Long-term reliability of PV-modules in alpine environment.

In 1988, a research PV power plant with a total output of 30 kW was built in the Austrian Alps (1600 m above sea level). Three types of PV modules, which differ in design and bill of materials (BOM), were installed over 30 years ago and have been in operation since-they are still active and generate electricity. Reliability data of more than three decades are now available and a lot of experience with operation and maintenance has been gained in this harsh environment. However, the degradation and failure rates differ greatly with the module type. Conclusions: This well maintained research PV power plant yields reliability data (over 30 years) of 3 types of crystalline Si- modules in identical environmental conditions (alpine climate) and operational time. Differences in the module types lie in the design (size, maximum power) and bill of materials (different cells, backsheets, encapsulants) which seem to drastically influence the annual performance degradation of the 3 sub-systems. Arco (total degradation: -20,4 -0,68year) Siemens (total degradation: -13,4 -0,45year) Kyocera (total degradation: -6,1 - 0,20year) The non-destructive identification of the materials was performed by mobile FTIR, Raman- and NIR-spectrometers. For the identification of the encapsulant within the PV-module, Raman and NIR were used, for the backsheet FTIR and Raman can be used for the outer layer and NIR to identify the whole layer stack of the backsheet. Although all 3 sub-systems were identified to use an EVA –type encapsulant and a TPT (Tedlar) backsheet, the module failures found were distinctive for each module-type. Arco: discolouration of encapsulant above the cell; degradation of AR-coating of cells -textgreater impact on electrical performance; many glass breakages Siemens: Yellowing effects could be attributed to a discolouration of the backsheet / encapsulant interface -textgreater no impact on electrical performance Kyocera: no material degradation; low annual power loss; no glass breakage; superior performance