Indoor measurement of GTE-matrix for energy rating

Energy rating input data acquired indoors is currently based on IV curves measured in a matrix of irradiances (G) and temperatures (T). This can lead to uncertainties in the energy prediction as one needs to make additional corrections for the effects of spectrum (E) and angle of incidence. Energy rating measurements derived outdoors inherently take those variations into account and are more accurate for that reason, but take a long time to acquire and site to site differences might show up more strongly. This paper demonstrates the first indoor GTE matrix measurements made with an LEDbased solar simulator prototype, opening the possibilities of much faster and more accurate energy rating of PV devices. The experimental set-up and measurement method used is explained in detail. Analysis shows a respectable uncertainty of 3.2% (k=2) in maximum power measurements with scope for further improvement

Effect of I-V translations of irradiance-temperature on the energy yield prediction of PV module and spectral changes over irradiance and temperature

Energy rating is gaining importance in the photovoltaic (PV) community as it, unless power rating at standard conditions, allows an accurate estimation of the performance of PV modules in different climatic conditions. The device characterisation currently requires the measurement of a performance matrix using irradiance and temperature where values between measurements might be interpolated. Spectral changes are included by correcting using a quantum efficiency measurement. I-V translations of PV modules give better idea about the measurements of the PV modules as a function of irradiance and temperature. Two methods of I-V translations are applied in this study. Bilinear interpolation between the consecutive points of three selective data sets of irradiance and temperature in the power matrix reduces the prediction error below 2.5% compared to over 6% with linear interpolation between two extreme data set points in the power matrix

Effect of timing and voltage dependency on inverter sizing

The effects of environmental data time steps and inverter’s voltage dependency on optimum inverter sizing are investigated in this paper. Three sites in the Europe with the specific climates and two detailed inverter characteristics including its dependence on the DC voltage during the operation are taken into account to demonstrate the differences in the inverter sizing required to allow for the site and inverter specifics. A model of a PV system linked to an inverter is developed to assess and optimise how the different factors influence the correct sizing of a given PV system. The environmental data with time resolution higher than 10 minutes is recommended since low frequency data (hourly data), which might ignore the irradiance peaks and underestimate up to 2.7% of total annual energy at high irradiances, cannot guarantee the correct sizing ratio of inverter. Inverter efficiencies change up to 1 to 3% as a function of input voltage which needs to be considered in inverter sizing. The overall inverter behaviour is also crucial in order to size appropriately. It is shown that some inverters perform better with undersizing, some better with oversizing

Validation of proposed photovoltaic energy rating standard and sensitivity

PV devices are currently compared on the basis of the power measurements, which might not be as meaningful as a comparator as the energy yield. The energy rating standard proposed by the IEC promises to overcome this shortcoming. It has been implemented in three institutes and the issues with the current drafts are evaluated. The data required as the input for the energy rating is normally not available and synthetic datasets will have to be used or parts need to be estimated for validation studies. The validation against outdoor data shows that the uncertainty of the input data, specifically the angular distribution of the diffuse irradiance, makes the energy prediction part virtually not applicable for energy yield calculations. The validation effort shows a reduction of the standard deviation in the measurements, indicating that all environmental effects are considered. The evaluation of the originally proposed standard days shows that there is little information to be gained in their application as they are not representative of realistic conditions; they are enveloping the possible environments. This will in some cases over-emphasise the importance of certain effects, as their contribution to the overall energy yield might be negligible. Overall, the proposed standard represents an important advance on power rating. The standard is able to identify differences in device technologies. Further work might be required to make the output more relevant to a wider variety of users, though