Semi-transparent neutral, red, green, and blue photovoltaics impacts on lettuce growth in agrivoltaic cold frames

Both color and transparency of partially transparent solar photovoltaic (PV) panels not only impact renewable energy yield but also crop yield in agrivoltaic systems. To determine design parameters for controlled environment agrivoltaics used to increase the growing season in northern environments, this preliminary screening study grows lettuce in cold frames under the shade of 55% semi-transparent neutral, red, blue, and green thin film PV in controlled cold-frame environments. Visible light spectra were taken inside the cold frames upcycled from EV-charging station crates for each type of PV module to quantify the spectral energy reaching the lettuce plants. The PV cold frames were modeled for electrical performance and the agrivoltaic impact on lettuce crops were monitored for air temperature and soil temperature (hourly) and height and leaf count weekly. Finally, the overall yield in each agrivoltaic setup and control was measured by mass of lettuce and compared to a control given identical nutrition and water. Although the impact of agrivoltaic treatment was mixed in terms of number of leaves, all agrivoltaic treatments had greater height than the control. Overall, agrivoltaic systems created microclimates in the cold frames that enhanced lettuce productivity: neutral semi-transparent modules produced 300% more, green 210% more, red 161% more and blue 120% more yield than the lettuce grown in open air environments. Based on the results, the balanced light spectra through neutral semi-transparent PV panels supports both plant growth and renewable energy generation and was found to be the preferred agrivoltaic design of lettuce under 55% transparent conditions.