Modelling Solar Energy Input in Greenhouses

Abstract

A semi one-dimensional climate model was used to investigate the relative importance of the constructional parameters that influence the solar energy collecting efficiency of greenhouses under Western European conditions. Parameters investigated were the transmittance of the greenhouse frame, the radiometric properties of the greenhouse cladding and the floor, as well as the type of condensation (as a film or as drops). Their effect on the auxiliary heating requirements and the several solar energy fluxes in the greenhouse were simulated for a year-round tomato crop. The results pointed out that greenhouses catch about two thirds of the solar radiation available. This rather poor efficiency is due to the fact that greenhouses are fixed constructions, so their efficiency highly depends on their position and geometry, which are mainly determined by horticultural constraints. Most of the solar energy entering the greenhouse was found to be absorbed by the vegetation. Auxiliary heating requirements were hardly influenced by changes of the frame or cladding transmittances, although the transmittance reduction caused by condensation as hemispherical drops caused a 2.8% increase of the energy demand. The floor characteristics had an impact on the greenhouse energy demand and on the amount of solar energy available to the canopy, only for small plants on an almost uncovered floor.