Hard data on module durability and performance allows manufacturers to target durability concerns and distinguish their products from those of their competitors, and it gives investors higher confidence in their expected return.
The PV Durability Initiative (PVDI) is a joint undertaking between the Fraunhofer Institute for Solar Energy Systems (ISE) and the Fraunhofer Center for Sustainable Energy Systems (CSE), initially announced in 2011. The goal is to develop a durability assessment procedure that ultimately will be adopted as a global industry standard. PVDI draws from existing accelerated stress reliability tests, with the intention to reach module wear-out in a variety of environmental conditions, and combines these with long-term outdoor testing. The actual outdoor field performance is compared to the accelerated testing to determine the tests’ acceleration factors, which at present are largely unknown. Until these factors are ascertained, assessing module lifetime based on test performance is best determined by using a relative rating system among different module technologies. As module durability becomes better understood, test protocols may be modified. Testing for the PVDI is ongoing. One round has been completed, a second round of testing is underway and a third round is planned to begin at the end of 2013.
For the five module types tested in the first round, differences in susceptibility to potential-induced degradation (PID), thermal cycling, and mechanical loads were distinguishable. Out of the two module types which experienced PID, one experienced irreversible degradation under negative bias, and the other experienced full recovery with light soaking, after degrading under positive bias.
Outdoor performance testing in Albuquerque, USA is only recently underway, but the goal is to evaluate the predicted, expected, and actual module performance for several mounting configurations. The “predicted “performance is the calculated by modeling the solar spectrum at the test site, using spectrum-influencing atmospheric conditions obtained from the Typical Meteorological Year 3 (TMY3) database. Actual site measurements of these same conditions are used to generate the “expected” performance, and finally the “actual” module performance is measured directly. With these results, performance will be forecasted and then verified in other locations.