Agrovoltaic on vineyards: preliminary resuls on seasonal and diurnal whole-canopy gas exchange

Abstract

Context and purpose of the study. Albeit standing as a fashionable research topic dual use of land as viti-voltaic still lacks of fundamental knowledge about whole canopy grapevine response to altered microclimate under panels vs open field conditions.

Material and methods. Solar panels (SP) were mounted at pre-veraison on half of four adjacent, 50 m long grapevine rows. Panels were mounted 3.13 m from the ground and were 109.2 cm wide. Half of the row was the open-field control (OF). Data were taken in the two central rows planted with Malvasia di Candia aromatica and Cabernet Sauvignon cultivars. Rows were 35° NE-SW oriented and panels were left horizontal from veraison until harvest. Whole canopy gas exchange was continuously measured from DOY 221 (9 August) until DOY 272 (29 September), whereas direct and diffuse total radiation were monitored with a BF-5 hemispheric sunshine sensor.

Results. On a seasonal basis, average direct radiation reaching the OF areas was 683 µmol m-2s-1 vs 361 µmol m-2s-1 (-47.2%). In both varieties, seasonal and diurnal reduction of canopy net CO2 exchange rate (NCER) and transpiration (T) generally diminished by 10-14% in SP as compared to OF, indicating that a wide margin of solar energy capture does exist without greatly compromising canopy function. When canopy water use efficiency (WUE) was calculated as the NCER/T ratio, average values for the two treatments were almost identical (5.3µmolCO2/mmolH2O). However, looking at averaged diurnal trends, it was clear that during the two daily time windows when solar panels cast direct shading over the canopies (8:00-9-30 and 13:30-16:00) the WUE significantly decreases under panels. This is likely due to the fact that PAR levels are lowered down the linear portion of the light response curve, whereas transpiration is less limited with VPD being the main driver under those conditions. Data are under completion for more single-leaf assessment, thermal analyses and agronomic behavior of the two varieties.