Land-based generation of electricity is limited.
Alongside aircraft using electricity, there are also aircraft which will be used to regularly generate electricity. The technology is known as AWES: Airborne Wind Energy Systems.
It was in 1978 that Mi. L. Lloyd at the Lawrence Livermore National Laboratory, Livermore, California applied for Patent US4251040 for large-scale wind power production by means of aerodynamically efficient kites.
Based on aircraft construction, these kites would fly transverse to the wind at high speed. The lift produced at this speed is sufficient to both support the kite and generate power. This would come to be known as crosswind kite power.
28 years later, Australian inventor Saul Griffith and kite designer Don Montague teamed up to build a similar type of generator, calling their company ‘Makani’ after the Hawaiian word for wind.
Funded by DARPA, they built a 20 kW turbine-carrying glider and flew it in 2009; the higher the altitudes where the winds are stronger and more reliable, the more electrical energy is harvested. By 2011 Makani were testing developed models from the tarmac of the former Alameda Naval Air Station.
In 2013 they were bought up by Google. Although facing significant regulatory obstacles including wildlife preservation issues as well as the technological challenges, they were eventually able to produce their eighth generation prototype designed by Damon Vander Lind, a 600-kW carbon-fiber energy kite with eight rotors rotors each of 7.5 ft (2m³0) in diameter and with the 85 ft (26 m) wingspan of a small jet airliner.
The turbine driven generators would also function as motor-driven propellers in a powered flight mode, which could be used for vertical take-off and landing. A perch adapted to facilitate the take-off and landing would pivot such that the pivot is oriented towards the tension direction of the tether.
On May 18, 2017 the Makani 600-kW kite produced power for the first time. The rotation of the 85 ft. wide kite’s rotors drives magnet motors/generators on board, producing electricity that transfers down the tether where it can be connected to an energy grid.
The electricity comes down in DC (direct current), but is converted to AC (alternating current) at its base station. In February 2019, Royal Dutch Shell invested in the firm, but unfortunately during the COVID epidemic, Makani had to file for bankruptcy.
Similar projects are taking place in the Netherlands with the Ampyx tethered glider and in Norway with Kitemill and their Spark airplane. And Swiss startup Skypull has developed an autonomous drone that can fly to almost 2000 ft (600m) – about three times the height of a traditional wind turbine.
The Skypull current prototype is a rigid wing, multi-copter “box-wing” drone that can take off and land by itself, with no need for a launcher or ground wind. The take-off is battery-powered, but once in the air the battery is recharged every time the kite loops back down towards the ground.
Discover solution 9: electric airplanes
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