Modelling and optimization of bifacial PV farm

Abstract

Solar photovoltaic (PV) has seen the most rapid growth among the renewable energy sources in the last decade. The market share of bifacial PV modules is expected to rise up to 70% in 2033. Such technology enables different farm configurations; however, it introduces complexities during the modelling phase, particularly concerning the estimation of incident irradiance on the rear side of the modules. The aim of this thesis is to investigate the potential of E/W vertical bifacial PV farms, in terms of market revenues, with respect to N/S tilted counterparts. A bifacial PV model is developed to estimate the power generated by a large-scale farm. This is based on the view factor concept and a 2D assumption is adopted to enable fast simulations. Such model takes into account the non-uniformity of the incident irradiance as well as the spectral impact. A multi-dimensional matrix approach is implemented to minimize the computational time while performing the calculations for individual cells and wavelength values. The model is validated in collaboration with the company KIPP&ZONEN, focusing on the broadband rear irradiance and its non-uniformity. Overall, the model shows sufficient agreement with the measured data, namely a mean bias deviation of −1.29W /m2 (−2.22%) and a RMSE of 12.65W /m2 (21.69%) are obtained. The validation highlights larger errors in case of higher tilt values, especially during the clear days and at the edge of the modules. Specifically, the error is proportional to the amount of unshaded ground seen by a cell, in alignment with the limitations of the view factor concept. The profitability of vertical modules is studied in relation with various variables, including design parameters, market conditions, curtailment strategies and hybrid vertical/tilted configurations. A global scale is achieved by extending the simulation to 102 locations worldwide. To calculate the revenues of the PV farms, electricity price curves are modelled considering lower noon prices, hence different market conditions are identified by the minimum price and the ratio between morning/evening and noon prices. Whether vertical or tilted configuration is favourable in terms of market revenues is not dependent on the curtailment strategy unless the maximum power is limited to 70% of the nominal value. Combining vertical and tilted modules within a PV farm is found to be advantageous only in case heavy curtailment is applied. Among the design parameters, the row-to-row distance has a higher impact on the market revenues with respect to the modules’ elevation. Specifically, larger distances are favourable for both configurations even though such benefit is more evident for vertical modules whereas optimal height values can be identified. A minimum ratio between morning/evening and noon prices is calculated, which represents the lower limit for the higher profitability of E/W vertical modules with respect to the N/S tilted case. Such value is dependent on the specific location and the design parameters. The locations characterized by a low diffuse fraction are recommended to implement vertical PV farms.