where PDC is the measured DC power, G is the measured irradiance (at panel plane), ɣ is the panel’s temperature coefficient of M and T is the panel temperature. For the REC Peak Energy Series 225Wp and REC Peak Energy Series 230 Wp, ɣ = –0.43%. The above correction formula is only applicable for high irradiance levels as panel efficiencies become non-linear at lower irradiation. Furthermore, any sensor or inverter failures and regular system maintenance needs will also affect the accuracy of the correction. In
order to increase the accuracy of such analysis, the U.S. Department of Energy’s primary national laboratory for renewable energy, NREL,proposed the following guidelines to filter measured data Daylight data only Removal of any record with missing data for any parameter Removal of any record where G < 500 W/m² In addition to NREL’s methods, any record with a Performance Ratio (PR) 95% (indicating shadowing or snow coverage, maintenance shut down, or other non standard operational mode) was removed