Model-based analysis of shading losses in ground-mounted photovoltaic power plants

Ground-mounted PV plants with multiple parallel mounting structure rows became the most common type of PV systems, where the shading of the adjacent rows results in significant energy losses. This paper presents a detailed modelling method of the inter-row shading to calculate irradiance distribution along the width of the PV rows. A modification of the Hay transposition model is proposed to account for the shading of the sky diffuse, circumsolar, and ground-reflected irradiance components. The effect of the uneven irradiance on the power output is considered by the cellwise calculation and aggregation of the I-V characteristics. The method is demonstrated by a case study, where the annual energy production and the reflection, shading, and cable losses are calculated for different string arrangements and row spacings. The proposed detailed shading model is compared to a simple shading calculation, where only the shading of the beam irradiance is considered. This simple method underestimates the shading losses by 50-80%, which underlines the importance of the proper calculation of the diffuse irradiance masking losses. The electrical mismatch losses due to the shading are compared for different string arrangements, where the best arrangement is also influenced by the number of the maximum power point trackers. As a general conclusion, the modules at the same height should be connected to the same string to minimise the shading losses. The presented method can improve the accuracy of PV simulations and the optimisation of the shading-related design parameters, like the module orientation and row spacing.