Performance analysis of solar desalination using crushed granite stone as an energy storage material and the integration of solar district heating

This study explores the feasibility of solar desalination using black powder coated crushed granite stone, evaluating their energetic, exergetic, and economic aspects, wherein the stone bed preheats water for the solar still. In addition, the system integrates with a district heating network to meet desalination needs during off-solar or high-demand hours in which water from the powder-stone grid's outlet flows through a heat exchanger, powered by district heating's return flow. Desalination pipe absorbs heat and cools district heating line. The outcomes illustrated that cumulative distilled water for a water depth of 1 cm was 13.1% and 28.2% higher than cumulative distilled water for water depths of 2 cm and 3 cm, respectively. The energy efficiency was improved by 9.5% and 15.7% and the exergy efficiency was enhanced to 13.6% and 27.2% at 1 cm water depth compared to 2 and 3 cm water depths. The integration of the system with the district heating network could lead to a great improvement in the productivity; summer's low district heating demand allows surplus heat to boost water production and lower outlet water temperature, benefiting both desalination and cooling process. The cumulative productivity will not be sensitive to the water depth anymore, increasing up to 105%, 135%, and 182% for 1, 2, and 3 cm water depths, respectively. This integration has a fascinating effect on the reduction in temperature of the district heating return flow (about 3 degrees C), improving the cooling potential of the flow.