Michael Kanellos

New tool in solar: the bathroom mirror May 7, 2008 at 2:13 PM

It’s a solar thermal system Fred Sanford would love.

MIT students have concocted a solar thermal electrical generator that employs lightweight, low-cost bathroom-grade mirror glass.  The mirror strips—which measure 12 feet long and about ten inches across—are formed into a dish that covers about 12 square meters. The mirror is then positioned onto a frame made from aluminum tubes. The mirror collects heat from the sun, which is then condensed and deployed to make steam. The steam then turns a turbine to generate electricity.

While the mirror can’t harvest heat from the sun as efficiently as smooth mirrors, it’s a lot cheaper, and thus could be more attractive to villagers in emerging markets. In optimal conditions, the system could generate 3.5 kilowatts of electricity and the equivalent of 10 kilowatts of heat.

“We’re using all commodity materials that are all in high production,” said Spencer Aherns, a graduate student in mechanical engineering at MIT, in a prepared statement. The group is in the midst of trying to determine a baseline cost.

The group also came up with a cheap guidance system to steer the mirrored dish toward the sun. On the side of the mirror, sets of baffles sit above photo receptors. When the baffles cast shadows, a signal is sent from the receptors to a small electric motor, which repositions the mirror.

A small, but growing number of companies and universities are working on ways to bring solar thermal to the masses. Most solar thermal projects are massive, involving hundreds of acres of land in the desert. The residential solar market is largely dominated by solar panels. Solar panels, however, do not provide power as cheaply as solar thermal systems.

Promethean Power, which spun out of a research project out of MIT, is building solar thermal heating/electrical systems for India while Sopogy in Hawaii has created a modular solar thermal system with a parabolic mirror that can generate both heat and electricity. 

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