Low-grade heat from renewable sources could be used to desalinate water - Energy & Green Tech

Graphical abstract. Credit: Desalination (2025). DOI: 10.1016/j.desal.2025.119103

A McGill University-led research team has demonstrated the feasibility of a sustainable and cost-effective way to desalinate seawater. The method—thermally driven reverse osmosis (TDRO)—uses a piston-based system powered by low-grade heat from solar thermal, geothermal heat and other sources of renewable energy to produce fresh water.

Though previous research showed promise, this study is the first to analyze TDRO's thermodynamic limits. The results have brought researchers closer to realizing the technology which could improve access to water and increase the sustainability of infrastructure.

"Most desalination is done by reverse osmosis, which uses electricity to drive water through a membrane," said Jonathan Maisonneuve, study co-author and Associate Professor of Bioresource Engineering.

"The challenge with using heat is that it takes a lot of it to do what you could with a little bit of electricity. So, if we can find a way to harness existing heat from renewable sources, that could be very advantageous, because it's so abundant," Maisonneuve said.

"Thermally driven reverse osmosis: thermodynamics of a novel process that uses heat for desalination and water purification," by Saber Khanmohammadi, Sanjana Yagnambhatt, Dan DelVescovo and Jonathan Maisonneuve, was published in Desalination on Oct. 15, 2025.

Addressing the water and energy crises

Electricity-based desalination, which is often inaccessible in remote areas, requires about one to four kilowatt hours (kWh) to produce one cubic meter of fresh water.

According to the researchers' analysis, which optimized several elements of a design proposed by MIT researcher Peter Godart, TDRO would require 20 kWh per cubic meter.

"There's still a big difference when you compare it to one to four kWh, but because heat is cheaper than electricity, we don't have to totally close that gap," Maisonneuve said.

TDRO works by heating and cooling a small amount of fluid in a sealed chamber, known as the working fluid. This temperature fluctuation expands the working fluid, causing it to drive a piston to push seawater through a reverse osmosis membrane—effectively combining a thermodynamic cycle with water purification.

By studying and optimizing the ratio of working fluid to seawater fluid, as well as the piston sizes, the researchers demonstrated that TDRO has better performance potential than previously thought. The method also compares well against existing thermal desalination technologies, but they say further study is required.

"Next, we need to model it in detail, see how quickly the system can operate and introduce a number of non-ideal effects, such as heat loss through the environment," Maisonneuve said. 

Provided by McGill University 

by McGill University

edited by Gaby Clark, reviewed by Robert Egan

Source: Low-grade heat from renewable sources could be used to desalinate water