Design and evaluation of a solar-based trigeneration system for a nearly zero energy greenhouse in arid region

Abstract

Greenhouses driven by renewable sources such as solar energy can be a reliable alternative to the traditional farming approaches, especially for geographically restricted locations. In light of such requirement, a solar-based greenhouse using a high efficient combined cooling, heating and power system is dynamically simulated for the Yazd city in Iran to cultivate lettuce and tomato, using Engineering Equation Solver and TRNSYS packages. In order to compute fuel saving and water saving values and their cost, the results are compared extensively with those of the reference system (a conventional or basic system). That is, for the cooling mode, a pad-fan system is defined as a reference system, while a gas heater is defined as a reference system for the heating mode. Thermodynamic and economic analysis of the devised set-up is presented. The results of simulation indicated that the annual electricity generated by turbine for tomato and lettuce can be calculated 21,392.33 kWh and 30,903.33 kWh, respectively, using R134a as working fluid. In comparison with the reference system, the annual fuel and water saved by the present set-up are obtained 1841.29 m3 and 266.5 m3 (for lettuce) and 10,675.04 m3 and 141.01 m3 (for tomato), respectively. In terms of cost evaluation, it is found that the payback time (PBT) for lettuce and tomato scenarios is calculated 12 and 15 years, respectively. Considering the first year of operation of the system, the annual net profit of the designed system when lettuce and tomato were cultivated are attained 3745.51 $ and 1651.48 $, respectively. Furthermore, in cold seasons, the heating load required for lettuce is appreciably lower than that for tomato. By contrast, in hot seasons, the cooling load required for lettuce is appreciably higher than that for tomato.