Cold lake during a winter morning

Evaporation could be an energy resource “comparable to current wind and solar”

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In the first detailed study considering natural evaporation as a potential energy resource, a team of researchers at Columbia University have estimated that 325GW of evaporation power is potentially available in the US.

Evaporation is a powerful natural process, with an average flux of 80W per metre square of open water. Recently, there have been advances in water-responsive materials and devices which generate work from evaporation by repeatedly absorbing and rejecting water via evaporation.

“Recent advances demonstrate our nascent ability to convert evaporation energy into work, yet there is little understanding about the potential of this resource,” the authors write in Nature Communications. In their study, they set out to study whether – like other natural processes – evaporation could be a feasible energy resource.

Led by Professor Ozgur Sahin, a professor of physics at Columbia University, the team plotted evaporation rates for different weather conditions across the US. They found that across the nation, there were average power densities of up to 10W per metre square.

“We find that natural evaporation from open-water surfaces could provide power densities comparable to current wind and solar technologies while cutting evaporative water losses by nearly half,” they commented. “We estimate up to 325GW of power is potentially available in the [US].”

Power densities for wind installations are 2.90W per metre square and 8.06W for solar panels.

This figure of 325GW – more than 69 per cent of the US electrical energy generation rate in 2015 – only takes into account natural evaporation occurring over large lakes and reservoirs (excluding the Great Lakes) in the US.

According to the researchers, this would also lead to nearly 100 billion cubic metres of water that could be recovered each year due to lower evaporation rates, which could be helpful in areas of the US suffering from water scarcity, such as the southwest.

While natural energy resources such as evaporation, wind, tides and sunshine have the benefit of being carbon neutral and renewable, they suffer from intermittency: without cutting-edge battery technology, electricity can only be provided at certain times of the day.

Investigating a workaround, the Columbia University team looked at the possibility of controlling power output from an evaporation-driven machine which uses water’s large heat capacity to store and release energy. This controls power input and improves reliability.

“Strikingly, we find that storing energy thermally in the water below an evaporation-driven engine could substantially reduce intermittency by varying power supply to match power demand,” they report.

With almost every country on Earth (although infamously no longer the USA) a signatory of the 2015 Paris Agreement  – which aims to significantly cut carbon emissions in order to mitigate global warming – governments will be on the lookout for upcoming technologies that improve the efficiency and reliability of renewable, carbon-neutral energy resources.

As research continues into materials and devices which could convert energy from evaporation while protecting freshwater resources, it is possible that evaporation could form part of the clean energy mix of the future.

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