Performance of Experimental Terrestrial Photovoltaic Modules

During the years 1977-1980, MIT Lincoln Laboratory (LL) placed over 11 000 photovoltaic (PV) modules at experimental PV power generating systems in a number of field test sites in the United States. Prominent among these are a 100 kW system at Natural Bridges National Monument in Utah, a 25 kW system at Mead, Nebraska, and a 15 kW system at Bryan, Ohio. The modules used in each of these systems were procured through the Jet Propulsion Laboratory´s Large Scale Procurement Program as part of the US Department of Energy´s National Photovoltaic Program. Through a program of periodic surveillance, measurements, and inspections at the aforementioned sites, over 320 electrically failed modules have been located, removed, and analyzed during this 4-year period. The principal causes of failure were: 1) cells cracked due to weathering or internal module stresses; 2) failed solder joints; 3) interconnects not soldered to rear sides of cells at assembly; 4) cells or interconnects electrically shorted to metallic substrates; and 5) broken or split interconnects. Details and photographs of many of the different types of failures are presented and some of the analysis techniques used to locate the failures are described.