Comparison of Degradation Rates of Individual Modules Held at Maximum Power

In this paper, we present a comparison of maximum power degradation rates of individual modules under outdoor conditions in Golden, Colorado. Test modules include single- and polycrystalline-Si (x-Si, poly-Si), amorphous Si (a-Si, single, dual, and triple junction), CdTe, CuIn-Ga-Se-S (CIS), and c-Si/a-Si heterostructure, from nine difference manufacturers. From monthly blocks of output power data, ratings were determined using multiple regressions to Performance Test Conditions (PTC). Plotting the power ratings versus time allowed degradation rates to be calculated from linear regressions. We also include a summary of module degradation rates obtained from the open literature over the past five years. Compared with the common rule-of-thumb value of 1% per year, many modules are seen to have significantly smaller degradation rates. A few modules, however, degrade significantly faster.