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A US company that aims to build giant 685m towers in deserts to capture renewable energy from the downdrafts within them has had its technology patented and is a year from breaking ground on its first project.
The towers Solar Wind Energy plans to build will be more than double the size of the Eiffel Tower and can be constructed in hot, dry, areas only.
Construction of the first tower will start next year and be complete by 2017 in San Luis, Arizona, after which the company will licence the technology to international partners around the world.
Ronald Pickett, president and chief executive of Solar Wind Energy Tower, said: “It’s like harnessing the hot air from a thunderstorm."
"The designed capacity is 1250MW. It will produce 1250MW/h during summer afternoons. Our business plan is to efficiently extract the maximum energy generated by the captured wind, with the least loss of power while compensating for the normal differentials in atmospheric conditions."
The towers, which could be grouped together like wind farms, will work by creating wind that travels down the inside of the tower at speeds of up to 70mph. This downdraft hits a base that is shaped like an upside-down funnel at the bottom, which diverts the wind through 25 tunnels with turbines in them. Each tunnel has a capacity of 50MW, said Pickett.
The downdraft is created by delivering a fine mist of water via a lattice injection system at the top of the tower that evaporates and cools hot air. This makes the air inside the tower denser and heavier than the warmer air outside, causing it to fall at an increasing rate.
The water is recaptured at the bottom of the tower and is pumped back to the top for use in the injection system. The pump system is powered by 18.2% of the energy from the turbines at the base of the tower. In suitable locations, vertical “wind vanes” may also be added to the outside of the tower to capture prevailing wind and produce supplemental power.
According to Pickett, the main energy gain is from the speed and pressure of the downdraft travelling through the tower. He said: “We have 20 years of weather data and software that makes the electrical output predictable. We can't make a scale model, but there is not one thing we have in this tower which isn’t proven by an algorithm. We’re now at the stage where we’re having definitive discussions with other partners around the world, including in the Middle East.”
Solar Wind Energy's towers will be made of reinforced concrete and be relatively simple to construct, Pickett said, compared to complex skyscrapers such as the 830m high Burj Khalifa in Dubai. The first tower is expected take 2.5 years to build, with concrete being poured at a rate of 9ft every other day.
Solar Wind Energy has partnered with Commonwealth Dynamics, a construction firm that constructs nuclear power station cooling towers, to design and build the tower. Pickett said: “The tallest cooling towers can be up to 850ft, it's just a matter of scaling up the build to our requirements.”
Height and diameter of the towers would be varied according to local conditions using software the firm has developed. The software uses local metrology data and applies it to the variables of the tower to predict energy production and the optimum design.
The idea of using giant towers to generate electricity from downdrafts was initially developed by the Technion University in Israel 25 years ago. But the scientific means to obtain the measurements required to create a predictable downdraft and build the towers have only become available during the last ten years, added Pickett.
According to Solar Wind Energy the first San Luis Tower has a design capacity on an hourly basis of up to 1250 megawatt hours, gross. Using a 60% capacity factor, the Tower’s potential hourly yield would be 600 megawatt hours from which approximately 18.5% will be used to power its operations, yielding approximately 500 megawatt hours available for sale to the power grid. Due to lower capacities during winter days, the average daily output for sale to the grid for the entire year is approximately 435 megawatt hours.