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Evaporation Can Drive Engines and Generate Electricity

Artificial muscles powered by expanding and shrinking spores could power robots, sensors, vehicles

2 min read
Evaporation Can Drive Engines and Generate Electricity
Photo: Joe Turner Lin

Evaporating water can generate electricity, a clean renewable energy source that could help power robots, sensors, and vehicles, researchers say.

Biology regularly uses evaporation as a source of energy. For instance, redwood trees rely on evaporation to pull water from the ground to their crowns. Now scientists at Columbia University and their colleagues have developed two new engines that generate power from evaporation.

The researchers previously found that when bacterial spores expand and shrink with changing humidity, they can push and pull other objects very forcefully, packing more energy gram for gram than many other materials.

As part of their latest work, the scientists built a piston-driven engine by gluing a dashed line of spores one side of a thin, double-sided plastic tape. They did the same on the other side of the tape, but offset the spores so dashes on one side overlapped with gaps on the other. When the air is dry, the tape curves, and if the air is moist, it extends. They call the systems  "hygroscopy driven artificial muscles" or HYDRAs.

In experiments, the researchers placed dozens of these spore-covered tapes side by side in a case filled partly with water. Humidity made the artificial muscles expand to open the shutters, allowing the air to dry out. When the humidity escaped, the artificial muscles shrunk to close the shutters, and evaporating water restarted the cycle of motion. This evaporation-driven piston generated enough power to cause a small LED to flash.

The scientists also build an evaporation-driven rotary engine, which contained a plastic wheel covered in tabs of tape that were each covered on one side with spores. Half the wheel sat in dry air, causing the tabs to curve, while the other half sat in moist air, making the tabs straighten. As a result, the wheel rotated continuously, enough to power a small toy car weighing 100 grams.

The researchers suggest HYDRAs could not only help power a variety of machines, but larger versions of the evaporation-driven rotary engines sitting on or above large bodies of water could steadily produce even more power per unit area than wind farms. The scientists detailed their findings online 16 June 16 in the journal Nature Communications.

The Conversation (0)
This photograph shows a car with the words “We Drive Solar” on the door, connected to a charging station. A windmill can be seen in the background.

The Dutch city of Utrecht is embracing vehicle-to-grid technology, an example of which is shown here—an EV connected to a bidirectional charger. The historic Rijn en Zon windmill provides a fitting background for this scene.

We Drive Solar

Hundreds of charging stations for electric vehicles dot Utrecht’s urban landscape in the Netherlands like little electric mushrooms. Unlike those you may have grown accustomed to seeing, many of these stations don’t just charge electric cars—they can also send power from vehicle batteries to the local utility grid for use by homes and businesses.

Debates over the feasibility and value of such vehicle-to-grid technology go back decades. Those arguments are not yet settled. But big automakers like Volkswagen, Nissan, and Hyundai have moved to produce the kinds of cars that can use such bidirectional chargers—alongside similar vehicle-to-home technology, whereby your car can power your house, say, during a blackout, as promoted by Ford with its new F-150 Lightning. Given the rapid uptake of electric vehicles, many people are thinking hard about how to make the best use of all that rolling battery power.

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