Solar

Solar power is rapidly developing.  The fuel is free; it is sustainable, safe, and can be generated where it is used (distributed energy). Even in northern climates, solar hot water and solar energy are freeing homeowners and businesses from fossil fuel dependency.

We've used the sun for drying food and clothes for thousands of years, but only recently have we been able to use it for generating power.

Just the tiny fraction of the Sun's energy that hits the Earth (around a hundredth of a millionth of a percent) is enough to meet all our power needs many times over.

In fact, every minute, enough energy arrives at the Earth to meet our demands for a whole year - if only we could harness it properly.

There are three main forms of solar energy:



Solar Cells (photovoltaic or photoelectric)


Solar cells convert sunlight directly into electricity. In a sunny climate, you can get enough power to run a 100W light bulb from just one square meter of solar panel.



Solar water heating

Heat from the sun warms water in pipes mounted on a panel.  

Solar Thermal

Mirrors concentrate the sun's energy into a small space and produce very high temperatures. Oil or water is heated and stored.


In California, the Solar One power station uses the sun's heat to make steam which drives a generator to make electricity. The station looks a little like the Odellio solar furnace , except that the mirrors are arranged in concentric circles around the "power tower".   

As the sun moves across the sky, the mirrors turn to keep the rays focused on the tower, where oil is heated to 3,000 degrees Celsius, The heat from the oil is used to generate steam, which then drives a turbine, which in turn drives a generator capable of providing 10MW of electrical power.

Alternatively, the mirrors focus on a tall tower. The hot air rises up the tower, fast - and can drive turbines along the way. This could generate significant amounts of power, especially in countries where there is a lot of sunshine and a lot of room.

Another alternative is to use a Fresnel lens which will directly heat water to a lower temperature of roughly 535 degrees F (280 degrees C) at a higher pressure, about 50 bars, or 50 times atmospheric pressure. Then, it uses the resultant steam to turn the same low-temperature turbines as those employed in nuclear reactors. This theoretically will provide storage so that it can be used as a baseload for electricity. Solar-thermal plants could supply 96 percent of the national electricity demand on a patch of land 92 miles by 92 miles, according to John O'Donnell, the executive vice president of one such company, Ausra.

Solar Advantages:

    * Solar energy is free - it needs no fuel and produces no waste or pollution.

    * Solar power can be used where there is no easy way to get electricity to a remote place.

    * Handy for low-power uses such as solar powered garden lights and battery chargers

http://www.darvill.clara.net/altenerg/solar.ht

California Utility Agrees to Buy Power Generated by Solar Array


By FELICITY BARRINGER and MATTHEW L. WALD

July 25, 2007

SAN FRANCISCO, July 23 — Pacific Gas & Electric, Northern California’s major utility, is announcing a commitment on Wednesday to purchase 550 megawatts of solar power to be generated by troughlike arrays of mirrors spread over nine square miles in the Mojave Desert.

The purchase, one of the largest ever of solar power, will help the utility meet California’s aggressive mandate that utilities have enough renewable sources online or under contract to supply one-fifth of the electricity they sell by 2010. The new solar plant is expected to begin producing energy in 2011 or 2012.

This contract, along with similar ones recently signed by Southern California Edison, represents the resurrection of thermal solar arrays, a technology first deployed in the 1980s that failed in the 1990s because of the collapse in the price of natural gas.

But with the price picture shifting and state mandates for renewable energy spreading, an Israeli company, Solel Solar Systems of Beit Shemesh, is betting that this technology will now pay off. The approach may lack the appeal of the more familiar rooftop photovoltaic cells, like the ones used in California’s “Million Solar Roofs” campaign, but it costs only around half as much for each unit of energy produced.

P.G.& E. executives said on Tuesday that during peak summer hours, power from the mirrors in the Mojave Solar Park Project would provide electricity to hundreds of thousands of homes. Fong Wan, P.G.& E’s vice president for energy procurement, said in an interview on Tuesday that “we view concentrated solar as one of the most promising technologies for us.”

While P.G.& E. executives and Solel’s president, Avi Brenmiller, would not specify how much the utility will pay, people close to both companies put it at slightly more than 10 cents a kilowatt-hour — roughly what an average kilowatt-hour sells for at retail to American residential customers.

Electricity will be produced using a six-foot trough-shaped mirror that focuses rays of the desert sun on a pipe less than three inches in diameter, heating a fluid inside to 750 degrees Fahrenheit; the fluid will make steam to drive a turbine. Small motors will tilt the mirrors to keep them facing the sun.

The solar plant, planned to be built in the desert between the Nevada state line and Barstow, Calif., would consist of four modules of 140 megawatts each, Mr. Brenmiller said. “It’s going to be similar to existing plants in style,” he said, but added, “it will be a little larger than the largest one ever built.”

A Spanish company, Acciona Energy, recently opened a similar but smaller plant near Boulder City, Nev., a 64-megawatt plant called Nevada Solar One.

According to Mr. Wan, about 12 percent of P.G.& E.’s electricity today comes from renewable sources, divided somewhat evenly among wind, biomass, small hydropower and geothermal. (California does not count traditional large hydroelectric dams toward the quota.)

Copyright 2007 The New York Times