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A key requirement for increasing the accuracy of energy yield modelling is the accurate estimation of the ground albedo value of a potential site. As most natural surfaces are not white, the colour as well as irradiance of reflected light needs to be considered. In this work we use spectral ground reflectance datasets from satellite data and ground-based stations in order to extract effective spectral albedo values and their uncertainties for bifacial PV system energy yield modelling. We demonstrate satellite spectral reflectance data as a realistic case for bifacial gain calculations and validate them with the ground-based data. An effective albedo calculation methodology is introduced, where the spectral albedo dataset, spectral irradiance and spectral response of the PV module type of the potential system are considered. Comparing 20 different locations and 3 different bifacial module types, we show that it is critically important to account for diurnal and seasonal variations in spectral albedo in bifacial gain calculations. We also show that there can be significant differences between front side and rear side spectral response in silicon bifacial PV modules which can lead to differences of greater than 20 % in the effective value of ground reflected irradiance.

Bifacial Photovoltaic (PV) technology is expected to acquire an increased market share of the solar PV industry in the future, due to the ability of bifacial PV modules to collect light from both the front and rear side, increasing the energy yield for a specific available area for a PV system. Accurate measurement procedures for bifacial products result in more accurate energy yield estimates, consequently improving the bankability of bifacial PV technology. This work aims to evaluate the procedures for the measurement of electrical power and bifacial parameters of bifacial solar devices, concerning to their applicability in calibration laboratories and production line environments. An intercomparison for bifacial PV cells and modules is carried out between nine different test laboratories across Europe, as part of the PV-Enerate project. The measurement procedures as described in IEC TS 60904-1-2:2019 are followed among the different test laboratories, to evaluate the applicability of these procedures. Three different types of bifacial PV cells and three different types of bifacial PV modules are measured. The intercomparison involves measurements with systems using both single and double-sided illumination conditions. The uncertainty budgets and systematic differences that these procedures result in between different laboratories are determined and discussed. Specific common mistakes are reported and improvements to the IEC TS 60904-1-2:2019 are proposed as a result of this intercomparison activity.

The IEC 61853 standard series “Photovoltaic (PV) module performance testing and energy rating” aims to provide a standardized measure for PV module performance, namely the Climate Specific Energy Rating (CSER). An algorithm to calculate CSER is specified in part 3 based on laboratory measurements defined in parts 1 and 2 as well as the climate data set given in part 4. To test the comparability and clarity of the algorithm in part 3, we share the same input data, obtained by measuring a standard photovoltaic module, among different research organizations. Each participant then uses their individual implementations of the algorithm to calculate the resulting CSER values. The initial blind comparison reveals differences of 0.133 (14.7%) in CSER between the ten different implementations of the algorithm. Despite the differences in CSER, an analysis of intermediate results revealed differences of less than 1% at each step of the calculation chain among at least three participants. Thereby, we identify the extrapolation of the power table, the handling of the differences in the wavelength bands between measurement and climate data set, and several coding errors as the three biggest sources for the differences. After discussing the results and comparing different approaches, all participants rework their implementations individually and compare the results two more times. In the third intercomparison, the differences are less than 0.029 (3.2%) in CSER. When excluding the remaining three outliers, the largest absolute difference between the other seven participants is 0.0037 (0.38%). Based on our findings we identified four recommendations for improvement of the standard series.

We present an independent analysis of expected real-world performance of single junction perovskite cells and tandem perovskite-on-silicon devices relative to single junction silicon cells. As energy-rating of perovskite devices is not yet realised and the technology is still rapidly maturing, this is a theoretical study. We create an “optimistic” scenario, which represents successful upscaling of current record-efficiency perovskite lab cells. Our model considers temperature, spectral, angular and junction mismatch effects. In this scenario, we find that single-junction perovskite cells perform better in many real-world climates than under standard test conditions; in one climate, the single junction perovskite cell has a higher absolute energy yield than a silicon cell that had 3 % higher efficiency under standard test conditions. For tandem cells, we find that tandem energy gains of between 29 % and 40 % are achieved when the band gap of the front cell is optimised to the climate. We also simulate less optimistic scenarios by reducing the performance of both the perovskite or silicon sub cells. We find that tandem energy gain is strongly affected by the initial choice of sub-cell efficiency, which largely explains the large variations in published modelling studies.