Abstract
The energy balance of a closed-type transplant production system with artificial lighting was investigated. Sweetpotato (Ipomoea batatas (L.) Lam. cv. Beniazuma) plants were grown for 15 days at photosynthetic photon flux on the tray surface of 100, 200 and 300 μmol m-2 s-1 on days 0-2, 3-11 and 12-14, respectively, air temperature of 30°C, CO2 concentration of 1000 μmol mol-1, relative humidity of 80/100% (photoperiod/dark period) inside the system and photoper-iod of 16 h d-1. The amount of electric energy consumption during the 15 days for lighting, cooling and the other equipment per planting area were 375.5, 80.8 and 41. 1 MJ m-2, respectively. Electric energy consumption per plant was 1.8 MJ (0.5 kWh), and its cost was approximately 4-5 Japanese Yen. Coefficient of performance for the cooling system was approximately 4.7, which was 2 times higher than the value described in the catalog, partly because the air temperature inside the system was higher than that of outside the system. The ratio of electric energy consumption to chemical energy assimilated by plants (energy use efficiency of the system) was 0.006. These results show that the closed-type transplant production system is feasible for the commercialization. Methods for further reduction of electric energy consumption (increasing the energy use efficiency of the system) and electricity cost are discussed.
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