Integration of bifacial PV in agrivoltaic systems

Abstract

Solar photovoltaic (PV) technologies offer a renewable alternative to power generation that is based on fossil fuels; however, to meet the rising demand in electricity a substantial amount of surface area is required. This will inevitably lead to the installment of these systems on agricultural land, subsequently intensifying the land-use conflict and threatening food security. To alleviate this, the use of agrophotovoltaic (APV) systems is investigated, which enable the simultaneous production of food and renewable energy. More specifically, the aim of this thesis is to determine the optimal topology for a medium-scale and stationary bifacial APV array, which is simulated under the climate of Boston, USA (42.37˚N, 71.01˚W). Irradiance modelling is performed with Radiance’s raytracing algorithm in combination with the daylight coefficient approach of Daysim and the Perez All Weather sky model, which is then coupled to the crop and electrical yield models to determine the overall land productivity. The modelling approach used is robust, while offering flexible manipulation of the array’s deployment configuration, which is crucial for multivariable optimization. The integration of bifacial PV offers various synergistic effects mainly due to the amplified ground irradiance necessary for crop growth. Owing to the decreased PV density and high elevation from ground, rear irradiance homogeneity and bifacial gain are enhanced. Widening of the row spacing resulted in a logarithmic increase of the incident ground irradiation, while the overall energy yield portrayed a negative exponential trend, which is attributed to the use of bifacial modules. East-west (E-W) facing and vertically installed topologies are better suited for shade intolerant species, or permanent crops since they permit additional light penetration, especially during the winter months. In contrast, south-north (S-N) facing and latitude inclined arrays lead to intense and non-homogeneous shading that is unfavorable for growth during winter or for crops that cannot acclimate to shade; nonetheless, energy yield and land equivalent ratio (LER) are significantly enhanced. Unlike previous studies where only conventional modules were examined, here the potential of a customized one is inspected to assess whether blueberries can grow effectively under shade. By integrating such a module in an E-W hinged PV topology, which is associated with the most optimal shading patterns and schedule, the agrivoltaic performance is optimized. In comparison to the reference case, the land’s productivity is increased by 59% with a reduction in electrical yield by a third. Through this holistic approach that incorporates a multi-scale sensitivity analysis, it is possible to achieve a spherical understanding of the limitations and potential synergies associated with the dual use of land, ultimately encouraging the sustainability of the agricultural sector.