Effect of photovoltaic module shading on internal light environment and fig (Ficus carica) yield in agrivoltaic system

The agrivoltaic system is a new development model that organically couples clean energy generation with agricultural production. It is not only one of the main sources of new energy power but also a significant green agricultural system. To fully ensure the land utilization and mechanization rates of agricultural production within agrivoltaic systems, provinces such as Jiangsu and Yunnan in China had issued guidelines requiring that the photovoltaic modules in agricultural projects be designed with a certain installation height while maintaining a specific tilt angle to ensure normal agricultural production. Although the minimum installation height of photovoltaic modules ensures agricultural production to some extent, many photovoltaic agricultural projects still exhibit a phenomenon of "prioritizing light over agriculture" during actual production processes. To ensure the photovoltaic (PV) power generation benefits in agrivoltaic projects, a large number of PV panels are typically installed on agricultural land. During the day, these PV panels block sunlight and create a considerable shading area on the agricultural land. To investigate the effects of shading from PV modules on the light environment, shading width, crop leaf photosynthetic characteristics, and yield within the agrivoltaic system, a study was conducted in the Nanjing city with agrivoltaic systems set at module installation heights (the vertical distance from the ground to the lower edge of the PV module) of 2.5, 3.2, and 3.9 meters. The solar radiation intensity of the planting area under and between the panels inside the photovoltaic agricultural system was tested, and the annual variation patterns of the shading width formed by the PV modules were calculated and analyzed. Additionally, differences in yield and leaf photosynthetic characteristics of figs (Ficus carica) in the planted areas between the modules were studied. The results indicated that during the testing period, the daylighting rate in the planted areas between the panels ranged from 55.4% to 68.9%, which was 2.1 to 3.3 times that of the area under the panels. For the 3 different heights of PV module installation, the daylighting rate in the areas between the panels decreased as the installation height increased, while the area under the panels showed the opposite trend. Throughout the entire growth period of the figs, the shading width caused by the PV modules increased with latitude and installation height. The shading from the PV modules resulted in an average yield reduction of 19.8% to 48.8% compared to the CK control. The photosynthetic characteristics of the leaves reflected the differences in yield among the treatments. Lower installation heights of the PV modules were more effective in increasing the net photosynthetic rate and stomatal conductance of fig leaves to alleviate photosynthetic suppression. This study quantitatively analyzed the impact of different PV module installation heights on the internal light environment, shading width, crop yield, and leaf photosynthetic characteristics within the agrivoltaic system, and proposed the optimal installation height of PV modules for the cultivation of figs and similar fruit trees under the agricultural-photovoltaic coupling model.