Establishment and application of solar radiation model in solar greenhouse

Solar radiation is an important parameter affecting light and thermal environment in solar greenhouse. Accurately obtaining the solar radiation value and variation of the interior wall and ground in the greenhouse can play an important guiding role in greenhouse design, construction, environmental regulation and crop production. On the basis of summarizing the previous models of solar radiation, a relatively perfect solar radiation model of solar greenhouse was established in this paper. Meteorological data, the laws of the earth and the movement of the sun, and the relationship between the sun's rays and the angle of the front roof were all considered in this solar radiation model. Internal radiation change of the greenhouse was analyzed based on the model. The model was verified in typical sunny days. The results showed that there were some differences between the calculated and measured solar radiation values, the MBE(mean bias error) was 63.46 W/m2, the MAE(mean absolute error) was 63.48 W/m2, the RMSE(root mean square error) was 79.18 W/m2 and the coefficient of determination R2 was high, ranged from 0.95 to 0.99. The model can be used to calculate the solar radiation intensity of the wall and the ground of solar greenhouse in any area anytime. Highly accurate analysis of the radiation change and the variation of light transmittance in the greenhouse in different seasons were achieved in this paper. It was found that the light transmittance is more affected by the solar azimuth and the solar elevation angle than by the roof angles at different positions. The solar radiation on the surface of the wall and the ground in greenhouse changes with the seasons. The spring equinox and autumn equinox are the days in which the wall and the ground received the longest solar radiation during the year. At this time, the surface of the wall is roughly equivalent to the solar radiation on the ground. From the spring equinox to the autumn equinox, the ground radiation is higher than the surface radiation, while it is opposite when it comes from the autumnal equinox to the vernal equinox. The daily accumulation of solar radiation on the wall changed little from the winter solstice to the start of spring, decreased from the start of the spring to the summer solstice and rose from the summer solstice to the start of winter. The time from winter to the start of the spring is the main production season in the greenhouse, and the heat accumulation of the wall is also the highest in the whole year. Therefore, it is of great significance to carry out research on the heat storage at this stage. Solar radiation in greenhouses in different regions is mainly affected by latitude. In lower latitudes, the amount of solar radiation in winter is large and the amount of radiation in summer is small. The research results can provide reference and related data for the study of wall heat storage, roof optimization, crop planting and energy balance of envelope in solar greenhouse. In addition, the change rule of solar radiation in greenhouse was analyzed just under clear and cloudless conditions. For the plant canopy shade, radiation under different weather conditions, insulation quilt position, different rear roof incline angles and lengths, azimuth angles, wall inclined angle and other aspects of the solar radiation change inside the greenhouse can be further explored by the method proposed in this paper. © 2019, Editorial Department of the Transactions of the Chinese Society of Agricultural Engineering. All right reserved.