BIPV: Aesthetics alone are not sufficient - Long-term Energy Yield and Safety are Equally Important

In Switzerland in the end of the nineties several aesthetically attractive PV plants with special solar tiles ("Sunslates") were realised. Pictures of these plants were often shown as examples for a successful building integration of PV plants. One of these plants with a peak power of 62.5 kWp was erected on the roof of the regional hospital in Burgdorf (RSE) and commissioned in the end of 1999. For this plant the local utility granted a feed-in tariff of CHF 1 per kWh for 20 years. The PV laboratory of BFH-TI in Burgdorf has registered since 1992 in the framework of long-term monitoring projects the energy yield of all PV plants in Burgdorf (1). Some of these plants are analytically monitored (with measurement of irradiance into array plane, V and I on the DC side, AC power). At some other plants, among which also the PV plant at RSE, due to the necessary investment or accessibility only the monthly energy yields received from the local utility are evaluated. As the PV plant at RSE degraded seriously in course of time (see table 1), in a mandate for the local utility in summer 2010 the PV laboratory of BFH-TI has carried out several measurements at this plant. In this paper, the results of this degradation and possible reasons for it are discussed.