Techno-economic optimization of solar thermal integrated membrane distillation for cogeneration of heat and pure water

The aim of this paper is to evaluate optimum design criteria for developing solar thermal integrated membrane distillation system for cogeneration of pure water and heat. The temporal and seasonal variability of the driving variables, such as ambient temperature and solar irradiance requires dynamic simulation of combined system using tools such as TRNSYS. Dynamic simulation and parametric analysis enables to design a functional system and then optimizes the design. In this study, the application of cogeneration system for residential households in United Arab Emirates is considered for per capita production of 4l/day of pure water and 50l/day of domestic hot water. The performance of cogeneration is optimized by varying various design parameters such as collector tilt angle, thermal storage volume and area of the solar collector field. Cogeneration solar fraction and payback period are considered as performance indicators for energetic and economic optimization. Further simulations are extended from small to large family application and for utilizing either flat plate (FPC) or evacuated tubular collector (ETC) systems. Optimized cogeneration system utilizes more than 80% of the available solar energy gain and operates at 45% and 60% collector efficiencies for FPC and ETC systems respectively Also, combined and system efficiencies of the cogeneration system are compared with standalone operational efficiencies for solar heaters and solar membrane distillation systems. Results show that, cogeneration operation reduces 6-16% of thermal energy demand and also enables 25% savings in electrical energy demand. Payback period could be reduced by 2.5-3 years by switching from regular solar water heating to cogeneration systems along with 4-fold increase in net cumulative savings.