The Magazine of The Sierra Club
Evaporation Could Provide On-Demand Renewable Energy
A new technology turns evaporating moisture from oceans and lakes into energy
As part of Earth's natural water cycle, moisture returns to clouds via evaporation from oceans and lakes. Columbia University researcher Ozgur Sahin and his colleagues saw the potential for a new kind of hydropower in that steady upward flow. A power plant based on evaporation that occurs throughout the day and night could provide reliable, on-demand renewable power. As oceans account for the majority of evaporation, power plants on lakes wouldn't have a noticeable impact on the water cycle. However, researchers have to investigate the potential effects on lake ecosystems before these theoretical clean energy systems can become a reality.
So far researchers have only proved their concept with a postcard-size device, but they say a full-scale evaporation power plant is feasible. The main structures would float on a lake, ideally in a hot and arid location, to make use of water rising from the surface.
The heart of the machine is a layer of spores—the dormant form of the harmless bacterium Bacillus subtilis. When there's moisture in the air, the spores absorb the water and expand; when they lose that water, they shrink. That expansion and contraction is a form of mechanical energy.
The mechanical energy created as the sheets of spores expand and contract can be used to push and pull the components inside a generator, thus producing clean electricity.
Shutters control the power plant's operation. When the shutters are closed, the air inside the structure is saturated with rising water vapor and the spores swell. When the shutters open, moisture evaporates away from the spores into the atmosphere. Unlike solar and wind, which generate power only when natural conditions are right, the evaporation power plant could be turned on whenever power was needed. The plant would be idle when the shutters were closed.
This article appeared in the March/April 2018 edition with the headline "The Evaporation Engine."
Infographic by Brown Bird Design
