Germany offers best European policy for agrivoltaics, claim researchers

Scientists in Canada studied romaine lettuce growth under cadmium telluride thin-film solar modules with varying transparency and photosynthetically active radiation, and found Germany’s regulatory framework most effective for maximizing agrivoltaic benefits.

Researchers from Canada’s Western University have experimentally tested the yield of romaine lettuce in agrivolaric set-ups, with different transparency and photosynthetically active radiation (PAR) levels in an effort to define a clear relationship between PV transparency, PAR, and crop productivity.

“To our knowledge, no prior research has systematically tested how varying PV transparencies affect PAR and crop yields in a controlled environment,” corresponding author Uzair Jamil told pv magazine. “Our study uniquely quantifies the impact of a wide range of PV transparencies on PAR and crop performance, providing empirical findings that can inform agrivoltaic policy. By contextualizing these results within already matured agrivoltaic jurisdictions globally, the study offers novel insights for regions like Canada, where policy has yet to fully integrate the agrivoltaic potential.”

The experiment was conducted in a controlled environment, where conditions in the biomes were representative of outdoor summer in London, Ontario, Canada. Daytime temperatures were maintained at 25 C, while nighttime temperatures were set at 19 C. To supplement illumination during the 16-h daylight phase, four 600 W high-pressure sodium fixtures were used. Seven different transparencies of cadmium telluride (CdTe) thin film solar modules, namely 10%, 30%, 40%, 50%, 60%, 70% and 80%. Six lettuce plants were cultivated under each module, while eight were planted without the modules to act as a control.

“The experimental timeline begins with seeding three plants per pot on Feb. 21, 2024. The first emergence of lettuce plants was observed on day 6, followed by the initial thinning of pots on day 12, reducing pots with three germinated seeds to two plants per pot. Final thinning occurred on day 20, establishing a single plant per pot across all treatments,” the team stated. “Fertilization was commenced on 20 March 2024, with subsequent applications on day 34, day 40, day 44, and day 47. Each pot received 0.75 g of fertilizer dissolved in 0.5 L of water per application.”

Measuring the PAR throughout the experiment and the lettuce yield at harvest, the researchers found that the 10% transparency module exhibited the lowest values in both PAR and fresh weight of lettuce. PAR values ranged from 43.75 to 52.34 micromol/m2-s [micromoles, per square meter, per second], while fresh weight varied between less than 1 g and 15 g. The 80% transparency module yielded the most favorable outcomes, with PAR values ranging from 70.31 to 117.19 micromol/m2-s, and fresh weight spanning from 34 to 424 g. The mean fresh weight of lettuce harvested from the control treatment was 417 g with a PAR value of 129.69 micromol/m2s.

Using those results, the team has tested the worthiness of growing lettuce under PV panels in four European markets. They checked Germany, where regulation rule that the crop should keep at least 66% of its yield; in France, were crops have to maintain 90% of their yield; in Itay, where a maximum PV land coverage of 40% is set; and in the Czech Republic, where only 10% are allowed to be covered by PV.

“One of the most surprising outcomes was the degree to which agrivoltaic policies could influence land use decisions and overall adoption,” said Jamil. “Our findings indicate that PV system design and module configuration not only directly affect crop yields but also have broader implications for how policymakers might incentivize or restrict agrivoltaic integration, highlighting the critical role of policy design in maximizing both energy and food production.”

The results of the study indicated that a minimum yield requirement could be set at 70%. This means that the German policy appears to be the most consistent with available data for maximizing agrivoltaic benefits while minimizing detriment.

“More importantly, policy makers should consider the use of dynamic mandates with a review cycle, i.e., 5 years minimum, to ensure policy alignment with evolving technological trends and agricultural practices,” the academics concluded.

Their findings were presented in “Photosynthetically active radiation complexities in agrivoltaic policy mandates: Insights from controlled environment yields under semitransparent photovoltaics,” published in the Journal of Cleaner Production.