A solar tower is an environment-friendly way of generating power by exploiting the temperature differential between air at ground level and air at a significant elevation. One design slated to be built in Australia as early as 2006 is a kilometer tall and would produce as much energy as a small nuclear reactor. A proof-of-concept design in Spain is 195 meters tall and was able to produce as much as 50 kW of power.
At the base of a solar tower is a solar collector - a huge (~25,000 acres or 100 square kilometers) transparent circular skirt made of plastic that creates a greenhouse effect and heats the air trapped in the skirt. The solar tower is hollow, like a chimney, and extracts energy from the hot air rising rapidly to the top of the tower using turbines. The taller the tower, the more energy is extracted. The tower works 24 hours a day because the ground underneath the tower retains heat absorbed during the day and continues to release it at night.
The Australian solar tower is forecasted to cost about $500 million and would be the tallest man-made structure in the world, almost twice the size of Toronto's CN Tower. Its construction would be undertaken by the Melbourne-based EnviroMission Limited, with support from the Australian government. It is estimated that the tower would produce 200 megawatts, enough electricity to power 200,000 homes, and keep almost a million tons of greenhouse gas out of the atmosphere annually. A solar tower would be a massive landmark, visible from as far as 80 miles away. It requires a staff of only 15 technicians to operate.
The solar tower is perhaps the most impressive proposed alternative to fossil fuels or nuclear power. It would be an ideal stopgap measure to supply the human race with cheap power until we develop fusion power, improve on fission, find a way to deploy large networks of solar panels, or come up with some even better idea to supply ourselves with the power we crave.