A study of solar energy parameters in plastic-covered greenhouses

Abstract

This investigation discusses the work carried out on the measurement of solar energy parameters and the heating requirements of a plastic-covered greenhouse during a winter season. Monthly averages of daily outside temperature, sunshine hours and total solar radiation followed the same pattern. The increased radiation in parts of the greenhouse was due to reflection from the interior surfaces and from the outside snow covering and dispersion of transmitted light. There was more reflected light above plant canopy than within. Albedos (the ratio of reflected to incoming radiation) of plant canopy varied between 33 and 46% with the highest values occurring during the afternoons. The albedos of greenhouse floor and small plants in pots varied between 12 and 19%. The ratios of the monthly average of solar energy to total energy input to the greenhouse varied from 11 to 53% with the minimum ratio occurring in December. Solar energy and fuel energy showed a linear relationship against outside air temperature and solar radiation. The seasonal cost of heating fuel which was estimated in the order of $6·67/m 2 of greenhouse floor was lower than that of a glass greenhouse obtained previously.