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Makani

Harnessing wind energy with kites to create renewable electricity

In development
Makani kite on tether against sky.

The challenge

Wind has the potential to power the world 100 times over, but only 4% of the world’s electricity comes from conventional wind power. Worldwide, hundreds of millions of people live within 25 miles of a coastline where winds are strong and steady, but two-thirds of coastal waters are too deep for conventional wind energy systems that sit on the seabed. It’s in areas like these, where conventional wind energy technologies don’t make economic or geographic sense, that energy kites have the greatest potential.

Over the last ten years, Makani has been prototyping and testing energy kites that can generate electricity by efficiently harnessing energy from wind resources that aren’t accessible or cost-effective today.

2015 global energy consumption chart showing that only 4% of the world’s electricity comes from wind. Source: World Energy Council

The Makani energy kite is an aerodynamic wing tethered to a ground station. As the kite flies in loops, rotors on the wing spin as the wind moves through them, generating power that is sent down a tether to the grid.

Design

Energy generating kites

  1. energy generation

    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.

  2. g-forces

    The kite’s airframe has to handle loads of 7-15 Gs.

  3. sensors

    Data from GPS and other sensors help the software steer the kite.

  4. navigation

    Onboard computers running custom flight controller software guide the autonomous kite’s flight path.

  1. stacked rotors

    8 stacked rotors are spun by the wind in crosswind flight. Each drives a permanent magnet motor/generator that generates electricity onboard.

  1. motor control

    1200V DC silicon carbide motor controllers handle high voltages efficiently with minimal mass.

Development

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 eight generations of prototypes, the team put the knowledge gained from years of testing into a commercial-scale carbon-fiber kite, the M600 — a kite with the wingspan of a small jet plane. The M600 is capable of generating up to 600 kilowatts, which is 30 times more energy than the previous prototype and enough to power about 300 homes.

The Technology

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 Makani Process

  1. The kite rests on a ground station ready for launch.
  2. The kite climbs to a desired altitude and positions itself downwind. The rotors initially consume a small amount of energy to produce thrust.
  3. The kite then transitions into crosswind flight. Aerodynamic lift allows the wing to fly autonomously in loops optimized for maximum power generation by our flight controller.
  4. Wind propels the kite around the loop. The rotors spin, driving onboard generators to produce electricity that is transferred back to the ground via the tether.

Today

Clean, affordable power from the wind

The Makani team continues to design, prototype, and test energy kites so that more people around the world can have access to clean, affordable wind power. The team is talking to potential partners and industry experts to understand the technical and economic requirements for integrating the energy kites with the existing energy ecosystem.

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