OK, LotR geeks, not those two towers (and not the 9/11 towers either) ... over the past couple of weeks I'd seen some "green" stories involving "towers", and thought that these two were interesting enough in their differences to pair up here.
Both of these came to my attention via the http://www.fastcoexist.com feed I follow on Facebook, and were sort of at the heart of that P.S. added to the Biodiesel post a week or so back. I didn't get any reader feedback on my queries there, and had these sitting around, so figured I'd pass along the info anyway (pretty much because *I* found them fascinating!).
The first of these is fairly low-tech/low-impact bamboo and netting construction that was computer-developed by an Italian design group, Architecture and Vision. It's called the WarkaWater, which
is a 9 m tall bamboo framework with a special fabric hanging inside capable to collect potable water from the air by condensation. The lightweight structure is designed with parametric computing, but can be built with local skills and materials by the village inhabitants.
This is intended for particular environmental niches - in the initial project, the mountainous rural regions of Ethiopia, where water is scarce, wells difficult to dig, and of questionable quality when obtained on the surface. Due to dramatic temperature differences between the night and day in these regions, there is a good deal of water condensation, and these towers are conceived to be able to effectively collect that on a daily basis. This will ultimately be a very "grass roots" project, as it takes 2-3 people about 10 days to build one, and each is likely to provide drinking water for 3-4 homes, making the construction of these a "village-level" venture, with as many as needed being built and utilized by the locals. More info here
In stark contrast to that is the proposed Solar Wind Downdraft Tower, which is HUGE and high-tech, yet (while being for the production of energy), uses evaporation as its key process. This is one of those freaky-to-wrap-your-head-around projects, as it is very simple in concept ... spray a mist across the opening at the top, the mist evaporates, cooling the air above the tower, which then sinks through the tower, gaining speed, and driving turbines at the bottom. Like the other system, this is pretty much environment-specific - you need a hot, dry location (I'm guessing Nevada, Utah, Arizona, New Mexico, and chunks of surrounding states might work), and is currently proposed for a site in the small border town of San Luis, AZ. Unlike the other tower, however, this is anything but "loving hands at home" construction, with the price tag coming in at around $1.5 billion to get it up and running.
Did I mention it is huge? The tower is projected to be 2,250 feet tall ... which would make it second only to the Burj Khalifa tower in Dubai for "world's tallest building" ... with a fairly substantial footprint (again, making it most plausible for empty desert areas) - but far less than a wind turbine field for equivalent output (which would require a "wind farm" stretching over 100,000 acres). Now, given the scope of this, one might say "yeah, it'll never get built", but the amount of energy it produces makes it tempting. Aside from producing the power of 156 square miles of wind turbines, it also would produce about the same amount of energy as the Hoover Dam ... while being self-supporting - taking only about 11% of the energy it produces to run its systems. The FastCompany piece notes:
The idea goes like this: Water is sprayed at the top, causing hot air to become heavy and fall through the tower. By the time it reaches the bottom, it's reaching speeds of up to 50 miles per hour, which is ideal for running the turbines. The advantage over standard solar and wind energy is the plant runs continuously, day and night. There are no intermittency issues from the sun failing to shine, and you don't need to dust off any solar panels to keep things going. As long as the air is warm enough (which is likely in Arizona), the tower will keep creating draft effects.
Needless to say, this last point is pretty attractive - you're not at the mercy of the weather, as long as it's warm in the desert. It also has the appeal of not damming a river, and being a localized eyesore (as opposed to mile after mile after mile of windmills). Obviously, there are serious "NIBY" issues with something sticking nearly a half mile into the sky, but there's a whole lot of "empty" out in the various desert locations where the Solar Wind Downdraft Tower is designed to work, so that is less likely to be a problem. This is certainly a system to keep an eye on to see if it will get built!
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