Design of a small-scale and off-grid water desalination system using solar thermal heating and mechanical vapor compression

Abstract

Water scarcity affects a large group of people across the globe. It diminishes their quality of life and economic activity. Most existing solutions for cheap water desalination are not suitable for small-scale applications, and they also generally require infrastructure such as power and plumbing. In this work, a small-scale and off-grid water purification system is proposed. The system utilizes solar energy through both solar thermal collection to rapidly heat up water and solar photovoltaics (PV) to power a mechanical vapor compression system, and is designed for low-cost and high output purification in a minimal footprint. The proposed system was analyzed in both transient warm up and steady state phases separately, and the results were combined to develop an expected performance based on the system parameters. A model was developed based on first principles of thermodynamics and water property correlations. The device was then optimized using a cost-centered approach. The best ratio of solar collection was found to be 71% solar thermal collector and 29% solar PV. It is expected to produce an output of 15.09 kg/m 2/day of pure water at a cost of 5.3 $/m3, which is competitive with existing technologies at the small scale. A prototype was constructed as a proof of concept and was tested under simulated solar flux to validate the model.