Years ago, as an engineering student, I attended a class on internal combustion engines. Our lecturer tried to elicit a strong reaction by boldly stating that piston engines are based on the worst possible engineering principle one could imagine.
"A piston starts accelerating and moves at high speed in one direction, than comes to a full stop, accelerates and moves again — but now in the opposite direction — stops, then moves," he said. "Once you start understanding how these engines function, it seems a miracle they could ever work at all. Yet, piston engines have today reached a level of reliability and durability for which superior alternatives still have to be found."
As I started thinking of my first Windpower Monthly column, this remarkable statement came back to mind. It made me realise that much about this technology is still unchanged today — despite many efforts to push forward promising alternative solutions such as rotary-type engines and gas turbines.
The automotive industry's rich past offers both useful lessons and striking parallels with modern wind-power advancement. The first lesson is that introducing new technologies requires a considerable amount of time, effort and financial resources. Unfortunately, success is never guaranteed.
The second lesson is that it can prove a costly mistake to prematurely write off proven mature technologies as obsolete, given that any successor technology is certain to have its own drawbacks. The third lesson is that healthy caution towards new technologies, especially when they are accompanied by bold claims, can protect against being drawn into developments with unforeseen consequences. What might initially look like a not-to-be-missed trend may ultimately prove a hyped development that could and should have been sidestepped.
Relatively recent automotive industry hypes include hydrogen and biofuels. Both were initially perceived by many as ultimate solutions and even mistakenly regarded as "CO2-free" alternatives to fossil-based fuels. Behind many of these hypes lies insufficient knowledge, combined with a gross overestimate of the potential benefits while largely ignoring any downsides.
A key development in the wind industry was a 500kW direct-drive — gearbox-free — turbine introduced in 1992 by wind pioneer and Enercon founder Aloys Wobben. His achievement was initially met with both enthusiasm and scepticism, and conventional wind turbines with a gearbox have continued to dominate the market. Right from the start, Enercon chose a classic generator design with electric field excitation and never changed to permanent magnet generators (PMGs).
Another popular wind technology that does not use permanent magnets is the doubly-fed induction generator (DFIG). Around 15 years ago, a 1.5MW Tacke — now GE — turbine prototype was the first to be fitted with a DFIG. The solution turned into a huge success and developed into a semi-standard for the industry within a few years. Interestingly, DFIGs were regarded as obsolete by electric power engineers before re-emerging in variable-speed geared wind turbines.
Five years ago, GE was the first supplier to install a PMG in a fast-speed geared 2.5MW turbine. Several competitors followed. Multibrid, now Areva Wind, was the first to install a medium-speed geared 5MW prototype fitted with a PMG.
Rise and fall of direct drive
Since around 2003, direct-drive systems have steadily been gaining popularity, with most new entrants opting for PMGs. By mid-2010, many believed it would only be a matter of time before the wind industry made a complete switch to PMG-based direct drive, combining design simplicity with superior reliability, efficiency and the lowest possible costs of energy.
However, the recent explosive price rise of rare-earth elements is causing much uncertainty. As well as being used in wind turbines, powerful neodymium-based magnets are also in high demand for electric and hybrid vehicles' electric motors and for consumer electronics.
Three years ago the price of neodymium magnets was about €25 per kilogram, compared with €240-250 early last month. Wind-turbine direct-drive PMGs need up to ten times more magnet material than fast-speed geared equivalents. In recent weeks two PMG-technology developers confided in me that Enercon's disputed classic generator design was perhaps not such a bad idea after all. Another drive-system expert said some of his calculations needed redoing with careful reconsideration for DFIG and other classic generator designs.
Uncertainties over price developments and availability have caused a global scramble for new rare-earth deposits, pushed forward co-operation deals and could even trigger a major rethink on drive technology choices.
Eize de Vries is Windpower Monthly's technology and market trends consultant.