Here's a technology particularly suitable for generating electricity in deserts and sun-rich wasteland. Sounds like some of the areas I passed through in southern California. Picture you're in a hot car on a sunny day but your car has a long chimney on the roof that let's the hot air rise out. Now picture a turbine built into the chimney that spins as the hot air passes and generates electricity. That's something like the idea behind a solar chimney.

Solar chimney power stations combine three things in one: the greenhouse, the chimney and the turbine. Air underneath a low circular glass roof open at the circumference is heated by radiation from the sun. The roof and the natural ground below it form a hot air collector ("greenhouse"). A vertical tower tube with large air inlets at its base stands in the center of the glass roof. The joint between the roof and the tower base is airtight. As hot air is lighter than cold air, it rises up the tower. Suction from the tower then draws in more hot air from the collector, and cold air comes in from the outer perimeter. The energy of the air flow is converted into mechanical energy by pressure-staged wind turbines at the base of the tower, and into electrical energy by electric generators coupled to the turbines.


It provides electricity 24 hours a day from solar energy alone. At night, heat-absorbing rocks or other heat sources in the "greenhouse" would slowly release the thermal energy built up during the day, maintaining the indoor-outdoor temperature differential. Then the solar chimney can operate around the clock, instead of depending on environmental factors, such as the wind needed for wind farms.

No fuel is needed. It needs no cooling water and is suitable in extreme drying regions. It is particularly reliable compared with other power plants. The materials concrete, glass and steel necessary for the building of solar chimney power stations are everywhere in sufficient quantities.

A prototype solar chimney was built and tested in Manzanares (south of Madrid), by Schlaich Bergermann and Partners. The solar chimney delivered power practically uninterrupted from July 1986 to February 1989 with a peak output of 50 kW. Its collector had a diameter of 787 feet, with surface area of 150919 square feet. The chimney was 33 feet in diameter and 640 feet tall. 

Efficiency increases with the height of the chimney, not linearly, but exponentially. For the power stations to generate electricity economically, not only large glass or plastic roof surfaces are necessary, but also a very high chimney. The height is needed simply from the fact that the updraft is proportional to the height, and also to make best use of the heat available.

The 1000 Meter (3281 feet) Solar Chimney in Mildura, Australia, will be the highest man-made structure on Earth, and can produce 200MW of electricity, providing power to 200,000 homes. The cost to build the tower is estimated at AUS$700 million (US$395 million), about 14 percent more than an equivalent coal-fired power station, and about 70 percent more per installed megawatt than a comparable wind farm. However, the investment will pay off in the long term because it is more reliable than wind farms in sun-rich Australia and requires no fuel. By building the solar chimney power plant, the Australian government target of producing 2% of energy from renewable sources by 2010 (9500 GigaWatt hours) could be met easily. The expected completion date is 2005.

Details of the solar Australian 200 MegaWatt chimney are as follows:

Location: Mildura, Australia
Type: Solar Tower power plant with steel-reinforced concrete tower and steel/glass solar air collector (alternatively with polymer glazing)
Features: The base of the tower will be between 557 to 656 feet. The chimney is a simple tube with wall thickness of 9.8 inches, diameter of 492 feet and a height of 3280 feet. The collector roof will be 16404 feet in diameter.
Power: Up to 500 Gigawatt hours per year
Company: Enviromission Ltd  - http://www.enviromission.com.au
Construction time: About 18-24 months
Expected completion date: 2005

Some estimates say that the cost of generating electricity from a solar chimney is more than from a gas turbine. Although fuel is not required, solar chimneys have a very high capital cost. The structure itself is massive and requires a lot of engineering expertise and materials to construct.  Would something like this be right for California?  Running a reliable, non-polluting power plant would add value to the electricity cost equations but how much remains to be seen.  I wonder if you painted a giant cat on the chimney, would it keep the birds away?