In Yuma, nestled at the intersection of California, Arizona and Mexico, you’ll find a community that receives more sunshine than any other in the United States. It’s here that daylight hours linger around, on average, for 11 hours, with cloudless days being the norm 90 percent of the time. And, it’s around here, at a site in the nearby town of San Luis, Ariz. that the region’s nearly year-round arid climate may someday be harnessed to help produce clean energy in such abundance, that it’ll rival traditional power plants.
The power generator that Maryland-based Solar Wind Energy hopes to erect is as massive as it is ambitious. From afar, the Solar Wind Tower would look something like a colossal chimney stack mounted atop a ring of wind turbines. It’ll require 2.5 billion gallons of water and, at a height of 2,250 feet, would be the nation’s tallest tower. All this is necessary, however, to put into motion a process that has the potential to generate an electrical output of about 435 megawatts
hours hourly per day. Enough, they say, to provide power to as many as one million residents.
The idea for such a structure has been kicked around for decades, with Phillip Carlson, a scientist at Lockheed Aircraft Corporation, being the first patent the technology back in 1975. Designed to generate what’s known as downdraft, water is first pumped to the top, where it is sprayed as a fine mist. As the air within the tower cools and sinks, the draft is funneled into a series of wind tunnels with enough force to turn the wind turbines housed inside. Water captured at the bottom is then pumped back to the top to keep the cycle continuous. In principle, the system would be entirely self-powered, operating throughout the daytime as well as the evening, though efficiency dips as the outside temperature drops.
As promising as it sounds on paper, the concept has yet to amount to anything that even resembles a working prototype. And there’s good reason for that. To demonstrate viability, the tower needs to be about a least kilometer high. Generally, you’d be hard pressed to find investors who’d be interested in a project that’s not only unproven, but also involves the seemingly impossible task of constructing something almost twice the height of the Empire State Building.
“Even when you did the math and it shows that it simply works, the problem for the longest time has been not having the construction techniques to build structures that tall,” Solar Wind Energy chief executive Ronald Pickett explains. “But since then, the construction industry has made great strides in figuring out how to pump concrete and other constructions material that high.”
Convinced that the science was sound, Pickett and his colleagues started the firm with the aim of first putting forth a vision of how the technology would work on a broad scale. Part of this entailed identifying a number of sites in hot, desert regions such as Saudi Arabia and Chile, where the tower would be most feasible (at least theoretically). He’s even put together sophisticated computer models showing that in certain environments, like southern Arizona, a tower could produce as much as 1,250 megawatt hours on sunny days. And while the tower would generate less power in the winter (as little as 75 megawatt hours actually), he points out that this also happens to be the time of year where electricity usage tends to be at its lowest with air conditioners being shut off.
For the Arizona project, he’s worked out a development rights agreement with the city of San Luis to break ground on construction on 600 acres of land. The deal also includes the rights to acquire the necessary water, most of which will be recycled, from a local utility. Any amount that needs to be made up will come from surrounding ground water that Pickett says eventually makes its way back to the source.
Compared to other green energy technologies, such as solar power plants, Pickett contends that downdraft energy towers, at an optimal location, would produce electricity at about a third of the cost. The claim comes from an internal long-term assessment of a possible location in the Middle East that showed the possibility for consumer rates as low as $0.05 per kilowatt hour.
“We are not competitors to solar,” he adds. “But where our technology would work, it would be foolish to put a solar plant next to us.”
However, observers in the industry who’ve followed the Solar Wind Tower project and other similar efforts aren’t quite convinced. In an editorial published on CleanTechnica, Mike Bernard, a senior fellow at the non-profit Energy and Policy Institute, pointed to a number of challenges that he thinks makes it unlikely that the technology will deliver on the purported benefits. Among them were unaccounted maintenance costs and the possibility of lower-than-expected net electrical outputs, due primarily to the energy-intensive process of preparing and pumping the water vertically across long distances.
For instance, while Pickett maintains that the pumping mechanism will only require 11 percent of the energy produced, Bernard argues that “laminar turbulence” during fluid flow often leads to energy losses that end up being “much higher in reality than models and simulations account for.”
“This means that pumping water would likely take a lot more than 50 percent of the energy produced,” he writes. So ultimately, “they never get the energy out that calculations suggest that they will.”
Still, whether we get see if these estimates pan out or not hinges on the company following through on an arrangement with National Standard Finance, an infrastructure fund that agreed to cover 100 percent of the project’s $1.5 billion construction and equipment costs, given that certain obligations are met. Under these terms, Solar Wind Energy will lease back the station over 20 years, starting in 2018, when the tower of power is slated to begin feeding the local grid.