Dr.-Ing. Michael Köhl, physicist, has been actively involved in the field of solar energy conversion since 1977. He presently works on service-life analysis of solar collectors and photovoltaic modules in the department Weathering and Reliability at Fraunhofer ISE. He was the coordinator of various successful EU projects on durability testing of solar energy systems, and leader of the German flagship project on durability of PV modules ?PV-Zuverlässigkeit?. Up till now he edited two textbooks on the durability of optical materials and on the potential of polymeric materials for solar thermal applications. Sandrin Saile, M.A. joined Fraunhofer ISE's department "Weathering and Reliability" in 2009 where she is responsible for the management and dissemination of the department?s research activities. Another field of work is networking in international solar energy committees with a special interest in transdisciplinary sustainability studies and the interconnection between environmental politics, culture and technology.

• INTRODUCTIONMarket needs and developments Design of presently used and future PV-devicesCharacterisation of PV-modulesOPERATION CONDITIONSWeathering, voltages, soiling, salt impactOUTDOOR MONITORINGSensors for climate-measurementsData-acquisition systemsIV-curve measurementsEVALUATION OF STRESS CONDITIONSCorrelation macro-climate and micro-climateModelling micro-climate: Module temperature, surface humidity, effective humidityComparison of the climate at different testing sites and evaluation of stress levelsACCELERATION FACTORS AND TIME TRANSFORMATION FUNCTIONSAcceleration possibilitiesAcceleration models (time transformation functions) for the different stress factorsDEFINITION OF ACCELERATED LIFE TEST (ALT) CONDITIONS FOR DIFFERENT LOCATIONS AND DIFFERENT STRESS FACTORSALT for tropical, arid, urban, maritime and alpine conditions for UV-load, moisture, humidity, temperature difference, potential induced degradation etc.SINGLE STRESS-FACTOR ALTRequirements for the test equipmentTest resultsEvaluation of the material-specific parameters for the time-transformation functionDESIGN OF COMBI-TESTSSimultaneous stress application (UV and humidity, temperature cycling and humidity)Modelling by FEMRequirements to the test equipmentSequential test proceduresEVALUATION OF COMBI-TESTS WITH DIFFERENT STRESS LEVELSService life estimation from combi-testsOUTDOOR EXPOSUREIV-curve monitoring and evaluationComparison with ALTANALYSIS OF DEGRADATION PRODUCTSNon-destructive optical methods (spectroscopy, luminescence)Destructive methods (Rheology, SEM/EDX)PROPOSAL FOR ACCELERATED SERVICE LIFE TESTING PROCEDUREMODELLING THE INTEGRAL ENERGY YIELD DURING THE LIFE-TIMEDegradation functions from combi-testsLow-light-behaviourComparison of different modules and systems operating at different locations