STC efficiencies are not sufficient to compare photovoltaic devices of different semiconductor material or device configurations. The energy yield changes as the variables of STC deviates from their original values when the modules are placed in various climatic conditions. The magnitude of this change for different modules is not always clear and needs to be investigated and modelled. A modeling and analysis method named site specific conditions (SSC) is demonstrated which is a measure-correlate-predict approach. It allows an accurate estimation of the actual energy yield for different sites based on the measurements at one single site. The method takes into account the effect of the physical operating environment and translates this to other meteorological conditions on the basis of physics related formulae. Our results show a large seasonal variation for modules for the different effects. For crystalline modules losses of up to 12% in the summer is due to the temperature effect while the multi-junction thin film losses of more than 30% in the winter is due to spectral changes and incidence angle effect for the UK.
"More specifically, a fundamental mathematical model used to predict the power produced by a PV system is the single-point efficiency model  which requires only the irradiance on the plane of array (POA), G POA , the area of the PV array, A, and the efficiency at standard test conditions (STC), η STC , of irradiance 1000 W/m 2 , cell temperature of 25 °C and air mass (AM) 1.5. The simplicity of this model's input parameters is compromised by the fact that it cannot sufficiently account for the deviations in efficiency associated with the different PV technologies and the climatic conditions of the place of operation . In order to optimize the prediction accuracy more elaborate models which include up to thirty different parameters have been developed in an attempt to fully model PV performance and account for factors such as temperature, angle of incidence (AOI), spectrum, mismatches, cable losses etc . "
[Show abstract][Hide abstract] ABSTRACT: Presented is a method for calculating the power-productivity of photovoltaic (PV) installations with sunlight concentrators and multijunction (MJ) solar cells (SC) allowing for variation of their power efficiency in dependence on real operation conditions - spectral composition and sunlight flux density and also on temperature of multijunction cells. The yearly totals of specific electric power generated by a module at constant and variable efficiency values have been calculated. It has been shown that allowing for the joint effect of the sunlight characteristics and multijunction SC temperature on the photovoltaic module efficiency must be realized in simulating the module operation in any power generating systems. These allows excluding the overestimations of the yearly power totals generated by a solar installation in determining the power productivity.
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