Company wins grant to develop airborne turbine

The  Advanced Research Projects Agency – Energy (ARPA- E) within the Department of Energy (DOE) has awarded California-based Makani Power, Inc. $3 million to continue development of an airborne wind turbine.

The Makani Airborne Wind Turbine

The Makani Airborne Wind Turbine (AWT) converts wind energy into grid quality, utility-scale electricity using tethered, high-performance wings outfitted with turbines, and promises to revolutionize the way energy is extracted from the wind. Like the tip of a conventional wind turbine blade, the wing flies crosswind in a circular pattern at many times the speed of the wind. Power is extracted by the wing-mounted turbines and transmitted to the ground through an electrically-conductive tether. Because the wing is not constrained to rotate around a hub, it can sweep a much larger section of the sky than a conventional wind turbine and fly at a higher altitude where the wind is both stronger and more consistent. These advantages result in a system that delivers twice the energy of a conventional turbine of equal power rating (60% capacity factor for class 4 wind sites).

The turbine’s tension-based design removes the necessity for a large tower and massive foundation, yielding a system that is less than 20% of the mass of a conventional turbine of equal capacity. Due to its low-wind performance, the turbine extends the developable terrestrial wind resource area by five times, to over 80% of the U.S. land surface, and promises to deliver energy at a cost 40% below that of conventional wind. Placing the turbines in the high-speed flow at the wing enables lightweight, direct-drive power generation and improves flight control through thrust and drag management. The Makani AWT can hover vertically to enable launching and landing and maintain elevation during lapses in wind or during turbulent conditions because the turbines may also be operated as propellers. The towerless design is well suited to offshore installations, allowing wind projects to be developed closer to demand centers, especially along the populous Eastern U.S. coast.

Grant Accelerates Technology Readiness

Since its inception in 2006, Makani has pioneered extended-duration tethered flight and continuous power generation during autonomous flight using small scale proof-of-concept prototypes. The ARPA-E grant, will help fund an 18-month R&D plan to demonstrate all operating modes including launch and land.

The ARPA-E selection process includes a rigorous review by an expert panel of the technical and commercial aspects of each submission. Makani was one of over 5,000 applicants to the first year’s solicitations and one of less than ten renewable energy generation technologies to receive the grant award.

Makani www.makanipower.com

Can an air leak give turbine rotors an efficiency boost?

An idea originally developed to increase lift in slow moving aircraft wings and simplify helicopter rotors may soon improve the efficiency of wind turbine rotors and possibly reduce their cost of manufacturing. This “circulation control” aerodynamic technology could let wind turbines produce significantly more power than current devices at the same wind speed, 30 to 40% more by some calculations.

Circulation control techniques blows compressed air from slots on the trailing edges of wings or hollow blades to change their aerodynamic properties. In aircraft, circulation-control wings improve lift, letting aircraft fly at much lower speeds, as well as take off and land in shorter distances. In helicopter rotor blades, the technique, also called “circulation control rotor”, simplifies the rotor and its controls, and produces more lift.

Research aimed at adapting circulation control technology to wind turbine blades will be conducted by a California-based PAX Streamline, in collaboration with the Georgia Institute of Technology. The two-year project will lead to construction of a demonstration pneumatic wind turbine with support from a $3 million grant from the Advanced Research Projects Agency-Energy (ARPA-E) the federal energy research and development organization.

“Our goal will be to make generation of electricity from wind turbines less expensive by eliminating the need for the complex blade shapes and mechanical control systems used in existing turbines,” said Robert J. Englar, principal research engineer at the Georgia Tech Research Institute (GTRI).

“Because these new blades would operate effectively at lower wind speeds, we could potentially open new geographic areas to wind turbine use. Together, these advances could significantly expand the generation of electricity from wind power in the United States.”

The ARPA-E project will apply the technique to controlling the aerodynamic properties of wind turbine blades, which now must be made in complicated shapes and controlled by complex control mechanisms to extract optimal power from the wind.

“The wind speed at which these turbines would begin operating will be much lower than with existing blades,” said Englar. “Location that wind maps have previously indicated would not be suitable locations for wind turbines may now be useful. The blown technology should also allow safe operation at higher wind speeds and in wind gusts that would cause existing turbines to be shut down to prevent damage.

“Because they would produce more aerodynamic force, torque, and power than comparable blades, these blown structures being developed by Georgia Tech and PAX could also allow a reduction in the size of the wind turbines.

“If you need a specific amount of wind force and torque to generate electricity, we could get that force and torque from a smaller blade area because we’d have more powerful lifting surfaces,” says Englar.

A major question awaiting study is how much energy will be required to produce the compressed air the blown blades need to operate. Preliminary studies done by Professor Lakshmi Sankar in Georgia Tech’s School of Aerospace Engineering suggest that wind turbines with the blown blades could produce 30 to 40% more power than conventional turbines at the same wind speed, even when the energy required to produce the compressed air is subtracted from the total energy production.

The new turbine blades will be developed at GTRI’s low-speed wind tunnel research facility located in Cobb County, north of Atlanta.

Officials of PAX Streamline see the circulation control technology as key to development of a new generation of turbines that could significantly lower the cost of producing electricity from the wind. “This is a significant validation of our established turbine R&D,” said PAX CEO John Webley. “With this grant, we can rapidly accelerate our research program and, within the next two years, deploy a prototype wind turbine which demonstrates our game-changing technology.”