Until recently, the idea of sourced energy from high altitude wind using tether and cable technology was not feasible. But the technologically-advanced materials and advanced computer knowledge that have emerged due to the interest in green technology, makes this now possible.
Just as people yearned to fly long before the Wright Brothers' first successful flight, as far back as 1833 John Adolphus Etzler envisioned a society that sourced energy from high altitude wind using a tether and cable technology. Today, the materials for this technology include a reinforced composite tether, aerodynamic surfaces on the wings, and advanced air turbines. Computers are used with sensors to adjust flight orientation and rotor speeds according to the environment.
Mouli Cohen at Joby Engery Inc. states their design, called the "multi-wing", is similar in design as the wings of one of the first airplanes made by the Wright Brothers. What is missing, because it is not needed, is the cockpit. According to Cohen, the parallel lines that make up its kite-like modular frame move in a circular pattern at about 400 to 600 meters above the ground where the wind is faster and more consistent. Turbines are positioned at each junction where the bars of the frame intersect. These turbines also serve to initially launch the device into the air.
The company's specifications for the "multi-wing" include a 2 MW (megawatts) airborne wind turbine produces that produces the energy equivalent of two 2 MW conventional turbines but requires approximately 1/20th of the materials. Furthermore, having five times the wind speed at the system's operating altitude, it can produce five times more electricity and has a capacity factor of 76% compared to the 42% of a conventional wind turbine. The "multi-wing" is not yet operating commercially, but there are plans to fly it outside of air traffic corridors and, eventually, offshore.
