Permeate gap thermo-osmotic system for simultaneous freshwater production, energy storage, and power generation

Abstract

The emerging thermo-osmotic system enables harvesting low-grade thermal energy below 100 °C for the simultaneous production of fresh water and electricity. Considering the fluctuation of low-grade heat sources, a novel permeate gap thermo-osmotic system without pump pressurization was proposed in this study, which also allows for energy storage. A lab-scale setup with a 32 cm2 membrane area was built, by which a 2 W light bulb was successfully illuminated through the thermal energy-potential energy-electricity conversion process. In the pressurization process of the permeate side, the hydrophobic membranes with non-woven support exhibit higher pressure resistance, capable of withstanding pressures exceeding 200 kPa. Through experimental and theoretical analyses, the influences of different operation conditions and membrane properties on system performance were studied. Furthermore, utilizing solar energy as the heat source, a case study was conducted based on real meteorological data from a typical coastal city over a consecutive 72-hour period. In the solar-driven PGTO system with a power capacity of approximately 150 kW, the exergy efficiency can achieve 1.04 %, with a power density surpassing 0.1 W m−2, and an average daily freshwater production of over 70000 t. The energy storage function enables stable power generation within the 72 h, and it can sustain steady operation for nearly 7 h thereafter in the absence of sunlight. This study demonstrated the potential of the proposed PGTO system to efficiently utilize fluctuating low-grade thermal energy.