Development of a desalination system driven by solar energy and low grade waste heat

•Productivity increases significantly up to critical waste gas flow rate.•Productivity decreases for waste gas flow rate higher than critical flow rate.•Increasing evaporator inlet waste gas temperature increases productivity.•The proposed system coupled with combined cycle has a fuel saving 1844kg/h.•The cost of potable water produced is 0.014USD/L. Various thermal power systems emit flue gases containing significant amount of waste energy. The aim of this research is to recover a valuable amount of this energy to develop an efficient desalination system coupled with solar energy. Experiments were performed in the month of June 2014 at Al-Qassim, Saudi Arabia (26°4′53″N, 43°58′32″E) for different hot air (waste gas) flow rates and evaporator inlet water temperature to study the effect on daily potable water productivity. The proposed setup comprised an evaporator, condenser, air blower, electric heaters, storage tank and evacuated tube solar collectors. It was found that increasing the hot air flow rate increases the water productivity up to the critical flow rate after which the productivity decreases. Analytical model was developed for this desalination setup and the results were compared to that obtained from experiments. The overall daily (9AM–5PM) potable water productivity of the proposed system is about 50L for corresponding useful waste heat varying from 130 to 180MJ/day and a global solar radiation on a horizontal surface ranging from 15 to 29MJ/m2/day. Water is produced at the cost of 0.014USD/L and the fuel saving equal to 1844kg/h is achieved for the proposed desalination system.