Researchers at the Massachusetts Institute of Technology unveiled a new material this week that provides a highly efficient way to convert sunlight into steam and holds major potential for improving technologies like desalination of water and solar thermal power — all with a four-inch graphite ‘sponge.’
The setup developed by MIT consists of a layer of graphite flakes and carbon foam beneath that. It’s porous, which enables the disc to float on water, and the dark color of the graphite attracts maximum energy from the sun.
The end result is a system that converts 85 percent of incoming solar energy into steam — far more efficient than previous methods. “Basically, if you heat up the whole volume of the water, you don’t raise the temperature very much,” Gang Chen, a professor of mechanical engineering at MIT, told ThinkProgress. “However, if you only heat up a small amount of water, then the temperature rise could be high.”
Chen explained that by floating the graphite on the surface of the water, the researchers were able to concentrate the maximum amount of incoming sunlight and adding the foam to the bottom provided a further layer of insulation.
The ability to create steam quickly and efficiently, with inexpensive materials and using only sunlight, has tremendous implications. “Steam is important for desalination, hygiene systems, and sterilization,” said Hadi Ghasemi, a postdoc in MIT’s Department of Mechanical Engineering who led the development of the structure. “Especially in remote areas where the sun is the only source of energy, if you can generate steam with solar energy, it would be very useful.”
Chen said there are two potential applications he’s particularly excited about: developing more efficient solar thermal power plants and creating a cheaper and more accessible way to treat water. Concentrated solar plants like the massive Solana facility in Arizona use a parabolic trough system — a large structure that incorporates mirrors to focus the sun’s heat on pipes, heating a synthetic oil that flows to boilers, which create the steam that drives turbines to produce electricity, much like a traditional power plant.
The plants require high intensity sunlight and the mirrors or lenses track the sun from east to west throughout the day. The system is costly and often results in significant heat loss. By contrast, MIT says its approach “generates steam at a solar intensity about 10 times that of a sunny day — the lowest optical concentration reported thus far.” Chen said his team will be working “to continue to improve [their setup] to reduce the tracking or eliminate the tracking.” If successful, the end result would be lower operating costs for the facility and the ability to power the plant with lower concentrations of sunlight.
“Clean energy is always competing against the fossil-based fuels,” he noted, making any cost reductions particularly important.
And it’s not just more efficient solar power generation that has the MIT team motivated to continue their research. “Think about the water treatment, desalination or treating wastewater,” Chen said. “One typical way is to evaporate the water, condense it, of course you need an energy source to do that. In this case, if we can use solar energy, it could produce better technology.”
For large scale desalination plants, energy is the single biggest expense. Desalination plants on average use about 15,000 kilowatt- hours of power for every million gallons of fresh water that’s produced, according to a 2013 report by the Pacific Institute — a reality that has serious implications from a carbon emissions perspective if production of desalinated seawater is increased.
Gripped by severe and prolonged drought, California is currently pouring millions of dollars into desalination plants and last year, the Marshall Islands, home to around 60,000 people, declared a state of national emergency and shipped in desalination plants to fight a severe drought.
Chen said the potential to commercialize their system to use distributed solar energy could could be huge for water treatment in isolated, impoverished areas. In fact, he’s already receiving emails from people around the world excited by the prospect of small-scale technology to produce potable water.
Chen was careful to emphasize, however, that their recent breakthrough in the laboratory was just a first step. There’s a long way to go before their solar ‘sponge’ could be used in water treatment or power generation. Moving forward, the MIT team plans to pressurize the system to figure out the upper bounds of temperature and pressure it can withstand and to take the next steps with water treatment applications by assessing the potential challenges associated with that process.