Rotor design for PM generators reflecting the unstable neodymium price

The price of rare earth metals such as neodymium is very unstable and has in recent years increased more than 1000%. This leaves the wind power business that uses permanent magnet generators with large insecurity. In this paper, a generator design with an interchangeable rotor is presented, which gives the option of having a rotor with different material depending on the current neodymium price. Thereby, the wind turbine has the same properties with only the generator rotor changing. The suggested alternative, a ferrite rotor, is much heavier than a neodymium rotor. The heavy ferrite rotor indicates an advantage for the vertical axis wind turbine technology with the generator placed on ground level, where the weight is not as important as in the hub. Two similar generator designs are presented, magnet material differences are discussed and the neodymium price limit for when the ferrite rotor is to be preferred is calculated.