Is the natural phenomenon going to become the main energy source for the future?

Promising potential: Similar to the sun and wind, evaporating water can also be used as an energy source. Researchers have now calculated how much energy could theoretically be produced by the use of this ubiquitous natural phenomenon in the future. According to this, evaporation has the potential to produce comparable amounts of energy as other renewable resources. The key advantage is that availability is subject to significantly lower fluctuations.

Every day evaporation takes place somewhere in the world like here in Phoenix - this process could be used to generate energy. © Central Arizona Project

Evaporation is an ubiquitous phenomenon. The process by which water gradually passes into the gaseous state influences water resources, weather and climate - and is an important energy source of nature: many plants use the force of evaporation to move their spore capsules and slit openings, and also in the microcosm, hygroscopic, water-absorbing materials convert moisture into mechanical energy.

However, the evaporation energy of water can also be used on a larger scale, as recent research results show. Two years ago scientists were able to use the power of evaporation as a source of energy. They developed a nano-material which, when the humidity changes, expands and contracts like a muscle and thus acts as a motor.

Unknown potential

Evaporation thus appears to be an unused force. Could humanity, besides solar energy, wind power, and geothermal energy, soon have another form of renewable energy available? In principle this would be conceivable. However, the extent to which the potential of evaporation as a source of energy for the future is real has been uncertain.

Researchers around Ozgur Sahin from Columbia University in New York have now investigated this question. They wanted to know: How much energy could evaporation evolve in nature in the best case by means of special evaporation machines? They calculated this using weather data and model simulations using the example of the USA.

325 Gigawatt of energy

The results may sound promising: by the evaporation of lakes and large water reservoirs, theoretically up to 325 gigawatts of energy could be generated in the US - according to the team, that's more than 69 percent of the electric power generated by the US in 2015.

Not yet included in the simplified model is the evaporation over the Great Lakes region. The conditions there would have made the model calculations too complicated and error-prone - but the five large connected freshwater lakes of North America are, of course, a significant source of evaporation.

aThe net radiative energy into a water body is balanced by convection and evaporation.
b An example of an evaporation-driven engine.
c Such an engine harnesses energy from evaporation through a 4 stage cycle.
d/e The flows between the water body and the atmosphere.

More constantly available than wind and co

Overall, Sahin and his colleagues conclude that the resource evaporation could generate a similar amount of energy like wind and solar - with a crucial difference: sun and wind are scarce in many regions. Because the availability of these energies fluctuates strongly, they must be stored in a complex manner. Evaporation, on the other hand, is more constant.

They could therefore be used as the main energy source and be supplemented with solar and wind energy, says Ahmet Hamdi Cavusoglu, one of Sahin's colleagues.

Another advantage is the use of water vapor: around 50 percent of the water normally evaporated and lost in the atmosphere could be absorbed in the energy recovery process and made available for further use. Particularly dry states like California, Arizona or Nevada could benefit from this, the scientists predict.

The team hopes that their study will now stimulate the exploration of new machines that use the power of evaporation to generate energy. Because, one day, we will be able to produce as much electricity as possible from the evaporation process, as the calculations of the researchers have shown, the technology has to develop further. It is still in the early stages of development.

Source: Nature Communications, 2017; doi: 10.1038 / s41467-017-00581-w