Patents: Wobben v Siemens - Blowing in the Wind

Offshore Wind Farm
Photo Anke Hueper
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Jane Lambert

Wobben Properties GmbH v Siemens Public Ltd Company and Others [2017] EWCA Civ 5 (19 Jan 2017)

The claimant company, Wobben Properties GmbH is the registered proprietor of European patent  EP0847496 for a method of operating a wind power station.  The invention is described as follows:
"The invention pertains to a method of operating a wind power station, especially to limit the load on a wind power station, preferably a pitch-controlled wind power station. The invention also pertains to a corresponding wind power station. The invention is designed to increase the output of a wind power station and yet limit the load on the wind power station at very high wind velocities. This is accomplished by reducing the power of the wind power station as a function of wind velocity as of a predetermined wind velocity, preferably by reducing the operating velocity of the rotor of the wind power station when a wind appears with a wind velocity above a maximum wind velocity or maximum velocity in the blower stream."
The patent specification is very short and consists of four claims:
  1. "Method of operating a wind turbine with pitch control, in which the power of the wind turbine as well as the operating speed of the rotor is continuously reduced when a wind velocity is reached which is in danger of overloading the wind turbine, in dependence on the rise in the wind velocity or incident-stream velocity.
  2. Method according to Claim 1, characterized in that the operating speed (n) of the rotor is reduced such that the load level acting on the rotor of the wind turbine remains approximately constant or is reduced when the wind velocity rises above the wind velocity which is in danger of producing overloading.
  3. Method according to Claim 1 or 2, characterized in that the reduction in operating speed is associated with a change in power matched to the load level.
  4. Wind turbine with pitch control, characterized by a means for automatic power and rotor-speed reduction when a wind velocity is reached which is in danger of overloading the wind turbine, in dependence on the rise in the wind velocity or incident-stream velocity or the true or relative wind velocity."
Wobben accused Siemens Plc and its subsidiaries ("Siemens") of infringing claims 1 and 4 by installing wind turbines in the UK. In particular, the off-shore sites at the London Array, Westermost Rough and Gunfleet Sands.  Wobben estimated the value of its claim in the order of £13 mn. Siemens denied infringement and contended that the patent was invalid for anticipation and obviousness.

The Trial
The action came on before Mr Justice Birss in Wobben Properties GmbH v Siemens Plc and Others [2015] EWHC 2114 (Pat) (20 July 2015). After a 6 day trial, His Lordship concluded at para [211]  that the patent was invalid and would not have been infringed even if it had been valid.

The Appeal
Wobben appealed with the permission of Mr Justice Birss contending:
"that the judge wrongly directed himself as to the legal test for obviousness and made a series of fundamental errors in assessing the evidence of the expert witnesses. It also argues that the judge erred in assessing infringement and made findings which had no basis in the evidence. Siemens responds that the judge's findings are properly supported by the evidence and are correct, essentially for the reasons that he gave."
The appeal was heard by Lords Justices Longmore, Kitchin and Floyd.

The Judgment
The Court of Appeal unanimously dismissed the appeal.

Delivering the lead judgment, Lord Justice Kitchin summarized the technical background and the common general knowledge between paras [7] and [23] and the teaching of the patent between paras [24] and [32].

Turning to the question of obviousness, the learned Lord Justice considered the prior art relied on by Siemens which was an article by Dr Ervin Bossanyi entitled "Probabilities of sudden drop in power from a wind turbine cluster" which had been published in 1982 ("Bossanyi") between paras [33] and [47] and the judges findings between paras [48] and [59]. He summarized the appellants' argument between paras [60] and [71] and considered them in paras [72] and [81]. He said at para [82]:

"In my judgment the judge was entitled to hold that the skilled person given Bossanyi in 1995 would consider implementing it on a VSVP machine and so would think about how to implement the ramp down above the normal shut down speed. That requires the power to be reduced as the wind speed increases and the skilled person would appreciate that this could be achieved by keeping the torque constant and reducing the rotor speed; by reducing the torque and keeping the rotor speed constant; or by reducing both the torque and the rotor speed. These findings had a proper basis in the evidence and the judge has made no error of principle in his reasoning. Mr Silverleaf has not established any ground upon which it would be appropriate for this court to interfere with the judge's evaluation of the evidence or to set about re-evaluating that evidence for itself."
Lord Justice Kitchin then considered infringement.  At para [32] he had summarized Mr Justice Birss's construction of claim 1 as follows:
"First, the claim covers any suitable measure of wind speed. Secondly, the claim calls for a dependency between the reduction in rotor speed and the rise in wind speed. To satisfy the claim, there must be a causal relationship between the rotor speed and the wind speed. So also, there must be a causal relationship between the power of the turbine and the wind speed. Finally, the claim covers a method in which two different approaches to determining wind speed are used, one to control power and the other to control the rotor speed."
He then considered the evidence that had been before the trial judge and the reasons for his finding that the claim had not been infringed.

Wobben had alleged that Siemens's variable speed, variable pitch ("VSVP") turbines infringed the patents by High Wind Ride Through (HWRT) which reduces the speed of rotation and the power output of the turbine in high-speed wind conditions. At para [108] Lord Justice Kitchin observed that at the end of the day the case was concerned with the operation of HWRT and whether it may fairly be said that the operating speed of the rotor is continuously reduced in dependence upon the rise in the wind speed. That required a consideration of both the way in which and the level at which the control algorithms in HWRT work. Lord Justice Kitchin believed that the judge was entitled and indeed right to find that HWRT reduces rotor speed in dependence upon a rise in filtered rotor acceleration and that it does so to protect the turbine from dynamic loads associated with accelerations and decelerations. It followed that HWRT was not using filtered rotor acceleration as a surrogate for wind speed and was therefore not infringing claim 1 or indeed claim 4.

Lord Justices Floyd and Longmore agreed with Lord Justice Kitchin.

There was no dispute between the parties as to the law to be applied. The leading authorities on anticipation, obviousness and the construction of claims were considered at first instance and the judge's analysis was impliedly confirmed on appeal.  Anyone looking for an exposition of those doctrines could do worse than look at Mr Justice Birss's judgment. The analysis of the facts and the construction of the claims were, of course, specific to this appeal.

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