Energy rating of PV modules: comparison of methods and approach

The Matrix and Performance Surface Methods of Energy Rating are related techniques under development for the determination of electrical yield that is intended to be a more useful predictor of performance for installers than W
_p
alone. Here a power matrix or performance surface as a function of irradiance and ambient temperature P(G
_i
; T
_a
) is linked to a climatic condition occurrence matrix N(G
_i
, T
_a
) for a particular location. The use of just two independent variables has the advantage of simplicity but it is important to evaluate the possible cost of reduced accuracy due to the exclusion of other variable parameters such as Air Mass for example. The power matrix may be determined by outdoor or indoor measurements, and the complete matrix may also be extrapolated from a reduced data set using models of cell behaviour thereby reducing measurement time. The present paper relates solely to crystalline Si and reports on the comparison of outdoor measurements at two sites, and their further comparison with indoor measurements.