The results of a measurement intercomparison between eleven European laboratories measuring PV energy relevant parameters are reported. The purpose of the round-robin was to assess the uncertainty analyses of the participating laboratories on c-Si modules and to establish a baseline for the following thin-film round-robin. Alongside the STC measurements, low irradiance conditions (200W/m) and temperature coefficients measurements were performed. The largest measurement deviation from the median at STC was for HIT modules from -3.6% to +2.7% in PMAX, but in agreement with the stated uncertainties of the participants. This was not the case for low irradiance conditions and temperature coefficients measurements with some partners underestimating their uncertainties. Larger deviations from the median from -5% to +3% in PMAX at low irradiance conditions and -6.6% to +18.3% for the PMAX temperature coefficient were observed. The main sources of uncertainties contributing to the spread in measurements were the RC calibration, mismatch factor and capacitive effects at STC and low irradiance conditions as well as the additional light inhomogeneity for the latter. The uncertainty in the junction temperature and the temperature deviation across the module were the major contributors for temperature coefficients measurements.

The purpose of the test “Performance at low irradiance” is to determine how the electrical performance of the module varies with load at 25°C and at irradiance of 200Wm-2, using natural sunlight or a simulator class BBB or better conforming to the requirements of IEC 60904-9, instead of 1000 Wm-2 standard conditions. A device to change the irradiance to 200Wm-2 is required; its implementation shan't affect the relative spectral irradiance distribution and the spatial uniformity in accordance with IEC 60904-10. To this purpose the IEC 60904-10 recommends the use of mesh filters or neutral density filters. Mesh filters are believed to be the best method for large surfaces. It would be important to compare results and uncertainties related to the different solutions and discuss about pros and cons. This paper matches the results of two laboratories that adopt two different approaches. The low irradiance performance test has gained importance due to the always extensive use of PV as integration elements on buildings.

Results of the European FP7 Sophia project roundrobinof c-Si module power measurements at STC andlow irradiance and temperature coefficients were used tocalculate annual energy yield at four sites. The deviationin the estimates solely due to the different measurementresults is reported, neglecting the uncertainty in themeteorological data and losses unrelated to theperformed measurements. While minimising thedeviation in Pmax measurements remains the keychallenge, the low irradiance and temperaturecoefficient contributions are shown to be significant.Propagating the measurement deviation in c-Si modulemeasurements would suggest that expanded uncertaintyin energy yield due to module characterization alone canbe as high as ±3-4%.

The results of a measurement intercomparison between eleven European laboratories measuring PV energy relevant parameters are reported. The purpose of the round-robin was to assess the uncertainty analyses of the participating laboratories on c-Si modules and to establish a baseline for the following thin-film round-robin. Alongside the STC measurements, low irradiance conditions (200W/m2) and temperature coefficients measurements were performed. The largest measurement deviation from the median at STC was for HIT modules from -3.6% to +2.7% in PMAX, but in agreement with the stated uncertainties of the participants. This was not the case for low irradiance conditions and temperature coefficients measurements with some partners underestimating their uncertainties. Larger deviations from the median from -5% to +3% in PMAX at low irradiance conditions and -6.6% to +18.3% for the PMAX temperature coefficient were observed. The main sources of uncertainties contributing to the spread in measurements were the RC calibration, mismatch factor and capacitive effects at STC and low irradiance conditions as well as the additional light inhomogeneity for the latter. The uncertainty in the junction temperature and the temperature deviation across the module were the major contributors for temperature coefficients measurements.

Cost of the energy generated by a Photo-Voltaic (PV) plant over the whole plant lifetime depends directly on the amount of energy the plant itself is able to generate under actual operating conditions (i.e. plant configuration and weather conditions). The so-called plant energy rating is a set of measures on arrays of PV modules or on complete plants over long periods, viz. months or years, carried out to measure actual module capability to generate current under different operating conditions. However, time required for these measures is generally incompatibles with industrial development, that need quick answer to address technological choices. Therefore, PV plant energy rating is estimated either by means of statistical-based assumptions, i.e. by coupling actual nominal module efficiency with standard derating factors, or by means of electrical and physical models simulating modules, strings, arrays and complete plants. The target of the present paper is the comparison between energy rating valuated with an yearly measurement on PV modules carried out at ENEL photovoltaic laboratory (Catania, Sicily) and the results obtained by an electrical model developed by Enel Research department in collaboration with Catania University. The technologies under testing were single-crystalline and multi-crystalline Silicon, CdTe, aSi/μcSi, heterojunction. The electrical model has been compared with several mathematical and physical models well known and currently used in scientific literature. Results show that while literature models fails under low irradiance conditions, good results have been obtained by the new model that was implemented, so that the new model guarantees much more precise energy rating capabilities. The model is now being used as the base for return on investment calculations of PV systems of different technologies and is being integrated into an on-line diagnostic systems for optimization of large-scale PV plant operation.