Water budget and crop modelling for agrivoltaic systems: Application to irrigated lettuces

The installation of tilting-angle solar panels above agricultural plots provides renewable energy and means of action to dampen some of the effects and hazards of climate change. When the panels are properly operated, their drop shadow reduces water consumption by the plants, as a consequence of alternating shade and sun bands with a short-term impact on the stomatal conductance and a global decrease of gas exchanges. This urged the development of a new model for crop growth and water budget, adapted here from existing literature to handle such transient conditions, characterized by short-term (infra-day) fluctuations. The main difficulty was to combine short-term fluctuations in the climatic forcings (radiation interception and rain redistribution by the panels) and long-term agronomic evaluation, hence the coexistence of several calculation time steps in model structure. All field experiments were conducted on purpose in the agrivoltaic plot of Lavalette (Montpellier, France). Specific adaptations consisted in describing the stomatal behavior of the plants for fluctuating solar radiations and varied water status, aiming at improving both the piloting of the solar panels and water management, i.e. the choice of irrigation amounts. Model simulations have been able to reproduce the expected benefits from agrivoltaic installations, for example showing that it is possible to improve land use efficiency and water productivity at once, by reducing irrigation amounts by 20%, when tolerating a decrease of 10% in yield or, alternatively, a slight extension of the cropping cycle. Agrivoltaism appears a solution for the future when facing climate change and the food and energy challenges, typically in the rural areas and the developing countries and especially if the procedure presented here proves relevant for other crops and contexts.