In future, superconductors will allow extremely efficient, compact and light-weight wind energy generators to be built, with the same performance as corresponding permanent magnet machines but which are only half their size. At the same time they can decrease the use of rare earths significantly for the expansion of wind energy. The “Life Needs Power” energy forum at the Hanover Trade Fair discussed how the pending scarcity of these raw materials could slow the expansion of wind energy. In his presentation, Dr. Michael Bäcker (Zenergy Power GmbH) explained the solutions second-generation superconductors offer.

For economic power generation with offshore wind farms, powerful and robust turbines are required, which do not cause disproportionately high logistical and foundation work with minimal weight. To date, direct-drive generators with permanent magnets are a technically and economically sensible solution. They are 30-50% smaller and lighter than copper-based machines with the same rated capacity.

However, China’s export restrictions for rare earths have decreased security for investments in systems with permanent magnet generators: construction of permanent magnets is currently the largest consumer of rare earths. At the same time, the demand for this application is growing fastest. In 2010, 26,000 tons of rare earths (neodyme/praseodyme, dysprosium, terbium) were used to produce permanent magnets. A demand of 48,000 tons is already predicted for 2015 – or a shortfall of 15-30% for the expected annual production. 40% of these magnetic rare earths are used for generators and other electric machines. A study estimates the demand of the wind energy industry in the USA alone at 10,000-15,000 tons for 2014.

As an alternative to permanent magnets, superconducting coils can also generate the magnetic fields required. They can even be used to produce generators with outputs of over 10 MW. Until now, the high price of superconductive wire prevented its use in commercial generator construction. A second generation of superconductors which can be produced inexpensively in large quantities have changed this situation. The innovative production process is based on a stratified architecture of the conductor material. These next-generation superconductors are already being marketed internationally. Rare earths are also required to produce these superconductors (cer, lanthan, yttrium). However, at 2 kg of rare earths per MW of installed generator output, they need less than one hundredth of the quantity necessary for permanent magnet generators with the same capacity. The substances required for superconductors are also more widely available than those for producing permanent magnets. Michael Bäcker estimates that the costs could decrease to the level of conventional copper wires as early as 2020.

Second-generation superconductors

BINE-Projektinfo brochure 6/2010 „High temperature superconductors“ describes the manufacturing process for second-generation superconductors, and the applications for which they are already in use.