Solar Radiation Allocation and Spatial Distribution in Chinese Solar Greenhouses: Model Development and Application

Solar radiation is the sole energy source for Chinese solar greenhouse agriculture. A favorable light environment is the foundation of a desirable crop growth environment, and it is key in solar greenhouse design. In this study, a mathematical model is established to quantitatively evaluate the solar greenhouse light environment. The model was developed considering the greenhouse shape parameters, materials' optical properties, and interior solar radiation evolution, including the beam radiation, diffuse radiation, and multi-reflection. The model was validated under different weather conditions, and the results reveal a mean percentage error of 1.67 and 10.30% for clear sunny weather and cloudy weather, respectively, and a determination coefficient of 0.9756. By using this model, the solar radiation allocation in a solar greenhouse was calculated to determine the solar radiation availability for the heat-storage north wall and the entire greenhouse, and the dynamical spatial distribution of the solar radiation was obtained to describe the light environment quality. These allow the optimization of the greenhouse lighting regulation and planting pattern. Moreover, several optimizing measures are derived according to the model for improving the low-light environment near the north wall and maximizing the north wall's heat storage/release capacity in a solar greenhouse.