Energy rating based on thermal modelling of five different PV technologies

Minute by minute outdoor measurements of five commercial PV modules including multi c-Si, HIT, a-Si/μc-Si, CIS, CdTe over one year were used to develop a model for predicting the individual module temperatures. The simulated module temperatures over a whole year in minute interval correspond to the outdoor measured values within a RMSE of 1.5°C. Input of the model includes irradiance measurements, which are extracted from the measured short circuit current ISC, the measured wind speed and the ambient temperature. The measured energy weighted module temperature for Zurich was found to be between 33.3°C and 38.0°C for the different module types with a maximum difference of 0.8°C relative to the simulated average module temperature. Due to the high module temperature, the annual average efficiency was reduced relative to the STC values by only 2.6% (HIT) and 5.6% (CIS). Another reduction of the STC efficiency could clearly be attributed to the efficiency at low ISC values which classify low irradiance values. The value is a decrease of the annual energy output of 4.7% and an increase of 1.1%. A further loss analysis was performed to separate spectrum related losses resulting in a relative difference of 2% for the tandem compared to the multi c-Si module

Verification of measured PV energy yield versus forecast and loss analysis

Yield forecasting of the commercial design tool PVsyst (v5.6) is compared to the performance measurements of multi crystalline modules in Dietikon, Zurich, during 2011. The total measured horizontal irradiance was 1146 kWh/m2 in 2011. This pyranometer measurement covers 91.5% of the total annual irradiance (determined using IDAWEB data with 100% uptime for Affoltern). The historical irradiance data averaged over decades are about 11.4% (Meteonorm) or 13.6% (PVGIS) lower than the IDAWEB data in 2011. The standard deviation between 2001 and 2011 is about 4.9% with respect to IDAWEB. The measured DC performance ratio (PRDC) is 0.937 with a measurement uncertainty of ±0.031 (k=2). Simulations with manufacturer and optimised parameters showed a deviation to the measurement between 4% and 8%. A second analysis considers shading losses for different shading angles. Calculated losses are about 2% lower than simulated losses with PVsyst using a model of partial shading for a shading angle of 20°. Interesting results could be achieved by determining the loss upon limiting the inverter output power. There is only 4.4% annual loss when the inverter output power is set to a limit of 70 % for the location Dietikon in 2011