Microclimate Reconstruction in Fixed Agrivoltaic Systems and Effects of Planting Density on the Physiology and Yield of Summer-Sown Peanut: A Two-Year Field Experiment

This two-year field study quantified microclimate modification using a fixed agrivoltaic (APV) array and evaluated planting-density effects on peanut physiology and yield specifically in the cultivable inter-panel strip, using an adjacent open field as the crop control. Trials were conducted in Nanjing, China, in 2023 and 2025 with ‘Sunonghua No. 1’ at hill spacings of 32, 36, and 40 cm. Solar radiation and air and soil temperature were monitored under the panels, between the panels, and in the open field, whereas plant measurements were restricted to inter-panel and open-field plots. The array produced a stable radiation gradient: mean relative solar radiation was 58.21% and 63.13% between panels in 2023 and 2025, respectively, but only 16.43% and 17.14% under the panels. Near-surface air-temperature variation among positions was small (daily means differed by no more than 0.24 °C on representative days), while inter-panel soil maxima were 0.60–2.21 °C lower and diurnal ranges 0.80–2.40 °C narrower than in the open field. Inter-panel SPAD and stomatal conductance decreased by 19.5–36.0% and 57.0–91.2%, respectively. Net photosynthesis generally declined; an anomalous 2023 contrast for the medium-density pair is reported but is not used as a mechanistic explanation of yield. Pod yield decreased by 51.2–55.0% in 2023 and 16.2–22.7% in 2025, mainly through lower pod and kernel mass. The 36 cm spacing produced the highest inter-panel yield in both years and the smallest relative loss. Under this site, cultivar, and array configuration, medium density was the most consistent option, although confirmation across additional seasons is required.