ACER Opinion 15-2026 on the Portuguese National Resource Adequacy Assessment

No 15/2026

OPINION

on the Portuguese National Resource Adequacy Assessment

2 September 2026

A C E R O P I N I O N N O 1 5 / 2 0 2 6

Executive summary

Under Regulation (EU) 2019/943, the European Network of Transmission System Operators for Electricity (ENTSO-E) conducts an annual European Resource Adequacy Assessment (ERAA). Member States may complement the ERAA with National Resource Adequacy Assessments (NRAAs) to take account of national specificities and recent developments that are not fully captured at the European level. Where an NRAA identifies an adequacy concern that was not identified in the ERAA, it must be submitted to ACER for an opinion, together with an explanation of the differences between the two assessments. Portuguese Directorate-General for Energy and Geology (DGEG) and Rede Elétrica Nacional (REN), the Portuguese transmission system operator (TSO), carried out an NRAA as part of a wider security of supply monitoring report of the Portuguese electricity system, RMSA-E 2025 (Relatório de Monitorização da Segurança de Abastecimento). The assessment identifies resource adequacy concerns across all target years, with the loss of load expectation (LOLE) exceeding the Portuguese reliability standard, in contrast to the results of the ERAA 2025 edition.

The identified adequacy concerns in the NRAA are primarily driven by assumptions that lead to a tighter supply-demand balance than in the ERAA. The NRAA assumes strong growth in electricity demand, driven by new energy-intensive consumers. At the same time, it reflects lower-than-expected renewable capacity deployment, assumes no demand response, and does not consider the 990 MW out-of-market Tapada do Outeiro gas-fired power plant as an adequacy resource. For 2030 and 2035, the adequacy gap increases further due to a conservative long-term battery deployment. Together, these assumptions lead to lower available resources relative to projected demand.

The resource deficit expected in the NRAA would typically create favourable market conditions for new resources to enter the market. The ERAA models market-based investment in adequacy resources via the so-called Economic Viability Assessment (EVA). Yet, in this case, the EVA of the NRAA is limited to evaluating the profitability of existing gas-fired capacity and omits modelling new market entries of various potential technologies. This may lead the NRAA to underestimate the capacity that could realistically be delivered by market-based investments, especially at high demand growth. Consequently, it remains unclear to what extent such investments could mitigate the projected adequacy gap, thereby reducing or eliminating the need for capacity mechanisms.

Thus, ACER’s key recommendation to the Portuguese authorities is to fully implement the EVA in the NRAA. The EVA should estimate the capacity of all relevant potential technologies that could realistically be delivered by the market by 2035 under the high-demand and low-resource scenario expected by the NRAA, including, in particular, non-fossil resources such as batteries and demand response. Lastly, ACER notes the relevance of developments in the planned Spanish capacity mechanism for Portugal’s resource adequacy assessment, as such developments may affect the availability of imports from Spain during scarcity periods.

A C E R O P I N I O N N O 1 5 / 2 0 2 6

1. Background

1 Article 20 of Regulation (EU) 2019/943 (Electricity Regulation) requires Member States to monitor resource adequacy within their territory based on the European Resource Adequacy Assessment (ERAA). It also allows to complement ERAA by conducting a National Resource Adequacy Assessment (NRAA) according to Article 24 of the Electricity Regulation. Either of the two assessments can identify resource adequacy concerns, but both assessments must be based on the ERAA methodology. The adequacy concerns identified through these assessments should be in the first place addressed by eliminating regulatory distortions or market failures, and, where it does not suffice, by introducing capacity mechanisms.

2 According to Article 24(3) of the Electricity Regulation, where an NRAA identifies an adequacy concern that was not identified in the ERAA, it must include reasons for the divergence between the two assessments. The Member State should publish the NRAA and submit it to ACER for an opinion. ACER assesses, on a case-by-case basis, whether the differences between the two assessments are justified. ACER primarily considers the differences identified and reasoned by the Member State, but may also identify further differences, if they also have a material impact on the results.

3 The national body responsible for preparing the NRAA, which can be a transmission system operator (TSO) or a different body designated by the Member State, must consider ACER's opinion, and, where necessary, amend the assessment. Where the body decides not to take ACER's opinion fully into account, it must publish a report with detailed reasons.

4 Portugal’s wind and solar generation capacity is expanding slower than anticipated by the national authorities, while electricity demand is expected to grow substantially. These developments could pose risks to security of electricity supply. Against this background, Portuguese Directorate-General for Energy and Geology (DGEG) and REN (Rede Elétrica Nacional), the Portuguese TSO, carried out an NRAA as part of a wider security of supply monitoring report of the Portuguese electricity system, RMSA-E 2025 (Relatório de Monitorização da Segurança de Abastecimento). The NRAA was submitted to ACER on 26 June 2026 by the Portuguese Government together with its ‘Justification for the divergence between Portugal’s NRAA and the ERAA’.

5 This Opinion evaluates whether the differences between the Portuguese NRAA and ERAA 2025 (`ERAA`) are justified and provides recommendations to improve the NRAA. It is addressed to the Portuguese Cabinet of the Secretary of State for Energy and is issued in accordance with Article 9(2) of Regulation (EU) 2019/942 and Article 24(3) of the Electricity Regulation.

2. Summary of the Portuguese NRAA

6 The NRAA presents adequacy results from two distinct models, the National methodology (operational LOLE) and the European methodology.

7 The National methodology model covers the Iberian Peninsula and is intended to assess whether sufficient resource capacity exists and whether the electricity system can operate securely and flexibly under a more detailed representation of the Portuguese electricity system. It includes demand and renewable generation uncertainties, start-up and ramp-up limitations of gas-fired power plants, and a more detailed representation of the hydropower system at the individual generating unit level, including water basins and their interconnected waterways. This national methodology is not based on the ERAA methodology and is, therefore, out of the assessment scope of this ACER opinion.

8 The European methodology model is based on the Europe-wide economic dispatch adequacy model developed for the ERAA 2025, aiming to ensure compliance with the requirements of the A C E R O P I N I O N N O 1 5 / 2 0 2 6 Electricity Regulation and the ERAA methodology. It provides the reference assessment for identifying a potential adequacy concern and, as such, is the subject of this Opinion.

9 The aim of the European methodology model is to complement ERAA by capturing recent market trends in demand and resource deployment within the Portuguese electricity system. This approach corresponds to the Trends and Projections scenario as defined in Article 3 of the newly amended ERAA methodology. In the NRAA, this scenario is referred to as Complementary Trajectory (Trajetória Complementar) and is further referred as the Central scenario in this Opinion.

10 Table 1 presents the adequacy results for the Portuguese electricity system as assessed in the NRAA`s Central scenario and in the 2025 edition of the ERAA. For all target years – 2028, 2030 and 2035 – the NRAA identifies new adequacy concerns that were not detected in the last ERAA, as the modelled Loss of Load Expectation (LOLE) in the NRAA exceeds the applicable reliability standard.

11 This divergence in the LOLE results is due to differences in the modelling assumptions and input data. The main differences between the NRAA and ERAA assumptions are discussed in detail and assessed by ACER in the following section.

3. ACER’s assessment: NRAA vs ERAA

12 The main differences in the Central scenario between the NRAA European methodology model and the ERAA 2025 edition fall into two categories: (i) methodological and (ii) input data. Each difference is listed in Table 2, along with its rationale, and potential impact on LOLE. A detailed description of these differences is provided below in this section. A C E R O P I N I O N N O 1 5 / 2 0 2 6

3.1. Partial economic viability assessment

13 Description and rationale: The NRAA does not fully comply with the ERAA methodology requirements concerning the economic viability assessment (EVA). In ERAA 2025, the EVA resulted in retirement of gas-fired capacity between 2028 and 2033 and expansion of demand response from 2030 onwards. In contrast, the NRAA only assesses the economic viability of the existing gas-fired power plants.

14 The projected gas capacity in the NRAA is found viable with a positive net profit for all assumed gas power plants across all target years (2028, 2030 and 2035). The NRAA posits that this is due to the significantly slower evolution of supply that is unable to meet the growing demand of data centers and large industrial consumers. However, the NRAA does not assess potential new entries of any technology, pointing to the lack of methodological maturity of the revenue-based EVA. Nevertheless, the Portuguese authorities have noted that the revenue-based EVA analysis will be implemented in the future adequacy assessments.

15 Relevance: The EVA assesses whether existing and prospective power resources are financially sustainable within an energy-only market. It serves as a proxy for investor behaviour, providing representation of market-driven investment and retirement decisions. Rather than relying solely on the model input, the EVA identifies a future resource mix that is economically viable and, therefore, closely aligned with expected market outcomes.

16 Assessment: The NRAA does not assess whether adequacy concerns and the associated scarcity rents could support additional economically viable resource capacity beyond the initial assumptions. According to data provided by the Portuguese authorities as an output of the economic evaluation performed, annual net profit of gas plants increases from almost 20 k €/MW in 2028 to 1.3 M €/MW by 2035. This increase is partially driven by much higher scarcity rents resulting from the increasing adequacy gap. Despite these results, the NRAA does not assess how much new capacity could enter the electricity market and operate with positive net profit.

17 Article 6(5) of the ERAA methodology indicates that the EVA is more than an evaluation tool for a single technology. The EVA is meant to shape the input capacity mix by determining whether to keep, retire, mothball, de-mothball, renew, or add various capacity resources (conventional as well as non-fossil resources such as batteries and demand response) based on their economic viability. Without full implementation of the EVA, the resource adequacy assessment risks misestimating adequacy concerns and materially misguide policy decisions. Although capacity delivery would be constrained by project development lead times in the short-to-medium term (2028, 2030), new capacity entry is especially relevant in the long-term (2035), given the NRAA’s ambitious demand growth under low renewable deployment.

18 In the context of high demand growth and high profits expected for existing plants, assessing the economic viability of the existing gas-fired power plants only and not assessing potential of new entries in the NRAA is not justified. The Portuguese authorities consider the revenue-based EVA approach insufficiently mature. ACER recalls that the ERAA methodology allows for an alternative EVA approach based on the minimisation of overall system costs, which has been regularly applied at both European and national level in recent years.

3.2. Capacity resources

19 Differences in capacity resources in the Central scenario between the NRAA and ERAA 2025 (post-EVA) are shown in Figure 1 for the three target years – 2028, 2030 and 2035. For context, actual and projected capacity mix is presented below. While the ERAA projection closely follows the ambitious Portuguese NECP targets, the Central scenario in the NRAA is described as the A C E R O P I N I O N N O 1 5 / 2 0 2 6 best available forecast of the evolution of the power system, reflecting current deployment trends at the time the study was undertaken.

20 Note, the EVA adjusts initial capacity assumptions based on economic feasibility and provides the updated resource mix as input to the economic dispatch adequacy model. In ERAA 2025 for Portugal, the EVA step decommissions 1770 MW gas-fired capacity across 2028 and 2030, and it adds demand-response capacity of 440 MW in 2030 and 730 MW in 2035.

21 Compared with actual values observed over the past five years, the NRAA in 2028 reflects an almost unchanged trend in wind capacity deployment and a continued gradual increase in solar capacity. In contrast, the ERAA projects a faster pace of renewable deployment by 2028. Between 2028 and 2030, total capacity in the NRAA remains broadly stable, as modest renewable and battery additions largely offset the closure of 990 MW Tapada do Outeiro gasfired plant. However, renewable capacity in the ERAA increases significantly over the same period. As a result, the projected NRAA capacity in 2030 falls considerably below the ERAA levels. With slower renewable build‑out, slower battery deployment and no demand response entry, the total projected NRAA capacity in 2035 remains below the ERAA projection.

22 ACER notes that part of the available generation capacity in the Portuguese electricity system (about 1.3 GW in 2028, rising to 1.8 GW by 2035) is reserved for grid balancing purposes to deal with sudden frequency drops. In both ERAA 2025 and NRAA, these balancing reserves are activated as the last resort before demand curtailment.

3.2.1. Lower wind and solar capacity

23 Description and rationale: In the NRAA, delivery of solar and wind capacities is slower than the NECP 2030 targets adopted in the ERAA 2025 assumptions. Instead, the NRAA projections are based on the current rate of capacity additions and DGEG’s best estimates , as depicted in Figure 1. By 2028, the NRAA capacities for wind and solar are 86% of the ERAA projection. By 2030, however, installed capacity in the NRAA amounts to roughly half of the ERAA projection. By 2035, the NRAA begins to close the gap, reaching 77% of the ERAA capacity.

24 Relevance: Wind and solar resource generation output depends on weather. It may not always be fully available during scarcity times. Still, its contribution to maintaining adequate electricity A C E R O P I N I O N N O 1 5 / 2 0 2 6 system operation remains significant, because of relatively high installed capacities compared with other resources. According to REN market statistics, July 2026 marked the first time solar power became Portugal's largest source of electricity generation, contributing 19% of consumption, followed by hydropower (16%) and wind power (13%).

25 Assessment: The projected wind and solar capacity in the NRAA in the first target year 2028, follows historical deployment trends of the last five years. By reflecting current trends, not NECP targets, the NRAA aligns with the Trends and Projections scenario approach according to the ERAA methodology. Article 3(3d) of the ERAA methodology describes that the projected evolution of supply in the Trends and Projection approach shall be ‘supported by concrete … evidence based on … historical deployment trends … and/or …new grid connection requests or investment plans … and/or … policy developments’. Compared to a linear trend based on historical data from Figure 1, the NRAA projections for solar broadly follow the observed trend, while those for wind are more optimistic. Although more conservative than the NECP targets, the renewable capacity expansion in the NRAA forecast is updated to historical trends and is, therefore, considered justified by ACER.

3.2.2. Exclusion of Tapada do Outeiro gas-fired power plant

26 Description and rationale: The NRAA considers the 990 MW Tapada do Outeiro gas-fired power plant as an out-of-market resource from 2028. The plant does no longer participate in the electricity market but remains available to the system operator to ensure security of supply and providing black start capability.

27 The NRAA does not consider the possibility that the plant could be activated before a supply shortage occurs, i.e. when market-based resources are insufficient to ensure an adequate level of upward reserves. Hence the NRAA does not consider Tapada do Outeiro in the adequacy assessment and the plant plays no role in the assessment.

28 In the ERAA, the plant is assumed operational until the end of 2030. Compared with the ERAA, the NRAA assumes earlier plant decommissioning, from the start of 2030 onwards, in line with guidance from the Portuguese Ministry of Environment and Energy (Order No. 18/MAEN/2026).

29 Relevance: Thermal resources provide highly available and dispatchable capacity during scarcity times. The Tapada do Outeiro plant represents one quarter of the existing thermal fleet capacity in Portugal. Thus, its operational decisions can have a significant impact on adequacy.

30 Assessment: According to Article 7(11)(c) and (d) of the ERAA methodology, the economic dispatch simulations shall provide results for LOLE both before and after activation of out-ofmarket capacity resources. Moreover, Article 8(1)(b) of the ERAA methodology describes that, a resource adequacy assessment ‘shall identify a resource adequacy concern if … the reliability standard is not fulfilled … if the LOLE after activation of out-of-market capacity resources … is higher than the LOLE RS’. In ERAA, out-of-market resources are normally modelled as such. The modelling assumptions for the Tapada do Outeiro plant being out-of-market resource reflects its current operational status. However, the NRAA does not reflect a possible activation of the out-of-market Tapada do Outeiro power plant during scarcity, contrary to the ERAA methodology. Therefore, this assumption is not justified. A C E R O P I N I O N N O 1 5 / 2 0 2 6

3.2.3. Conservative long-term battery deployment

31 Description and rationale: Compared to the ERAA 2025, the NRAA changes projected battery capacity considering mostly capacity receiving out of market remuneration which is either already awarded or is in the process of being awarded. It assumes 1000 MW battery capacity by the end of 2028 (see Figure 1). This is 3 times higher than the ERAA assumption. However, the NRAA assumes lower battery capacity in the longer term , with 1750 MW in 2030 (13% lower than in the ERAA) and 1875 MW in 2035 (25% lower than in the ERAA).

32 Relevance: Realistic battery deployment projections are essential for a renewable-heavy energy transition, as batteries provide flexibility to the electricity system and can, to some extent, replace fossil-fuel-fired power plants. This is particularly relevant for Portugal, as its location on the Iberian Peninsula limits opportunities to optimise cross-border flexibility resources. As a result, domestic flexibility solutions, including battery storage, is expected to play an increasingly important role in supporting system reliability and renewable integration.

33 Assessment: The Recovery and Resilience Plan has already financed 43 storage projects in Portugal with an investment of 100 M€ supporting at least 500 MW of installed battery capacity. An additional 750 MW of battery deployment is expected through competitive procedures, including compensation mechanisms for municipalities hosting the projects.

34 While the short-term battery deployment projections in the NRAA are broadly aligned with current trends, the long-term projection seems overly conservative. Between 2030 and 2035, the projected increase in battery capacity is only 125 MW.

35 ACER recognises that Portugal has a relatively large pumped-hydro storage capacity that competes with batteries for energy arbitrage and flexibility services and can reduce the profitability of additional battery capacity. However, without properly applying the EVA step, it is unclear up to what extent this competition would actually constrain new battery entry.

36 Under the ERAA methodology, the Trends and Projections scenario should reflect the best estimate of the expected evolution of the electricity system, based on observable trends and concrete evidence. Yet, in the absence of an EVA assessment, it remains unclear how many batteries could realistically enter the market on a merchant basis once public support schemes end. Therefore, ACER cannot conclude whether the conservative long-term battery deployment assumed in the NRAA is justified or not.

3.2.4. Lower hydro availability

37 Description and rationale: The NRAA assumes lower pumped-hydro storage availability in Portugal: about 500 MW lower in the first four months of each year compared to ERAA 2025. This adjustment is based on historical observations of maximum hydro generation pattern. Despite this reduction, the NRAA assumptions still allow pumped-hydro generation to operate slightly above the historical generation peaks observed over the past five years. In the model, the availability factor limits the installed capacity of hydro power plants, ensuring that simulated generation does not exceed historically observed peak output.

38 Relevance: Historical availability data reflect the combined effects of hydrological conditions, outages and environmental regulations allowing to capture seasonal operational constraints for more accurate modelling. This is particularly relevant for the Portuguese system adequacy assessment, where hydro resources combined provide the largest capacity (8174 MW). A C E R O P I N I O N N O 1 5 / 2 0 2 6

39 Assessment: The adjusted availability assumed in the NRAA is still 100 MW higher than the highest five-year historical evening generation peak (observed in January 2026) based on data from the ENTSO-E Transparency Platform. The adjustment of hydro availability in the NRAA, grounded in historical observations, is justified as it supports more realistic modelling of hydro generation.

40 ACER welcomes REN's submission of updated hydro availability data to ENTSO-E for use in the upcoming ERAA.

3.3. Ambitious demand growth

41 Description and rationale: The annual electricity demand in the Central scenario in the NRAA is close to that in the ERAA 2025 edition in the first target years: it is 1% higher than ERAA in 2028 and 4% lower in 2030. Meanwhile, in 2035 it is 11% higher than in ERAA. As scarcity events are more likely to occur during periods of high electricity consumption, Figure 2 compares the peak demand projections from both studies alongside historically observed peak demand in Portugal. The historical values illustrate a significantly slower peak demand growth trend than assumed in both ERAA and NRAA. By 2035, the NRAA peak demand projection deviates most significantly from the historical trend, exceeding it by 3.4 GW.

42 The projected peak demand difference between the two assessments is relatively small in the first two target years: the NRAA peak is 413 MW higher in 2028 but 287 MW lower in 2030. By 2035, however, the difference increases significantly, with the NRAA projecting peak demand 1896 MW higher. The main difference between the assessments is primarily driven by assumed volume of new energy-intensive consumers, particularly data centres, reflecting the current queue of connection requests. According to the Portuguese authorities, Portugal’s geographical position – connected to several submarine fibre-optic cables linking Europe and North America – strengthens the commercial rationale for data centre investment, reinforcing the higher demand outlook assumed in the NRAA.

43 As of February 2026, approximately 41 GW of connection requests from large electricity consumers had been received, of which around 9.2 GW were already secured through gridconnection permits. A further 4.6 GW of requests entered the Continental Large Demand Zone Procedure (Order No. 1135/2026), subject to financial guarantees linked to their respective project implementation and connection schedules. Taken together, approximately 13.8 GW was therefore either secured or at an advanced stage of allocation. Figure 2 illustrates the distribution of these allocated grid connections across the respective target years.

44 Relevance: The high demand growth assumption in the NRAA provides a stress test for a rapidly electrifying power system, yet it risks overstating future adequacy concerns, if projected demand does not fully materialise.

45 Assessment: Article 3(3e) of the ERAA methodology requires that the Trends and Projections scenario approach, such as the demand projection in the NRAA, is ‘supported by concrete … A C E R O P I N I O N N O 1 5 / 2 0 2 6 evidence based … new demand connection requests or investment plans’. The high-demand assumption in the NRAA is broadly aligned with the methodology, as it is supported by a substantial pipeline of formal connection requests. The NRAA also applies differentiated materialisation rates reflecting project maturity and commitment. These range from 80% for projects contracted under the stricter Continental Large Demand Zone Procedure to 20% for general-access projects. These rates result in the discounted capacity presented in Figure 2.

46 The NRAA demand forecast broadly reflects probability-weighted capacity estimates, assuming that not all grid connection requests will eventually materialise. This is in a line with the Commission Notice on Guidance on efficient and timely grid connections also recognises that a grid connection request does not necessarily result in a project ultimately materialising. It recommends milestone-based filtering of connection requests and use-it-or-lose-it mechanisms to release capacity where projects do not progress. In addition, also other national studies project lower new demand utilisation rates than those reflected in granted connection offers . Based on the above, ACER considers the NRAA high-demand assumption justified.

3.4. No demand-side flexibility

47 Description and rationale: The NRAA does not consider demand response in any of the target years, assuming that demand response capacity is not yet a sufficiently mature technology and no policy or target has been set for development of demand response in the country. While demand response capacity is also absent from the initial ERAA projection, the EVA phase results in entry of 440 MW demand response capacity in 2030, increasing to 510 MW in 2033 and 730 MW in 2035.

48 Relevance: Accurately capturing the future magnitude of demand-side response helps avoiding overinvestment in peaking generation capacity and ensuring a realistic and cost-efficient resource mix. Demand response can unlock additional system flexibility, which is particularly important for Portugal given its relatively limited interconnection with the wider European power system. Located at the western edge of the Iberian Peninsula, Portugal is connected only to Spain, which itself has currently constrained transmission links to the rest of Europe. Furthermore, in the context of the high demand growth expected in Portugal, demand response could be a key resource to lower peak demand and reduce the impact of the additional load on adequacy.

49 Assessment: Even though the Portuguese regulatory authority (ERSE) identified a demand response potential of 700 MW in its report and the Portuguese government recognised demand management as a viable solution for maintaining electricity system security in response to rising demand, demand response was not considered in the NRAA. Moreover, ERSE’s MPGGS already enables consumers and aggregated small flexible resources to participate in system services through aggregation, baseline programming, and mechanisms for managing energy procurement.

50 Furthermore, ACER considers that demand side flexibility is a key instrument in a scenario with high data centre growth. For reference, other national assessments have assumed a portion of the data centre demand to be flexible, e.g. the Adequacy and flexibility study for Belgium 2026- A C E R O P I N I O N N O 1 5 / 2 0 2 6 2036 assumed 20% of the data centre load to be flexible in the central scenario. See also Communication from the Commission on data centre flexibility.

51 While policies to develop demand-side response are currently not in place in Portugal, pursuant to Article3(3c)(c) of the ERAA methodology, ‘For policies not yet implemented, the scenario shall reflect the best estimate of their expected impact …’. In the current Portuguese context, with the expected rapid demand growth and a clear signal from the government to support the development of demand response, the exclusion of demand flexibility from the assessment is not justified.

4. Conclusions and recommendations

52 Across all target years – 2028, 2030 and 2035 – adequacy concerns in Portugal, that were not present in ERAA 2025, stem from the differences in assumptions between the NRAA and the ERAA 2025. In particular, from strong demand growth outpacing available capacity. The projected capacity shortfall is driven by (i) slower-than-expected renewable deployment, (ii) the absence of demand response, (iii) the exclusion of the 990 MW out-of-market Tapada do Outeiro gas-fired power plant from the adequacy assessment, and (iv) lower hydro availability. Conservative battery deployment assumptions further contribute to the adequacy risks identified for 2030 and 2035.

53 If demand grows while capacity additions lag, an adequacy gap inevitably emerges. This highlights the need for the EVA to be conducted as part of resource adequacy assessments. The EVA can identify which potential market-based investments are economically viable, estimate how much new capacity could realistically enter the market, and determine when additional capacity would no longer be profitable. Without fully implemented EVA, it remains unclear to what extent market-driven investments could lower the projected adequacy gap.

54 Against this background, Table 3 presents ACER’s assessment of whether the differences in the Central scenario in the Portuguese NRAA, compared against the ERAA 2025 edition, are justified.

55 ACER considers three of the seven differences are justified. However, the partial implementation of the EVA, the exclusion of the out-of-market gas-fired power plant from adequacy, and the absence of demand response flexibility are not justified. Regarding the conservative long-term battery deployment assumption ACER cannot conclude whether the difference is justified. The available information does not allow ACER to draw a conclusion on this matter. A C E R O P I N I O N N O 1 5 / 2 0 2 6

56 Addressing these issues would provide a more robust assessment of the adequacy of the Portuguese electricity system. ACER therefore recommends the following:

57 Recommendation 1: Fully implement the EVA in the NRAA, as required by the ERAA methodology to appropriately assess whether current and potential capacity is financially viable in the market and therefore likely to be built or maintained.

58 Recommendation 2: Include out-of-market resources that contribute to system adequacy assessment.

59 Recommendation 3: Incorporate realistic demand side response capacities into future adequacy projections and allow for further expansion during the EVA phase, particularly in the context of significant demand growth.

60 Additionally, ACER highlights that capacity market (CM) developments in neighbouring countries can affect resource adequacy, as recognised in the ERAA methodology under the with-CM scenario. This scenario is present neither in the NRAA nor in the ERAA and therefore is not a difference between the two assessments. However, ACER considers the with-CM scenario particularly relevant for Portugal, given its strong interconnection with Spain. Developments in Spain’s capacity mechanism, including any additional capacity expected to be procured under it, may affect the availability of imports from Spain during periods of energy scarcity and are therefore relevant to the assessment of Portugal’s resource adequacy.

61 Finally, ACER stresses the importance of ensuring that ENTSO-E receives up-to-date information on resource capacities and demand for preparing future ERAA editions, to ensure that adequacy projections in the ERAA reflect the most recent information available. This Opinion is addressed to the Portuguese Cabinet of the Secretary of State for Energy. Done at Ljubljana, on 2 September 2026. — SIGNED — V. ZULEGER, ACER Director ad interim