Distribution of solar radiation on greenhouse convex rooftop

Abstract

Photovoltaic greenhouses became popular in many countries for growing crops and, at the same time, generating electricity mainly for own usage to control the air temperature inside the greenhouse. Solar radiation is essential for their photosynthesis process for crop growing, however, high levels of solar radiation may adversely affect the crop quality. Therefore, a balance between the need for sufficient solar radiation for plant grows and the need for electricity is important to maintain. Many greenhouses are built with curved rooftops of convex shapes and flat-plate photovoltaic (PV) modules are deployed on the rooftops. The present study proposes using flexible PV modules adhering to the curvature of the roof. The incident solar radiation on a curved surface is not uniformly distributed along the surface, therefore the density of the solar irradiation attains higher levels at regions where the PV modules may be deployed to generate greater amounts of electric power. The present study determines the density variation of the solar irradiation, in Wh/m2, (direct beam, diffuse and global) along the curvature of the convex surface of the greenhouse, and proposes the location of the PV modules to be deployed on the roof to obtain desired levels of solar radiation needed for designing the PV systems. North-south and east-west greenhouse orientations are considered.