AGRONOMICAL RESULTS OF SOLAR ENERGY RECOVERY AND HEATING BY THE SUN-STOCK SYSTEM ON AN EARLY TOMATO CROP UNDER PLASTIC POLYETHYLENE GREENHOUSE
The Sunstock solar energy recovery system consists of a water bassin for the storage and the accumulation of solar energy, a small electric waterpump of about 250 Watt, with supply and distribution pipes on which the solar energy collector-distribution system is connected. The collector is composed of flat black PVC tubes of 40 cm of large, in which water is circulating by gravity discharged again by means of a collector pipe to the water reservoir.
In the first greenhouse the ridges between two tomato crop rows were covered with 3 flat black PVC tubes, used as a radiant mulch, obtaining in this way a 60% covering of the soil. The soil covering in the second greenhouse was 40% and this by placing only 2 radiant mulch film tubes on the ridges between two tomato rows.
Water was distributed during the day to raise gradually the temperature of water in the water bassin. At 4.30 p.m. the circulation was interrupted until 10.30 p.m. and this to preserve for a quick energy loose when the sun is disappearing. From 10.30 p.m. temperature in the water bassin is dropping to his minimum early in the morning resulting in a heating of soil and air.
During the period of observation (January-April) this resulted in a higher average minimum ambient temperature and a lower average maximum day temperature, just as a higher average soil temperature.
The tomato plants growned under the greenhouses with the Sunstock system were taller, stronger and presented a better flowering and an earlier fruiting than those grown under the control greenhouse, equiped with a black polyethylene mulch between the tomato rows.
Planting of the young tomato plants was realised on 10 December with a planting rate of 3.5 plants/m2.
Production started in the beginning of March. Early production (before 10 April) and exportable production (before 10 May) was much higher under the greenhouse with the Sunstock system and this was the result of a better average fruit weight under the heated greenhouse. Exportable production reached 49 T/ha in the greenhouse with 60% covering, 34 T/ha in the greenhouse with 40% covering and only 24 T/ha in the control greenhouse. Total yield was 15–20% higher in the heated greenhouses.
The possibilities of this system for the heating of polyethylene greenhouses are discussed.