Recycling Initiative: Solar thermal power plants - Solar Chimney Power Plants

All three technologies described earlier can only use direct normal irradiance. However, another solar thermal power plant concept – the solar chimney power plant – converts global irradiance into electricity. Since chimneys are often associated negatively with exhaust gases, this concept is also known as the solar power tower plant, although it is totally different from the tower concepts described earlier. A solar chimney power plant has a high chimney (tower), with a height of up to 1000 metres, and this is surrounded by a large collector roof, up to 130 metres in diameter, that consists of glass or resistive plastic supported on a framework (see artist’s impression). Towards its centre, the roof curves upwards to join the chimney, creating a funnel.

The sun heats up the ground and the air underneath the collector roof, and the heated air follows the upward incline of the roof until it reaches the chimney. There, it flows at high speed through the chimney and drives wind generators at its bottom. The ground under the collector roof behaves as a storage medium, and can even heat up the air for a significant time after sunset. The efficiency of the solar chimney power plant is below 2%, and depends mainly on the height of the tower, and so these power plants can only be constructed on land which is very cheap or free. Such areas are usually situated in desert regions.

However, the whole power plant is not without other uses, as the outer area under the collector roof can also be utilized as a greenhouse for agricultural purposes. As with trough and tower plants, the minimum economical size of solar chimney power plants is also in the multi-megawatt range.



Electricity Generation Costs

Due to the poor part-load behaviour of solar thermal power, plants should be installed in regions with a minimum of around 2000 full-load hours. This is the case in regions with a direct normal irradiance of more than 2000 kWh/m2 or a global irradiance of more than 1800 kWh/m2. These irradiance values can be found in the earth’s sunbelt; however, thermal storage can increase the number of full-load hours significantly.

The specific system costs are between €2000/kW and €5000/kW depending on the system size, system concept and storage size. Hence, a 50 MWe solar thermal power plant will cost €100–250 million. At very good sites, today’s solar thermal power plants can generate electricity in the range of €0.15/kWh, and series production could soon bring down these costs below €0.10/kWh.

The potentials for solar thermal power plants are enormous: for instance, about 1% of the area of the Sahara desert covered with solar thermal power plants would theoretically be sufficient to meet the entire global electricity demand. Therefore, solar thermal power systems will hopefully play an important role in the world’s future electricity supply.