Birmingham’s Professor Rex Harris (FREng) is drawing attention to a recent article in the Guardian Review on wind energy giving an up-beat view of off-shore wind farms which, he agrees, are showing a lot of promise, particularly compared with the very expensive and increasingly problematic nuclear option. He comments:
“However, in this article, there was no mention of the vital role played by NdFeB-type permanent magnets in the direct drive generators provided by companies such as Siemens”.
The untutored writer consulted a second engineer who said that readers may have noticed wind turbines of rather different shapes starting to appear. The more traditional ones have a nacelle behind the rotor – the gearbox to convert slow rotation to a higher speed required by the generator.
He continued: “These gearboxes are expensive and heavy, bringing new problems to solve. One solution is the turbine with NdFeB, otherwise known as rare earth magnets. They eliminate the need for the gearbox, driving the generator directly at the speed of the blades. They can be recognised by a large ring structure behind the blades. (The traditional gearbox opposite has the low speed shaft to the left. It makes the high speed shaft to the right turn approximately 50 times faster than the low speed shaft.)
Stanford Magnets reports on the emergence – over the last two years – of commercial-scale & direct drive permanent magnet generator systems with the hub directly connected to the generator (right). Being direct drive, these turbines have significant advantages over the geared variety:
- significantly increased reliability,
- reduced maintenance costs,
- reduced downtime for maintenance
- improved efficiencies in the power conversion process and
- greater efficiencies when wind speeds are not at full rating.
The second engineer warns that “engineering is always a compromise and there is a clue in the name RARE earth: these generators need a large quantity to make the magnets required. There is a limited amount of these materials and they are predominantly found in China”.
Mineral reserves: resources known to be economically feasible for extraction economically and technically feasible to extract. Note that the New Scientist reports that in what is said to be the first detailed report on the country’s supply, the US has 13 million tonnes of rare earth metals – but it would take years to extract them.
Professor Harris and his colleagues David Kennedy and Adrian Arbib end: “With this medium to long term threat to the magnet supply very much in mind, the West, including Europe and the USA, should recreate its previous manufacturing capacity for the production of NdFeB-type sintered magnets, start to exploit alternative rare earth reserves and develop and support NdFeB-type magnet recycling. Simply leaving matters to market forces will certainly not be sufficient”.