Harnessing wind energy with kites to create renewable electricity

Wind could power the world 100 times over, but only 5% of the world's electricity comes from wind power

Makani aimed to enable more people around the world to have access to clean, affordable wind power by developing energy kites, an airborne wind energy technology that used a wing tethered to a ground station, to efficiently harness energy from the wind.

By replacing the massive steel towers of conventional wind turbines with lightweight hardware and smart software, Makani hoped to unlock access to wind resources too expensive or impractical to access with traditional wind technologies.

Makani spent 13 years developing energy kites that generated electricity by flying in loops and sending power down a tether to the grid.

The Makani team preparing a wind energy kite for flight

From kitesurfing to energy kites

Makani started in 2006 when a group of devoted kitesurfers had the novel idea that kites might be able to harness enough wind energy to power the world. The earliest kites were made of fabric and closely resembled kiteboarding gear. Testing these early prototypes proved that the kites needed more efficiency and control than fabric could afford. This led to the idea of rigid kites that could support onboard rotors to harness apparent wind for higher lift and more energy production.

After building rigid kites, their next step was to test small-scale kite prototypes in a broad range of wind and environmental conditions. Here, the team had to solve some major technical problems like how to transition between vertical hover flight, and how to generate energy in crosswind flight when the kite flies in acrobatic loops.

In December 2016, after many generations of prototypes, the team put the knowledge gained from years of testing into a utility-scale carbon-fiber kite with the wingspan of a small jet plane. This kite was capable of generating up to 600 kilowatts of electricity, which is 30 times more energy than the previous prototype and enough to power about 300 homes.

In 2019, Makani became an independent business and partnered with Shell to bring energy kites to offshore environments. That year, the team flew the world’s first offshore flight of an airborne wind turbine off the coast of Norway.

An aerodynamic wing tethered to a ground station

The airflow acting on a moving kite is many times faster than the wind experienced by a stationary object. This powerful apparent wind spins the kite’s rotors, generating a large amount of electricity.
The kite’s airframe has to handle loads of 7-15 Gs.
Data from GPS and other sensors help the software steer the kite.
Onboard computers running custom flight controller software guide the autonomous kite’s flight path.
1200V DC silicon carbide motor controllers handle high voltages efficiently with minimal mass.
8 stacked rotors are spun by the wind in crosswind flight. Each drives a permanent magnet motor/generator that generates electricity onboard.

How the energy kite works

Propellers on the wing act like rotors on a helicopter taking off and lift the kite off the ground station. The kite takes off perpendicular to the wind and climbs to a height of 1,000 ft, at which point the kite begins looping without consuming any energy. This looping is called “crosswind flight,” a phenomenon you can experience if you take a kite to a park on a windy day. The air moving through the rotors on the wing forces them to rotate, which drives a generator, producing energy that is sent down a specially engineered tether to the ground. The kite’s path is managed by the flight computer which guides the kite even in turbulent winds and safely returns it to the ground station.


The Energy Kite Collection: sharing Makani’s lessons

In 2020 Makani’s journey as a company came to an end. To share the lessons and insights the Makani team gained from their 13 year journey developing an entirely new kind of wind energy technology, the team created The Energy Kite Collection, a portfolio of resources including a technical report, Makani’s entire avionics, flight controls and simulation code repositories, flight logs for every crosswind flight of the M600 prototype, technical videos, a new simulation tool called KiteFAST created with the National Renewable Energy Laboratory, and a non-assertion pledge for the free use of Makani’s worldwide patent portfolio.

The Energy Kite technical report consists of three parts:

Part I
provides an overview of best practices and lessons from Makani’s most advanced energy kite (the M600) and offers suggestions on how to complete a next generation energy kite system.

Part II
is a collection of technical artifacts that outline the design of the energy kite system, Makani’s understanding of the physics of tethered flight, and includes a user guide for the flight logs available online.

Part III
includes reports on flight tests and illustrates Makani’s progress toward long-term permitting and type certification for airborne wind turbines.

We think these materials will be especially interesting to airborne wind developers and researchers, aerospace experts, engineering students, and people who are curious to learn about novel flight vehicles. A full copy of the report and multimedia assets are also available on Internet Archive.

Pulling Power from the Sky: The Story of Makani

The Makani team also created a documentary film, Pulling Power from the Sky: The Story of Makani. The film follows the team on their mission to create energy kites to help with the climate crisis. This intimate portrait of the team and the technology they developed features footage from Makani’s beautiful test sites in Hawai’i, California, and Norway.