This week, a small town near the US-Mexico border gave an unusual company the right to build a 2,250-foot (685 metre) tower on its land. That would make it the tallest structure in the United States.
The company, Solar Wind Energy Tower Inc, is only three years old. But the idea it's putting forward dates all the way back to the 1960s.
It's called an "energy tower": a massively tall, hollow, concrete structure situated in a warm, arid climate. The sun's rays super-heat the top of the tower, and a cool mist gets sprayed across. The water evaporates and the cool, heavy air is then sucked down into the base at speeds of up to 50 miles per hour. At the bottom, the whooshing gusts of air push through a circle of wind turbines—producing energy.
Solar Wind, which is based in Maryland, wants to start construction on the first major energy tower in the country, in San Luis, Arizona. It doesn't have funding for its energy tower outside of Yuma yet--that's the next step--and it plans to have construction underway by 2018. The town of 26,000 residents has also agreed to sell the company the water it needs to continually spray a fine mist over the 1,200-foot-wide (365 metre) top of the tower, which will nearly match the height of the Burj Khalifa. This mega-structure will sit on a 600-acre piece of desert near the Mexican border where the temperatures regularly reach 41C —perfect for the technology, which relies on hot, dry climates.
So, where does this fairly incredible-sounding idea come from? It turns out that the energy tower dates back to the 1960s, when an engineer names Dr. Philip Carlson floated the idea. In a December 1981 issue of Popular Mechanics, Carlson, then an engineer at Lockheed, describes how the idea came to him while working on a desalinisation plant in the 1960s:
We ran some calculations and found that, theoretically, we'd get out eight times the energy we put in to pump the water to the top of the chimney. But, in 1965, there didn't seem to be any need for new energy sources.
Carlson did patent the concept in 1975, but it seems the idea was tabled. Since then, two engineers named Professor Dan Zaslavsky and Dr. Rami Guetta from Technion-Israel Institute of Technology have resurrected the idea, studying it extensively and publishing a number of papers on the topic.
So, why isn't the American Southwest dotted with 2,000-foot-high energy towers? First of all, there are considerable challenges involved in actually building them—including not only funding the construction of such a huge tower, but also the cost of pumping water up to the top at a constant rate. Building Solar Wind's tower, in Arizona, will require $1.5 billion in capital, according to Businessweek.
It's also easy to imagine that communities aren't excited to welcome huge, industrial-looking towers that would loom over their homes. But as a San Luis city official told Forbes, it's also an economic driver and an opportunity for smaller, struggling cities:
In Arizona you do get a lot of dreamers who say, 'You could really do something with this.' With (Solar Wind Energy), they have already gotten permission and concurrence from federal agencies in Washington. They weren't starting with the Air Force, they weren't starting with BLM. They were starting at the top. It isn't a guarantee of success, but it is a lot more feasible than a lot of the other things I've seen.
The deal with San Luis no doubt hinges on the fact that the construction and upkeep of the tower would bring thousands of jobs to the area—not to mention producing 1,200 megawatt-hours of power in the hotted, driest months.
Still, there are plenty of questions about how their plan would work—starting with who's going to put up the $1.5 billion to build it. But Solar Wind doesn't seem to be letting that slow it down: beyond putting up a tower in San Luis, the company reportedly wants to licence its technology to developers all over the world. For now, winning approval from the small town is a huge step forward. [SMH; Businessweek; Forbes; Solar Wind Energy Tower]