Maybe you’ve heard of a solar updraft tower, a tall, hollow cylindrical tower where sunlight heats the air at the base of the tower and creates a chimney effect, causing air to rapidly shoot upward and exit the top. Wind turbines placed at the bottom convert wind energy to electricity.
Image credit: Kilohn Limahn (Wikimedia Commons)
Although the concept was first proposed over a century ago, it wasn’t until the early 1980s that a prototype was built near Manzanares, Spain. That experiment came to halt in 1989 when the guy wires failed and strong winds toppled the tower. Since then, a handful of experimental solar updraft towers have been built, but none seem to hold much promise as a significant player in renewable energy. Efficiency is a function of tower height, and increasing height causes more stability issues and higher manufacturing costs. That’s probably why we don’t see solar updraft towers all over the planet.
Introducing the Solar Downdraft Tower
While the above design has warm air rising through the tower, engineers at Solar Wind Energy Tower have turned the concept inside-out, as it were, creating a tower that causes cool air to move down through the tower. Here’s a video describing its operation:
Video courtesy of Solar Wind Energy Tower
The First of Its Kind
The company will begin building its first commercial Solar Wind Energy Tower (SWET) near San Luis, Arizona. The site was chosen after two years of evaluating the conditions at various locations. The tower’s dimensions are custom-tailored to the site and its microclimate. The company is not yet revealing the dimensions of this tower, but they expect it to produce about 18 megawatts on average. The project was approved on April 23, 2014. No word yet on a tentative completion date.
Patented Technology
Whether the tower itself proves to be cost-effective, reliable, and durable remains to be seen, but the project includes patented technology that could potentially be used in other areas of renewable energy production. For example, each wind tunnel at the base of the tower includes three turbines in series, as shown below. The turbines don’t generate electricity directly - they convert wind power to hydraulic power. The hydraulic to electric converters (HECs) operate most efficiently when there is a large pressure differential. A computer system turns HECs on or off depending on hydraulic pressure caused by varying wind conditions. The system ensures optimal pressure for the HECs that are operating, as opposed to giving a little pressure to all HECs.
Image: Solar Wind Energy Tower US patent application US 8120191 B1
I’ve seen wave systems that convert wave power to hydraulic power, which is then used either to generate electricity or to desalinate seawater through a reverse-osmosis unit. It’s possible that this hydraulic control system could be used in that application as well.
Show Me the Results
I have to say I’m pretty skeptical about the concept itself, even though the design may eventually produce some interesting spin-off technology. Although the company claims that the tower recovers the majority of the water that’s used, it still seems wasteful to use energy to pump that water to the top of the tower rather than using the natural convection of an updraft tower. Granted, the SWET has a much smaller footprint than an updraft tower since large solar collectors aren’t needed, so it could prove to be a better design overall. I’ll check back in a couple of years to see how well it’s producing power. Until the SWET proves itself, I’ll remain a Doubting Thomas.