THE USE OF ROCK-BED FOR STORAGE OF SOLAR ENERGY SURPLUS IN HIGH PLASTIC TUNNELS - PRELIMINARY RESULTS OF THE FULL SCALE PROJECT

A surplus of solar energy is observed in plastic tunnels for most of the growing season in many countries. The idea of storage of that energy in heat accumulators and further recovery is known for several decades and has been studied in different countries, usually in a laboratory scale. The presented paper discloses the preliminary results of the full scale project on a rock-bed heat storage system that has been started in Poland recently. The heat accumulator is located below a 9×15 m high plastic tunnel destined for tomato and cucumber production and contains two sections of 12.7 m³ of rock and one section of 26.1 m³ of rock. Several charging and discharging cycles have been conducted between 29 April and 14 May 2012 to evaluate storage potential and gain an insight into dynamics of storage operation. When the regular day-night charging and discharging cycles were conducted the mean night temperature between plants was higher by 3.7-9.5°C than mean temperature outside. As expected, the temperature difference was lower for warm nights and higher for cold nights. The mean temperature inside the tunnel was maintained between 16.2 and 21.3°C. During a cold period, when daily charging was not possible the accumulated energy was sufficient to heat the plants for at least three consecutive nights.