Comparing methods for the long-term performance assessment of bifacial photovoltaic modules in Nordic conditions
Lauri Karttunen, Sami Jouttijärvi, Aapo Poskela, Heikki Palonen, Hugo Huerta, Milica Todorović, Samuli Ranta, Kati Miettunen
Abstract
The main objective of this study is to discover which performance loss rate (PLR) calculation methods provide the most reliable results for vertical bifacial photovoltaics (VBPV) in Nordic conditions. For this purpose, over 1600 filter-metric-aggregation-model combinations for PLR calculation are compared. Accurate determination of PLR is crucial for estimating the economic profitability of a PV system, but standardized methodology is lacking as is the understanding on how the common PLR calculation frameworks perform for both VBPV technology and Nordic climatic region. Here, four-year, minute-resolution datasets from adjacent VBPV modules and a weather station in Turku, Finland (60°N) are used. After removing crude outliers, a benchmark PLR of −1.46±0.03 %/year was obtained by averaging the remaining over 1200 filter-metric-aggregation-model combinations. The year-on-year method with a daily/weekly aggregated temperature- and irradiance-corrected performance model was found robust and reliable to Nordic high seasonality. In contrast, several commonly used methods, such as the PVUSA model, produced unrealistic results. Unexpectedly, temperature correction increased the seasonal pattern of the performance ratio, and PLR varied with irradiance conditions and between the front and rear sides of the module. This work expands the best practices of PLR calculation to complement the development of global PLR calculation standards.