The process by which water evaporates and turns into water vapor is actually a form of solar energy and it can be harnessed and used to power small machines. The team is using bacteria spores that are by nature great at absorbing water. When they absorb water, they swell and when they lose water, they contract, and they can do this repeatedly without breaking down. This movement, like that of a small muscle is what is being used by the team to power small engines.

The researchers glued billions of these spores on a plastic tape-like surface and then attached several pieces of the tape together. The result was a measurable difference between the when the bacteria were swollen with water and when they were shrunken from water loss. They then began building small machines harnessing this movement.

One machine is a set of shutters that lift as the "muscles" extend when wet and then close when the water evaporates. Another is a rotary engine that spins because only one side is exposed to the moist air that fuels the spores' work. That engine is being used to drive a wheel in a toy car like device.

“I do not believe that this kind of system will revolutionize transport or other high-power applications, but it may provide the small power needed in remote places to operate communication devices,” Peter Fratzl, a biomaterial researcher at the Max Planck Institute of Colloids and Interfaces, said to Quartz.

This idea is still at the beginning stages and will never have the efficiency of solar cells, but because it is so low-cost, it could still be a very valuable source of energy. Covering in-land bodies of water like reservoirs with water evaporation-powered machines could have two advantages: one would be the power generated and the other would be that covering the body of water slows its evaporation.

One of the major issues that the researchers still have to deal with is that the spores will have to be genetically modified to not germinate into bacteria. If they do, the machines would no longer work.