Simulation analysis of distribution of energy consumption for year round cucumber production in multi-span greenhouse in China

Distribution of energy consumption per unit yield of greenhouse crops is essential information for assessing the risk of greenhouse investment and optimizing greenhouse climate control in different regions. In order to predict the energy consumption per unit yield of greenhouse crops, a Venlo type greenhouse and cucumber crop were used in this study. Firstly, hourly meteorological data (air temperature, global radiation, water vapor pressure and wind speed) were derived based on the 25 years (1980-2005) average meteorological data (daily maximum and minimum air temperature, water vapor pressure, sunshine hours and wind speed) of 224 weather stations in China. The hourly meteorological data were then used as input of a greenhouse energy consumption model and a crop growth simulation model to calculate the greenhouse energy consumption, cucumber potential yield and the energy consumption per unit yield of cucumber under two different strategies for greenhouse temperature (daytime and nighttime set-point for temperature control for strategy I: Tset,d=24 ℃ and Tset,n=19℃，for strategy II: Tset,d=20 ℃ and Tset,n=15℃) and CO2 (CO2 enrichment: 1000 mL/L, natural ventilation CO2: 350 mL/L) control used for commercial greenhouse cucumber production. Based on the simulation results, maps of the distribution of energy consumption per unit yield of greenhouse cucumber in China under the two different strategies for greenhouse temperature and CO2 control conditions were obtained by using GIS software. The results showed that energy consumption per unit yield of greenhouse cucumber increased from the south to the north and higher altitude regions. Under the two strategies for greenhouse temperature control, CO2 enrichment reduced greenhouse energy consumption in a greater degree in the south than in the north and higher altitude regions. With the two temperature control strategies, the variation of energy consumption per unit yield of greenhouse cucumber was less than 8%, but with temperature control strategy II and CO2 enrichment, it could be reduced up to 29%-67% (from the north and higher altitude regions to the south). Greenhouse energy consumption in China mainly depend on outside climate conditions and set-point for temperature control. Under the given two temperature control strategies, the potential yield of greenhouse cucumber is mainly affected by outside solar radiation and inside CO2 concentration. CO2 enrichment can greatly increase crop potential yield, and can be an effective approach to increase the use efficiency of greenhouse energy consumption. The results obtained in this study can be used for assessing the risk of greenhouse investment and optimizing greenhouse climate control in different regions of China.