Quantifying CO₂ emissions from ground-mounted solar parks in temperate climates and the potential mitigating role of surface vegetation

In the context of the environmental crisis and steadily increasing energy demand, diversifying energy sources has driven the deployment of renewable energies, particularly photovoltaics. Photovoltaic energy is generally considered a low-carbon alternative to fossil fuels due to the absence of direct emissions during electricity generation. However, beyond these debated considerations, gaps remain in post-installation assessments of surface areas. Photovoltaic panels alter the surrounding microclimate, and these changes can affect soil and vegetation, which are major controls on how carbon is released to or absorbed from the atmosphere. To our knowledge, no study in temperate regions has yet quantified the CO₂ fluxes directly resulting from post-installation land surface changes.

Between 2022 and 2024, we measured CO₂ fluxes at two solar parks in France. The first, located in northwest France (Normandy), covers 19 ha of former industrial land with partly impermeable soils and sparse vegetation. The second, in southwest France (Gironde), spans 127 ha on a former maritime pine plantation within a predominantly forested landscape and is characterized by wet heathland soils.

In 2024, both sites exhibited neutral to positive annual NEE balances (carbon sources), with values of 20 ± 9 gC/m² in Normandy and 184 ± 55 gC/m² in Gironde. Although biomass was greater at the Gironde site, annual GPP in 2024 was 654 ± 27 gC/m² compared with 842 ± 53 gC/m² in Normandy, where the growing season was significantly longer, partly explaining the differences in annual NEE. Total respiration was 838 ± 16 gC/m² in Gironde and 862 ± 56 gC/m², in Normandy. Differences between sites in the sensitivity of vegetation cover and its ecophysiological processes to climate and soil conditions, as well as in their efficiency in using light and water, partly explained the overall patterns and seasonal partitioning of carbon fluxes. Vegetation and land management also played an important role in regulating emissions. In Gironde, practices such as mowing and grazing contributed to the low GPP. These results highlight the key role of the vegetation cover in regulating carbon fluxes and its potential to mitigate emissions under suitable conditions and management in photovoltaic ecosystems.