Curtailment Minimisation Legal Obligations in Renewable-Heavy Grids

1. Introduction

Curtailment minimisation means reducing the unnecessary reduction or stopping of renewable electricity generation. In a renewable-heavy electricity grid, large amounts of wind and solar power may be available, but the network may not have enough capacity to carry all of it. Curtailment may therefore happen because of transmission congestion, system-security requirements, low demand or insufficient flexibility.

Legal obligations are important because network operators should not rely on curtailment as the normal solution to grid problems. Modern electricity law increasingly requires them to use better planning, grid investment, flexibility, storage and transparent redispatch procedures.

2. Duty to Minimise Renewable Curtailment

The European Union provides a strong example through Regulation (EU) 2019/943.

Article 13 requires redispatching to be based on objective, transparent and non-discriminatory criteria. It also generally requires market-based selection of resources and financial compensation for redispatching.

More specifically, Article 13(5) requires transmission and distribution system operators to ensure that their networks can transmit renewable electricity with minimum possible redispatching. They must also take appropriate grid-related and market-related measures to reduce downward redispatch of renewable generation.

This creates an important legal responsibility: network operators must actively work towards reducing avoidable renewable curtailment.

3. Grid Planning and Investment

A major part of this obligation is proper network planning.

Where repeated congestion prevents renewable electricity from reaching consumers, operators may need to consider:

upgrading transmission lines;

constructing new network infrastructure;

increasing transformer capacity;

strengthening interconnectors;

improving distribution networks;

installing advanced grid-control systems; and

increasing network flexibility.

However, the law does not require operators to eliminate every instance of curtailment at any cost. EU law allows network planning to take account of limited redispatch where the operator can demonstrate transparently that this is more economically efficient. For certain renewable installations directly connected to the relevant grid, the Regulation refers to a 5% annual-generation threshold, subject to the conditions and exceptions in the legislation.

4. Flexibility and Alternative Solutions

Curtailment minimisation is not limited to physical grid expansion.

Operators can also use:

Battery storage: Excess renewable electricity can be stored and used later.

Demand response: Consumers can increase electricity consumption during periods of high renewable generation.

Interconnection: Electricity can be transferred to neighbouring regions where demand or network capacity is available.

Digitalisation: Real-time monitoring and automated grid management can identify congestion and improve system operation.

Regulation 2019/943 specifically refers to measures including investment in digitalisation of grid infrastructure and services that increase flexibility when reducing future renewable downward redispatch.

5. Limits on Non-Market Curtailment

The law also places limits on arbitrary curtailment.

Where non-market-based downward redispatch is used, renewable generators should generally be curtailed only when no alternative exists or when alternatives would create significantly disproportionate costs or serious risks to network security. Such decisions must be duly and transparently justified.

This requirement is important because it prevents a system operator from simply choosing renewable curtailment whenever congestion occurs without considering other solutions.

6. Compensation as a Legal Protection

When non-market-based downward redispatch is used, Regulation 2019/943 generally requires financial compensation from the system operator requesting the redispatch. The compensation may include additional operating costs and the net revenues that the facility would have earned in the day-ahead market. Certain non-firm connection arrangements are treated differently.

Therefore, the legal framework combines two protections:

Prevent unnecessary curtailment, and

Compensate generators when legally permitted curtailment occurs.

7. Regulatory Oversight

Regulatory authorities also have an important role. Operators must report the reasons, volumes and types of redispatching, together with measures taken to reduce future renewable curtailment. These reports can include investments in digitalisation and flexibility services.

This reporting obligation allows regulators to examine whether repeated curtailment reflects a genuine system-security problem or inadequate network development.

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 ACER Board of Appeal decision, highlighting the need for a proper legal basis and reasoning when determining congestion-management cost-sharing rules.

This is relevant because the costs created by congestion and redispatch can influence decisions about future grid investment and curtailment management.

TransnetBW GmbH v ACER, Case T-476/21

In T-476/21, also decided on 25 September 2024, the General Court considered ACER's methodology for sharing redispatching and countertrading costs under Article 16(13) of Regulation 2019/943.

The case demonstrates the importance of clear and lawful rules for allocating congestion-management costs between interconnected transmission-system operators.

9. Conclusion

Curtailment minimisation legal obligations are particularly important in renewable-heavy grids. They require network operators to do more than simply switch off renewable generation during congestion. Operators must consider grid reinforcement, storage, demand response, interconnection, digitalisation and other flexibility measures.

At the same time, the law recognises that zero curtailment may not always be economically practical. The main legal objective is therefore to achieve minimum reasonably necessary curtailment, while maintaining network security and protecting renewable generators through transparent rules and appropriate compensation. The EU framework under Regulation 2019/943 provides a clear example of this balance, supported by the principles examined in TenneT v ACER and TransnetBW v ACER.