GreenSpur Renewables

GreenSpur RenewablesThe Next Revolution in Wind Turbine Technology

The Next Revolution in
Wind Turbine Technology

Frequently Asked Questions

Frequently asked questions (FAQ) are our listed questions and answers commonly asked in context, and pertaining to our generator technology.

What has stimulated market interest in large scale (multi MW) DD PMGs?

The move towards large scale offshore wind farms has resulted in a market move towards bigger generators that can facilitate upscaling and deliver reductions in the Levelized Cost of Energy (LCOE). The principle advantages of DD PMGs is that they do not require a gear box, which is the main source of wind turbine failure and can become more problematic as generator sizes increase. Consequently, many commentators see DD PMGs becoming increasingly important in the drive to upscale and deliver further reductions in LCOE. 

What are the drawbacks associated with large scale DD PMGs?

Traditional wind turbines use a gear box to convert the slow rotational speed of the rotor blades up to a sufficiently high rpm to drive conventional generators. With the absence of a gearbox, DD PGMs need to be of a large diameter to achieve an adequate translational speed between the generator's stator and its rotor to enable the generation of an adequate electrical power output. This necessitates the building of large cross section nacelles to house generator components. A lesser, but relevant consideration is the transportation challenges associated with delivering large and heavy generator components to site.

Why do existing large scale DD PMGs use neodymium iron boron (NdFeB) magnets?

To a certain extent the designers of existing DD PMGs have been seduced by the power of NdFeB magnets, which are 3 times the strength of standard ferrite magnets. This means that when compared directly in the same design less NdFeB is required to create the magnetic field, resulting in a lower magnet weight requirement. 

What are the drawbacks associated with using NdFeB magnets?

The principle problems associated with using NdFeB magnets are:

a) Expense - the material is a very expensive as a metallic component and subject to high demand, and
b) Security of supply. Over 95% of NdFeB magnets are supplied from China. Annual output of all rare earth elements including Neodymium is estimated at approximately 135,000 tonnes and there is increasing world demand from many high growth industries including defence, computing, mobile phones and medical. There is also a significant forecast uplift from the rapidly expanding electric automotive industry.

In the case of NdFeB magnets to ensure they can operate safely at raised temperatures, they must be dosed with dysprosium, a "rare earth" element of very limited supply, which heightens the security of supply risk.

Further practical difficulties relate to generator assembly processes. NdFeB are dangerously attractive and need to be handled with the utmost care. They are also vulnerable to corrosion in sea water atmospheres and can also de-magnetise if safe operating temperatures are exceeded (160°C). By contrast, ferrite magnets are inert and can operate at temperatures of up to 460°C.

How has it been possible for GreenSpur Renewables to replace NdFeB magnets with ferrite magnets in its DD PMG?

The GreenSpur team went back to basics. We looked at the design of a new ferrite based DD PMG from first principles. The result is a new DD PMG design that leverages the attributes of ferrite and is capable of delivering comparable output at a comparable weight.

Can the GreenSpur DD PMG be scaled to multi MW levels and in what time frame?

Yes, the GreenSpur DD PMG has been designed to deliver multi MW solutions. We are current working on 3MW and 6MW designs and have a goal to develop a 15MW unit within 5 years.

Is there a limit on how big the GreenSpur DD PMG could get to?

At the moment we are working towards a 15MW design. However, with the right partnerships and manufacturing relationships in place it would be possible to go significantly beyond 15MW, but to do so would obviously need to be linked to market demand.