Solar chimneys, also known as solar towers, have been around since the 1980s and work by converting the sun's power into usable energy. Despite their name, solar chimneys don't emit smoke or noxious fumes like traditional chimneys, but only eject hot air, which is harmless to the environment.
A demonstration solar chimney was constructed in a remote area of Spain during the 1980s. The chimney successfully produced a significant amount of thermal energy, but stopped being used in 1989 after it was damaged in a storm. Repair work was not carried out due to the huge expense of doing so. However, with the increase in fuel prices since the start of the 21st century, viable sources of alternative energy, including solar chimneys, are being investigated again.
Solar chimneys work on a basic principle of thermal heating. As sunlight passes through glass surfaces, such as those found on a greenhouse, the light is transformed into heat and trapped behind the glass. This is most evident when you get into a car on a sunny day to find the interior is scorching hot, due to the sun rays that have shone through the window. The temperature of the car's interior has risen to a significantly higher level than the air temperature. This is one of the principles by which solar chimneys operate.
The second principle governing the working of a solar chimney is the fact that hot air rises. Solar chimneys are built in a similar fashion to greenhouses, with most of the surface area covered by panes of glass. At the centre of the greenhouse, however, is a tall solar chimney, which is the only route through which hot air can escape from the greenhouse. The greater the height of the chimney, the cooler the air will be at the peak of the chimney. The process of air rising through the chimney creates a current of thermal energy, which can be transformed into electricity by use of turbines.
Due to how they work, solar chimneys can't be built anywhere. They are usually vast structures, so they can only be built on areas of wide open land. Depending on the area, such land can be expensive to purchase, which may limit the likelihood of solar chimneys becoming widespread. Expense will also increase if infrastructure, such as transmission lines, needs to be built if the solar chimneys are to built in barren areas such as deserts.