Microclimate under agrivoltaic systems: Is crop growth rate affected in the partial shade of solar panels?

Agrivoltaic systems are mixed systems that associate, on the same land area at the same time, food crops and solar photovoltaic panels (PVPs). The aim of the present study is to assess whether the growth rate of crops is affected in the specific shade of PVPs. Changes in air, ground and crop temperature can be suspected due to the reduction of incident radiation below the photovoltaic shelter. Soil temperature (5 cm and 25 cm depth), air temperature and humidity, wind speed as well as incident radiations were recorded at hourly time steps in the full sun treatment and in two agrivoltaic systems with different densities of PVPs during three weather seasons (winter, spring and summer). In addition, crop temperatures were monitored on short cycle crops (lettuce and cucumber) and a long cycle crop (durum wheat). The number of leaves was also assessed periodically on the vegetable crops. Mean daily air temperature and humidity were similar in the full sun treatments and in the shaded situations, whatever the climatic season. On the contrary, mean daily soil temperature significantly decreased below the PVPs compared to the full sun treatment. The hourly pattern of crop temperature during daytime (24 h) was affected in the shade. In this experiment, the ratio between crop temperature and incident radiation was higher below the PVPs in the morning. This could be due to a reduction of sensible heat losses by the plants (absence of dew deposit in the early morning or reduced transpiration) in the shade compared to the full sun treatment. However, mean daily crop temperature was found not to change significantly in the shade and the growth rate was similar in all the treatments. Significant differences in the leaf emission rate were measured only during the juvenile phase (three weeks after planting) in lettuces and cucumbers and could result from changes in soil temperature. As a conclusion, this study suggests that little adaptations in cropping practices should be required to switch from an open cropping to an agrivoltaic cropping system and attention should mostly be focused on mitigating light reduction and on selection of plants with a maximal radiation use efficiency in these conditions of fluctuating shade. (C) 2013 Elsevier B.V. All rights reserved.