Evaporation might be the next big thing in renewable energy

Energy harvested from evaporating water could generate nearly 70 percent of the power the US currently produces.

Researchers at Columbia University have found that converting evaporation from US lakes and reservoirs to energy could produce 325 gigawatts of power a year. That’s nearly 70 percent of what the US currently produces overall. The researchers evaluated how much energy could be harvested using a conversion method they developed, in which generators rest over a body of water and use bacterial spores to harness energy from evaporating water. Lead author Ahmet-Hamdi Cavusoglu tells us more.

ResearchGate: How do you convert evaporation to energy?

Ahmet-Hamdi Cavusoglu: Many things in nature already harness energy from evaporation. For example, trees use evaporation to pump water and nutrients from their roots up to their leaves for photosynthesis. This process is called transpiration. In Prof. Sahin's lab, we use B. subtilus spores. These spores expand when wet and shrink when dry. We use this expansion and contraction to make proof-of-concept evaporation-driven engines that generate energy as water evaporates through the engine. Harnessing energy from evaporation could also be done through nanostructured carbon materials.

RG: What are the advantages of evaporation as a source of energy?

Cavusoglu: A big challenge for solar and wind power is that they cannot produce power on-demand without incorporating batteries or other external energy storage solutions. By using the evaporation of water as a source of energy, we can use the water as a natural “battery” where we can store un-used energy as heat and release that energy as evaporation on-demand. This energy storage feature could be a very powerful tool in the future for helping us move toward a more resilient and diversified electrical energy grid.

RG: Are there drawbacks?

Cavusoglu: Water is an important component of the ecosystem, and of human life and society. In this case, we would be covering part of an open lake or reservoir with an evaporation driven engine, cutting it off from wildlife and recreation. This leads to a techno-policy question: When is the energy produced and water saved worth more than the effect on local wildlife and on our desire to relax by swimming and boating? That’s just one of many open questions that dictate where and when such technology could be deployed.

RG: How much energy could this theoretically provide?

Cavusoglu: In a typical year, up to 325 gigawatts of power could be produced by evaporation from lakes and reservoirs in the United States. That's enough energy for over 260 million American homes. This estimate is fairly conservative since we restricted this to only lakes and reservoirs in the United States, and excluded other sources of evaporation, such as coastlines, the Great Lakes, rivers, and farms.

RG: What might evaporation-harvested power look like in practice?

Cavusoglu: One vision of this technology is a “farm” of evaporation driven engines placed on top of lakes. As water evaporates through the engines, they would produce power.

An interesting finding we made is that the reliability of energy from evaporation varies not just due to the typical climate of a location, but with how much energy we expect. With future advancements in energy efficiency technologies, we may be able to provide power more reliably—along with wind and solar power—in a mixed electrical grid where the electrical load could be shifted.

RG: Could using evaporation for energy production affect the local climate?

Cavusoglu: At the scale proposed in the current paper, there should not be major changes in the local climate. That is because climate is heavily influenced by the heat content of our oceans and largest bodies of water, the same bodies of water we chose to exclude for this study.

RG: What are the next steps for this technology?

Cavusoglu: Prof. Sahin's laboratory is researching how to make better spore-based materials to improve the performance of evaporation-driven engines.

We are also providing our code and data for analysis!


Featured image courtesy of Central Arizona Project.