Thermodynamic and economic analysis of a solar hydroponic planting system with multi-stage interfacial distillation units

The shortage of irrigation with clean water is one of the major factors restricting grain production. To provide sufficient irrigation water for crops via utilizing the solar distillation process, a solar hydroponic planting system combined with multi-stage interfacial distillation units is proposed in this work, and its water production per-formance and economy are evaluated. The system adopts a tubeless design to reduce irrigation costs, and the collected solar energy can be reused many times to distillate seawater for directly irrigating crops. An experi-mental prototype with four-stage desalination units was tested in outdoor weather. According to the energy and mass transfer relation of each component, a thermodynamic model is established, and its correctness is verified by experimental data. Through the model, the temperature, water production, evaporation efficiency, and GOR (gain output ratio) of the system are evaluated, and the optical and thermal losses are investigated in detail. Results indicate that with the increase of irradiation and the decrease of interlayer spacing, the evaporation efficiency and GOR could be significantly improved. Under the condition of 1000 W/m(2) irradiation, the GOR of the ten-stage system can reach 2.64, and the evaporation efficiency of the first-stage desalination unit achieves 84.2 %. Additionally, through the established model, the annual water production of the system under the weather conditions is predicted in different cities in China, and the water production cost is estimated to be 0.013 $/L in Guangzhou City. This study provides a potential solution to alleviate the shortage of irrigation water in offshore areas.