FAQ

Makani Power is a Bay Area based company that is developing a revolutionary energy generation technology to access the vast, untapped wind resources at altitude. Makani Power is developing a utility scale Airborne Wind Turbine for clean, renewable energy generation.

Makani Power, Inc. was founded in 2006 by Corwin Hardham, Don Montague and Saul Griffith, for the purpose of broadening the world’s renewable energy supply. Initial funding came from Google.org as part of their RE<C program.

Makani uses on-wing generation for enhanced control, safety, operability in a wider range of conditions and simplified launching and landing. The rotors on the wing can be used either as propellers to generate thrust or as turbines to generate energy. This enables the AWT to remain in the air (consuming a small amount of power) when wind speed is low and enables autonomous launching and landing. On-demand thrust also provides additional control in turbulent conditions where the wind speed and direction may change drastically.

The AWT performs better at low wind speeds than traditional wind turbines, and because low wind speeds occur more often, the system operates at its rated power more consistently than a conventional wind turbine. Improved low wind performance enables the AWT to produce about twice the power of a traditional wind turbine of the same size. For information about our power curve, see this post by our Chief Engineer.

The short answer is: The wind keeps the wing aloft. The wing harvests kinetic energy by creating lift and gaining energy, which would make it accelerate. However, the onboard turbines are dragging the volume of air they interact with along with them, generating power and keeping the wing at a constant velocity (they are keeping the wing from accelerating). For more about lift, drag and energy, see our Chief Engineer’s explanation here.

The operational area of an AWT is a hemisphere with the tether mount located in the center and a radius the length of the tether. In a farm, AWTs will be spaced a distance of one tether length apart in a hexagonal pattern.

The cost of conventional wind power is highly variable because it is site-dependent. Due to the low incidence of very good wind sites, Makani estimates that the cost of energy will generally be about half the cost of conventional wind. At a typical onshore site, the cost of wind energy is about $0.10/kWh. At particularly good wind sites (for instance sites located in the middle of Kansas, where there is powerful wind and easy access to the grid) wind energy is already cost competitive with coal, around $0.04/kWh on a windy day. Conventional offshore wind farms, however, typically have a cost of energy closer to $0.20/kWh. In Kansas, Makani’s cost of energy would be slightly less than that of conventional wind.  However, at a typical onshore site or offshore it would be less than half the price.

Widespread use of AWTs will reduce energy related emissions. The AWT is rapidly scalable because of its low mass and low material usage. Combined with their large market potential, Makani systems could replace approximately 19.7 TWh/yr of energy production by 2020 (based on the expected installation of 4.5 GW). This is roughly the amount of electricity used by 1,713,640 average U.S. households.

The Makani Airborne Wind Turbine flies no higher than 600 meters (1,950 feet) above ground level, well below normal commercial and civilian aviation. This is a similar altitude to radio towers and other permanent obstructions. Makani’s AWT will incorporate the lighting and radio beacons typical of airborne devices. Makani’s test sites are awarded NOTAMs (Notice to Airmen) from the FAA.

Contrary to popular belief, conventional wind turbines harm relatively few birds or bats when compared with buildings, radio tower guy wires and cats. Compared with conventional wind turbines, the Makani Airborne Wind Turbine (AWT) has three key advantages for sharing airspace with avian life. First and foremost, it flies at an altitude well above that of most birds. Secondly, the absence of a tower makes the Makani system much less prone to nesting or perching. Finally, the wing travels at the same speed as the tip of a modern, utility scale wind turbine, and studies suggest that birds, including the higher-flying migratory birds such as cranes, safely navigate the blades of these turbines.When sited correctly, turbines have very low impact on birds (early turbines were sited along ridgelines and places preferred by raptors and other birds). The AWT offers greater siting flexibility because the Makani system need not be positioned on ridges and can happily fly above valleys or low places in the terrain. This flexibility enables AWTs to be placed outside of migratory paths and further from large bird populations.

Causes of bird fatalities

The noise level of the Airborne Wind Turbine (AWT) should be comparable to that of traditional wind turbines. The sound emitted from the AWT is higher frequency than that of a conventional turbine and high frequency sound diminishes quickly with distance. At the operational altitude of the AWT, the noise level is expected to be consistent with conventional wind turbines; as illustrated below, conventional wind turbines are actually quieter than the inside of a home or office. Additionally, the versatility of the AWT provides siting flexibility which allows the AWT systems to be placed in remote locations further out of earshot.

Comparative noise levels

Airborne Wind Turbines (AWTs) will be installed in wind farms similar to large, conventional wind turbines. However, since AWTs require less wind to make power and can reach the stronger winds at altitude, AWT wind farms can be sited in many more locations. Additionally, AWTs fly above disturbances introduced by local topography, so can be sited in valleys and other onshore sites unsuitable for conventional wind turbines.

Wind Resources in the Continental US

The Makani AWT is well suited to offshore deployment because its lightweight floating platform can cost effectively access intermediate depths and extend into deeper waters. The tether of the AWT decouples the wing from the foundation and transfers the aerodynamic forces to the anchor moorings near the waterline. This allows for the use of a lightweight floating platform, which is easier to install and gives more siting flexibility.

Floating Offshore Turbines

In extreme cases, the wing may use its high thrust-to-weight ratio to avoid stall. However, the Makani Airborne Wind Turbine is designed to be reliable and robust in a diverse range of conditions. The wind at altitude is typically more consistent than that near the ground, but large scale variations in speed and direction are expected. Wind speed variations (gusts) do not significantly affect the trajectory of the wing since they are typically small in comparison to the speed of the wing.

Wind consistency at operating altitude

Makani AWTs are capable of operating in still air. However, when the wind is below 3 m/s (6.7 mph), the AWT consumes a small amount of power supplied by the tether. During extended periods of low wind the system can land, relaunching itself autonomously when the wind conditions improve. The Makani system is equipped with standby battery power in the event that a drop in wind speed coincides with a transmission grid failure.

The Makani AWT has been shown in simulation to operate in hurricane conditions: winds in excess of 50 m/s (111.8 mph) with gusts reaching 80 m/s (179.0 mph). During particularly extreme weather the AWT can land until conditions normalize.

The design of the Makani AWT incorporates component redundancy that includes duplicate avionics and control surfaces, as well a watchdog system to detect failures. The AWT is designed to ensure that the system can tolerate individual component malfunctions in the same way that commercial aircraft can. In the event of such malfunctions, the wing can land autonomously for maintenance.