Solar Updraft Power PDF Print E-mail
R-Energy Solutions For Africa's Electrification - Forms Of CSP Technology

 



Solar Updraft Tower, also known as Solar Chimney or Solar Aero Power Plant:

Unlike the CSP plants with reflecting mirrors, Solar Updraft Tower uses translucent (transperent) roof heat collector (greenhouse) to trap heat and warm up air inside the green house. Solar Updraft Tower uses warm air escaping a sun heated canopy trap to drive turbine to generate electricity, unlike reflecting-mirrors-based CSP plants which use superheated steam/fluid to drive turbine to make electricity. Updraft tower also operates with cloudy sky, as well as utilizes diffuse light, while reflecting-mirrors-based CSP plants can utilize only direct light.
With sun heat, air beneath a translucent roof of the mega greenhouseis warms up. The hot air mass drifts up the tower placed at the center of the roof while cold air from outside drift into the green house to occupy the space left. The hot air creates an updraft (i.e it drifts up) along the tower to escape the green house and in the process drives wind turbines placed inside the tower which in turn generates electricity.
To set up a solar Updraft power station basically three major components are required: - a large translucent canopy (green house) for solar heat trapping, a tower (chimney) at the center of the green and turbines.

The solar Updraft power station operates1 like a hydroelectric power plant, but it uses hot air instead of water. 

1Operational similarities with hydroelectric power plant:

·         Solar Updraft Tower power plant uses dynamic energy of up-drafting buoyant warm air. Hydroelectric power plants use the dynamic energy of falling water due its gravity.

·         Both use turbines in order to transform part of their fluid’s dynamic energy to rotational energy and through their geared electric generators to produce electric energy.

·         The efficiency of the of Solar Updraft Tower power plant is proportional to the solar chimney’s height, in the same way the efficiency of the hydroelectric power plant is proportional to the dam height.

Net energy payback is estimated to be 2-3 years.
Advantages: continuous electricity generation is possible: heat can be stored inside the greenhouse, to be used for warming the air later at night when there is no sunshine. Materials with high specific heat capacity are used for heat storage. Such materials as water can be filled in black tubes placed under the collector. The tubes radiate heat at night to heat up air and cause it to rise just like in the day time. This ensures operation during cooler days during rainy season, dependent upon the temperature differential between the air inside the translucent canopy and air at the top of the tower.

Even though this technology is simple, for it to be efficient it requires a large area of greenhouse and a very tall tower. 

Disadvantages: a solar updraft tower power station would uses a significant area of land if it were designed to generate as much electricity as is produced by modern power stations using conventional technology. but when looking at electricity output versus total size, they use less land than hydroelectric dams (including the size of the lake behind the dam) or coal plants (including the amount of land required for mining and excavation of the coal). While all power plants require land and have an environmental impact, the best locations for solar Updraft tower is the desert, arid sahel and savanna areas:- with plenty of land.