Abstract
There is a great need to establish a method for energy-saving environmental control using renewable energy resources for a stable, year-round production of greenhouse crops with high sustainability and profitability. Solar radiation is a widespread and accessible renewable energy resource. However, owing to the distribution gaps in time and space between the supply and demand of energy, the processes of collection, storage and release of energy need to be optimized for the effective utilization of solar energy in agriculture. The latent heat storage materials (LHSM) can store and release solar energy as latent heat by changing its phase, and can be expected to be used for temperature control for eliminating excessively high and low temperatures inside the greenhouse by adjusting the distribution gaps. In this study, conducted during the cold season (from January to May 2012), we installed 520 capsules of LHSM in a greenhouse, each weighing 2.5 kg, with 189 kJ kg-1 of latent heat, and a phase change temperature of 25°C. The greenhouse was 42 m long, 24 m wide, and 3 m high, and was equipped with an oil heater which worked when the inside air temperature dropped below 18°C. During the sunny daytime, the LHSM stored a large amount of solar energy as latent heat, thus moderating the extremely high temperature inside the greenhouse. At night, the LHSM released the stored heat resulting in a decrease of 19% in the operation time of the oil heater. Therefore, the LHSM should be effective for energy-saving temperature control in greenhouse horticulture.
