Analysis of a PVT-powered multi-effect mechanical vapor compression desalination system at different feed configurations: energy, exergy, and economic aspects

Abstract

Energy, exergy, environmental, and economic analysis of an externally preheated multi-effect mechanical vapor compression (ME-MVC) desalination system coupled with photovoltaic/thermal (PVT) collectors was conducted. Four arrangements of inlet feed to the ME-MVC system were tested and compared: forward (FF), parallel (PF), parallel/cross (PCF), and backward (BF). A complete steady-state system mathematical model was constructed, numerically solved, programmed inside MATLAB, and validated. The performances of the four systems were compared with a single-effect MVC (SE-MVC) system powered by PV panels. The results show that modifying the ME-MVC system to be externally preheated reduced electricity consumption on account of low-grade thermal energy. The PF and PCF arrangements had a wider range of design conditions where PVT could be applied compared to the BF and FF arrangements, especially with a higher number of effects. The use of PVT/ME-MVC in the PCF and PF arrangements showed the best performance followed by BF and FF, while PV/SE-MVC had the lowest performance. The systems in the PF and PCF arrangements had the lowest collectors' surface area per unit of distillate produced, i.e. 6.58 m² m⁻³ d⁻¹. The value for PV/SE-MVC was 8.59 m² m⁻³ d⁻¹. The FF system had the lowest unit water cost of 5.32 $ per m³, while the PV/SE-MVC system had the lowest cost of 5.45 $ per m³. The proposed PVT/ME-MVC system allowed reducing the required collector surface area, increasing the exergetic efficiency, and reducing the required battery capacity compared to previous solar thermal distillation systems. Moreover, the system carbon mitigation is 62.65 and 60.68 tons per year for electrical and thermal power savings, while the PV/SE-MVC system mitigation is 76.03 tons per year.