Will the Carbon-Free Power Plant of the Future Look Like a Giant Sponge?

MIT scientists have invented a simple but ingenious device that absorbs water and sunlight to generate steam.
Jul 23, 2014· 1 MIN READ
Kristine Wong is a regular contributor to TakePart and a multimedia journalist who reports on energy, the environment, sustainable business, and food.

Solar thermal power plants are futuristic looking, deploying hundreds of thousands of mirrors that focus the sun on water-filled boilers sitting atop tall towers. The heat creates steam that drives an electricity-generating turbine.

But if MIT scientists are right, the power plant of the future might resemble a giant black sponge.

The researchers have invented a spongelike device that soaks up water and sunlight to generate steam, and they say it’s 85 percent efficient. In contrast, the huge solar thermal power plants operating today are about 30 percent efficient.

“It’s cheaper than what’s used today because [the structure] is a stationary source,” said Gang Chen, a professor of mechanical engineering at MIT and one of the scientists who recently published research in the journal Nature Communications. “We don’t need a large lens or moving [equipment] to track the sun and concentrate sunlight. We can apply this method to produce steam used in water treatment or desalination.”

The four-inch-wide solar sponge they constructed floats on water and is made of a porous carbon foam base topped with a pile of graphite. When sunlight strikes the graphite, it creates a hot spot that heats the water absorbed by the foam to produce steam.

“The sponge has several characteristics that make it work,” said Chen. “First, it’s black in color, so it absorbs the light very effectively. Second, it’s porous to allow water to come in. Third, it’s insulating, so it absorbs sunlight and turns it into heat.”

But don’t expect sponges to replace smokestacks anytime soon.

So far, Chen and his team have tested the sponge only in the laboratory. They still need to show that the steam produced by the sponge can be pressurized to power a turbine so it can be used in water treatment and other commercial applications. They also need to run the numbers to quantify just how much cheaper sponge-generated steam would be compared with current solar thermal technology.

Chen thinks that if subsequent experiments are successful, he can envision a future in which people use solar sponges to power their homes, allowing them to pull the plug on their local utility.

“My feeling is that if we develop smaller sponge structures rather than big ones, there will be a better chance to get into the market, as you can scale the technology up or down,” he said.