UNDERGROUND STORAGE OF SOLAR ENERGY FOR GREENHOUSES HEATING. I. ANALYSIS OF SEASONAL STORAGE SYSTEM BY SCALE AND NUMERICAL MODELS
ABSTRACT Possibilities of seasonal storage of solar energy in the soil under a greenhouse have been investigated and compared with those of daily storage. We assumed a system composed of collectors, a greenhouse, pipes connected to the collectors and buried under the greenhouse for water circulation, and another set of underground pipes for greenhouse air circulation. The soil under the greenhouse was assumed not to be insulated. Solar energy collected by collectors from summer through winter is transferred to the soil by circulating water. A scale model experiment showed that the amount of heat recovered is approximately doubled when circulating greenhouse air as needed, compared to the case in which air is not circulated. A numerical experiment showed, however, that under the conditions tested, electric energy consumed in water and air circulations in seasonal storage [18.14 MJ/m2 (greenhouse floor)] is greater than the energy saved in greenhouse heating (6.54 MJ/m^), resulting in a negative net energy saving (-11.60 MJ/m^), while the energy saving in daily storage is positive (6.52 MJ/m2). This poor performance of seasonal storage could be attributed to the heat loss through the boundaries of the heat storage region. KEYWORDS. Solar Energy, Heat storage. Protected cultivation. Energy savings. Seasonal storage.