 6 foot by 12 foot rack, i.e. they are in the same plane. This assures equal access to sunlight. All modules were measured with the same instruments in the same places. Ambient air temperature was 27.4¡C. (81.3¡F.) to 31.7¡C (89¡F.) with a slight breeze blowing. The Photovoltaic Players Siemens We used a brand-new, M55 Siemens module sent to us by its maker. This is a current production, single-crystal, PV module. This module contains 36 series connected square PV cells. Solarex We used a brand-new, MSX60 Solarex module sent to us by Dave Katz at Alternative Energy Engineering. The performance data of this multicrystal module is printed on its back. This data is the result of flash-testing of this specific module, not a "generic" rating like almost every other module. After flash-testing, a computer prints a label with the data for that specific module. This module contains 36 series connected square PV cells. Kyocera We used a brand-new, K51 Kyocera module provided by BobÐO Schultze at Electron Connection. This module contains 36 series connected square multicrystal PV cells. Hoxan We used a brand-new, 4310 Hoxan module provided by Dave Katz at Alternative Energy Engineering. This module contains 32 series connected square single crystal PV cells. Carrizo This module is a set of four ARCO M52 laminates wired in series to make a module. This seven year old module was suppled by Mike Elliston of Carizzo Solar. The resulting module of four laminates contains 48 series connected cells and a total cell count of 144 PV cells. The PV cells used to make these laminates are 3.75 inches square and are single crystal types. Real Goods This module is a set of four ARCO M52 laminates wired in series to make a module. This seven year old module was suppled by John Schaeffer of Real Goods. The resulting module of four laminates contains 48 series connected cells and a total cell count of 144 PV cells. The PV cells used to make these laminates are 3.75 inches square and are single crystal types. Photocomm This module is a set of three ARCO M52 laminates wired in series to make a module. This seven year old module was suppled by Ron Kenedi of Photocomm. The resulting module of four laminates contains 36 series connected cells and a total cell count of 108 PV cells. The PV cells used to make these laminates are 3.75 inches square and are single crystal types. ARCO This seven year old ARCO 16-2000 module was supplied by Wayne Robertson at Solar Electric Specialties. It has 33 series connected, single crystal, round PV cells. Sovonics This is an amorphous silicon module supplied by Nick Pietrangleo of Harding Energy Systems. We've had this module out in the sun for the last 2 years. The Data We are content to let the data speak for itself. We used manufacturer's ratings at a 25¡C. module temperature. In the comparison tables that follow this maker's performance specification is listed in the column called "Rated Value". Our measured data is in the column labeled "Measured Value". The column called "Percent of Rated" compares our measured results with the maker's ratings. The solar insolation data from the Li-Cor Pyranometer is accurate. At Agate Flat we often have solar insolation as high as 110 milliWatts per square centimeter. Conclusions The 25¡C. rating standard for PV module rating was poorly selected. Out in the sun, these modules are cooking at 50¡C. or more. This causes voltage loss in the cells which in turn lowers the modules power output. If you live in a warm climate, then derate the maker's 25¡C. power spec by 15% to 25% to compensate for module heating. A more realistic temperature for rating PV modules would be in the range of 40¡C. to 50¡C. because this is where most modules spend most of their operating lives. We're not finished yet. We are going to continue testing modules out in the sun. We are going to do it on cloudy days, on freezing cold days, as well as the hot ones like today. We're going to test every module we can get our hands on. We invite you to do the same and send in your data for publication. Access Richard Perez, C/O Home Power, POB 130, Hornbrook, CA 96044 ¥ 916-475-3179. BobÐO Schultze, Electron Connection, POB 203, Hornbrook, CA 96044 ¥ 916-475-3401.