Energy transfer from airborne high altitude wind turbines: Part III. performance evaluation of a small, mass-produced, fixed wing generator

High altitude, airborne, wind-energy extraction-systems are the only true alternative to carbon and nuclear produced energy. Airborne Wind Turbines are very efficient due to the possibility to search the altitude with the nominal wind velocity. Winds are very stable and fast at altitudes from 4,000m (13,000ft)-11,000m (36,000ft). It is possible have many airborne generators near consumers in restricted airspace regions. In the first two parts, autogiro solutions demonstrated to be fully feasible but not economically convenient. This third part of the paper deals with the design of a mass-produced fixed wing system for power generation. A fixed wing drone with a minimal airframe was conceptually designed for this purpose. The power generated is 220 kW at 13,600ft (4.15 km) as in the first parts of this paper. 13,600ft (4.15 km) is statistically the best altitude for high power availability and reasonable tether length. The drone is a simplified, unmanned ultralight aircraft. Therefore, it has all the advantages of ultralights: the simplified design rules, the vast knowledge and the mass-produced commercial parts and subsystems. Ballistic parachutes are also available for emergency. As in the first two parts of this paper, the airborne system is tethered to transfer the electric energy to the national grid. On ultralight-generator deployment, the reversible electric generator works as a motor and the airborne generator flies as an aircraft. This UAV (Unmanned Aerial vehicle) can take off from a very short grass field due to the low wing loading. The UAVs unfolds and holds the tether up the required altitude. In the climbing phase, the tether powers the aircraft using the national grid electric power. Once the airplane reaches the operating position, as the nose is turned into the wind, the wind provides the lift and the propeller is reversed to windmill. In this way, it is possible to convert the electric motor into a generator. The autopilot keeps the airplane in the desired position. In nominal attitude and altitude (100km/h@4,150m-54kn@13,600ft), the rotor-generator outputs 0.22 MW. A preliminary design of a mass produced prototype is introduced in this paper with a cost per kWh competitive with fossil generated energy.