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Brewington's Power Tube is a sealed tube, four-foot wide and 185-feet long, containing a vapor-driven generator. The idea is to bury the Power Tube deep enough to touch hot rock.
The tip of the Power Tube contains a pair of hydrocarbons, isopentane and isobutene, that turn to vapor when in contact with rock that's at least 220 degrees Fahrenheit (104 C). The vapor rises to drive a generator above. The vapor is then cooled back into a liquid by helium that is compressed and expanded using sound waves. The liquefied hydrocarbons are then pumped back to the tip to restart the cycle in an unbroken loop. Magnetic suspension, rather than lubrication, eliminates friction in the turbine.

Brewington has designed a half-size prototype that is just over two-feet in diameter and 85 feet long. It is expected to produce a megawatt of electricity, enough to power 750 homes. The first Power Tubes to go into operation will be in Hawaii and Costa Rica, Brewington said. He is still talking to authorities, and didn't say when it would go into the ground.

Brewington said full-size Power Tubes will produce 10 MW, enough to light up a small residential town. Unlike old-fashioned geothermal sites, which consume up to 10 acres of land, Power Tubes will have only a small maintenance shed on top. And because Power Tubes run silently, homes and offices could be built over them.

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