The Influence of a Hybrid Solar Energy Saving System on the Growth and the Yield of Tomato Crop in Greenhouses

The use of solar energy saving systems contributes to the reduction of greenhouse heating cost for the off-season crop production. Moreover, the improvement of the microclimate conditions can result in higher yields and product quality. At the northern latitudes of the Mediterranean region, the greenhouse cultivation period is mainly starting at early spring time, as a result of the high thermal needs during the winter, although the solar radiation levels may be acceptable on plant growth. For these reasons a research project was conducted during the winter period, to investigate the effect of a hybrid solar energy saving system on plant growth and production in greenhouses. Water filled transparent polyethylene sleeves have been used as a hybrid solar system in a conventionally heated part of a greenhouse at Northern Greece, (plot A), were tomato plants were hydroponically cultivated above the polyethylene sleeves. Another part of the greenhouse (plot B) operated only with conventional heating and the tomatoes were placed on plastic gutters. During the experiment, the following plant growth parameters were measured: a) tomato plants growth rate, b) total number of tomato fruits per truss and c) total yield, for both parts of the greenhouse. Also, microclimatic data were recorded concerning the: 1) air temperature and humidity of the greenhouse plots, 2) temperature of the rockwool slabs, 3) water temperature in the sleeves, and 4) intensity of solar radiation. The results showed that application of the hybrid solar energy saving system in plot A led to qualitative differences on plant growth while the crop yield was almost equal compared to plot B.