Degradation of different photovoltaic technologies under field conditions

Over the past years a number of testing facilities have been monitoring the performance and degradation of PV systems according to the established standards of indoor and outdoor testing. The objective of this paper is to present the initial first year and longer-term rate of degradation of different PV technologies installed at the testing facility of the University of Cyprus, based on outdoor field measurements and methodologies. The first year degradation of the technologies was obtained using a data filtering technique of DC generated power at Maximum Power Point (MPP) at irradiation points of higher than 800 W/m² and normalising the measured power to Standard Test Conditions (STC). Over the first year, mono-crystalline silicon technologies showed degradations in the range 2.12%-4.73% while for multi-crystalline technologies the range was 1.47%-2.40%. The amorphous silicon system demonstrated the highest first year decrease in power with an average degradation of 13.82%. For validation purposes the first year degradation was also obtained using a second technique by evaluating outdoor measured data-sets under Air Mass (AM) 1.5 (morning and afternoon) conditions and during noon (high irradiance and temperature). In this case the evaluated results showed deviations of up to 6% and 3% for mono-crystalline and multi-crystalline technologies respectively whereas for thin-film this was 5%. Finally, the longer-term degradation rates were evaluated by using the least-square fit method on average monthly data-set blocks of (i) Performance Ratio (PR), (ii) PR evaluated by filtering outage data-sets and restricting to high irradiance conditions and (iii) the Photovoltaic for Utility Systems Applications (PVUSA) rating methods, for the period June 2007-June 2009.