CASELAW-EPO - reviews of EPO Boards of Appeal decisions

T 500/20 – On sufficiency of disclosure

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The patent relates to a wind turbine, a method for controlling a wind turbine in an idling power producing situation.

The wind turbine control and method is aimed at damping or eliminating undesirable edgewise oscillations of the rotor blades that may appear in an idling power producing situation.

The control of the wind turbine alters the yaw angle if it detects the presence of blade edgewise oscillations. Changing the yaw angle changes the conditions that influence the presence of edgewise oscillations to dampen or eliminate them.

Brief outline of the case

The opponent appealed the decision to reject the opposition.

For the opponent, the invention is not sufficiently disclosed.

A late filed document from the opponent himself (E18), not admitted by the OD should be admitted into the proceedings.

Granted claims 1 and 11 lack novelty and inventive step.

The board dismissed the appeal.

Sufficiently of disclosure

The opponent’s position

The opponent objected, for both claim 1 and claim 11, that the invention cannot be carried out due to a contradiction of claim features.

The claim requires to change the nacelle yaw position while the turbine is at idle, the latter in their view meaning that no operation at all (including change in nacelle yaw position) is possible.

The board’s position

The board found that such a contradiction neither exists in the claim language nor in the accompanying description. The term “idling” is generally understood as meaning “to run while disconnected from load or out of gear, so that it performs no external or useful work” (OED).

In the field of wind turbines this simply means that the turbine runs but without generating power, normally when not coupled to the power grid.

For the board, the exact workings of the claimed invention are amply clear to a skilled reader if they genuinely approach the patent and its disclosure constructively, with a sincere willingness to understand.

As variously stated in case law, isolated cases of non-working or not ideally working embodiments is of no importance for the issue of sufficiency in the light of the large number of conceivable and realisable alternatives indicated in the description, cf. in this respect G 1/03 reasons 2.5.2, T 0857/16 reasons 35.

The Board found it necessary to add that the general argument, made in this case and unfortunately heard ever more often not only in the present field but more widely in mechanics, that the invention would not be sufficiently disclosed across the entire breadth of the claim misapplies an approach developed mainly in the field of chemistry for inventions where a central aspect of the claimed invention is a range of compositions or of parameter values, cf. CLBA, 10th edition, 2022, II.C.5.4.

There it is important that an effect associated in the patent with the range is plausible or plausibly demonstrated across the whole breadth of the claimed range (leaving aside issues of proof of plausibility, the subject of current referral G2/21). Otherwise the claimed invention would be insufficiently disclosed, because the effect is not plausible across the whole breadth of the range.

In claimed inventions that do not involve a range of parameter values or compositions basing an argument of insufficiency on this approach is inappropriate and can be rejected offhand for that reason.

This is especially so where, as in the present case, an invention is directed at a broadly defined concept expressed in terms of generic structural or functional features of an apparatus or of a method.

There it normally suffices to provide a single detailed example or embodiment to illustrate how this concept can be put into practice, cf. CLBA, II.5.2., in such a way that the underlying principles can be understood by the relevant skilled person and they can reproduce the claimed invention using their common general knowledge without undue burden, CLBA, II.4.1.

For the board, it is thus not enough to demonstrate insufficiency to conceive of an example falling within the terms of the claim that does not work because it does not achieve the claimed effect fully or at all. Such an example does not prove that the claimed concept does not work; rather it reflects the limitations that are inherent in any technological endeavour and which may provide the scope for future (inventive) development.

To successively argue insufficiency in a case such as this a very high burden of proof applies: the party must demonstrate through cogent argument based on the underlying principles, if necessary supported by evidence, that the claimed concept does not work, because it does not achieve the desired effect in any measure or indeed is counter to the laws of nature.

Or they must demonstrate that the disclosure lacks information on an important aspect of the claimed invention, without which the skilled person cannot realize the claimed invention without undue burden.

The opponent has failed to present any such arguments in the present case.


The board made clear that insufficiency cannot generally be claimed for the reason that sufficiency is not disclosed over the entire breadth of the claim.

This concept might be valid in chemistry for inventions where a central aspect of the claimed invention is a range of compositions or of parameter values, but should not be applied in other fields.

Hypothetical embodiments are also not encompassed by claims, e.g. T 2166/17 or T 875/11

An unreasonable interpretation of claims has nothing to do with lack of sufficiency, e.g. T 1599/16.

In T 288/09, the board already noted that is established case law that occasional failure is part of any scientific work and does not impair the reproducibility of an invention if no evidence showing that the claimed technical effect can definitely not be achieved within the whole range of application or that it can be achieved only with undue burden

In T 983/18 the board gave a nice summary of what sufficiency of disclosure means:

  • according to established jurisprudence whereas a claim attempts to define [the invention] in ideal conditions, the skilled person understands that actual operating conditions will not be ideal and so there may be occasional failures
  • with respect to any gaps in the disclosure, it is also established jurisprudence that where a claim does not make reference to certain elements of an invention essential to its operation, this does not necessarily mean that the invention is insufficiently disclosed.


Art 83

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