Curtailment Transparency Reporting Requirements

1. Introduction

Curtailment transparency reporting requirements are legal obligations requiring electricity-system operators to provide information about the reduction or stopping of renewable electricity generation. Curtailment happens when a renewable-energy project, such as a solar or wind plant, is capable of producing electricity but is instructed to reduce output because of grid congestion, network limitations, low demand, or system-security requirements.

Transparency is important because curtailment can cause financial losses for renewable generators and can also affect consumers, investors and electricity-market efficiency. Reporting requirements allow regulators to understand why curtailment happened and whether the system operator is taking sufficient steps to reduce it.

2. Legal Purpose of Reporting

The main purpose of reporting is to make curtailment decisions visible, reviewable and accountable.

A proper reporting system should help answer:

Why was electricity curtailed?

How much renewable electricity was curtailed?

Which type of generation was affected?

How long did the curtailment continue?

What network constraint caused it?

What alternatives were considered?

What was the financial cost?

What action will reduce future curtailment?

Under Article 13 of Regulation (EU) 2019/943, redispatching must be based on objective, transparent and non-discriminatory criteria.

3. Annual Reporting Obligation

One of the clearest examples is provided by EU electricity law.

Article 13(4) requires transmission-system operators and distribution-system operators to report at least annually to the competent regulatory authority on:

the development and effectiveness of market-based redispatch mechanisms;

the reasons for redispatching;

the volume of electricity in MWh affected;

the type of generation source subject to redispatch; and

measures being taken to reduce future downward redispatch of renewable generation or high-efficiency cogeneration.

The measures can include grid digitalisation and flexibility services.

This is important because reporting is not limited to showing how much curtailment occurred. It also requires operators to explain what they are doing to reduce future curtailment.

4. Publication and Regulatory Review

The regulatory authority receiving the report must submit it to ACER (Agency for the Cooperation of Energy Regulators) and publish a summary of the relevant information together with recommendations for improvement where necessary.

This creates a chain of accountability:

System operator → National regulator → ACER → Public information

Such a system allows regulators and market participants to identify repeated congestion and assess whether network investment or flexibility measures are necessary.

5. Transparency of Curtailment Decisions

Reporting should also provide sufficient information to understand individual curtailment events.

Important information may include:

date and time of curtailment;

affected generating facility;

amount of electricity reduced;

technical reason;

relevant transmission constraint;

duration of the event;

type of redispatch;

compensation paid; and

corrective measures.

The exact level of public disclosure can be limited where information is commercially sensitive or security-sensitive. Therefore, transparency must be balanced with legitimate confidentiality requirements.

6. Non-Discrimination

Reporting obligations also help enforce non-discrimination.

If similar renewable generators are repeatedly treated differently, regulators can examine whether there is an objective technical or legal reason.

EU law requires redispatching to be open to generation technologies, storage and demand response and to be based on objective, transparent and non-discriminatory criteria.

Therefore, reporting is not merely an administrative requirement. It can become evidence for regulatory review of potentially unequal treatment.

7. Reporting and Curtailment Reduction

Transparency also connects reporting with future grid investment.

Article 13(5) requires network operators to seek minimum possible redispatching of renewable electricity, while allowing limited redispatching where it can be demonstrated transparently to be more economically efficient within the conditions set by the Regulation.

Operators must therefore consider whether repeated curtailment can be reduced through:

transmission expansion;

network reinforcement;

storage;

demand response;

digitalisation;

better forecasting; and

flexibility services.

8. Relevant Case Laws

TenneT TSO GmbH and TenneT TSO BV v ACER, Case T-482/21

The General Court decided T-482/21 on 25 September 2024. The case concerned ACER's methodology for sharing the costs of redispatching and countertrading in the CORE electricity region.

The Court annulled the relevant Board of Appeal decision in part because of illegality concerning the determination of the threshold for legitimate loop flows and an inadequate statement of reasons.

The case is relevant to transparency because it shows that important electricity-market methodologies must be supported by clear reasoning and a lawful regulatory basis.

TransnetBW GmbH v ACER, Case T-476/21

This case was part of the same group of disputes concerning the methodology for allocating redispatching and countertrading costs. It demonstrates the importance of clear regulatory methodologies when congestion-management decisions create financial consequences for transmission-system operators.

9. Conclusion

Curtailment transparency reporting requirements create an important system of legal accountability in renewable-heavy electricity markets. Operators should report the reasons, volumes, generation types and measures relating to redispatching, while regulators should review and publish relevant information.

The EU framework under Regulation 2019/943 provides a strong example because it connects reporting with non-discrimination, renewable-curtailment reduction, grid investment and regulatory supervision.

Ultimately, transparent reporting helps ensure that curtailment is not treated as an unexplained operational decision. It allows regulators to identify repeated network problems, evaluate whether investment is required, monitor compensation and ensure that renewable generators are treated according to clear and objective rules.