Solar Updraft Towers

The chimney effect of tall towers generates an updraft because the atmospheric pressure is higher at the bottom of the chimney and lower at the top. Therefore, the heavier colder air from outside of the chimney pushes the lighter warm air upward inside the chimney. Static home cooling systems utilize this effect to pull the cold air into homes from underground ducts during the summer. On the other hand, in the winter, this chimney effect can be harmful because it sucks cold air into the building and thereby increases the heating load on high rise buildings. (The method of eliminating such chimney effects is described in Chapter 2, Section 2.3.2.)

In solar towers, thermal storage can be provided by covering the ground with heat-absorbing surfaces so that power generation continues at night. In the case of this design, both the investment cost (about $30/m2) and the solar energy collection efficiency (about 5%) are low, while the energy payback period is expected to be 3-5 years.

The solar updraft tower is illustrated in Figure 1.37. It is a solar energy converter that converts solar-based thermal energy into aerodynamic energy (wind). In this system, air is heated under a circular greenhouse-like canopy. The roof of this canopy slopes upward from the perimeter toward the center, where the tower stands. Under the canopy, the Sun heats the air, which rises up the tower and generates electricity by driving an array of turbine generators.

This low-tech solar energy collector concept is over 100 years old. The Spanish Colonel Isidoro Cabanyes first proposed it in 1903, but the first patent for this design was applied for by Robert E. Lucier in 1975. The first 50 kW working model was built in 1982 in Ciudad Real, south of Madrid, Spain.

This project was funded by the German government. The chimney of this model had a 10 m (33 ft) diameter and was 195 m (640 ft) tall, whereas the diameter of the canopy was 244 m (800 ft) in diameter (about 11 acres, or 46,000 m2, in area). This prototype operated for 9 yr and reached a maximum production of 50 kW.

Today, much larger installations (50-200 mW) are planned in Australia, China, and the American Southwest. This year, construction will start on the world's first commercial plant in Australia. The 2 mi diameter canopy of this 50 mW power station at Tapio will be 2.4 m (8 ft) tall at the perimeter and will rise to 15 m (50 ft) at the center near the tower. The tower will be 79 m (260 ft) in diameter and 488 m (1,600 ft) in height. It is anticipated that this power plant will meet the electricity needs of 100,000 homes. The government-financed plant is expected to cost $75 million.

Another plant in China, designed by EnviroMission, will consist of a 38 km2 canopy and a 1 km (0.62 mi) tall tower to provide 200,000 homes with electricity. The 200 mW power plant will abate about 1 million tons of greenhouse gases and will cost some $800 million.

Getting Started With Solar

Getting Started With Solar

Do we really want the one thing that gives us its resources unconditionally to suffer even more than it is suffering now? Nature, is a part of our being from the earliest human days. We respect Nature and it gives us its bounty, but in the recent past greedy money hungry corporations have made us all so destructive, so wasteful.

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    How does atmospheric pressure affect the efficiency of solar updraft tower?
    2 years ago
  • juliane
    How the number of water tanks effect the energy put out of a solar updraft tower?
    8 months ago

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