Estimation of maximum photovoltaic cover ratios in greenhouses based on global irradiance data

In this study, a method for estimating the maximum PV (photovoltaic) cover ratio for plastic greenhouses based on various years of global horizontal irradiance (GHI) data is presented and illustrated with an exemplary site in southeastern Spain. CAMS (Copernicus Atmosphere Monitoring Service) GHI data from 2005 to 2023 were analyzed to estimate the DLI (daily light integral) inside the greenhouses for various PV coverage ratios with East-West or North-South orientation. The conversion from GHI to photosynthetically active radiation is performed with the usage of a regression model from literature based on satellite and measurement data. The shading effect of the PV cover is estimated with a regression model from literature based on radiation distribution simulations in different greenhouse types. The maximum PV cover ratio was derived for different minimal DLI thresholds, corresponding to different crops. The proposed methodology has been tested for the Almeria region in southeastern Spain which is characterized by high solar irradiance and can be applied also to other regions with similar climatic conditions. With a required DLI of at least 12 mol/m2/day, a theoretical maximum PV coverage of about 44% is acceptable even in December at the studied site for East-West orientation, while it reaches up to 100% (June) during the year. Further, the maximum PV cover ratios for a DLI threshold range have been calculated and compared with experimental results for plastic greenhouses from literature. In 87.2% of the case studies analyzed from literature, the proposed method showed an agreement in the estimation of the effect of PV shading ratios on marketable crop yields. The study indicates that significant PV cover ratios are theoretically possible even for light demanding crops considering DLI thresholds only and can help to select a useful PV cover ratio in PV greenhouses.