The Solar Wind Downdraft Tower
by Tina Casey
Man-made wind for the turbines of the future
Low cost wind power is extending its reach throughout the U.S., even in regions where wind conditions aren’t exactly optimal for powering a wind turbine. New transmission lines like the Grain Belt Express are helping to make that happen, and there could be a third option on the horizon if all goes well for Clean Wind Energy Tower, Inc. The company has developed an energy efficient way to generate wind in a steady, reliable stream, and the technology is promising enough to catch the eye of ARPA-E, the US Energy Department’s cutting-edge research funding arm.
Low cost wind power from man-made wind
Clean Wind calls its technology the “Solar Wind Downdraft Tower,” and that pretty much describes what it’s all about: a hybrid system that harnesses solar energy to create wind. The infrastructure basically consists of a large cylindrical tower in which a fairly powerful downdraft is created when water meets hot, dry air.
To heat the air in the tower, the system relies on ambient energy from the sun. The water is introduced as a fine mist across the top of the tower. As it evaporates, the air becomes cooler and denser, and this air falls through the tower at a pretty good clip, reaching speeds in excess of 50 mph. At the bottom of the tower, the wind is diverted into tunnels in which the wind turbines are located.
Depending on the prevailing wind conditions in any particular region, the company also anticipates outfitting the tower with vertical wind vanes that capture additional wind energy.
You’ll notice that there are a couple of catches, namely that the basic technology is best suited for regions where ambient temperature and water supply are sufficient, but that still accounts for a pretty good chunk of the U.S. With the aforementioned wind vanes included, the system’s cost effectiveness could span a wider area.
Making wind without using energy
In case you’re wondering how that water gets to the top of a tower without using energy, it doesn’t. The water is pumped, but the system generates enough wind energy to power its own operations, with plenty left over of course.
Here’s what the company is looking at in terms of the system’s capacity:
“…As currently designed, we anticipate that each Downdraft Tower will be capable of generating, on an hourly basis, up to 2,500 megawatt hours, gross, of which approximately 1/3 will be used to power its operations. From normal to ideal circumstances the Tower should have a potential hourly yield of 1,100 to 1,500 megawatt hours available for sale to the power grid.”
From downdraft towers to silos
Obviously, Clean Wind is banking on bigness, but you can see the same basic concept at work at the other end of the scale. One example is a system for small and medium-sized farmers to generate low cost wind power by converting their existing silos to create a steady, compressed air flow strong enough to power a small wind turbine. Not for nothing, but the silo project is being partly funded by a U.S. Department of Agriculture grant.
In that regard, it’s worth noting that the developer of the technology, an Air Force veteran and Arkansas native, was partly inspired by a desire to help his fellow Arkansans create a sustainable rural economy, enabling small communities to remain viable.
Meanwhile, Clean Wind Energy Tower is hoping for some big love from the Department of Energy. The company was selected as a semi-finalist for the the 2012 Advanced Research Projects - Energy (ARPA-E) Innovation Summit , which features a new $150 million funding opportunity for breakthrough technologies.