Measurement of Light Interception by Crops under Solar Panels using PARbars

Abstract

To analyse agrivoltaics systems and understand crop responses to shading, measurements of available light for the crop and light interception by the crop are important. Especially in row crops, there is a lot of variation in the amount of light at different heights, different positions relative to the row and over time. This spatial and temporal variation in light is difficult to capture with standard point measurement technology. Commercially available line quantum sensors are not long enough to cover the desired width within an agrivoltaics system and come at high cost. Therefore, custom made PARbars were used: bars of 1.5 m long having light sensors every 5 cm facing the sky and giving a total (line) irradiance value per time step. PARbars were installed above and below a raspberry crop row in both the agrivoltaics system and the control with a plastic foil cover, and a point sensor was installed in the open field. The difference between open field radiation and the top PARbar gives the light interception by the panel construction or the foil cover, the difference between the top and bottom PARbar gives the light interception by the crop. This information can be used in conjunction with destructive crop measurements to analyse impacts on leaf area and light interception, dry matter production and derived efficiency of photosynthesis. The crop in the current agrivoltaics system received half of the amount of light compared to the control system, but total biomass production was less reduced because of compensation by increasing specific leaf area and photosynthesis efficiency. Further analysis is needed to evaluate the agrivoltaics system and the impact of increasing shade on the crop, and to assess the trade-off between electricity production and crop production.