New procedure and field-tests to assess photovoltaic module performance

The theoretical performance of a photovoltaic (PV) module is typically evaluated by using models based on equivalent circuits whose parameters are derived from data listed in manufacture's datasheet. Few manufactures provide detailed enough datasheets to allow using highly accurate models. In many cases simplified models have to be used due to missing information. This paper proposes a new procedure to evaluate PV modules performance. The procedure is based on the four-parameter model, which can be used with input data provided by most manufactures. Firstly, the parameters extraction in standard test conditions is discussed. Secondly, an algorithm for PV module performance estimation under real weather conditions is proposed. The procedure is validated on a commercial PV module. Estimations and field-test data are found to be in good agreement. The difference between the response time of the pyranometer (tens of seconds) and the response time of the PV module (almost instantaneous) is found to be an important source of errors. This aspect has not been previously discussed in literature with sufficient detail. The proposed procedure represents a feasible tool for calculating the performance of PV modules described by a limited set of data, operating in arbitrary weather conditions.