A new breed of solar tower may soon be sprouting up in Namibia, providing the nation with a carbon-free source of electricity and food during the day and night. At one and a half kilometers tall and 280 meters wide, these massive solar updraft towers could potentially produce 400MW of energy each – enough to power Windhoek, the nation’s capital. Proposed by intellectual property company Hahn & Hahn, the towers generate energy by forcing heated air through a shaft lined with wind turbines. Additionally, the base of each tower will function as a 37 square km greenhouse where crops can be grown.
Solar updraft towers are an oft-overlooked source of alternative energy, although they do require a great expanse of space and copious amounts of sunlight. Theo von Backström from the Department of Mechanical Engineering at South Africa’s Stellenbosch University states: “One of the main reasons why commercial solar chimney power plants have not been built that they have to be very large to be economically viable”. Fortunately Namibia’s arid desert region provides plenty of space for such a generator, and the country sees around 300 days of sunshine per year.
Solar updraft towers generate energy by using sunlight to heat the air within a vast transparent greenhouse situated at the base of the chimney. As the hot air rises, it is funneled into the reinforced concrete chimney, driving a series of wind turbines which in turn generate energy.
The structure’s greenhouse base provides the perfect environment for growing crops, which actually allow the plant to produce energy after the sun has set. The water used for crops is heated during the day and transfers this energy to the tower at night. Once the towers are constructed they require very little maintenance, and Namibia has agreed to finance half of the costs of the $780,000 pre-feasibility report.
We’d love to see the towers incorporate a Seawater Greenhouse and produce their own water as well!
+ Hahn & Hahn inc
Via Pruned and SciDev
Tip via Ryan Herbert
I can see the potential in this concept, but from a capital standpoint, it seems unfeasible. Simply, the resource construction and maintenance cost is unrealistic for the proposed design with such limited output. If one could adapt this to a multistory dome structure that uses a closed cycle convector with habitation also provided around the core, it may be feasible to create a self-supporting village. The lowest story could be used for sewage treatment via algae aquaculture. The second and higher stories could grow food. The rising water vapor could be collected and redistributed for drinking and crop irrigation. The falling condensation would create a downdraft at the core with updraft from the green houses toward the exterior of the structure. PV technology could be added, also to boost energy production. The core could also house a ring of gravity batteries for storage. This way, rising and falling air currents generate power within the structure and PV adds another electrical component. Meanwhile, you're also providing housing and food, justifying the investment, creating a self-sufficient community.
@uiteioi Thanks for the thoughtful comments! The prime advantage of using the open pit is the pneumatic tubes aren't freestanding. To me, this represents a significant cost reduction. The waste heat from the condenser has to go somewhere, why vent it to the atmosphere when you can use it to drive an air mass in a pneumatic tube. The Pit Power Tower design has heliostat fields on both sides of the pit and so you need two receivers. I'm unclear on what you mean by sub-optimal heliostat-receiver alignments. The advantage of using the open pit is the "stadium seating" which removes the "line of sight" blocking experienced by outer heliostats in a field on a flat surface.
@gwaz, "Low-grade exhaust heat from the condenser in the solar power block is collected and released into the bottom of the Pneumatic Tubes" You absolutely need to understand the theory behind energy conversion efficiency, in particular the Carnot cycle, to be able to evaluate the efficiency of thermal power plants, solar or not. If you reuse exhaust heat from the condenser it means that the condenser is not cooling the condensed fluid as much as it could and therefore reduces the energy efficiency (Carnot cycle) of the first stage (i.e. the solar power block). This second stage is therefore counter productive and a better design with a single solar stage would produce more power for less capital expenditure. Also in the proposed design there are many receivers that might contribute to lower heat grade at the receiver vs a single high temperature receiver. Lower grade heat also reduces conversion efficiency per the same Carnot cycle. A single receiver design would therefore allow for better efficiencies at lower capital costs. You also need to look at losses from suboptimal heliostat-receivers alignment resulting in further losses. There are good reasons why solar tower power plants have a single receiver providing the best solar to electricity energy conversion efficiency in the industry. The only advantage I can see from reusing mine pits is that the accumulated water at the bottom might be used to improve condenser efficiency reducing capital expenditures vs an air-condenser and improving energy conversion efficiency per the same Carnot cycle.
Take a look at the "Pit Power Tower" concept. It suggests laying the tube down in an open pit mine, rather than having it freestanding. This could seriously reduce the structural costs. The Pit Power Tower also integrates a Solar Power Tower with the Aero-electric tower in this article. http://www.altenergymag.com/emagazine.php?issue_number=09.02.01&article=gwiazda * As a matter of disclosure: the Pit Power Tower is my concept ~ :)
I think it is impossible to assess renewable technologies without any capital cost figure. A durable 1.5 km high tower could cost over one billion dollars to build requiring enormous amounts of cement that requires an enormous amount of energy to produce. The greenhouse itself, considering its very large surface could cost billions of dollars. All this to generate only 400 MW could be considerably more expensive than other solar technologies. Also don't count on growing crops under high temperature air and little, if any, water. The only advantage of this technology is its natural ability to store thermal energy for electricity production at night. The $1 Million cost for the study sounds like third-world reap-off to me, nothing less. They need a study of less than $10000 to figure out the cost per peak watt produced. If this is above $3 per watt, or $1.2 Billion for the 400 MW, drop it. Read wikipedia article "Solar updraft tower" for more information about the possible (high) cost of these designs.
I think this a a great idea but to double as a green house idk if it will work having a warm breeze constantly will dry out the plants and watering them will do nothing but cool down the air your trying to heat up so its a double edge sword
I think this is completely unrealistic—not necessarily from a technological standpoint, but from basic economic reality. This would be a mega-project of enormous cost. For who? Namibia? I'm not saying they don't deserve it or need a reliable source of energy, They do. But what organization is in a financial position to fund something of this magnitude with absolutely no assurance or even prospect for a return? Just getting basic building materials to the area would be prohibitive. And then there's the question of the electricity you would need just to do any sort of construction. Housing for workers, etc., etc. IF, something like this is going to be built, it's going to be built in a very rich nation first. United Arab Emirates, I'm looking at you. Interested?
~1M is just for the pre-feasibility report, I only wish that was for the whole project. That video Chublez linked to laid out a solar tower built in Spain in 1982 as a pilot project to test the idea. It consistently generated between 30 and 50 MW. Currently there is a project in Australia to install a 200 MW solar tower, they plan to open in 2012. Really cool idea, if you have lots of extra desert space, it seems to make sense. There are, of course, going to be ecosystem consequences (diversion of wildlife, for example), but you get those kind of trade offs with most renewable energy. The alternative, however, is more coal, and we can\\\'t have that! Aaron fireignblog.com
This is amazing, it's the first time I've seen it, but it just makes sense to me. At a cost of about $1M USD you get an unmanned power plant producing 3000MW of power? Why wouldn't you want to produce these? Well ok, tornadoes may be a problem, but I think it's just too simple and cost effective of an idea to ignore. I'm all for it. Brian http://www.total-solar-solutions.com
What pray tell can one grow in a greenhouse in a the desert as a matter of interest, seems like it would be crazy hot?
There's other benefits as well. About 10-15 years ago, I saw this being proposed for the US Gulf Coast areas. The day to day benefit of this would be to use brackis/salt water around the base and collect condensation from the cooling rising air to provide a fairly significant source of fresh water for the area. The primary benefit of the proposal though was to defend the area from Hurricanes (such as TX/LA is looking at now. By reducing the amount of warm air trapped by inversion and harvesting the energy that is stored there, the high energy areas that Hurricanes feed on and trend toward would be minimized and thus reduce the chance of landfalls around these towers. And if landfalls did occur, they would be of lower power as the hurricanes would be less able to build in strength in the wamer water closer to the costline as that energy would already have been harvested/dissapted. But yes, the primary problem is construction - these structures promise to be difficult and expensive to build.
great idea - but at more than twice as high as the worlds tallest manmade structure i\'m not sure who and how this will get built??