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Renewables - Mar 1

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How Many Windmills Does It Take to Power the World?

Kurt Cobb, Scitizen
Power densities are a measure of the land required for both energy sources and energy users. The current infrastructure matches the small footprint of energy sources against the large footprint of energy users. With the drive toward renewable energy sources, this relationship is about to be reversed with consequences few people understand.

Though nowadays people sometimes rail against the deployment of wind generators because they mar the view, such deployments are the logical outcome of our desire to move away from fossil fuels. We may be concerned about the greenhouse gasses and toxic pollution emitted by coal-fired power plants, but most people do not worry about such plants ruining their view unless they live very nearby. Neither do they worry about coal mines unless, of course, they live in proximity to them, and only a very small segment of the population does.

But windmills can be put anywhere there is sufficient wind. And, that often conflicts with the aesthetic desires of people who must look at them and deal with the attendant disruption that servicing them causes. It's not just that coal-fired power plants can be plunked down pretty much wherever we want them. It's also that watt for watt they are far more compact than their equivalent in wind turbines.
(26 February 2008)
Kurt Cobb publishes regularly at Energy Bulletin.


Today's solar cells give more than they take

Patrick Barry, Science News
Solar power produces, per unit of energy, only about one-tenth as much carbon dioxide and other harmful emissions as does conventional power generation, a new study shows.

Solar panels don't release harmful gases during use, but making the solar cells does consume materials and energy-mainly from conventional power sources such as coal-fired power plants, which in turn produce emissions. Industrial techniques for making glass and other materials in solar panels also produce gases such as carbon dioxide.

In the 1970s, manufacturing a solar cell required about as much energy as the cell could produce over its 20-year lifetime, so using solar power provided little if any energy gain. Also, as recently as 10 years ago, total emissions from solar cells were about twice what the new study shows. "Solar power has been criticized in the past" for requiring too much energy to produce, says Vasilis M. Fthenakis of the Brookhaven National Laboratory in Upton, N.Y. "But what we find out is that those criticisms are not true with the new technologies."
(1 March 2008)


Solar without the Panels

Peter Fairley, Technology Review
Utilities are using the sun's heat to boil water for steam turbines.
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Investors and utilities intent on building solar power plants are increasingly turning to solar thermal power, a comparatively low-tech alternative to photovoltaic panels that convert sunlight directly into electricity. This month, in the latest in a string of recent deals, Spanish solar-plant developer Abengoa Solar and Phoenix-based utility Arizona Public Service announced a 280-megawatt solar thermal project in Arizona. By contrast, the world's largest installations of photovoltaics generate only 20 megawatts of power.

In a solar thermal plant, mirrors concentrate sunlight onto some type of fluid that is used, in turn, to boil water for a steam turbine. Over the past year, developers of solar thermal technology such as Abengoa, Ausra, and Solel Solar Systems have picked up tens of millions of dollars in financing and power contracts from major utilities such as Pacific Gas and Electric and Florida Power and Light.
(29 February 2008)
Contributor SP writes:
The economic analysis referred to in the text is at www.ucei.berkeley.edu/PDF/csemwp176.pdf

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