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A new type of solar greenhouse for growing out-of-season winter crops in arid regions has been designed and tested. The main concept on which the system is based is the separation of the greenhouse structure into two sections: a "crops section" and a "solar energy section. The crops section, where the crop is grown, is equipped with a movable screen to reduce heat losses, mainly during the night, and ventilation windows covered with insect-proof nets and movable plastic curtains that are rolled down over the windows to regulate greenhouse temperature. The solar energy section comprises one or two solar cells attached on each side of the crop section. Each solar cell consists of a battery of plastic sleeves (placed horizontally or vertically) filled with water. The solar cells are isolated from the outside air by a double layer of transparent plastic. In addition, a reflective outer plastic film is rolled over the cells at sunset to reduce heat losses to the environment. The two sections are separated from one another by a movable plastic sheet coated with a reflective material facing inwards. The heat transfer between the two sections is facilitated by "on/off' positioning of the barrier curtain between them, as determined by the difference between the air temperatures in the two sections.

This paper presents the experimental results on the thermal aspect of this method, which were performed on two prototype structures, placed at different orientations. The greenhouse with the north-south orientation was equipped with two solar cells, on the sides facing east and west, and the greenhouse with the east west orientation had one solar cell on the south-facing side. The main modification to be made as a result of the study are also described. The results showed that under the climatic conditions of Beer-Sheva, Israel (31 degrees 15' N, 45 degrees 34' E, 315 m above MSL), the proposed method could be used successfully for growing crops that can tolerate minimum night air temperatures of 11 degrees C and less, such as tomatoes.