Ground Irradiance Modelling: Of Key Importance for Designing Nature Inclusive Solar Parks and Agrivoltaics Systems

Solar electricity from solar parks in rural areas are cost effective and can be deployed fast therefore play an important role in the energy transition. The optimal design of a solar park is largely affected by income scheme, electricity transport capacity, and land lease costs. Important design parameters for utility-scale solar parks that may affect landscape, biodiversity, and soil quality are ground coverage ratio, size, and tilt of the PV tables. Particularly, low tilt PV at high coverage reduces the amount of sunlight on the ground strongly and leads to deterioration of the soil quality over the typical 25-year lifetime. In contrast, vertical PV or an agri-PV designed fairly high above the ground leads to more and homogeneous ground irradiance; these designs are favored for pastures and croplands. In general, the amount and distribution of ground irradiance and precipitation will strongly affect which crops can grow below and between the PV tables and whether this supports the associated food chain. As agrivoltaics is the direct competition between photosynthesis and photovoltaics. Understanding when, where and how much light reaches the ground is key to relate the agri-PV solar park design to the expected agricultural and electricity yields. We have shown that by increasing the minimum height of the system, decreasing the size of the PV tables and decreasing the coverage ratio, the ground irradiance increases, in particular around the gaps between the tables. The most direct way of increasing the lowest irradiance in a solar park design is to use semi-transparent PV panels, such as the commercially available bifacial glass-glass modules. In conclusion: we have shown that we can achieve similar ground irradiance levels in an east- and west-facing design with 77% ground coverage ratio as is achieved by a south-facing design at 53% coverage.