An old idea gets a solar spin

A Greenback-based designer and inventor is putting a new spin on an old idea to create a low-cost, high-efficiency solar heating solution that he wants to manufacture in East Tennessee.

Matthew Davis, a 1995 industrial design graduate of Purdue University, has developed the Solar Boiler Electrical Generator and Heat Machine, which converts solar energy to usable steam for heating, cooling and power generation.

Davis has entered his idea into the NASA Tech Brief's Create the Future Design Contest.

At the heart of Davis' system is a century-old idea - first developed by electrical pioneer Nikola Tesla - based on a highly efficient steam-driven turbine. The spinning turbine is used to drive a generator to produce electricity.

Davis has also designed a unique parabolic trough mirror that focuses the sunlight on a "receiver" that heats the water and makes steam to drive the turbine. The mirror is made of cast concrete covered in an acrylic reflective material.

"Concrete is easy to work with and the weight helps stabilize the mirror," he said.

Competing photovoltaic technology, which turns sunlight directly into electricity, can achieve only about 15 percent efficiency, he said. Most photovoltaic systems are also limited by a life span of about a decade.

Ultimately, Davis said his system might achieve more than 100 percent efficiency if it is able to produce excess energy that could be returned to the grid and purchased by the power company.

On the other hand, such comparisons may not be exact even if Davis' idea works perfectly. Stefan Partin, business manager of the Tennessee Solar Energy Association, said most comparisons with photovoltaic technology are based on the current state of the art and don't take into account ongoing research. Some new photovoltaic technologies, he said, may offer potential efficiencies of 40 percent or more.

At its most basic level, Davis' idea converts sunlight to steam heat, which can be used for heating a house floor or heating water for household use. He said 70 percent of the average household's energy bill is spent on heating and hot water.

By focusing sunlight on a linear boiler, making steam and putting that steam through an efficient steam turbine connected to a permanent magnet alternator and a condensing thermal storage tank, it is possible to make heat, hot water and electricity at higher efficiencies and lower cost than using a photovoltaic system, Davis said.

"This solar system would cost about 25 percent of what a photovoltaic system might cost," he said.

Currently there are no solar-focusing steam electrical generation systems on the market designed for household heating, cooling and electrification, Davis said.

The solar system is made from common materials and can be built by almost anyone from power consumers in postindustrial economies to off-grid Third World consumers, Davis said.

The market for this kind of solar system includes anyone who desires to have a stable energy and heat source who can't afford a complete photovoltaic system, he said.

Davis intends to make this design available with an open license so that anyone can build a system. He plans to manufacture his highly efficient turbine here in Tennessee and to make it available on the open market.