With Kyoto in the news and the search for non-polluting forms of energy intensifying, the time may be ripe for a whole new technology–and as it happens, there’s a company in Australia that’s got one all lined up.
It’s called the Solar Tower, and I confess that the real reason I wanted to write about it is that, much to my astonishment, I’d never heard of it before this week–although it was apparently announced several years ago.
It made the news this week because the company behind it, EnviroMission Ltd. in Melbourne, has just purchased a 10,100-hectare sheep ranch on which to build it. If that sounds like an awfully big plot of land just to build a tower on, well, it’s an awfully big tower: an astonishing 1,000 metres–a full kilometre–tall. Or, to put it another way (and a way that may alarm Canadians), twice as tall as the CN Tower in Toronto.
Despite its size, in some ways the proposed Solar Tower is a very simple device. Made out of reinforced high-strength concrete, it’s hollow in the middle, like a chimney, and surrounded by a solar collector–an enormous transparent skirt covering all of that former sheep ranch, turning it into a huge greenhouse. Air under the skirt is heated by the sun to a temperature 35 degrees Celsius hotter than the ambient temperature. Hot air rises, and the only place for it to go is up the chimney, at 15 metres per second, creating a strong, constant wind that spins 32 turbines to generate electricity–as much as 200 megawatts, enough for 200,000 typical Australian homes. Since peak usage of electricity is tied to air-conditioner use, and both that and the tower’s production peak on the hottest days, it’s even self-regulating.
The constancy of that wind is what makes the Solar Tower superior to traditional windmills, like the ones dotting the southwest corner of Saskatchewan: its turbines spin even when its dead calm outside. It also works when it’s overcast, and even at night, when the ground gives up the heat it stored during the day.
The Australian Solar Tower is a scaled-up version of a 200-metre-tall, 50-kilowatt prototype constructed in Manzanares, Spain, in 1982. Designed by German engineer Jörg Schlaich, it operated successfully for seven years.
EnviroMission isn’t saying exactly how much it will cost, but estimates range from $500 million to $750 million U.S. However, new innovations in engineering could bring that cost down, according to Roger Davey, chairman of EnviroMission, and rising fuel costs and the world-wide desire to reduce greenhouse gas emissions are also making the project look more appetizing. (Putting the Solar Tower into the energy grid would reduce greenhouse gas emissions by 750,000 tonnes annually.)
Schlaich’s engineering company, Schlaich Bergermann und Partner, commissioned a study that indicated electricity from solar chimneys should be just 20 percent more expensive than that from coal. That’s based on a gross interest rate of about 11 percent and a construction period of four years. Just reducing the interest rate to eight percent in that equation makes solar-tower electricity competitive today. It might be even more competitive in countries with lower wages for construction workers.
And there are other advantages: a solar tower is very ecologically friendly–since it’s made out of concrete and glass (in other words, stone and sand), it takes very few resources even to build. The construction cost is high, but construction also generates local jobs. And once they’re built, says S.A. Sherif, an engineering professor at the University of Florida and technical editor of the Solar Energy journal, solar towers “essentially produce energy for free.”
So how close are we to seeing a kilometre-tall Solar Tower in Australia? Well, EnviroMission originally said it would be completed this year. Now the company says construction won’t begin until 2006 at the earliest. Most analysts think that the fact it will take 10 years or more of operation before private investors would see a profit from the Solar Tower means that it will take some government investment to actually get the thing built.
But once it is built, if it works as advertised–and, given the laws of physics, it pretty much has to–it may be the start of a bumper crop of giant towers around the world.
Hey, how cool would one of those look down in southwest Saskatchewan?
