The TISO 10 kWp m-Si PV plant was set up on 13th May 1982. It was the first plant in Europe to be connected to the electricity grid. It consists of 252 ASI 16-2300 Arco-Solar m-Si modules and is sited on the flat roof of the LEEE-TISO. At first, the aim of the piant was to study possible technical and safety problems when connecting a plant to a public grid, whilst now, the aim is the study of mechanical and electrical degradation as well as that of the lifespan of PV modules. The detailed observations of the various PV components and, above all, of the modules supply important information on the critical spots of the PV plants. Observation of the life cycle of the modules makes it possible in particular to verify reliability and working life predictions that are also used for economic evaluation. The initial electrical performance of the plant was measured in January 1983, and system operation has been monitored continuously. Furthermore, indoor measurements have been performed periodically at ESTI on a reference batch of modules. This combination of systematic monitoring and laboratory measurements provide a unique opportunity to study the system at the end of its 20-year design life. More recently, particular emphasis has been placed on the reliability of the modules: at present a special study is being performed to correlate field reliability with accelerated lifetime tests in order to assess PV module reliability.

Initially the purpose of this work was to study the phenomenon of degradation induced by exposition to sun-light (Staebler-Wronski effect) on triple junction a-Si modules. Then the modules were connected to the grid. The aim of this plan is to compare the behaviour of old (TISO 4kW plant) and new generation of amorphous modules observing the cycles of degradation and regeneration.

At the Testing Centre for photovoltaic components (TISO-LEEE) the modules, chosen among the ones most frequently used in the PV power grid connected plants in Switzerland, undergo a series of tests in order to verify their characteristics, reliability, medium and long-term performance and high voltage reliability. The most important aspect of the tests is to compare energy output of modules exposed in identical real outdoor conditions. The aim of these tests is to answer the questions which need to be posed when planning a PV plant. At the moment of purchase 1/3 of the modules are no longer under guarantee, while after a year of exposure under real environmental conditions and at MPP, 2/3 of the modules have a power which is lower than the limit stated in the guarantee. Not only do the amorphous-Silicon modules undergo initial degradation, but also a number of crystalline-Silicon modules show significant degradation. Comparison between c-Si modules exposed to different high voltage conditions demonstrate that, in the short term, a correlation between the degradation observed and the voltage applied does not exist

1National Renewable Energy Laboratory (NREL), USA 2Sandia National Laboratories (SNL), USA 3PV Testing Laboratory-Arizona State University (PTL-ASU), USA 4Florida Solar Energy Center (FSEC), USA 5 European Commission, Directorate General Joint Research Centre, (IES-RE-ESTI), European Union 6Laboratorio Energia Ecologia Economia (LEEE), Switzerland 7Immisssionsschutz und Energiesysteme GmbH Test Centre for Energy Technologies (TUV), Germany 8Institute of Solar for Energy Systems (Fraunhofer ISE),Germany 9Japan Electrical Safety & Environment Technology Laboratories (JET), Japan 10National Institute of Advanced Industrial Science and Technology (AIST), Japan

The LEEE-TISO testing centre for PV components has, since 1991, carried out systematic tests, under real operating conditions, on the most important modules currently on the market. PV c-Si modules coming from production shows a typical degradation in performance when exposed to light of up to -5%. This initial degradation of c-Si modules takes place during the first hours of exposure. During the first year of operation some of the tested modules shows almost no further degradation and some a very small degradation. The long term degradation of c-Si modules has been extensively studied on one of the LEEE-TISO plants. In 21 years of service, the Arco Solar ASI 16-2300 modules of the 10 kW TISO plant showed several signs of physical degradation. Yellowing of PVB encapsulant and hot-spots affected the module efficiency. Nevertheless, the results of the indoor performance measurements of all plant modules indicate that the ASI 16-2300 modules are still working in a very satisfactory manner.

The Nominal Power of PV module (Pn) measured at STC, the only standard parameter stated by the manufacturers, only partially describes module performance and does not give any information about energy production; in fact two modules with equal power may have dissimilar energy production. At the LEEE-TISO Test Centre, the most commonly sold modules on the market undergo a series of tests in order to examine their quality and reliability in terms of energy production (Wh/W) and power degradation over time. The testing procedures we developed over the years were slightly modified in order to evaluate the initial degradation of silicon crystalline module. In 10 years of activity around 80 different types of modules have been tested: a summary of this activity is also presented in this paper.

Power P "at STC" (1000 W/m2, Tc=25°C, AM1.5 spectrum) of PV modules, the only standard parameter stated by the manufacturers, only partially describes module performance and does not give any information about energy production: in fact two modules with equal power may have dissimilar energy production. At the LEEE-TISO Test Centre, the most commonly sold modules on the market undergo a series of tests in order to examine their quality and reliability in terms of energy production (either PR or Wh/W) and power degradation over time. Not only do the amorphous-Silicon modules undergo initial degradation, but also a number of crystalline-Silicon modules show significant degradation.

The real electrical parameters rarely correspond to the nominal electrical parameters supplied by the manufacturers. Moreover initial degradation occurs in almost all types of modules during the first period of exposure. Project planners and installers are increasingly asked to provide production and behaviour estimates for the systems they install. Therefore a direct performance comparison of PV modules is needed. The ISAAC-TISO centre carried out systematic outdoor testing, under real operating conditions, and indoor tests on the most important modules currently on the market. In March 2006 a new 15 month test cycle (no.10) started. Fourteen different module types were chosen, trying to include the greater part of available technologies: 8 mc-Si, 2 sc-Si, 1 HIT, 2 a-Si and 1 CdTe. All the modules were purchased anonymously. I-V measurements @STC are periodically performed. In test cycle 10 the power at the purchase of a c-Si module is on average 1.5% lower with respect to Pn but ranging from 0.2% and -3.8%. Stabilized power after 15 months is on average 3.6% lower with respect to Pn and ranging from -0.7% and -8.2%. All types of modules are in the warranty limits. Differences (average of 2 modules) in annual energy production (kWh/kWp), of 14 different module types compared to the best module, with nominal power Pn as reference, reach 10%. The thin-film modules have a slightly higher energy yield with respect to c-Si modules but evaluation of these technologies is complicated by the fact that their STC power changes in time (degradation and recovery effects).

The MTBF project is a collaboration between the LEEE-TISO and the ESTI laboratory (JRC, Ispra) to determine the Mean Time Before Failure of the 10 kW PV plant installed on the roof of the University of Applied Science of Southern Switzerland (SUPSI). The importance of this study is improved by the fact that it concerns the first grid-connected PV plant in Europe (1982).

The aim of the collaboration between the LEEE-TISO and the ESTI laboratory (JRC, Ispra), is to determine the Mean Time Before Failure (MTBF) of the first PV plant connected to the public electrical grid in Europe (1982). This entails investigation of the physical degradation mechanisms in action and to correlate field reliability with accelerated lifetime tests (IEC/CEI 61215). The combination of systematic monitoring and laboratory measurements provide a unique opportunity to study the system. The main work of the collaboration has entailed, detailed visual inspections and Infra Red analysis, performance measurements of strings and individual modules, analysis of the evolution of the system Performance Ratio over time, repeated accelerated lifetime tests and correlation of all these data. First results obtained on this study, evidence the good condition of the plant and the remarkable resistance of its

At the Testing Centre for photovoltaic components (TISO - LEEE) the modules, chosen among the ones most frequently used in the PV power grid connected plants in Switzer land, undergo a series of tests in order to verify their characteristics, reliability and medium and long-term performance. In previous years, the modules underwent outdoor exposure and high voltage operation: emphasis was placed on power loss and verification of the data supplied by the manufacturers. The results of the second cycle of exposure of the latest modules are displayed below. Two new tests have begun recently: one to evaluate the effect of high voltage power loss, the other to compare energy output of modules exposed in identical outdoor conditions.

The monitoring of the 16.8 kWp grid-connected PV plant with CIS (Cupper Indium diselenide) modules, situated on the roof of the Ludains ice rink in St Moritz, is finished.