MIT researchers boost the power of solar energy

Advances could increase energy output and efficiency, while also cutting costs

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Using computer modeling, researchers at MIT are working to boost the output and efficiency of solar cells while lowering the cost of solar power.

A team of MIT physicists and engineers say they have been able to boost the output of solar cells by as much as 50% by adding a combination of antireflection coatings and multilayered reflective coatings to silicon films on the cells. The research team said that the advancement could dramatically reduce the cost of using solar power because the amount of very pricey high-quality silicon traditionally used is slashed down to 1% of the normal amount.

MIT announced in a report late last week that the multilayered reflective coatings, along with a tightly spaced array of lines called diffraction gratings, are added to the back of ultrathin silicon films on the solar cells. Peter Bermel, a postdoctoral researcher in MIT's Research Laboratory of Electronics who has been working on the project, noted in a statement that the added layers force light to bounce around longer inside the silicon, which gives the light time to deposit energy and produce an electrical current. Otherwise, the light is quickly reflected back out of the silicon and is lost in the air.

Sunlight has the greatest potential of any power source to solve the world's energy problems, Daniel Nocera, the Henry Dreyfus Professor of Energy at MIT, said in an earlier interview. In one hour, enough sunlight strikes the Earth to provide the entire planet's energy needs for one year, he added.

The problem, however, is how best to harness that energy.

Just four months ago, MIT reported that a team of researchers there had made an energy storage breakthrough that could transform solar power from an alternative energy source to a mainstream source.

The problem with using solar power has long been figuring out an inexpensive way to store the sun's energy for those times when the sun isn't shining, said Nocera. Although it can be done, the cost is prohibitive with current technologies.

Taking a page from photosynthesis in plant life, Nocera and Matthew Kanan, a postdoctoral fellow in Nocera's lab, came up with a process (see video) to use the energy from the sun to split water into hydrogen and oxygen gases, according to MIT. Later, when they are needed, the gases can be combined inside a fuel cell. That reconnection creates carbon-free electricity that can be used to power an office building, a home or even an electric car -- whether the sun is shining or not.

Nocera said that he's hopeful that within 10 years, people will no longer power their homes using electricity wired from a central source. Instead, homeowners will be able to power their homes with solar power during daylight hours and use this new energy-storage method for electricity at night.

Last July, MIT announced that its researchers had created a new way to harness the sun's energy by turning windows of big buildings into solar panels.

That technology, dubbed solar concentrators, harvests light over a wide area, such as a window pane, and then concentrates or gathers it at the window's edges, Marc Baldo, a professor at MIT and head of the effort, explained in an MIT video. Baldo added that the technology also could be used to soup up more traditional solar panels, increasing their efficiency by 50%.

For the research announced last week, MIT said, the team ran thousands of computer simulations in which they tried out variations in the spacing of lines in the grid, the thickness of the silicon and the number and thicknesses of reflective layers deposited on the back surface. The latest effort is the first step toward producing advanced commercial solar cells.

"If the solar business stays strong, implementation within the next three years is possible," said Lionel Kimerling, the Thomas Lord Professor of Materials Science and Engineering, who directed the project.

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