Airborne wind power projects

Joby Energy is developing airborne wind turbines which will operate in the upper boundary layer and the upper troposphere. While knowledge of the tremendous energy in high-altitude wind is not new, recent advances in power electronics, sensors, and control systems now make our technology practical.

The multi-wing structure supports an array of wind turbines. The wind turbines connect to motor-generators which produce thrust during takeoff and generate power during crosswind flight.

Orientation in flight is maintained by an advanced computer system that drives aerodynamic surfaces on the wings and differentially controls rotor speeds. A reinforced composite tether transmits electricity and moors the system to the ground. The high redundancy of the array configuration can handle multiple points of failure and remain airborne.

How It Operates

For launch, the wind turbines are supplied with power to enable vertical take-off. Upon reaching operating altitude, the system uses the power of the wind to fly cross-wind in a circular path. The high cross-wind speeds result in the turbines spinning the generators at high speeds, eliminating the need for gearboxes and increasing efficiency. The energy is transferred to the ground through the electrical tether. During occasional periods of low wind the turbines are powered to land the system safely.

The 30 kW wind energy prototype should be tested at an altitude of 600 metres. High-altitude wind harnessing projects were already conceived over 40 years ago.

In fact, between 7,000 and 15,000 metres, wind currents are exceptionally stable and reach very high speeds, 5 to 10 times higher than surface winds. But even at a 500-metre altitude, wind is twice as fast as on the ground. However, this has become a practical option only in the last few years, due to technological innovations.

Indeed, wind energy developers are creating new models and are planning to send them high up in the sky, attached to large kites, in the near future.

One of these developers, US-based Joby Energy, is testing a turbine system transported through the air by a particular multi-wing structure that uses an advanced computer for orientation in order to follow the direction of the wind, also allowing it to land safely when the wind is low.

According to its developers, the model can withstand strong winds, but in any case the security systems allow it to keep working even in case of failures and to land without any damage even if the tether should break down. The latter is used to transmit energy to the ground.

The prototype developed by Joby has a capacity of 30 kW, while the first commercialized model should reach 300 kW. The wind turbines can in theory fly at altitudes up to 10,000 metres but, for the time being, the US Federal Aviation Administration has established a maximum height of 600 metres.

According to the founder of Joby Energy, Joe Ben Bevirt, the total potential capacity of wind energy at high altitudes is 870 million MW, over 50 times higher than the capacity of surface winds, estimated at 17 million MW. In theory, this source is abundant and affordable in most parts of the world.