Rare-earth-free permanent magnet generators (PMG) for offshore wind turbines with nameplates of 20MW are expected to be a reality “within three years”, following trials of a new-generation concept at the UK Offshore Renewable Energy (ORE) Catapult facility.

A 250kW version of the axial-flux design being developed by GreenSpur Wind, which uses ferrites – an iron-rich ceramic – for its magnets, would be part of a four-module 1MW unit that is foreseen to be scaleable to a power rating roughly twice that of the biggest PMGs in service today.

“It was our intention from the outset to design a generator that could be scaled for the next generation of offshore wind turbines,” said Hugh-Peter Kelly, GreenSpur’s head of technology and the inventors of the design.

“The feedback that we’ve received is that current designs have known limitations and new concepts will be needed to deliver next generation 20MW offshore wind turbines.”

ORE Catapult’s test and validation director Tony Quinn added: “Our facilities [in Blyth, in northern England] have provided the perfect testbed for GreenSpur to further develop their innovative generator technology.

“It is a great example of how [we are] supporting UK SMEs [small- and medium-size enterprises] to develop technologies that have the potential to be an integral part of the next-generation of offshore wind farms.”

GreenSpur is now moving forward with modelling for “significantly bigger, multi-megawatt generators”, with the target of designing a 12MW-plus concept for offshore turbine created by “stacking” three 4MW units in parallel.

Replacing high-price rare-earth materials with ferrites – a waste material produced in steel-making – would cut the cost of PMG magnets from £40/kg ($50/kg) to around £1/kg, according to GreenSpur calculations, meaning the design could carve around 33% out of the capital cost of direct-drive generator, and so almost 5% off the price of a turbine.

Andrew Hine, GreenSpur’s commercial director, noted: “We have proven our technology at a credible scale and developed a network of expert partners. Our plan is to work with a co-development partner with the expertise and capability to deliver a rare-earth free solution to the global wind turbine market.”

Discussions to use the PMG are “underway” with a number of OEMs, Hine confirmed to Recharge recently, but Greenspur was “unable to disclose names at the moment”.