Desert Power: A Solar Renaissance

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(This is one very big way that we can turn this country around...by investing in solar technologies...thereby reducing our use of fossil fuels as well as reducing our dependency on foreign oil)

A Department of Energy-sponsored pilot solar thermal project built in California's Mojave Desert in 1981, shown here, was a 10-megawatt power tower surrounded by more than 1,800 sun-tracking mirrors.

Carolyn Gramling

Sandy wastes, brutal sun, forbidding emptiness — those are the stark images of a desert. But these vast, sunburnt areas are also home to a powerful renewable energy resource: the sun. And solar energy is likely to become increasingly important as the world looks ever more urgently for alternatives to fossil fuels.

A recent renewed interest in alternative energy technologies has also revitalized interest in solar thermal technology, a type of solar power that uses the sun's heat rather than its light to produce electricity. Although the technology for solar thermal has existed for more than two decades, projects have languished while fossil fuels remained cheap. But solar thermal's time may now have come — and mirrored arrays of solar thermal power plants may soon bloom in many of the world's deserts.

Solar rising

As a result of the oil crises of the 1970s, alternative energy sources, including solar power, received increased attention. From the mid-1970s through the mid-1980s, the solar industry grew from 45 solar collector manufacturing firms to 225 firms, according to the U.S. Energy Information Administration (EIA). During this period, construction began on nine solar thermal power plants, collectively referred to as the Solar Energy Generating Systems (SEGS), in California's Mojave Desert. These power plants — still the largest solar plant system in the world — were hybrids, using solar energy by day but fossil fuels at night.

In the late 1980s, oil prices fell and remained low through the 1990s — and construction of new solar plants stalled. But more recently, with oil prices soaring past $100 per barrel, solar power has once again become economically attractive. In the United States, the solar energy industry has been growing rapidly since 2003, fueled not only by high energy prices but also by an increased focus on reducing carbon emissions, as well as by new renewable power standards in many states and federal tax credits for solar installations (which went into effect in January 2006 as part of the Energy Policy Act of 2005).

They do it with mirrors

When it comes to solar power, many people are most familiar with photovoltaic cells. These cells convert sunlight to electricity by absorbing photons from the sun's rays; the photons kick some electrons loose from atoms of silicon in the cells, and the resulting flow of electrons through the material produces electricity.

In addition to providing electricity, hot water and heat to homes and businesses, photovoltaic systems supply power to everything from ocean weather buoys and communications equipment to streetlights and satellites. But cost is an issue: Photovoltaic solar power is still more expensive than electricity generated by fossil fuels, costing between 10 and 40 cents per kilowatt hour, depending on whether it comes from a solar power plant or from cells on a small building. Coal, on the other hand, costs 2 to 4 cents per kilowatt hour.

Some of the high costs relate to the costs of raw materials used to manufacture the cells, such as copper and high-grade silicon. Newer thin-film solar cells (using a very thin coating of silicon or an alternative) cost less than conventional crystalline silicon technology to manufacture, but also tend to be less efficient (producing less power with the same amount of sunlight).

However, there is a way to "boost" solar power to make it more affordable: Instead of converting sunlight to electricity, solar thermal power plants, also called concentrated solar power (CSP), harness the sun's energy by converting it — with the help of mirrors that focus the intense energy — to heat. There are several different configurations of mirrors that CSP plants can use. Some plants — such as the California SEGS plants — use "parabolic troughs," curved mirrors that focus the energy onto pipes containing circulating oil, which absorbs the energy and uses it to heat steam to power a standard generator.

Another kind of concentrating solar technology, solar "power towers," uses a large field of sun-tracking mirrors called heliostats that face a central tower and focus the solar energy onto a receiver on its top. The intense energy concentrated onto the tower produces temperatures up to 1,500 degrees Celsius (2,732 degrees Fahrenheit). That thermal energy then heats up water, producing steam that drives a turbine to produce electricity.

More recently, an innovation to temporarily store the heat, improves on one of solar energy's primary limitations — the inherent intermittency of sunlight. Many newer plants use insulated tanks filled with molten salt for heat storage, which — although only possible for a few hours — means the plant can still provide power on cloudy days or at night. Such technological advances, combined with an economic atmosphere once again receptive to alternative energy, have created new interest in solar thermal.

Renewed interest in renewables

When it comes to solar thermal energy, "'renaissance' is the term I hear a lot," says Ben Paulos, program officer for renewable power at the Energy Foundation in San Francisco, Calif. Formed in 1990 as a partnership of 15 to 20 large foundations, the Energy Foundation's goals are to fund research and new technologies for renewable energy in both the United States and China, two of the world's biggest energy markets.

High oil prices aren't the only reason that "Big Solar" is gaining increasing interest, Paulos says. Also key is the recent adoption of renewable power standards in many states (currently 25), requiring that state utilities buy a growing amount of renewable power each year. Concentrated solar power, one option to help meet these standards, requires a lot of intense sunlight — and in the United States that means the Southwest. The region is particularly well matched to solar power because power loads (intense sunlight) and power needs (intense air conditioning) coincide at midday. Within that region there is plenty of local demand for solar power — more, in fact, than the utilities can currently satisfy, he says. "That's the thing that makes the Southwest so attractive for concentrated solar power. Not only is the resource there, but demand is there, and power prices are high enough to pay for it."

The utility sector in western states has therefore become especially interested in solar, with several new projects recently constructed — and many more proposed. For example, the Nevada Solar One solar thermal plant, which came online in June 2007 and uses solar power towers to produce 64 megawatts of power, is one of the largest solar plants built in the last 16 years, according to EIA. Spread across more than 160 hectares of the El Dorado Valley near Las Vegas, the plant's nearly 219,000 mirrors concentrate sunlight onto 18,000 receiver tubes, generating enough electricity to power 15,000 households.

Other proposals are hot on Nevada Solar One's heels. In February, the Spanish company Abengoa Solar filed for approval for a new solar thermal plant to be built in a hot patch of land southwest of Phoenix, Ariz., called Gila Bend, where summer temperatures can reach up to 48 degrees Celsius (120 degrees Fahrenheit). If approved, the plant would produce 280 megawatts, enough to supply 70,000 homes with power. Arizona's renewable power standards will require state utilities to get 15 percent of their electricity from renewable sources by 2025 — and state officials say the Abengoa plant would be a big boost to meet those standards, bumping them up to 5 percent by 2011.

In 2005, the utility Southern California Edison (the nation's leading purchaser of renewable energy) announced a contract with the solar company Stirling Energy Systems to construct a giant solar-power generating station northeast of Los Angeles. The power station is intended to produce 500 megawatts of power, which would make it the world's largest. The station would use a new type of solar technology that has been successfully tested at Sandia National Laboratories in Albuquerque, N.M., but never deployed. The project consists of a dish-shaped mirror array (eventually to include about 20,000 dishes) that focuses the sun's rays on a receiver connected to a Stirling engine, heating up hydrogen gas that expands and drives the pistons of an engine (which resembles an internal combustion engine).

Internationally, sunny Spain has been a leader in solar power, not only financing projects in the United States, but implementing its own solar thermal projects. In March 2007, a solar-power tower plant was constructed near Seville; the plant currently produces 11 megawatts but plans to increase production to 300 megawatts by 2013. And two 50-megawatt parabolic trough plants are in construction in Andalucia, one of which will be completed this summer.

Stirling Energy Systems and utility Southern California Edison are building a 500-megawatt solar power plant to open in 2009. The plant will be the first commercial application of the Stirling Solar Dish (a smaller prototype is shown here at the National Renewable Energy Laboratory in Golden, Colo.).

Desert power

But an even larger project is on the table, spanning not only Europe but also North Africa and the Middle East. The sunburnt Sahara Desert seems like an obvious place to harvest solar energy — but a multinational initiative, dubbed "Desertec," plans not only to harvest solar thermal energy from proposed plants in North Africa (and the Middle East) for local use, but to transfer much of that energy across the Mediterranean Sea to European consumers. If it succeeds, proponents say, Desertec will not only provide affordable, renewable solar power to two continents — eventually supplying one-sixth of Europe's power needs — but will also help to promote political and financial stability.

The project began six years ago, when German physicist Gerhard Knies began to consider the possibility of solar power from the world's deserts as the most promising source of clean, renewable energy. The success of California's SEGS plants demonstrated that the technology is not a limiting factor, and that solar power can be competitive economically, Knies says. What's been missing, he notes, is political will to wean nations off of fossil fuels.

In 2003, he approached the Club of Rome, a global think tank that consists of scientists, businessmen and current and former heads of state from around the world, hoping to enlist their help in determining the feasibility of using this source. They were interested, he says, but skeptical: "They said we'd need a disaster first before people will change."

Still, that year Knies and other members of the Club of Rome formed the Trans-Mediterranean Renewable Energy Cooperation (TREC). TREC began to develop the Desertec concept, a sweeping plan to build an array of solar thermal power plants in North Africa and the Middle East that would transmit power to Europe. Desertec was intended not only to provide energy, but also water and security, while reducing harmful carbon dioxide emissions and promoting peaceful relations and cooperation between the countries.

for the rest of the article...

http://www.geotimes.org/apr08/article.html...ture_solar.html