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High-flying turbine produces more power

Thu, 05/15/2014 - 7:40am
Rob Matheson, MIT News Office

The Buoyant Air Turbine (or BAT), developed by Altaeros Energies, uses an inflatable shell to float 1,000 to 2,000 ft above ground, where winds blow five to eight times stronger, and more consistently, than winds at tower level. Image: Altaeros EnergiesFor Altaeros Energies, a startup launched out of Massachusetts Institute of Technology (MIT), the sky’s the limit when it comes to wind power.

Founded by alumni Ben Glass and Adam Rein, Altaeros has developed the world’s first commercial airborne wind turbine, which uses a helium-filled shell to float as high as a skyscraper and capture the stronger, steadier winds available at that altitude.

Proven to produce double the energy of similarly sized tower-mounted turbines, the system, called Buoyant Air Turbine (or BAT), is now readying for commercial deployment in rural Alaska.   

Surrounded by a circular, 35-ft-long inflatable shell made of the same heavy-duty fabric used in blimps and sails, the BAT hovers 1,000 to 2,000 ft above ground, where winds blow five to eight times stronger, as well as more consistently, than winds at tower level (roughly 100 to 300 ft).

Three tethers connect the BAT to a rotating ground station, automatically adjusting its altitude to obtain the strongest possible winds. Power generated by the turbine travels down one of the tethers to the ground station before being passed along to microgrids.

“Think of it as a reverse crane,” says Glass, who invented the core BAT technology. “A crane has a nice stationary component, and an upper platform that rotates in order to suspend things down. We’re doing the same thing, but suspending things up.”

Next year, the BAT will test its ability to power microgrids at a site south of Fairbanks, Alaska, in an 18-month trial funded by the Alaska Energy Authority. People in rural Alaska rely on gas and diesel generators for power, paying upward of $1/kWhr for electricity. The BAT, which has a capacity of 30 kW, aims to drop that kilowatt-hour cost down to roughly 18 cents, the co-founders say.

But despite its efficiency, the BAT is not designed to replace conventional tower-mounted turbines, Rein says. Instead, its purpose is to bring wind power to remote, off-grid areas where towers aren’t practically or economically feasible.

Conventional turbine construction, for instance, requires tons of concrete and the use of cranes, which can be difficult to maneuver around certain sites. The modular BAT, Rein says, packs into two midsize shipping containers for transport “and can just be inflated out and self-lift into the air for installation.”

Target sites include areas where large diesel generators provide power—such as military bases and industrial sites—as well as island and rural communities in Hawaii, northern Canada, India, Brazil and parts of Australia. The BAT could also provide power to places blacked out by natural disasters, as well as at amusement parks, festivals and sports venues.

“It’s really about expanding wind energy to all those places on the fringes where it doesn’t really work today, and expanding the amount of wind power that’s able to be deployed globally,” Rein says.

Aerostat innovation
Much of the BAT’s innovation lies in its complete autonomy, Glass says. Such aerostats usually require full-time ground crews to deploy, land, and adjust. But the BAT automatically adjusts to optimal wind speeds and self-docks in case of emergencies, eliminating the need for manual labor.

“When winds are low, typically we want to go as high as possible—because, generally speaking, the higher you are, the stronger the winds,” Glass explains. “But if winds get too high, above the maximum [capacity] of the turbine, there’s no reason to operate in those very strong winds, so we can bring it down, where it operates at rated power, but is not subject to very strong winds.”

To guide its positioning, the BAT is equipped with anemometers installed in the airborne unit and ground station. When the anemometers detect optimal wind speed, a custom algorithm adjusts the system’s tethers to extend or contract, while the base rotates into the wind. In rare instances, when wind conditions are optimal on the ground, the system will self-dock, but continue rotating.

Designed to handle winds of more than 100 mph, the system is unaffected by rain or snow. However, should the weather get too inclement, or should a tether break loose, the BAT’s secondary grounding tether—which protects the system’s electronics from lightning strikes—will self-dock.

Because the BAT is an advanced aerostat platform, Glass says, customers can use it to lift additional “payloads,” such as weather monitoring and surveillance equipment.

But perhaps the most logical added “payload,” Glass says, is Wi-Fi technology: “If you have a remote village, for instance,” he says, “you can put a Wi-Fi unit up, outside the village, and you’re much higher than you’d get with a traditional tower. That would allow you to cover six to eight times the area you would with a tower.”

Source: Massachusetts Institute of Technology

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