A solar updraft tower is nothing but a power plant that makes use of two natural sources of energy, namely wind energy and solar energy, to generate electricity. The technology behind its working is still in its prototype or experimental stage, with plans to build towers as tall as 3000 feet or more, to harness wind power and energy of the sun. The concept of a solar updraft tower first came up in 1903. The tower makes use of the physical phenomenon of air flow due to convection and the greenhouse effect.
Does the energy generating capacity of a solar updraft tower depend on the height of the tower alone? Not exactly, because the area of the collector region at the base of the chimney or tower, also counts; the greater the collector area, the higher the amount of electricity generated. Talking about towers so tall, one might wonder what are such towers made of. Well, the basic structure is made using reinforced concrete. Since the tower makes use of the greenhouse effect to heat up the air, a part of the collector area is surrounded by glass, which captures heat. Here we shall learn more about a solar updraft tower, how it works and its benefits over conventional power plants.
The solar updraft tower works on a very simple process of air flow due to convection currents. The base of the tower or the collector region, is made of transparent, clear glass. Sunlight penetrates through the glass and on hitting the ground, gets converted to heat energy. The heat generated by the rays of the sun hitting the ground, causes the air surrounding the base, to get heated up as well. We know that hot air is denser than cold air and so the air in the collector region, which is at a high temperature, rises up through the tower, causing a low pressure to develop in the collector region. Since air flows towards a region of low pressure, air from outside rushes into the collector, causing the turbines on its path to rotate. The speed with which the turbines rotate is determined by the speed with which the hot air rises up the tower, which in turn is directly proportional to the amount of solar radiation entering the collector region.
A solar updraft tower functions not only during the day, but also at night; the only difference being that after sunset, the air in the collector is heated indirectly using heat released from preheated water. Containers filled with water are placed inside the collector, which serve as a "storehouse of energy". The water in these containers gets heated up as a result of being exposed to solar radiation throughout the day, and at night, this accumulated heat is released to power the solar updraft tower. Note that larger the collector area, more will be the volume of air contained in it, and so when this air rises up, more volume of air shall flow into the collector, making the turbines turn more rapidly.
The solar updraft tower has many advantages and these are mentioned as under.
- It is relatively easier to build a solar updraft tower as compared to a thermal or nuclear power plant.
- It is economical due to lower installation and running costs.
- Unlike a nuclear power plant, where there is a danger of explosion, a solar power plant, such as an updraft tower, is relatively safe for the people living in the area next to the tower.
- The simplicity of the structure makes it easy to install even in the developing and under-developed countries, where advanced technology and infrastructure is not available.
- Unlike a solar cell that functions only when exposed to a particular intensity of light, a solar updraft tower works effectively even in the absence of direct sunlight i.e., when the weather is cloudy.
In addition to the many advantages, the solar updraft tower has some drawbacks as well. One of the major drawbacks is that it requires a very large area to build one. Secondly, in its present form, it is not as efficient as other conventional power plants. However, these drawbacks can be overcome, to some extent, by utilizing deserts and wastelands for the purpose, and installing these towers in areas that experience extremes of temperature and very little rainfall.
The first prototype of the solar updraft tower was built in Spain, near the capital city of Madrid, in 1982. The world's tallest such tower is slated to rise to an astounding height of 2600 feet and will be built in Arizona in the U.S. by an Australian company, EnviroMission. When working to its full capacity, it would have the potential to "light up"around 200,000 homes!