Exergy Optimization of a Hybrid Multi-Evaporative Desalination Plant Powered by Solar and Geothermal Energy

Abstract An energy and exergy analysis has been conducted on a hybrid desalination system powered by solar energy using vacuum collectors and geothermal energy. This system is specifically designed to operate under the environmental conditions of southern Tunisia. The desalination plant is mainly constituted by a solar collector field, a thermal energy storage system, a multiple effect distillation (MED) unit system, an evaporative condenser, and a geothermal energy recovery system. The analysis is performed using computational code established with ees software. A parametric study is conducted to examine the effects of key operating parameters on plant performances. The operating mode is determined for winter and summer seasons. The obtained results show that the thermal storage system provides thermal power permitting continuous operation for about 8 h during the nighttime period. The storage tank is the most contributor in exergy destruction with approximately 4.3 kW in winter and 5.5 kW in summer followed by the solar collector field of about 3.6 kW in winter and 3.8 kW in summer. The exergy efficiency of the desalination effects reaches 70% in winter and 75% in summer. The daily production of drinking water is about 12 m3/day in winter and 14 m3/day in summer. This meets the daily drinking water needs of around 3000 people.