Wobben Properties GmbH v Siemens Public Ltd Company & Ors

For obviousness, a skilled person given prior art proposing gradual power reduction above normal shut-down wind speed would seriously consider applying it to a variable-speed variable-pitch turbine. Obvious implementation choices include reducing torque, rotor speed, or both. Reducing rotor speed can reduce dynamic thrust loads and fatigue. The teaching remains relevant even where the modelled shut-down speeds differ and high-wind events are rare.

For infringement, a claim requiring rotor speed to be reduced in dependence on rising wind speed does not demand direct measurement. The speed must nevertheless be determined by and contingent upon wind speed, directly or through a genuine surrogate. A controller responding to filtered rotor acceleration is not such a surrogate merely because gustiness generally increases with wind speed.

Wobben, proprietor of a patent concerning operation of pitch-controlled wind turbines in high wind speeds, alleged infringement by Siemens entities. Siemens challenged validity for obviousness and insufficiency and denied infringement.

Birss J held that the patent was invalid for obviousness in light of an article by Dr Bossanyi and held, alternatively, that the patent would not have been infringed: [2015] EWHC 2114 (Pat). Wobben appealed, challenging the obviousness analysis, the assessment of expert evidence and the construction and application of the infringement claim. The central issues were whether the claimed reduction in rotor speed was obvious and whether Siemens’s High Wind Ride Through system reduced rotor speed in dependence on rising wind speed.

1. Disposition. The Court of Appeal dismissed the appeal. Kitchin LJ gave the judgment, with Floyd LJ and Longmore LJ agreeing.
2. Obviousness. The relevant teaching of Bossanyi was its proposal to keep a turbine operating above the normal shut-down wind speed while gradually reducing power. Its significance did not depend on the paper having studied fixed-speed turbines or on its modelled shut-down speeds being lower than those commonly used later. A skilled person in 1995, when the industry was focused on variable-speed variable-pitch turbines, would seriously consider implementing that teaching in such a turbine. The relative rarity of high-wind events did not deprive the teaching of practical relevance because gradual reduction would reduce the risk of severe power ramps.
3. In implementing the teaching, it was obvious to consider reducing torque while maintaining rotor speed, reducing rotor speed while maintaining torque, or reducing both. Reducing rotor speed as wind speed increased had an obvious advantage in reducing static and dynamic loads, particularly thrust loads, and fatigue. The trial judge was entitled to rely on the common general knowledge and expert evidence. Deficiencies in one expert’s calculations did not fatally undermine the evidence, and no error of principle justified appellate interference with the trial judge’s evaluative conclusion.
4. Construction and infringement. The requirement that rotor speed be reduced in dependence on rising wind speed did not necessarily require direct measurement of wind speed. Purposively, rotor speed had to be determined by and contingent upon wind speed, whether the correlation was effected directly or through a genuine surrogate. Siemens’s High Wind Ride Through system controlled power using a filtered pitch reference but controlled rotor speed by reference to filtered rotor acceleration derived from acceleration and deceleration readings. The possibility that gustiness generally increases with average wind speed was insufficient. Wind speed could rise gradually during a period of low turbulence without triggering the relevant filtered acceleration and speed reduction. The controller therefore did not use filtered rotor acceleration as a surrogate for wind speed and did not infringe.

• Court of Appeal (Civil Division): The appeal was dismissed. The court upheld the findings that the patent was invalid for obviousness and, alternatively, would not have been infringed.
• High Court of Justice, Chancery Division (Patents Court): Birss J held the patent invalid for obviousness in light of Bossanyi and held that, if valid, it would not have been infringed: [2015] EWHC 2114 (Pat).