The patent, identifed as EP 0 847 496, is owned by Wobben Properties, part of the Enercon group, which was placed in the Aloys-Wobben Foundation in October 2012. Siemens calls the storm-control facility used in its turbines high-wind ride-through.
Wobben Properties filed the Patent EPO 847 496 with the European Patent Office (EPO) on 29 August 1996. The patent was granted in 2000 and the patent specification was published by the EPO on 9 August 2000. Within the ensuing 3 months, the patent was validated in Spain, Denmark, United Kingdom, Greece, Ireland, Portugal and Germany. On 8 May 2001,Vestas filed an opposition against the patent but the EPO Opposition division rejected the opposition and confirmed the patent on 2 November 2002.
It seems that Siemens may be installing technology covered by the EP 0 847 496 patent, as applied in the UK, in turbines being used in UK offshore wind projects, but the customers may not be activating the technology until the patent expires in August 2016. If this is the case, there may be a surge of productivity by the Siemens turbines from August 2016.
That this situation exists is indicated in a transcript passage of a London High Court hearing related to the patent dispute in the UK held in October 2014. Mr. Justice Morgan is quoted as saying: "There is also the curious fact that the technology has been installed on a large number of turbines, but Siemens have stated at two points of time in the past that it was not at those points of time activated."
"Is that because of this dispute or for other reasons?" Morgan asked.
His next questions were: "If Siemens had to tell its customers that it may be safer not to use the technology until this litigation is resolved, how damaging in the end would that be to the customers? In relation to new orders from further customers, what is the likely scale of such orders and for what period prior to August 2016, when the patent expires, would a new customer really wish to use the technology?"
He was addressing the issue argued by Siemens that fulfilling Enercon's request for Siemens information on its customers with turbines equipped and using the technology would damage its reputation.
Morgan concluded in the October 2014 High Court hearing that Enercon's wish should be met because Enercon cannot know which customers have arguably committed patent infringement by using the technology "unless it is told that the technology has been activated in the case of such a customer". Making this information available would prevent time and money being wasted by Enercon going to court against users of Siemens turbines that were, in fact, not relevant to the dispute.
Enercon is not currently arguing that mere installation of the technology in wind turbines supplied to a customer is an infringement by the customer. But it does argue that the activation of that technology leading to its use by a customer "is an infringement by the customer," according to the transcript of the October 2014 court hearing  EWHC 3173 (Pat).
Siemens and its customers continue to dispute the validity of the patent.
Much is at stake. The transcript noted: "It is said use of the technology is very profitable both for Siemens and for a customer who uses it."
Aside from Siemens plc, Siemens Wind Power and the Siemens Group, other companies listed in the patent dispute with Enercon are project companies Dong Energy Westermost Rough (wind-farm commissioning began in September 2014) and Dong Energy Gunfleet Sands Demo (UK), where commissioning began in April 2013 three months before Enercon launched its appeal of patent infringement. Also under fire are offshore wind installation and services companies A2Sea and A2Sea Limited, jointly owned by Dong Energy and Siemens Wind Power.
Separately, Enercon has also sued the project company for the London Array offshore wind farm, which is equipped with Siemens turbines. The London Array company has pleaded that to prove non-infringement, "it will rely upon an additional piece of prior art not (so far) relied upon by Siemens and the other defendants," the transcript said.
A crucial feature of the patented strom-control technology is that wind turbines using it avoid a lagging-behind effect. Prior art storm control saw turbines cutting out at the high wind cut-out speed — around 25 metres per second — and then not cutting in again until the wind consistently drops to a lower value, of perhaps under 20 metres per second — an effect called hysteresis, according to Enercon.
The EP 0 847 496 patent-covered technology allows the turbine to continue operating including during wind gusting at speeds between around 20-25 metres per second. Enercon said that in class Ia (high wind) areas its turbines may have an annual additional power output of 2-3% more than competitors' wind turbines.
The effect is achieved by slightly pitching the rotor blades out of the wind, Enercon said. Once the wind speed drops, the blades turn back into the wind and the turbine immediately resumes operation at full power, "preventing yield-reducing shutdown and start-up procedures".
Enercon stressed its storm-control feature contributes to grid security because at extremely high wind speeds there is no risk of a major disturbance caused by longer feed-in interruptions at many turbines. Such interruptions could have the same negative effect on transmission network stability as simultaneous shutdowns of several conventional power plants, the company said.
The UK court case in which the validity of the patent is judged is scheduled for June 2015 and expected to take about eight days.
Legal proceedings against Siemens in connection with the German part of the same European patent are running in parallel in Germany. No other procedures are pending in connection with other companies or in other countries with respect to EP 0 847 496, according to Enercon.
In late 2013, Enercon won a court case in Spain in a dispute with Gamesa over infringement of the same patent. Gamesa went to appeal in the first quarter of 2014. The earliest possible date for a final court decision is probably the end of 2015, according to Enercon. But further appeals by either party may take the dispute into a further round.