Low-tech Sponge Generates Heat from Sunlight

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The “steampunk sponge” works as effectively as methods that require solar generators for conventional steam production, and produces clean energy from readily available materials.
ImHope | Shutterstock.com

Researchers have designed a low-tech yet ingenious way of converting water into steam using ambient sunlight. The “steampunk sponge” works as effectively as methods that require solar generators for conventional steam production, and produces clean energy from readily available materials.

Generating steam energy using conventional methods requires expensive magnifiers that concentrate sunlight to heat a mass of water.

This process often results in high thermal losses due to the heated reflective surfaces of the magnifiers, and the near-boiling temperatures of the water itself.

Researchers at the MIT Department of Mechanical Engineering have developed a low-tech and portable design capable of generating steam from sunlight, and without expensive optics or additional heating. Even more amazing is that this little gadget functions just as efficiently on a cloudy day.

Steampunk Sponge

In 2014, the team designed a similar “absorber” made of a spongy substance that floats over water. The design featured a composite of graphite flakes layered on a carbon foam bed, and was able to convert up to 85% of the solar energy absorbed directly into steam.

Building on their initial design with the goal of limiting thermal loss, the team conducted several experiments (including drawing inspiration from their kids’ Science Fair projects) to find the best way to maximize heat retention in the upper layer of the “sponge”.

Sponge Baths and Bubble Wrap

This newest design insulates the sponge by covering the top layer with a specialized absorbent material. This type of metallic film is already widely used in solar thermal panels lining for heating water and is effective in limiting thermal loss because it allows only a minuscule amount of heat to radiate back out.

To further minimize thermal loss the team covered the metallic heat collectors with an additional layer of bubble wrap. Yes, the same plastic bubble wrap often used in packaging for fragile objects. The result is a highly permeable top layer able to maximize both the sponge’s absorption and retention of solar energy.

Accessible Energy

This low-tech but high-yield invention has enormous potential to create energy from limited amounts of sunlight and relatively inexpensive materials. The absorbent film already used in solar panels is really the only specialized material that must be our hard, and even then cheaper alternatives than the film used in the MIT prototype are available.

For these reasons, the MIT researchers note that their  “Solar Vapor Generator” or “sponge island” would be particularly beneficial in remote regions and developing countries where energy infrastructure is scarce or unreliable.

Aside from utilizing materials that aren’t especially exotic or expensive, most of the sponge’s components can be found in a landfill. Although most bubble wrap is made of recyclable plastics, most municipalities do not deem it cost effective enough to include bubble wrap in their recycling programs. As a result, much of this material ends up going to waste in the form of pollution. This steampunk sponge encourages repurposing waste materials to produce clean energy and promotes circular economies.

In addition to generating clean energy efficiently, this technology also has applications in the desalination of seawater, hygiene, sterilization, and waste water treatment.

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