kWh/Wp measurements & predictions of 13 different PV modules

At the begin of 2009 the Swiss PV module Test Centre at SUPSI-ISAAC started a new measurement campaign investigating thirteen different modules commercially available on the market. Two modules of each type have been exposed outdoors for energy yield monitoring and a third module, stabilised in advance, has been stored indoors as a reference. The modules covered a large range of different technologies ranging from multi-crystalline silicon (mc-Si) of which two with back-contact cells, 3 single-crystalline silicon (sc-Si), 1 hybrid mono-crystalline technology with amorphous silicon layer (HIT), 1 double junction amorphous silicon (a-Si/a-Si), 1 micromorph (a-Si/μc-Si), 1 Cupper-Indium-Sulfide (CIS) and 1 Cupper-Indium-Gallium-Diselenide (CIGS). The aim of the measurement campaign was to assess the quality of current technologies and the understanding of observed differences between technologies. Outdoor and indoor performance of the modules were analyzed over 15 months performing measurements under real operating conditions. The modules were therefore installed on a ventilated rack where each single module was connected to a maximum power point tracker delivering Im, Vm values in minutes intervals. The indoor measurements consisted in regular measurements under standard test conditions (STC) and 200W/m², to determine the stability of the devices over time, and some initial temperature coefficient measurements and measurements at different irradiance levels. The annual energy output in kWh/Wp was calculated and simulations were performed based on the indoor measurements. The scope of the simulations was to explain the differences in energy output, by quantifying the losses generated by the two primary mechanisms: the temperature effect given by the temperature coefficient and the efficiency loss at low irradiances. Requirements for future energy rating of PV modules are given together with a discussion about the involved measurement uncertainties.