Shading and electrical features of a photovoltaic array mounted inside the roof of an east-west oriented greenhouse

Sunlight energy irradiated on a greenhouse is useful as an electrical energy source for environment control appliances in the greenhouse after conversion of light energy into electricity by photovoltaic (PV) cells. This study assessed the spatial distribution of sunlight energy in an east-west oriented single-span greenhouse equipped with a PV array (12.9% of the roof area) inside a Gothic-arch style roof. The study also examined the electrical energy generated by the PV array. Two geometrical arrangements of the PV array were tested--straight-line (PV_s array) and checkerboard (PV_c array)--each of which comprised 30 PV modules facing the southern sky. The PV_s array casts a shadow on the same position in the greenhouse continuously for 4 months. In contrast, the PV_c array casts a shadow intermittently on the same position during a single day, providing a more uniform spatial distribution of long-term irradiation in the greenhouse than that provided by the PV_s array. However, a wider area in the greenhouse can be partially obscured by the PV_c array's intermittent shadows. Under a cloudless sky assumption, the PV_s and PV_c arrays are respectively estimated to generate 4.08 GJ y^-1 and 4.06 GJ y^-1 electricity. The calculated annual values of sunlight energy received in the greenhouse equipped with the PV_s and PV_c arrays are, respectively, 5.31 GJ m^-2 and 5.03 GJ m^-2. These results demonstrate that the checkerboard arrangement improves the unbalanced spatial distribution of received sunlight energy in the greenhouse, with only slightly reduced amounts of received sunlight energy and generated electrical energy.