Energy transfer from airborne high altitude wind turbines: Part II performance evaluation of a autogiro-generator

High altitude, airborne, wind-energy extraction-systems have the advantage of larger wind stability and higher power production. The efficiency of these systems is optimal because the nominal speed can be searched by varying altitude. Several airborne generators can be grouped in restricted airspace regions near consumer sites. This second part of the paper deals with the design of the simplest and cheapest autogiro for power generation. A single rotor autogiro with a minimal airframe was conceptually designed for this purpose. The power generated is 800 kW at 13,600ft (4.15 km) as in the first part of this paper. The rotor of a known helicopter, the CH-53E Super stallion, was used for the design. Generalpurpose equations for helicopters were adapted to evaluate the weight of the system. As in the first part of this paper, the airborne system is tethered to bring the power to the national electric grid. The altitude of 13,600ft (4.15 km) is statistically the best compromise between power available and tether length. On autogiro-generator deployment, the reversible electric generator works as a motor and the autogiro becomes a helicopter. This helicopter hold the tether and climbs up the required altitude. In this phase, the tether supplies the power from the national grid. Once the helicopter reaches an altitude slightly higher than the desired one, the power is turned off and the helicopter begins the autorotation. The electric motor becomes a generator. The autogiro begins to work with the rotor inclined. The control system inclines the autogiro to the required angle of attack into the incoming wind. In this configuration, the rotor produces electric power and provides the necessary lift to the airborne generator. In this configuration, the generator outputs 0.8 MW with a wind velocity of 54 knots (100 km/h). Unfortunately, the cost per kWh is one order of magnitude higher than the carbon produced one. This solution is more convenient than the one of the previous paper in which the cost was an order of magnitude higher. Still, it is not competitive with traditional energy production.