Coproduction of Solar Energy on Maize Farms – Experimental Validation of Recent Experiments

Developing methods for the sustainable coproduction of food, energy and water resources has recently been recognized as a potentially attractive solution to meeting the needs of a growing population. However, many studies have used models, but have not performed an actual experiment to directly validate all their predictions. Here, we report a recently-constructed test site on the ACRE farm in West Lafayette, Indiana, consisting of single-axis trackers in a novel configuration atop a maize test plot. We present a methodology to measure irradiance therein with 10-minute temporal resolution, which allows us to validate prior PV aglectric farm irradiance models. In spring 2019, an experimental aglectric system was constructed at the Purdue University Agronomy Center for Research and Education (ACRE) farm. This experiment, commonly referred to as the ACRE Solar Array, comprises of 4 single-axis solar trackers implemented in east-west tracking mode. The solar trackers are raised 20 ft above ground level and welded to steel I-beams for compatibility with current high-yield agricultural practices such as mechanized farming. This work modifies and leverages a previously developed ray-tracing model that calculates irradiance reaching the ground. Using the open-source library PVLib, spatial maps of intensity variation are calculated for direct and diffuse light. Solar input was based on astronomical data calculated in PVLib and historical weather data from West Lafayette. The percentage reduction in irradiance for a simulated structure in comparison with an open field is calculated and referred to as shadow depth (SD). The model is capable of simplistic systems as well as custom array layouts such as the ACRE Solar Array. A methodology for validation of spatial and temporal irradiance maps of non-uniform shadow distributions has been evaluated and shows significant agreement.