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The Cutting Edge: Focus on Technology | Science Watch

Old Concept and New Technology Reheat the Promise of Solar Power

May 08, 2000|LEE DYE

Using an old idea and new technology, researchers are developing systems that promise to bring down the cost of using energy from the sun to produce electricity.

The technology could finally bring electricity to isolated villages around the world that are beyond the reach of urban power grids. One system is scheduled to be installed on an Indian reservation in the Southwest this winter, providing power to pump water and irrigate land that now lies fallow.

Much progress has been made in recent years in producing electricity directly from sunlight through photovoltaics, but that technology--promising as it is--remains expensive and inefficient. The cost can be five times greater than electricity from conventional power plants.

So researchers recently returned to the old idea of using the solar energy we know best--heat--to produce electricity. Leaders in the field include Science Applications International Corp. in San Diego, Boeing Co.'s Huntington Beach operations, and the Department of Energy's Sandia National Laboratory in Albuquerque.

"This is probably the cheapest solar energy there is," said Craig Tyner, manager of the Sandia program.

Tyner is negotiating with several Indian tribes to pick the best site for a demonstration project, which he expects to see fully operational within a year.

Similar technology has been tested over the last three years near Phoenix under a joint program between SAIC and Arizona Public Service Co., perhaps the nation's most aggressive public utility when it comes to solar energy. But SAIC's "power towers," as they are called, are an integral part of the urban grid. Tyner's tower will be a stand-alone facility, providing electricity where there is none now.

Though they differ some in their technology, all the systems being tested operate in a similar way.

A large dish of several hundred square feet, resembling a radio telescope covered with mirrors, collects sunlight and concentrates it on a receiver above the dish. Gas inside the receiver expands as it is heated, driving an engine that runs a generator that produces the electricity.

"It's a closed cycle," Tyner said. The system uses a Stirling engine "with a proven track record of hundreds of thousands of hours of operation."

The beauty of the concept lies in its simplicity, using mostly off-the-shelf components.

"It's basically a mechanical system," Tyner said. "Somebody with experience as an auto mechanic or whatever can maintain it out in the field. You've got to know which end of the wrench to grab on to, but it needs very little maintenance."

The test towers will be 10 kilowatts, which is about the energy required to supply 10 homes.

They will be fully automated. A computerized solar-tracking device will tell the mirror where to point. It will "wake up" in the morning, Tyner said, and point to the sun. It will follow the sun across the sky and then shut itself down at night.

Of course, that means it can't produce electricity in the evening, but there is a solution for that. Because any type of heat will drive the engine, an auxiliary burner can fill in when the sun drops over the horizon.

The first Sandia installations will not have that capability, but Tyner expects to include it in subsequent prototypes. The units are expected to cost between $30,000 and $40,000, not much considering they will supply electricity for 30 years with no cost for fuel. But that's still a lot of money for some regions of the country, so the Department of Energy will foot the bill for the test facilities.

Two Indian tribes, the Kaibabs of northern Arizona and the Laguna Pueblo in New Mexico, are under contract with Sandia for training to operate the facilities, and six other tribes have asked to be included. A decision on where to put the first one will come within a few months, and Tyner expects to have several operating over the next few years.

The main demand, however, is expected to be international, and some analysts see a multibillion-dollar annual market abroad. Running water pumps and electrifying villages are expected to be the main applications, but such things as water desalination, hydrogen production and heat for industrial processes are also being studied.

In the U.S., solar energy has been kept largely on the fringes, favored for its benign environmental impact but unable to compete economically with other sources. That has led some utilities, like Arizona's APS, to be a bit innovative.

Arizonans living in isolated areas can lease a photovoltaic system from APS and the utility will install it and maintain it. The cost depends on the size of the system.

The utility also invites customers to become "solar partners," volunteering to add a little to their electric bill to support solar projects. So far, about 1,300 "partners" have signed up.

The participants pay an additional $2.64 for 15-kilowatt hour "increments," and they can sign up for as few, or as many, increments as they wish.

A 15-kilowatt hour, by the way, will run a 19-inch color television set for five hours a day.

The solar partners hardly offset the fivefold increase in the cost of solar power, but the utility cited public participation as one of the motivating forces behind its recent decision to double the use of solar energy over the next year by adding 388 kilowatts.

With 350 days of sunshine per year, according to Arizona's image makers, the state is an ideal laboratory for solar energy.

It is also a prosperous state, but one with pockets of poverty, many on Indian reservations, that have no power at all.

It is that challenge that Tyner is addressing.

*

Lee Dye can be reached via e-mail at leedye@gci.net.

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