Light Thresholds and Shading Effects on Strawberry and Raspberry Yields and Quality Under Agrivoltaics Systems in Switzerland

Abstract

In Switzerland, a large proportion of strawberries (Fragaria × ananassa Duch.) and raspberries (Rubus idaeus L.) are cultivated under protective covers such as rain covers, tunnels, and greenhouses to safeguard against adverse weather. However, rising summer temperatures increasingly threaten fruit yield and quality, prompting interest in agrivoltaic (AgriPV) systems as a climate-smart solution. AgriPV enables dual land use by combining photovoltaic energy production with crop cultivation, though shading from solar panels may impact crop performance. This four-year study assessed the effects of shading on yield and quality of strawberries and raspberries grown in substrate systems with fertigation across 21 case studies in Switzerland, including 13 AgriPV configurations at three sites. Light availability was measured as daily light integral (DLI), and its influence on yield, fruit weight, firmness, sugar content, and acidity were analysed using linear mixed-effects models. We report slopes with standard errors and p-values to quantify effect sizes. Results show a positive linear relationship between DLI and both yield and sugar content in both species, with stronger effects observed in strawberries. Based on the DLI at which the standardized yield regression crosses zero, we recommend minimum DLIs of 25 mol m⁻² d⁻¹ for strawberries and 15 mol m⁻² d⁻¹ for raspberries to avoid disproportionate yield loss. Strawberry firmness also declined at low DLI, likely due to reduced UV exposure. Fruit weight and acidity were unaffected. Our findings inform the design of AgriPV systems that balance renewable energy production with high-quality berry yields, emphasizing the importance of species-specific light requirements.