Bifacial and Mismatch Factors of Agri-Photovoltaics Systems

We use ray tracing and circuit simulation to examine bifacial and mismatch factors in three very different types of Agri-PV systems: (A) east–west waves with semi-transparent modules above crops; (B) single-axis trackers with greenhouses between the rows; and (C) east–west facing vertical modules. We determine the annual bifacial gain to be 6%, 4% and 70%, respectively, where the gain for Systems A and B is considerably reduced by crop absorption, and where the gain for System C is close to the bifaciality of the modules. We quantify the shading and transmission factors of the Agri-PV systems, finding them to be significantly higher than for equivalent conventional systems, largely due to extra shading from crops and greenhouses, extra spacing between modules and bays, and, in the case of System A, semitransparent modules. We also quantify the electrical mismatch loss that arises from non-uniform irradiance, finding it to be moderate for System A (0.8%), small for System B (0.3%) and very high for System C (3.9%), primarily due to row-to-row shading when the sun is low in the sky. In addition to quantifying their annual values, we show that these factors depend strongly on the solar position and the diffuse fraction (cloudiness), and we quantify the error introduced into forecasts of output power when this dependence is neglected.