Performance analysis of integrating photovoltaic-radiative sky cooling and humidification-dehumidification for combined power and all-day desalination

Abstract

Although the state-of-the-art photovoltaic-thermal-driven humidification-dehumidification desalination has a high potential for electricity and freshwater cogeneration, this technology can only operate when there is sunlight and has zero output during the night. This research exploits the photovoltaic cell's nighttime radiative sky-cooling ability to achieve dehumidification of ambient humid air and subsequently nighttime desalination. By combining this with the usual daytime operation, the proposed system increases the all-day productivity while keeping the system structure simple. The proposed system is analyzed via steady-state thermodynamic models of the photovoltaic panel, radiative sky cooling, seawater flow, and humidification-dehumidification subsystems. A series of parametric studies and a time-dependent analysis are conducted to evaluate its cogeneration performance. Results reveal that the nighttime and daytime freshwater productivities are a maximum of 0.13 kg/(h m2 PV area) and 0.6 kg/(h m2 PV area), respectively. The corresponding all day productivities are 1.114 kg/(day m2) and 5.371 W h/(day m2), respectively, which demonstrate that the photovoltaic cell's radiative sky cooling ability can offer an additional 20% of productivity. Notably, desalination is weakest during the sunset and sunrise periods because the radiative cooling and solar irradiance effects cancel each other here.