MIT team plays with fire to create cheap energy

New solar dish harnesses power from heat – at a size and cost that make soaking up the sun even more attractive.

Melanie Stetson Freeman – Staff
Spencer Ahrens, Matthew Ritter, and Eva Markiewicz created a solar dish that boils water (or sets wood ablaze) at a cost cheaper than heat from gas, oil, or coal.
Melanie Stetson Freeman – Staff
The MIT team shows off its solar dish by lighting a wooden board on fire.

Out on a lawn at the Massachusetts Institute of Technology with joggers and traffic passing nearby, Spencer Ahrens is demonstrating what looks like either the future of solar power – or perhaps a death ray.

Thrusting a 12-foot board up into the air in front of a large mirror-covered satellite-type dish, Mr. Ahrens, an MIT graduate student, waves the board, looking for an elusive sweet spot where reflected sun rays converge.

With three student teammates looking on, he steadies the board once its tip begins to glow. Shining white in the reflected solar rays, the wood suddenly bursts into flames. Students laugh as smoke billows in the breeze.

This burning-board trick may seem like a YouTube stunt, but it’s actually a visceral demonstration of a device with a serious purpose: to make super-cheap solar heat.

From garage inventors to government scientists, many have tried to make a solar dish that focuses sun rays to generate power. What makes this student project different is not that they’ve done it – but that they’ve done it so cheaply, building this dish with off-the-shelf parts.

“A lot of good people have built working dishes, but generally they’re more expensive, more complex, and harder to build,” says Matthew Ritter, an Olin College of Engineering student who’s also part of the team. “We use widely available materials – that’s our breakthrough.”

The student team has already formed a company – Raw Solar – that they hope will one day have an assembly line cranking out cheap solar dishes that individually or in large arrays could supply affordable heat to a college campus, suburban home, or third-world village.

A few minutes later, the real demonstration begins. A pole protrudes from the front of the solar dish – similar to the rod that sticks out from satellite-TV dishes. Wrapped around the end of it is spiral tubing, which the team fills with water from a garden hose. With the dish swiveled to face the sun, the tubing glows white. Boiling water sputters from the far end of the hose, which lies in the shade beneath the dish.

The secret: frugal design
Materials and construction are fairly simple. Aluminum tubing is riveted to a steel cross bracing. Affixed to that frame are strips of mirror from a local supply house. High-heat barbecue paint coats the coil collector at the apex of the pole.

“Small solar thermal is a kind of power that has really been traveling under the radar,” says Micah Sze, an MIT business school graduate tapped to help market the technology. “People have been focusing on electricity from the sun, not the heat market. We think there’s an opportunity to supply heat to large institutions like universities and someday individual homes.”

“Concentrating solar power,” as this type of system is called, is seeing a boom. At least 4,500 megawatts of capacity is in the development pipeline, according to the Solar Electric Industries Association in Washington. That power is about 13 to 20 cents per kilowatt – cheap enough to compete with peak power prices of fossil fuel plants – but not yet off-peak regular prices.

The goal is to bring the price down. Many older and current systems are very complex, involving a host of motors to keep dozens or hundreds of carefully polished mirrors focused on the sun. So the team focused instead on making a dish that only requires a simple electronic system to keep it aimed at the sun – and pump water into the collector coil to be heated into steam. The MIT team says their unit will produce steam heat for less than the cost of heat from oil or natural gas.

The steam is “low temperature” – about 212 to 400 degrees F. – not high temperature steam generally used to power electric turbines in conventional power plants – which can surpass 700 degrees F. Still, this “process heat” can be used cost effectively in manufacturing, food pasteurization, and heating buildings.

Making good ideas better
Part of the genius here may also be all about knowing where to look for technology. The MIT students, for instance, did not take a go-it-alone approach. As part of his “Energy Ventures” class, MIT lecturer David Pelly was hunting for some of the best new energy ideas that needed development and marketing – and discovered Doug Wood’s solar dish.

An inventor who lives on Fox Island off the coast of Washington State, Mr. Wood’s backyard is filled with all manner of solar dishes he has built – but most are enormous, he says. After working with the MIT team, they settled on a dish that is just 12 feet across.

“Our big discovery was that small worked better, cheaper, than any of our huge old models,” Wood says. “Getting the size right was the critical breakthrough.”
This summer, the team plans to relocate its fledgling company to the San Francisco area in order to find funding, as well as to tap the burgeoning solar-power expertise in the region.

Fortunately for traffic and pedestrians here at MIT, the Raw Solar dish is unlikely to be of any use as a laser-style device. When lowered toward street level the beam deflects.

“Yes, I know it probably looks like a ray that could fry Boston,” Ritter says. “But it actually loses power very quickly beyond the focal point, so there’s no actual danger. You can’t accidentally step into the focal point. Nobody walking along the sidewalk will get toasted.”

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