TCS Daily

Solar Tower of Power

By Roy Spencer - May 16, 2005 12:00 AM

In a recent speech, President Bush addressed the need to start building more oil refineries, nuclear power plants, and natural gas terminals to meet the growing demand for energy in the U.S. While improved fuel efficiency for cars was also mentioned, the speech was met with disdain from environmentalists for its reliance on the further expansion of the fossil fuel industry infrastructure.

In today's world, and in the foreseeable future, it's impossible to not have foreign oil as part of the energy mix, but there are advances in new technologies that may make renewables a more viable option for future generations. For instance, in the next year or so, construction will begin in Australia's Outback on the most expansive, and tallest, manmade structure on Earth. The "Solar Tower" will be a 200 megawatt electrical generating plant that gets its energy from harnessing the daily solar heating of the desert surface. This heat creates a self-contained wind field that drives a network of 32 turbines. The concept is marvelously simple, but is still an engineering challenge. The 3,000 foot tall "chimney" at the center will dwarf other buildings around the world, standing nearly twice as tall as "Taipei 101" in Taiwan. The glass-covered canopy surrounding the tower will be about four miles in diameter. A much smaller version of the Australian facility was built in Spain, and operated continuously between 1982 and 1989. Once built, the facility will continue to produce electricity indefinitely.

Most solar energy technologies have historically been rather expensive. This is partly because the solar collector surface has always been man-made. Since the amount of energy falling on each square foot of a collector is relatively small (100 watts at the most when the sun is directly overhead), even a perfectly efficient system does not get much energy bang for the buck. The solar tower design instead uses the Earths surface, probably a desert location, as the solar collector. It simply requires a clear canopy for the sunlight to enter, but to contain the solar-heated air, preventing it from rising until it is naturally sucked up the chimney.

Since the current Solar Tower design is expected to be somewhat more expensive than a coal-fired power plant with comparable output, it has been partially subsidized by the Australian government. Yet, I can see hope for improving the power output efficiency of the basic design, which currently runs around 1 to 3 percent. After reading technical papers on the subject, the first advance I could see is covering the ground under the canopy with a thin layer of black material, maybe crushed lava rock, to maximize the absorption of solar radiation. Similarly, engineering advances that could bring down the cost of the two main structural components, the central tower and the huge glass-covered canopy, would also improve its cost competitiveness.

The Solar Tower is about as green as you can get. It generates no waste or pollution. It is safe. People can work under the canopy since the wind speeds it generates are less than about 30 mph. And of course, it uses no fossil fuels. It also continues to generate electricity at night, at reduced output, because the soil that is heated during the daytime continues to release its heat to the air at night.

From what I have been able to determine, the U.S. government is not currently funding research into solar towers. (Or, if it is, it has been a well kept secret). If the current administration would like to enhance its green credentials, maybe it is time to spearhead a major solar tower research initiative here in the United States. The first one built would be a source of national pride, and a tourist attraction, to boot. This is the first solar power technology I have personally been excited about, and I have a feeling that it will eventually be a major component of our energy generation future. In combination with a future hydrogen fuel technology, solar towers could eventually provide the electricity needed to make hydrogen to fuel cars. Or, battery powered cars could be charged directly.

We don't know if the Solar Tower is the answer, if hydrogen will become workable or if there is some other, new, yet undiscovered energy source that will provide future generations' energy. What we do know is that we won't find the answer unless we continue to fund research and technology. Technology will eventually make all of our energy cleaner -- fossil-fuel based and renewable.


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