Wind-turbine makers have forged strong partnerships with generator manufacturers, in particular covering the design for new models. Some have even pursued full-scale vertical integration, with Siemens acquiring Loher in 2005 and GE buying Converteam in 2011.
In a bid to meet turbine manufacturers' requirements, generator manufacturers have developed several technologies. Doubly-fed induction generators (DFIGs) coupled with a doubly-fed converter still dominate the market. This highly mature technology is popular for its simplicity, cost (around 30% below that of rival technologies) and its high efficiency at full load.
However, DFIGs supremacy is increasingly challenged by permanent magnet generators (PMG). This technology is more costly than DFIG, and its supply is sometimes regarded as insecure, as 95% of rare-earth metals, the principal raw materials used in the manufacture of permanent magnets, come from China and have been subject to price hikes and export restrictions.
On the other hand, a PMG generator is more efficient at a partial load than a DFIG system, enabling a slightly higher level of annual electricity generation. Another reason to change to PMGs, say some generator manufacturers, is the high maintenance costs associated with DFIG. While these costs linked to the generator itself are limited compared to the overall maintenance costs, we must look at how to cut these costs.
Maintenance costs can skyrocket when critical components - such as generators - fail without notice, requiring unscheduled maintenance visits, emergency orders of spare parts, additional transportation costs and other expensive emergency measures.
Let's work together
By stepping back to the design process, and looking at sudden generator failures, we can see that involving the supplier in the design process would benefit the final product design. A stronger technical partnership between manufacturers and their suppliers would lead to optimal technical solutions being adopted - for example selecting the best materials for smaller components such as slip rings, brush holders and carbon brushes and designing the technical assembly in a way that reduces the wear of these parts. This could drastically reduce unexpected generator failures.
Re-engineering options are also available from component suppliers, helping to provide solutions when a repair is necessary. What's more, technical solutions have evolved and the assemblies designed ten years ago are not always as effective as the latest versions. By replacing parts with new products, future downtime can be reduced, by doubling or even trebling the useful life of some items, such as carbon brushes, increasing the timespan between maintenance visits.
At a time when wind-energy efficiency is questioned by the increasing competitiveness of other energy sources, such as gas, all parts of the wind industry, from manufacturers to wind farm operators, must work more closely with their tier-1 and tier-2 suppliers, to jointly develop new technical solutions that improve performance. That is the key for a sustainable development of the wind energy industry.
Luc Themelin is CEO of materials and electrical equipment supplier Mersen.
For more information, visit mersen.com.