Wobben Properties GmbH v Siemens Plc & Ors

A patent for operating a pitch-controlled wind turbine was invalid for lack of inventive step. A skilled person applying a prior-art proposal for gradually reducing power at high wind speeds would consider implementation in a variable-speed, variable-pitch turbine. Reducing rotor speed as well as power was an obvious option, with an apparent advantage in reducing loading and fatigue.

Infringement also failed. A claim requiring reductions to depend on a rise in wind speed requires a causal relationship, not merely correlation. A control system responding to filtered rotor acceleration did not use that quantity as a measure or surrogate for wind speed. It responded to dynamic loading and could reduce speed when turbulence increased without a corresponding rise in wind speed.

The claimant owned a patent entitled “Method of Operating a Wind Power Station” and alleged that Siemens wind turbines, including turbines operating with High Wind Ride Through technology, infringed method and product claims. Siemens denied infringement and challenged validity on novelty and inventive step grounds, relying principally on Shozaburo and Bossanyi.

The claimant amended the claims by the Main Request. The court considered the construction of the amended claims, common general knowledge, anticipation, obviousness and infringement. The central issues were whether Shozaburo disclosed the claimed operating method, whether the claims were obvious over Bossanyi, and whether the Siemens control system reduced rotor speed in dependence on a rise in wind speed.

1. Amendment and construction. The court allowed the unopposed amendments in the Main Request and a correction to the German-language claims. The claims were not limited to operation only above a conventional shutdown wind speed, nor to any particular technique or moving average for measuring wind speed. “Dependent on” required a causal relationship; coincidence or correlation alone was insufficient.
2. Novelty. Applying the enabling-disclosure approach stated in Synthon v SmithKline Beecham [2005] UKHL 59, Shozaburo did not disclose the claimed method. Read as a whole, its reference to cut-out wind speed 29 described a time-dependent shutdown procedure, not continuing operation with progressively reduced speed and power. The claims were therefore novel.
3. Inventive step. The court applied the structured approach in Pozzoli v BDMO [2007] EWCA Civ 588, having regard to the circumstances identified in Conor v Angiotech [2008] UKHL 49. A skilled person given Bossanyi would seriously consider applying its gradual power-reduction proposal to a variable-speed, variable-pitch turbine. The obvious implementation options included reducing torque while maintaining speed, reducing speed while maintaining torque, or combining the approaches. Reducing rotor speed was an obvious way to reduce loading and fatigue. Claims 1 and 4 therefore lacked inventive step.
4. Infringement. The power-control aspect of High Wind Ride Through satisfied the relevant requirement when considered alone. The speed-control aspect did not. Filtered rotor acceleration was not a measure of wind speed. Wind speed could rise smoothly without a corresponding rise in filtered acceleration, while turbulence at a lower wind speed could trigger speed reduction. The system measured filtered rotor acceleration for the purpose of protecting the turbine from dynamic loads.
5. Disposition. The patent was invalid. In any event, it was not infringed.