Where:
kWhAC = total measured AC energy production (kWh)
A = total module area (m2)
Gpoa = total measured global insolation on the plane ofthe array (kWh/ m2)
To = reference temperature (STC) (oC)
Tm = average module temperature (calculated per [1]) (oC)
? = module temperature coefficient of power (%)
Figure 2 shows the regression fit for an urban Southern California system during the dry summer period using ŋtemp. The results of the preliminary study support the use of linear approximations of performance degradation due to system soiling and suggest that ŋtemp gives the most accurate approximation of performance degradation overtime.y