Solar Updraft Towers: Variations and Research
I came across this interesting article in Renewable Energy World.com’s blog this morning. The concept is new to me, and I’m fascinated by it. It seems to be quite an elegant concept. It’s not terribly economic at this point in time, as the article itself says: Estimates for the cost of electricity produced range from €0.05 per kilowatt-hour (kWh) up to €0.25 [US $0.07 to 0.34 per kWh], depending on the cost of land and the financing scenario. However, it is carbon neutral and there is very little maintenance after the initial investment, (keeping the membrane repaired and the turbine/generator serviced and maintained.) I wasn’t very far into reading the article before I wondered: Why wouldn’t this work better using some portion of the top half of one of Buckminster Fuller’s Geodesic Domes? Go to http://www.renewableenergyworld.com/rea/news/story?id=53742 to read more about this concept. The article is too long to include all of it here.
Solar Updraft Towers: Variations and Research
by Tom Bosschaert
Rotterdam, the Netherlands [RenewableEnergyWorld.com]
Aerial Photo of Solar Updraft Tower
The idea of using solar radiation to generate air convection that can subsequently be converted to an energy source has been around since the start of the 20th century, when a Spanish Colonel called Isidoro Cabanyes proposed it in a scientific magazine. Solar Updraft towers, also called solar wind or solar chimney plants, provide a very simple method for renewable electricity generation, with a constant and reliable output. Other renewable energy sources such as wind turbines and solar arrays suffer from high diurnal and seasonal fluctuations, or unpredictable patterns of output.
Due to the large initial investment required, unfamiliarity with the system and the solar updraft tower’s relatively low capture efficiency, only one prototype was ever built, in the 1980’s in Spain. This prototype however, performed above and beyond expectations, and continued to operate for almost 7 years after its designed life span of 3.
The solar updraft tower has been left on the shelf due to its perceived low efficiency, which is to a large degree undeserved. Most studies on this elegant and simple renewable energy producer consider the land occupied by the tower and its collector as one of the largest resource inputs required for this process. However, Except Architecture & Consultancy is investigating the possibility of more creative applications of the system, which would combine the tower with other land uses.
The Classic Solar Updraft Tower Scenario
The small experimental solar updraft tower plant, built in Manzanares, Spain in 1982 by Schlaich Bergermann, can be considered the classic example of the system. The design calls for a large, unused plot of land to house a collector between 500 m and 10 km in diameter, with a centrally located chimney ranging from 100 m to 1 km in height. The collector is a transparent membrane suspended several meters off the ground, which can be made of glass or a strong transparent polymer. (See pilot plant image left, as well as lead image, above.)
Sunlight penetrates this membrane, and the solar radiation is converted to heat upon hitting the ground. The air underneath the membrane quickly increases in temperature due to the greenhouse effect and flows towards the chimney, which, through the stack effect, becomes the lowest point of pressure in the system. This continuous airflow spins a turbine located at the base of the chimney. The nighttime difference in temperature between the ground and the air allows this effect to continue. Thermal storage devices can be used to smooth out the differences in intensity between night and day temperature differentials. As with other solar technologies, a higher latitude placement translates into a lower energy output. (See Figure 1, below.)
Schematic of Solar Updraft Tower
Figure 1: Classic Solar Updraft Tower Diagram…
To read the rest of the article, go to: http://www.renewableenergyworld.com/rea/news/story?id=53742
Tags: Alternative Energy Source, Electricity, Solar Power, Wind Power
October 9th, 2008 at 2:48 pm
This is a neat idea.
I wonder how much energy you could get from simply enclosing an ACRE of land…. and making the whole thing out of plastic sheets like a greenhouse.