Polskie sieci elektroenergetyczne S.A. and Others v European Union Agency for the Cooperation of Energy Regulators (C-281/23 P)

Contents

Judgment of the Court (Second Chamber)23 October 2025^note(Appeal — Internal market for electricity — Regulation (EU) 2019/942 — Board of Appeal of the European Union Agency for the Cooperation of Energy Regulators (ACER) — Regulation (EU) 2017/2195 — Articles 20, 21 and 37 — Balancing electricity — Transmission system operators — Establishment of European platforms for the exchange of balancing energy — European platform for the exchange of balancing energy from frequency restoration reserves with manual activation (mFRR platform) — European platform for the exchange of balancing energy from frequency restoration reserves with automatic activation (aFRR platform) — Development and approval of the implementation frameworks for those platforms — Functions required to operate those platforms — Cross-zonal capacity for the exchange of balancing energy — ACER decision rejecting the common proposal of the system operators)In Joined Cases C‑281/23 P and C‑282/23 P,TWO APPEALS under Article 56 of the Statute of the Court of Justice of the European Union, brought on 30 April 2023,Polskie sieci elektroenergetyczne S.A., established in Konstancin-Jeziorna (Poland),RTE Réseau de transport d’électricité, established in Paris (France),Svenska kraftnät, established in Sundbyberg (Sweden),TenneT TSO BV, established in Arnhem (Netherlands),represented by B. Byrne, advocaat, D. Jubrail, Solicitor, and M. Levitt, avocat,the other party to the proceedings being:European Union Agency for the Cooperation of Energy Regulators (ACER), represented by P. Martinet, A. Tellidou and E. Tremmel, acting as Agents, and by E. Abril Fernández, E. Ameye, abogados, and M. de Sousa Ferro, advogado,THE COURT (Second Chamber),composed of K. Jürimäe, President of the Chamber, K. Lenaerts, President of the Court, acting as a Judge of the Second Chamber, and Z. Csehi (Rapporteur), JudgeAdvocate General: M. Campos Sánchez-Bordona,Registrar: A. Lamote, Administrator,having regard to the written procedure and further to the hearing on 24 October 2024,after hearing the Opinion of the Advocate General at the sitting on 16 January 2025,gives the following

Judgment

1By their two appeals brought on 30 April 2023, Polskie sieci elektroenergetyczne S.A., RTE Réseau de transport d’électricité, Svenska kraftnät and TenneT TSO BV ask the Court of Justice to set aside, respectively, the judgment of the General Court of the European Union of 15 February 2023, Austrian Power Grid and Others v ACER (T‑606/20, EU:T:2023:64), and the judgment of the General Court of 15 February 2023, Austrian Power Grid and Others v ACER (T‑607/20, EU:T:2023:65) (‘the judgments under appeal’), by which the General Court dismissed as unfounded the actions for annulment brought against Decisions A‑001‑2020 (consolidated) and A‑002‑2020 (consolidated) of the Board of Appeal of the European Union Agency for the Cooperation of Energy Regulators (ACER) of 16 July 2020 (‘the decisions at issue’), by which the Board of Appeal had confirmed ACER Decisions No 02/2020 and No 03/2020 of 24 January 2020 (‘the ACER decisions’), relating to the implementation framework for the European platform for the exchange of energy from frequency restoration reserves with automatic activation (‘the aFRR platform’) and to the implementation framework for the European platform for the exchange of energy from frequency restoration reserves with manual activation (‘the mFRR platform’).

I.Legal context

A.Regulation (EU) 2017/2195

2Recitals 1, 6, 7 and 10 of Commission Regulation (EU) 2017/2195 of 23 November 2017 establishing a guideline on electricity balancing (OJ 2017 L 312, p. 6) state:(1) A fully functioning and interconnected internal energy market is crucial for maintaining security of energy supply, increasing competitiveness and ensuring that all consumers can purchase energy at affordable prices.…(6) This Regulation pursues the objective of ensuring the optimal management and coordinated operation of the European electricity transmission system, while supporting the achievement of the [European] Union’s targets for penetration of renewable generation, as well as providing benefits for customers. [Transmission system operators (TSOs)], working with [distribution system operators (DSOs)] where relevant, should be responsible for organising European balancing markets and should strive for their integration, keeping the system in balance in the most efficient manner. To do so, TSOs should work in close cooperation with one another and with DSOs, coordinating their activities as much as possible to deliver an efficient electricity system, across all regions and voltage levels, without prejudice to competition law.(7) … However TSOs should remain responsible for the tasks entrusted to them pursuant to [Directive (EU) 2019/944 of the European Parliament and of the Council of 5 June 2019 on common rules for the internal market for electricity and amending Directive 2012/27/EU (OJ 2019 L 158, p. 125),] for the development of [Europe]-wide methodologies, as well as the implementation and operation of the [Europe]-wide balancing platforms. Where, in a Member State, the expertise and experience of operating imbalance settlement lies with a third party, the TSO of the Member State may request the other TSOs and [the European Network of Transmission System Operators for Electricity (ENTSO-E)] to enable such third party to assist in the development of the proposal [for terms and conditions or methodologies required by this Regulation]. However, the responsibility for developing the proposal remains with the TSO of the Member State in conjunction with all other TSOs and such responsibility cannot be transferred to a third party.…(10) The integration of balancing energy markets should be facilitated with the establishment of common European platforms for operating the imbalance netting process and enabling the exchange of balancing energy from frequency restoration reserves and replacement reserves. Cooperation between TSOs should be strictly limited to what is necessary for the efficient and secure design, implementation and operation of those European platforms.’

3Article 2 of that regulation, entitled ‘Definitions’, provides:‘For the purposes of this Regulation, …the following definitions shall also apply:…(1) “balancing” means all actions and processes, on all timelines, through which TSOs ensure, in a continuous way, the maintenance of system frequency within a predefined stability range …;…(4) “balancing energy” means energy used by TSOs to perform balancing and provided by a balancing service provider;…(24) “exchange of balancing energy” means the activation of balancing energy bids for the delivery of balancing energy to a TSO in a different scheduling area than the one in which the activated balancing service provider is connected;…(39) “activation optimisation function” means the function of operating the algorithm applied to optimise the activation of balancing energy bids;…’

4Article 3 of that regulation, entitled ‘Objectives and regulatory aspects’, provides, in paragraphs 1(c) and 2(c) thereof:1.This Regulation aims at:…(c) integrating balancing markets and promoting the possibilities for exchanges of balancing services while contributing to operational security;…2.When applying this Regulation, Member States, relevant regulatory authorities, and system operators shall:…(c) apply the principle of optimisation between the highest overall efficiency and lowest total costs for all parties involved’.

5Article 20 of that regulation, entitled ‘European platform for the exchange of balancing energy from frequency restoration reserves with manual activation’, provides, in paragraphs 1 to 3 thereof:1. By one year after entry into force of this Regulation, all TSOs shall develop a proposal for the implementation framework for a European platform for the exchange of balancing energy from frequency restoration reserves with manual activation.2. The European platform for the exchange of balancing energy from frequency restoration reserves with manual activation, operated by TSOs or by means of an entity the TSOs would create themselves, shall be based on common governance principles and business processes and shall consist of at least the activation optimisation function and [the function of performing the settlement of cooperation processes between the TSOs (the TSO-TSO settlement function)]. This European platform shall apply a multilateral [model for the exchange of balancing services where the balancing service provider provides balancing services to its connecting TSO, which then provides these balancing services to the requesting TSO (TSO-TSO model)] with common merit order lists to exchange all balancing energy bids from all standard products for frequency restoration reserves with manual activation, except for unavailable bids pursuant to Article 29(14).3.The proposal in paragraph 1 shall include at least:(a) the high level design of the European platform;…(c) the definition of the functions required to operate the European platform;…’

6Article 21 of Regulation 2017/2195, entitled ‘European platform for the exchange of balancing energy from frequency restoration reserves with automatic activation’, provides, in paragraphs 1 to 3 thereof:1. By one year after entry into force of this Regulation, all TSOs shall develop a proposal for the implementation framework for a European platform for the exchange of balancing energy from frequency restoration reserves with automatic activation.2. The European platform for the exchange of balancing energy from frequency restoration reserves with automatic activation, operated by TSOs or by means of an entity the TSOs would create themselves, shall be based on common governance principles and business processes and shall consist of at least the activation optimisation function and the TSO-TSO settlement function. This European platform shall apply a multilateral TSO-TSO model with common merit order lists to exchange all balancing energy bids from all standard products for frequency restoration reserves with automatic activation, except for unavailable bids pursuant to Article 29(14).3.The proposal in paragraph 1 shall include at least:(a) the high level design of the European platform;…(c) the definition of the functions required to operate the European platform;…’

7Article 37 of that regulation, entitled ‘Cross-zonal capacity calculation’, provides, in paragraphs 1 to 3 thereof:1. After the intraday-cross-zonal gate closure time, TSOs shall continuously update the availability of cross-zonal capacity for the exchange of balancing energy or for operating the imbalance netting process. Cross-zonal capacity shall be updated every time a portion of cross-zonal capacity has been used or when cross-zonal capacity has been recalculated.2. Before the implementation of the capacity calculation methodology pursuant to paragraph 3, TSOs shall use the cross-zonal capacity remaining after the intraday cross-zonal gate closure time.3. By five years after entry into force of this Regulation, all TSOs of a capacity calculation region shall develop a methodology for cross-zonal capacity calculation within the balancing timeframe for the exchange of balancing energy or for operating the imbalance netting process. Such methodology shall avoid market distortions and shall be consistent with the cross-zonal capacity calculation methodology applied in the intraday timeframe established under [Commission Regulation (EU) 2015/1222 of 24 July 2015 establishing a guideline on capacity allocation and congestion management (OJ 2015 L 197, p. 24)].’

B.Regulation (EU) 2019/942

8Article 6 of Regulation (EU) 2019/942 of the European Parliament and of the Council of 5 June 2019 establishing a European Union Agency for the Cooperation of Energy Regulators (OJ 2019 L 158, p. 22), entitled ‘Tasks of ACER as regards the regulatory authorities’, states, in paragraph 10 thereof:‘…ACER shall be competent to adopt individual decisions as specified in the first subparagraph in the following situations:(a) where the competent regulatory authorities have not been able to reach an agreement within six months of referral of the case to the last of those regulatory authorities, or within four months in cases under Article 4(7) of this Regulation or under point (c) of Article 59(1) or point (f) of Article 62(1) of [Directive 2019/944]; or(b) on the basis of a joint request from the competent regulatory authorities.…’

II.Background to the dispute

9The background to the dispute was set out by the General Court in paragraphs 2 to 18 of each of the judgments under appeal and, for the purposes of the present proceedings, may be summarised as follows.

10Regulation 2017/2195 provides for the implementation of several European platforms for the exchange of balancing energy, including the mFRR and aFRR platforms.

11On 18 December 2018, the TSOs sent to all the national regulatory authorities (‘NRAs’), for approval, their common methodology proposals for the implementation of the mFRR and aFRR platforms. By letter dated 24 July 2019, the Chair of the Forum of Energy Regulators (FER), on behalf of all NRAs, informed ACER that they had jointly decided to request ACER to decide on those proposals.

12Following several exchanges between ACER, the NRAs and the TSOs, which led to ACER rejecting the first to third proposals submitted by the TSOs, the TSOs, on 18 December 2019, sent ACER an amended version of their third methodology proposals.

13The TSOs proposed, in essence, that a single entity, namely a single TSO or a company owned by TSOs, would be responsible for performing the functions specifically required to operate the mFRR and aFRR platforms, namely the activation optimisation function and the TSO-TSO settlement function, and that the performance of the function of managing the availability of cross-zonal capacity for the exchange of balancing energy or for operating the imbalance netting process (‘the capacity management function’), which is a cross-platform function, could be entrusted to another single entity, namely a single TSO or a company owned by TSOs.

14On 20 December 2019, ACER finalised its draft mFRR and aFRR methodology decisions, which were communicated to the TSOs.

15On 24 January 2020, ACER adopted two decisions relating to the mFRR and aFRR methodologies. In its decisions, ACER considered, in essence, that all TSOs had to appoint one entity, whether a single TSO or a company owned by TSOs, to be entrusted to operate the activation optimisation function and the TSO-TSO settlement function of the mFRR and aFRR platforms. No later than eight months before the deadline when the capacity management function was to be considered as a function required to operate those platforms, all TSOs had to have developed a proposal for amendment of the implementation frameworks for those platforms, designating the entity performing that function and clarifying whether those platforms would be operated by a single entity or multiple entities.

16On 23 March 2020, Austrian Power Grid AG, ČEPS, a.s., Polskie sieci elektroenergetyczne, Red Eléctrica de España SA, RTE Réseau de transport d’électricité, Svenska kraftnät, TenneT TSO BV and TenneT TSO GmbH brought two appeals before the Board of Appeal of ACER against the ACER decisions.

17On 16 July 2020, by the decisions at issue, the Board of Appeal of ACER dismissed those two appeals and upheld the ACER decisions.

III.The procedure before the General Court and the judgments under appeal

18By applications lodged at the Registry of the General Court on 30 September 2020, the appellants brought two actions for annulment of the decisions at issue, in so far as those decisions concern them.

19In support of those actions, the appellants raised three pleas in law. First of all, by their first plea in each action, each of which was divided into two parts, they claimed that the Board of Appeal had erred in law by failing to find that ACER had exceeded the limits of its competence in adopting the ACER decisions. The appellants submitted, in essence, that the Board of Appeal had incorrectly concluded, first, that ACER had not departed from the NRAs’ common position as set out in the joint requests and, second, that, in any event, ACER was permitted to depart from the NRAs’ common position.

20Next, by their second plea in each action, each of which was divided into eight parts, the appellants complained, inter alia, that the Board of Appeal had erred in law by finding that the inclusion of the capacity management function among the functions required for the operation of the mFRR and aFRR platforms had not been imposed on the TSOs by ACER, but resulted directly from the application of Regulation 2017/2195.

21Last, by their third plea in each action, they claimed, inter alia, that the Board of Appeal had applied an incorrect standard of review by carrying out only a limited review of the ACER decisions, that is to say, a review confined to the search for manifest errors of assessment of complex factual issues of a technical nature.

22By the judgments under appeal, the General Court dismissed those two actions.

23As a preliminary point, the General Court, in paragraphs 24 and 25 of each of the judgments under appeal, declared inadmissible the second head of claim in each of the actions for annulment brought by the appellants, in so far as they were directed against the ACER decisions and the annexes thereto. The General Court stated that, since the appellants did not have the status of privileged applicants, they could only bring proceedings before the General Court against the decisions adopted by the Board of Appeal. Accordingly, in those judgments, the General Court confined itself to reviewing the legality of those decisions.

24In response to the first plea in each action, the General Court found, in essence, that ACER was empowered to rule, or to adopt individual decisions, on regulatory issues or issues falling within the competence of the NRAs, such as the development of methodologies for the implementation of the mFRR and aFRR platforms, where, as in the present case, the NRAs make a joint request to ACER to that effect, without its competence being limited solely to points of disagreement between the authorities concerned.

25In that regard, the General Court also noted that the explanatory memorandum of the proposed Regulation 2019/942 and the previously applicable Regulation (EC) No 713/2009 indicated a clear intention of the EU legislature to make decision-making on cross-border issues more efficient and expeditious by strengthening ACER’s individual decision-making powers. It therefore follows, according to the General Court, in paragraph 48 of each of the judgments under appeal, that ACER has been granted regulatory functions and decision-making powers of its own, which it exercises independently and under its own responsibility, in order to be able to deputise for the NRAs where their voluntary cooperation does not allow them to take individual decisions on particular issues or problems falling within their regulatory competence.

26Consequently, in paragraph 60 of each of those judgments, the General Court concluded that the Board of Appeal had not erred in law by not finding that ACER had exceeded the limits of its competence by ruling on points of the mFRR and aFRR methodologies which had been the subject of agreement between the NRAs. Accordingly, the General Court rejected the first plea in each action in their entirety.

27In response to the second plea in each action, the General Court held, inter alia, in paragraphs 120, 122 and 124 of each of the judgments under appeal, that the inclusion of the capacity management function among the functions required for the operation of the mFRR and aFRR platforms had in no way been imposed on the TSOs by ACER, but resulted from the application of Regulation 2017/2195.

28In that regard, the General Court examined whether capacity management constituted one of the functions required to operate the mFRR and aFRR platforms within the meaning of Regulation 2017/2195. It stated at the outset that that inclusion was decisive in assessing whether the proposals developed by the TSOs had to comply with the additional requirements set out in that regulation where, as in the present case, the TSOs envisage designating several entities to perform the different functions required. Thus, the General Court found, in paragraph 105 of each of the judgments under appeal, that, in accordance with that regulation, the proposed methodologies submitted by the TSOs must include the definition of the functions required for the operation of the mFRR and aFRR platforms. In that regard, it considered that, while it followed from a literal interpretation of that regulation that those platforms are to include at least the activation optimisation function and the TSO-TSO settlement function, it could not be ruled out that another function, such as the capacity management function, might also be considered to be required for the operation of those platforms, in particular if the addition of such a function appears to be necessary to ensure a high-level design of those platforms, in line with common governance principles and business processes.

29Furthermore, the General Court noted, in paragraph 110 of each of those judgments, that an interpretation of the notion of function required for the operation of the mFRR and aFRR platforms, in the light of the context and objectives pursued by Regulation 2017/2195, suggested that it is a function which, both technically and legally, appears to be necessary for the efficient and safe establishment and operation of those platforms.

30From a legal point of view, that regulation requires TSOs continuously to update the availability of cross-zonal transmission capacity for the exchange of balancing energy or for operating the imbalance netting process. From a technical point of view, the continuous updating of the availability of that capacity, which underpins the capacity management function, is an ‘essential input’ to the activation optimisation function. That management function was added to the mFRR and aFRR platforms by the TSOs themselves, in order for them to meet the requirements of a high-level design in terms of efficiency and safety required by Regulation 2017/2195.

31Consequently, the General Court concluded, in paragraph 122 of each of the judgments under appeal, that the function of continuously updating the available cross-zonal transmission capacity, which underlies the capacity management function, and hence the capacity management function itself, had to be broadly qualified as functions required to operate the mFRR and aFRR platforms.

32In its response to the fifth and sixth parts of the second plea raised in each action before it, the General Court held, in paragraph 135 of each of the judgments under appeal, that capacity management was also taken into account in the third mFRR and aFRR methodology proposals as a cross-platform function, the performance of which was necessary to operate the mFRR and aFRR platforms, even though it had not been qualified in those proposals as a function required to operate the mFRR and aFRR platforms within the meaning of Article 20(3)(c) and Article 21(3)(c) of Regulation 2017/2195. The General Court considered, however, in accordance with the conclusion it had reached in paragraph 122 of each of those judgments, that the Board of Appeal had been correct to consider that capacity management, as provided for in Article 37 of that regulation, constituted a function required to operate the mFRR and aFRR platforms, within the meaning of Article 20(3)(c) and Article 21(3)(c) of that regulation.

33Similarly, in its response to the seventh part of the second plea raised in each action before it, the General Court held, in paragraph 143 of each of the judgments under appeal, referring to its assessment in paragraph 122 of each of those judgments, that capacity management was a function required to operate each platform.

34In response to the third plea in each action, as regards the intensity of the review carried out by the Board of Appeal of ACER, the General Court rejected, in paragraphs 200 to 205 of each of the judgments under appeal, the complaint alleging infringement of the Board of Appeal’s obligation to carry out a full review of the ACER decisions.

35In that regard, the General Court noted, in the first place, that the Board of Appeal had, in accordance with its decision-making practice at the time, carried out a full review only of the legal assessments in the ACER decisions, and that it had confined itself, as regards ACER’s complex factual assessments of a technical nature, to carrying out a limited review, confined to the search for manifest errors. However, it acknowledged that it was apparent from the judgment of 18 November 2020, Aquind v ACER (T‑735/18, EU:T:2020:542), that the Board of Appeal was required to conduct a full review of the legal and technical assessments made by ACER in its decisions.

36Nevertheless, the General Court held, in the second place, following a careful examination of the decisions at issue, that, first, the Board of Appeal had essentially focused its review on legal assessments made by ACER, with respect to which it had exercised a full review, and that, second, where it had been called upon to review complex technical assessments, the Board of Appeal had, in practice, carried out a review which went beyond a mere limited review, so that, de facto, it had complied with its obligations as regards the intensity of the review it was required to carry out in respect of the ACER decisions.

37Since none of the pleas raised by the appellants was upheld, in paragraph 214 of each of the judgments under appeal, the General Court dismissed the actions in their entirety.

IV.Procedure before the Court of Justice and forms of order sought by the parties to the appeals

38The appellants claim that the Court of Justice should:– set aside, either in whole or in part, the judgments under appeal;– annul, either in whole or in part, the decisions at issue; and– order ACER to pay the costs.

39ACER contends that the Court of Justice should:– declare the appeals inadmissible, either in whole or in part, and, in any event, unfounded and dismiss them accordingly; and– order the appellants to pay the costs.

V.The appeals

40In support of their appeals, the appellants put forward two grounds of appeal. The first ground of each appeal alleges that the General Court erred in law in holding that the Board of Appeal of ACER had not failed to fulfil its obligation to carry out a full review of the ACER decisions. The second ground of each appeal, each of which is divided into two parts, alleges, in essence, that the General Court erred in law in finding that, under Regulation 2017/2195, the capacity management function was a function required to operate the mFRR and aFRR platforms.

A.Admissibility

1.Arguments of the parties

41ACER submits that the appeals must be dismissed as inadmissible on the ground that the grounds of the appeals seek only a re-examination of the pleas put forward at first instance. The Court of Justice does not have jurisdiction to carry out such a review when an appeal is brought before it.

42In addition, ACER submits that the first ground of each appeal has no practical relevance and that it constitutes a purely hypothetical or theoretical issue, since the appellants do not challenge the General Court’s assessment that the Board of Appeal, de facto, carried out a full review of the ACER decisions.

43The appellants submit that the appeals are admissible.

2.Findings of the Court

44According to settled case-law, provided that an appellant challenges the interpretation or application of EU law by the General Court, the points of law examined at first instance may be discussed again in the course of an appeal. Indeed, if an appellant could not thus base his or her appeal on pleas in law and arguments already relied on before the General Court, an appeal would be deprived of part of its purpose (see judgments of 13 July 2000, Salzgitter v Commission, C‑210/98 P, EU:C:2000:397, paragraph 43; of 16 May 2002, ARAP and Others v Commission, C‑321/99 P, EU:C:2002:292, paragraph 49; and of 12 June 2025, ZR v EUIPO, C‑364/23 P, EU:C:2025:428, paragraph 34).

45In the present case, the appellants do not seek a mere re-examination of the applications submitted at first instance, but seek, first, to call into question the legal reasoning which led the General Court to find that the Board of Appeal had not failed to fulfil its obligation to carry out a full review of the ACER decisions, and, second, to claim that the General Court did not correctly apply Articles 20, 21 and 37 of Regulation 2017/2195, which govern, respectively, the mFRR and aFRR platforms and the capacity management function, in its assessment of the legal bases and of the functions required to operate those platforms.

46In that regard, the appellants claim, inter alia, in the first ground of each appeal, that the General Court disregarded the case-law of the Court of Justice stemming from the judgment of 9 March 2023, ACER v Aquind (C‑46/21 P, EU:C:2023:182), from which it is apparent that that Board of Appeal must conduct a full review of the legal and technical assessments made by ACER. In particular, they do not criticise the General Court’s assessment that the Board of Appeal de facto carried out a full review of the ACER decisions, but rather the fact that the General Court’s conclusion that such a review had been carried out by the Board of Appeal overrode that board’s explicit statement, in its decisions, that it was limiting its review to manifest errors.

47In addition, in the second ground of each appeal, they complain, in essence, that the General Court failed to distinguish between the separate legal obligations imposed in Article 37 of Regulation 2017/2195 and the performance of the functions required to operate the platforms concerned. Moreover, according to the appellants, the General Court erred in law by extending the scope of Article 20(1) and (2) and Article 21(1) and (2) of that regulation to functions ‘broadly qualified’ as required as a means of justifying the designation of the capacity management function as a function required to operate the platforms.

48Where they challenge the interpretation or application of EU law, the appellants have indicated to the requisite legal standard the passages of each of the judgments under appeal which they claim to be vitiated by errors of law and have set out the legal arguments underlying those grounds of appeal, which enables the Court to carry out its review.

49It follows that the grounds of inadmissibility put forward by ACER must be rejected and that, accordingly, the appeals must be declared admissible.

B.Substance

1.The first ground of each appeal

(a)Arguments of the parties

50In the first ground of each appeal, the appellants dispute the General Court’s assessment, set out in paragraphs 203 to 205 and 214 of each of the judgments under appeal, in so far as it rejected their complaint alleging infringement of the Board of Appeal’s obligation to carry out a full review in the context of its examination of the ACER decisions.

51The appellants submit, in essence, that the General Court erred in law in finding, on the one hand, that it was apparent from the decisions at issue that that board had incorrectly stated that it would carry out only a limited review of the ACER decisions, but that, on the other hand, despite the finding of that error, it was apparent from the decisions at issue that the Board of Appeal had, in practice, carried out a review which went beyond a mere limited review, so that, de facto, the Board of Appeal complied with its obligations as regards the intensity of the review to be carried out. In so doing, according to the appellants, the General Court disregarded the case-law stemming from the judgment of 9 March 2023, ACER v Aquind (C‑46/21 P, EU:C:2023:182). Thus, in assessing the legality of the decisions at issue, the General Court should have confined itself to finding that the Board of Appeal had erred in law by stating that it was applying an incorrect standard of review. The General Court could not have disregarded that statement by examining the standard of review that the Board of Appeal applied ‘de facto’ or ‘in practice’.

52ACER contends that the first ground of each appeal must be rejected as manifestly unfounded.

(b)Findings of the Court

53By the first ground of each appeal, the appellants claim that the General Court erred in law in its assessment of the intensity of the review carried out by the Board of Appeal.

54In that regard, in paragraphs 201 and 202 of each of the judgments under appeal, the General Court held, in essence, that the Board of Appeal’s review of complex technical and economic assessments in the ACER decisions should not be confined to a limited review of the manifest error of assessment, but that that review had to be full.

55It must be held, in that regard, that the judgments under appeal are consistent with what the Court of Justice held in the judgment of 9 March 2023, ACER v Aquind (C‑46/21 P, EU:C:2023:182), relied on by the appellants in support of their appeals.

56It must therefore be determined whether the mere finding made by the General Court, in paragraph 200 of each of the judgments under appeal, that it was apparent from footnote 81 to the decisions at issue, and from paragraph 192 of those decisions, that the Board of Appeal had suggested that, in accordance with its decision-making practice at the time, it had confined itself to carrying out a limited review, should have led the General Court to annul those decisions.

57In that regard, it should be noted that the General Court was entitled to consider that, even though the Board of Appeal had referred on several occasions to the requirement stemming from its decision-making practice to apply a limited review with regard to the ACER decisions, the reference to such a review cannot lead to the annulment of the decisions at issue, in so far as that reference did not prevent that board from carrying out the full review required of it (see, by analogy, judgment of 8 December 2011, Chalkor v Commission, C‑386/10 P, EU:C:2011:815, paragraph 82).

58That is what the General Court specifically verified in the assessment set out in paragraphs 203 to 205 of each of the judgments under appeal, holding that it was apparent from the decisions at issue that, first, the Board of Appeal had essentially focused its review on the legal assessments made by ACER, with respect to which it had exercised a full review. Second, it considered that, in the rare cases where that board had been called upon to review complex technical assessments, it had, in practice, carried out a review which went beyond a mere limited review. The General Court concluded that, de facto, the Board of Appeal had thus complied with its obligations as regards the intensity of the review to be carried out.

59In their appeals, the appellants do not claim that that assessment is vitiated by any error of law.

60It follows that the first ground of each appeal must be rejected as unfounded.

2.The second ground of each appeal

(a)The first part of the second ground of each appeal

(1)Arguments of the parties

61By the first part of the second ground of each appeal, the appellants claim that the General Court erred in law, in paragraphs 115 to 124 of each of the judgments under appeal, in so far as it held that the function allowing for the continuous calculation and updating of the available cross-zonal transmission capacity, provided for in Article 37 of Regulation 2017/2195, had to be regarded as falling within the functions required to operate the mFRR and aFRR platforms, provided for in Articles 20 and 21 of that regulation. They claim that the General Court incorrectly assimilated the requirements stemming from Article 37 of that regulation into the functions referred to in Articles 20 and 21 thereof, whereas that regulation provides for separate legal regimes applicable, on the one hand, to TSOs and, on the other hand, to those platforms.

62According to the appellants, contrary to what the General Court held, the obligations imposed in Article 37 of Regulation 2017/2195 cannot be assimilated into Articles 20 and 21 of that regulation. Thus, TSOs are not required, under the latter articles, to entrust the entity in charge of the mFRR and aFRR platforms with updating or calculating cross-zonal capacity. Contrary to what was held by the General Court, ACER was not entitled to impose that obligation on them.

63Thus, although the appellants accept that cross-zonal capacity data are inputs necessary for the proper functioning of the balancing platform, they state that it does not follow that the calculation of those data must, as a necessary function, be performed by the entity entrusted with operating the platform or by the platform itself.

64ACER contends that the first part of the second ground of each appeal must be rejected.

(2)Findings of the Court

65In connection with the first part of the second ground of each appeal, it is necessary to examine whether the General Court erred in law in holding that, in accordance with Articles 20 and 21 of Regulation 2017/2195, the capacity management function falls within the functions required to operate the mFRR and aFRR platforms, within the meaning of Article 20(3)(c) and Article 21(3)(c) of that regulation.

66As a preliminary point, it should be recalled that, according to settled case-law, when interpreting a provision of EU law, it is necessary to consider not only its wording but also the context in which it occurs and the objectives pursued by the rules of which it is part (see judgments of 17 November 1983, Merck, 292/82, EU:C:1983:335, paragraph 12, and of 9 March 2023, ACER v Aquind, C‑46/21 P, EU:C:2023:182, paragraph 54).

67As regards, in the first place, the literal interpretation, it should be noted, as the General Court noted in paragraph 103 of each of the judgments under appeal, that the concept of ‘functions required to operate the [mFRR and aFRR platforms]’ is not defined in Regulation 2017/2195, but is used only in Articles 20 and 21 of that regulation.

68However, in accordance with Articles 20 and 21 of Regulation 2017/2195, it is the responsibility of the TSOs to develop the methodology proposals for the implementation frameworks for the mFRR and aFRR platforms. As the General Court correctly stated in paragraphs 104 and 105 of each of the judgments under appeal, those proposals must include, at least, ‘the high level design of the European platform’ and ‘the definition of the functions required to operate the [mFRR and aFRR platforms]’. Those platforms, operated by TSOs or by means of an entity the TSOs would create themselves, are to be based on common governance principles and business processes and are to consist of at least the activation optimisation function and the TSO-TSO settlement function. Thus, the activation optimisation function and the TSO-TSO settlement function are functions required, in any event, to operate the mFRR and aFRR platforms.

69As the General Court correctly held in paragraph 105 of each of the judgments under appeal, it cannot be ruled out that, in connection with Articles 20 and 21 of Regulation 2017/2195, other functions may be added to the methodology proposals for the implementation frameworks for the mFRR and aFRR platforms. As the General Court noted, in that paragraph of each of those judgments, Article 20(2) and Article 21(2) of that regulation provide that the mFRR and aFRR platforms are to include ‘at least the activation optimisation function and the TSO-TSO settlement function’. In that regard, the expression ‘at least’ indicates that that clause does not set out an exhaustive list. In the light of that clause, the General Court was entitled to find that those provisions did not preclude the possibility that, in the context of the design of those platforms, a function, other than activation optimisation and TSO-TSO settlement, such as capacity management, might also be considered to be required for the operation of those platforms.

70In addition, it should be noted that the General Court also relied on the finding that the addition of such a function appeared to be particularly necessary in order to ensure a high-level design of those platforms complying with common governance principles and business processes. Thus, it is apparent from paragraph 106 of each of the judgments under appeal that the General Court did not interpret Article 20(2) and Article 21(2) of Regulation 2017/2195 in isolation, but also relied, in accordance with the settled method of interpreting the provisions of EU law, on a teleological and contextual interpretation of the concept of ‘functions required to operate the [mFRR and aFRR platforms]’ in order to conclude that capacity management, like activation optimisation and TSO-TSO settlement, had to be regarded as such a required function.

71As regards, in the second place, that teleological and contextual interpretation, the General Court first relied, in paragraphs 107 to 109 of each of the judgments under appeal, on the objectives pursued by Regulation 2017/2195, as set out in recitals 1, 6, 7 and 10 of that regulation, and in Article 3(1)(c) and (2)(c) of that regulation. Those objectives relate in particular to the efficient and secure implementation and operation of the Europe-wide energy balancing platforms. On the basis of that interpretation, which, moreover, is not disputed by the appellants, the General Court was fully entitled to conclude that those objectives support the inclusion of the capacity management function among the functions required to operate the mFRR and aFRR platforms, in so far as, both technically and legally, that function appears to be necessary for attaining those objectives.

72In that regard, first, the General Court noted in paragraph 113 of each of the judgments under appeal that, technically, as the appellants themselves acknowledge, the continuous updating of available cross-zonal transmission capacity is an ‘essential input’ to the activation optimisation function, which is itself a required function of the mFRR and aFRR platforms. The latter function is intended to optimise the activation of the highest-ranked balancing energy bids, taking into account the limited available cross-zonal transmission capacity. Thus, the General Court was fully entitled to consider that the capacity management function, in which the continuous updating of the available cross-zonal transmission capacity takes place, was a technically indispensable element for the proper functioning of those platforms.

73Second, in paragraph 114 of each of the judgments under appeal, the General Court correctly took into account, in its contextual interpretation of Articles 20 and 21 of Regulation 2017/2195, the requirements stemming from Article 37 of that regulation, which impose on TSOs the legal obligation to calculate cross-zonal capacity.

74It is true, as the appellants submit, that those requirements are, prima facie, essentially addressed to TSOs. Nonetheless, Articles 20 and 21 of Regulation 2017/2195 make TSOs responsible for the implementation of the mFRR and aFRR platforms in compliance with the objectives pursued by that regulation. In that regard, it is apparent from Article 20(2) and (3) and Article 21(2) and (3) of that regulation that the design of those platforms, operated by TSOs or by means of an entity the TSOs would create themselves, must be of a high level and comply with common governance principles and business processes.

75It follows that a function which, while addressed to the TSOs under Article 37 of Regulation 2017/2195, appears to be necessary in order for the TSOs’ implementation of those platforms to attain those objectives, must be regarded as a function falling within the ‘functions required to operate the [mFRR and aFRR platforms]’, within the meaning of Article 20(3)(c) and Article 21(3)(c) of that regulation, which must be performed by the entity entrusted with operating those platforms or by those platforms themselves and not by the TSOs.

76The appellants themselves acknowledge that cross-zonal capacity data are inputs necessary for the proper functioning of those platforms. Thus, contrary to what the appellants claim, that means that the function allowing for the continuous calculation and updating of the available cross-zonal transmission capacity must be performed by the entity entrusted with operating the mFRR and aFRR platforms or by those platforms themselves and not by the TSOs.

77The General Court was therefore fully entitled to hold, in paragraph 115 of each of the judgments under appeal, that the function allowing for the calculation and updating of the available cross-zonal transmission capacity, as a function underlying capacity management, had to be regarded as a function required to operate the mFRR and aFRR platforms, in accordance with Article 20(3)(c) and Article 21(3)(c) of Regulation 2017/2195.

78In the light of all the foregoing considerations, the first part of the second ground of each appeal must be rejected as unfounded.

(b)The second part of the second ground of each appeal

(1)Arguments of the parties

79In the second part of the second ground of each appeal, the appellants claim that the General Court made an error of law in paragraphs 122, 135 and 143 of each of the judgments under appeal, in so far as it did not distinguish between, on the one hand, the obligations incumbent on TSOs, with regard to the functions ‘required’ to operate the mFRR and aFRR platforms, and, on the other, the TSOs’ right to include additional functions in those platforms. In so doing, the General Court incorrectly extended the scope of Article 20(1) and (2) and Article 21(1) and (2) of Regulation 2017/2195 to functions ‘broadly qualified’ as required as a means of justifying the designation of the capacity management function as a ‘function required’ to operate the platforms.

80ACER contends that the second part of the second ground of each appeal must be rejected.

(2)Findings of the Court

81At the outset, it should be noted that the first and second parts of the second ground of each appeal are closely linked.

82In the light of the considerations set out in paragraphs 65 to 78 of the present judgment, the General Court did not err in law in classifying, in paragraphs 122, 135 and 143 of each of the judgments under appeal, the capacity management function as a function ‘required’ to operate the mFRR and aFRR platforms.

83In those circumstances, the second part of the second ground of each appeal must also be rejected and, therefore, the second ground of each appeal must be rejected in their entirety.

84Since none of the grounds raised has been upheld, the appeals must be dismissed in their entirety.

Costs

85Under Article 184(2) of the Rules of Procedure of the Court of Justice, where the appeal is unfounded, the Court is to make a decision as to costs.

86Under Article 138(1) of those rules, which applies to the procedure on appeal by virtue of Article 184(1) thereof, the unsuccessful party is to be ordered to pay the costs if they have been applied for in the successful party’s pleadings.

87Since the appellants have been unsuccessful and ACER has applied for costs, the appellants must be ordered to pay the costs.

Operative part

On those grounds, the Court (Second Chamber) hereby:

1.Dismisses the appeal;

2.Orders Polskie sieci elektroenergetyczne S.A., RTE Réseau de transport d’électricité, Svenska kraftnät and TenneT TSO BV to pay the costs.

Delivered in open court in Luxembourg on 23 October 2025.