Effects of photovoltaic module shading on internal light environment and fig (Ficus carica L.) yield in agrivoltaic systems

An agrivoltaic system has been one of the most promising potential sources of clean energy power in green agriculture. Some guidelines have been released to fully meet the requirement of the photovoltaic (PV) modules in agricultural projects. Particularly, it is the high demand for land utilization and mechanization of agricultural production in agrivoltaic systems, such as in Jiangsu and Yunnan provinces in China. Among them, the minimum installation height of PV modules has been standardized to maintain a specific tilt angle. However, the "prioritizing light over agriculture" can often occur during actual production. A large number of PV panels are typically installed on agricultural land in order to ensure the PV power generation in agrivoltaic projects. Furthermore, these PV panels can block the sunlight to form a considerable shading area on agricultural land during the day. This study aims to investigate the effects of shading from PV modules on the internal light environment, shading width, crop yield, and leaf photosynthetic characteristics in the agrivoltaic system. A series of tests were conducted on the agrivoltaic systems at the 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 m in Nanjing City. A systematic measurement was performed on the solar radiation intensity of the planting area under and between the panels inside the PV agricultural system. A quantitative analysis was implemented to calculate the annual variation patterns of the shading width formed by the PV panels. Additionally, there were significant differences in the yield and leaf photosynthetic characteristics of figs (Ficus carica L.) in the planted areas between the modules. The results indicated that the daylighting rate in the planted areas between the panels ranged from 55.4% to 68.9% during the testing period, which was 2.1 to 3.3 times that of the area under the panels. Specifically, the daylighting rate in the areas between the panels decreased at the three heights of PV module installation as the installation height increased, while the area under the panels showed the opposite trend. The shading width caused by the PV modules also increased with latitude and installation height throughout the entire growth period of the figs. Shading from the PV panels led to a reduction in average yield across treatments compared to the CK control, ranging from 19.9% to 48.9%. Additionally, the photosynthetic characteristics of the leaves effectively reflected the yield differences among treatments. A lower installation height of the PV panels can significantly enhance the net photosynthetic rate and stomatal conductance of fig leaves, thereby alleviating the photosynthetic suppression caused by shading. In summary, compared to agrivoltaic systems with panel heights of 3.2 m and 3.9 m, the system with a panel height of 2.5 m offered a better internal light environment and shorter shading width, effectively reducing the decline in fig yield and demonstrating practical value for photovoltaic agricultural projects in various regions.