Comparison of MgB₂ and Coated Conductor Based 5 MW Superconducting Wind Turbine Generator

Direct drive superconducting generators might become attractive in large offshore wind turbines, because the drive train must provide a torque scaling with the radius of the rotor blades as R3 due to limitation of the tip speed of the blades. We have previously found that a coated conductor based generator can technically compete with a gear box drive train equivalent to the 5 MW NREL reference turbine [1]. However the price of the coated conductor results in a generator price exceeding the expected price of the entire turbine. MgB2 conductors can be seen as a low cost alternative to the coated conductors, but the operation temperature in range of T = 15-20 K and the engineering current density Je is smaller. We have found that a 16 pole synchronous generator with active diameter D = 4.2 m and length L = 1.5 m based on a MgB2 wire with Je = 70 A/mm2 in approximately 4 Tesla field would result in a wire usage in the order of 330 km. This has the potential to decrease the price of the superconductor wires in the generator by a factor of 10 compared to the coated conductors, but the cryogenics will be a challenge and is discussed. Finally we will use turbine load simulations to discuss the torque events that such a 5 MW generator would experience if installed in the NREL turbine.