The optimization of vertical bifacial photovoltaic farms for efficient agrivoltaic systems

An unprecedented demand for Food, Energy, and Water (FEW) resources over coming decades and the rising climate concerns require integrated FEW innovations with least environmental footprint. Collocating photovoltaic (PV) technology with agriculture is a promising approach towards dual land productivity that could locally fulfill growing food and energy demands particularly in rural areas. This 'agrivoltaic' (AV) solution can be highly suitable for hot and arid climates where an optimized solar panel coverage could prevent excessive thermal stress during harsh weather thereby increasing the crop yield and lowering the water budget. One of the concerns with using standard fixed tilt solar array structure that faces North/South (N/S) direction for AV farming is the spatial heterogeneity in the daily sunlight distribution for crops and soil water contents, both of which could affect crop yield. Dynamic tilt control through a tracking system can eliminate this problem but could increase the system cost and complexity. Here we present the investigation of vertically tilted bifacial AV farms which can be especially attractive for climates where PV losses due to dust are high. The relative food-energy performance for the vertical East/West faced bifacial panel (bi-E/W) scheme is compared with the standard monofacial tilted panels facing North/South (mono-N/S) through integrated models for energy conversion, spatial/temporal shade patterns, and the crop yield that is benchmarked against the reported field experiments for lettuce. We show that both schemes have similar food-energy yields for shade-sensitive crops which require a relatively low array density (i.e. <= 1/2 of that for the standard ground mounted PV systems). On the other hand, the two PV schemes have remarkably different food-energy yields for denser PV array configuration for which bi-E/W provides higher crop yield and mono-N/S exhibits higher energy yield. To preserve > 80% of lettuce yield, the maximum array density is limited from half to twice of the standard PV systems corresponding to the varying shade response for the crop. Similarly, to preserve 80% of the energy yield, the lettuce yield is predicted to vary from 65% (shade-sensitive) to 100% (shade-tolerant). The vertical bi-E/W scheme is although not superior in terms of the combined food-energy performance, it could be attractive for its distinct advantages such as spatial homogeneity for shades and rainfall under panels, convenient architecture for farm machinery mobility, and an inherent resilience to soiling.