• 08.01.14

This Black Sponge Isn’t Dirty, It’s Making Cheap, Solar-Powered Drinking Water

A new sponge-like system could be an alternative to expensive water desalination plants.

This Black Sponge Isn’t Dirty, It’s Making Cheap, Solar-Powered Drinking Water

In drought-stricken California, a giant billion-dollar desalination plant is now under construction, and 15 others are proposed along the coast. While the plants could help provide desperately needed water, the current technology has at least two major problems: it uses a lot of energy, and it’s very expensive. An alternative now in the early stages of development at MIT might help.


The new technology looks a little like a sponge. A black material, made from graphite and filled with tiny holes, floats on top of water, soaking up sunlight. As the material heats up, it heats up a small area of water around it, and a layer of foam at the bottom keeps everything hot. The water starts to turn into steam that could be used for everything from drinking water to sterilization in places off the grid.

“The most exciting thing is it’s simple,” says Gang Chen, head of the mechanical engineering department at MIT. “You could even hand-build this. It could be done with a simple manufacturing process–and that can lead to lower cost.”

Unlike a typical large-scale desalination plant, which has to be hooked up to huge amounts of electricity, the new technology is so efficient that it could in theory be used anywhere around the world, relying solely on the sun.

The system could also be used to generate ultra-efficient, cheap solar thermal power. Right now, large solar thermal plants–like the enormous Solana Generating Station in Arizona, which sprawls over three square miles–make electricity by using a expensive system of mirrors that track sunlight throughout the day. MIT’s technology may someday be able to generate that same power without all of the extra equipment.

The next step for researchers will be figuring out whether it makes sense to focus on desalination first, or renewable energy, and then working on the details of the design.

Will it be ready soon enough for places like California to potentially avoid investing billions more in energy-hungry desalination plants? “In terms of really taking this into a commercial system, it’s hard to put a timeframe on the technology,” Chen says. “But overall the principle is simple enough . . . it really depends on whether we decide it’s desalination or power we should pursue. That will happen in the next year or two.”

About the author

Adele Peters is a staff writer at Fast Company who focuses on solutions to some of the world's largest problems, from climate change to homelessness. Previously, she worked with GOOD, BioLite, and the Sustainable Products and Solutions program at UC Berkeley.