China’s monopoly over rare earth ores for the permanent magnets used in some wind turbines has prompted the search for cutting-edge alternatives
Wind power could meet around 15 % of EU electricity consumption by 2020, according to a 2014 report by the European Wind Energy Association (EWEA), achieving a total installed capacity of 192.4 GW.1 Offshore installations will account for around 23.5 GW of this total. These impressive figures are largely thanks to a revolution in turbine technology a decade or so ago, which allowed the offshore wind industry to become commercially viable. Today the industry is looking for yet another technology revolution to sustain its future growth.
While onshore wind is likely to dominate the sector for a long time, in Europe at least, the technology relies mostly on relatively slow and heavy, geared turbines that convert mechanical energy to electricity through electro-magnets, using copper induction coils. The weight, relatively low efficiency and heavy maintenance requirements of this technology mean that it is not ideal for offshore installations.
At the beginning of the last decade, the development of direct drive turbines that dispensed with the heavy copper wire and gearing used in electromagnets was hailed as a breakthrough in turbine technology. These turbines use permanent magnets containing an alloy of so-called ‘heavy-group’ rare earth metals (neodymium and dysprosium), together with iron and boron. Neodymium-iron-boron alloys make the strongest known magnets and, when dysprosium is added, can operate at very high temperatures (over 100 degrees Celsius). These magnets are used in magnetic resonance imaging (MRI) machines – and miniature versions make cell phones vibrate when they receive a call. They are lightweight and resilient, making them ideal for offshore use, where they allow direct-drive turbines to rotate at higher speeds and temperatures, and require significantly less maintenance than electromagnet-based turbines. Also, a decade ago, high copper prices made the (then) relatively cheap rare earth permanent magnets especially attractive.
By the end of the decade, though, just when technological innovations in turbine design had started to bring down the cost of offshore wind installations, a crisis developed in the supply of dysprosium and neodymium. Around 90 % of the known global reserves of these rare earths are found in China, giving that country a virtual monopoly – not only of the raw materials, but also of the technology to mine them and to manufacture the magnets. Keen to protect its expanding domestic wind energy market and maintain its position as a leading global turbine manufacturer, China imposed export restrictions on rare earth metals and also repatriated the magnet manufacturing technology.
As a result, prices of the rare earth ores – and hence the permanent magnets – rocketed, reaching a peak in 2011 at about 100 times their price in 2002-3. Although prices quickly dropped again, stabilising at about 2–3 times their pre-crisis level, the uncertainty in the supply chain prompted European and US manufacturers, who feel particularly vulnerable to China’s monopoly, to search once again for new turbine technologies that do not rely on rare earth permanent magnets.
Under the EC Seventh Framework programme (FP7), 15 European research centres and manufacturers – with external advisors in Japan and USA –joined forces in 2012 in a consortium that aims to reduce Europe’s dependence on imports of rare earth magnets and raw materials from China. Called ROMEO (Replacement and Original Magnet Engineering Options), the project has two phases. The initial focus is on improving the properties of permanent magnets based on light rare earth elements (i.e. not dysprosium and neodymium) – especially their ‘coercivity’, or resistance to becoming demagnetised – so that they can be used for applications above 100°C, such as wind turbines. “The second ambitious goal,” according to ROMEO’s objectives, “is to develop a totally rare-earth free magnet.”
Meanwhile, another FP7 project, Suprapower, aims to completely sidestep wind turbines based on the use of permanent magnets by developing a “superconducting, reliable, lightweight and more powerful offshore wind turbine.” This innovative project is not only driven by the need to find an alternative to Chinese rare earth-based magnets, though. The consortium of European research centres and manufacturers also claims that existing geared and direct-drive turbine technologies cannot easily be scaled up beyond their present 10 MW power ceiling. “Their huge size and weight”, says the project’s latest progress report,2 “drives up the cost of both fixed and floating foundations, as well as operation and maintenance costs.” Superconductivity, believe the consortium partners, will allow scaling even beyond 10 MW “by a radical reduction of the head mass.”
Suprapower’s superconducting direct drive generator exploits the superconducting properties of magnesium diboride (MgB2) wires – already used in the coils of commercial MRI systems. It will weigh about 200 tonnes with a power of 10 MW and a rated speed of 10 rpm. According to the project’s report, the new design should be 30 % lighter than current alternatives. Once tested, the prototype will pave the way for developing large generators of 10, 15 or even 20 MW, “up to the power and load level approaching the aerodynamic limit of the [rotor] blades.”
Outside Europe, other manufacturers, such as US-based GE Power Conversion and AMSC have also been testing 10 MW direct-drive turbines based on high temperature superconductors. And, perhaps frightened by its own rare-earth shadow, China’s own turbine manufacturers XEMC and Dongfang have also been looking for alternative designs that do not rely on permanent magnets. Although mostly servicing China’s domestic market, XEMC has installed a prototype 5 MW direct drive offshore turbine in the Dutch province of North Holland, using copper coils and electrical excitation. Ironically, the high price of copper was originally one of the reasons for developing rare earth permanent magnets in the first place, but it is now cheaper, with a more predictable supply chain.