Curtailment Forecasting and Regulatory Oversight

1. Introduction

Curtailment forecasting means predicting when and how much electricity generation, particularly from wind and solar projects, may have to be reduced because the electricity network cannot absorb or transport all available generation. It is becoming increasingly important as renewable-energy penetration increases.

Curtailment may result from transmission congestion, low demand, inadequate network capacity, system-security requirements, or insufficient flexibility. Accurate forecasting helps system operators plan redispatch, storage, transmission use and balancing actions before curtailment occurs.

Regulatory oversight ensures that these forecasts and curtailment decisions are transparent, accurate, non-discriminatory and legally justified.

2. Importance of Curtailment Forecasting

Renewable generation depends heavily on weather conditions. Solar output changes with sunlight, while wind generation depends on wind speed and direction. Therefore, system operators need forecasts of:

expected renewable generation;

electricity demand;

transmission capacity;

network congestion;

storage availability;

interconnector capacity; and

expected balancing requirements.

When these variables are combined, operators can estimate the probability and volume of future curtailment.

Forecasting can reduce unnecessary curtailment because operators may arrange storage, demand response, interconnection or redispatch before the constraint becomes critical.

EU electricity rules require transmission and distribution operators to maintain appropriate information about generation, demand, network availability, flexibility and balancing resources. Regulation 2019/943 also requires relevant operational data to be made available for system planning and market functioning. (Eur-Lex)

3. Forecasting and Redispatch

Forecasting is directly connected with redispatching. If an operator predicts congestion in advance, it can use market-based redispatch to change generation or demand.

Article 13 of Regulation (EU) 2019/943 provides that redispatching should be based on objective, transparent and non-discriminatory criteria. Market-based redispatch is generally preferred and must be financially compensated. Non-market-based redispatch is permitted only in specified circumstances. (Eur-Lex)

This creates an important legal relationship:

Better forecasting → earlier congestion identification → better redispatch decisions → potentially lower renewable curtailment.

4. Regulatory Oversight

Regulatory authorities have several responsibilities.

First, they can examine whether transmission and distribution operators are using reasonable forecasting methods.

Second, regulators can require operators to publish information about curtailment. Article 13 requires transmission and distribution operators to report at least annually on the effectiveness of market-based redispatch, the reasons and volumes of redispatching, and measures taken to reduce future downward redispatching of renewable generation. Regulatory authorities must submit the relevant report to ACER and publish a summary with recommendations where necessary. (Eur-Lex)

Third, regulators can examine whether curtailment decisions discriminate between different generators.

5. Transparency and Data Accuracy

Forecasting systems depend upon reliable data. Incorrect generation forecasts or inaccurate network information can result in unnecessary curtailment.

EU Regulation 2019/943 requires transmission-system operators to report accurately and transparently on capacity calculations and requires information supplied for regional coordination to be accurate and fit for purpose. (Eur-Lex)

This is particularly important where several countries share interconnected electricity networks. A forecasting error in one area may affect congestion and redispatch decisions in another area.

6. Renewable-Energy Protection

Regulation 2019/943 places limits on unnecessary downward redispatch of renewable generation. Renewable facilities should generally be curtailed through non-market-based redispatch only where no alternative exists or alternatives would involve significantly disproportionate costs or serious network-security risks. The decision must also be properly and transparently justified. (Eur-Lex)

The framework also requires networks to be capable of transmitting renewable electricity with minimum possible redispatching, while allowing limited redispatch where it can be demonstrated to be economically efficient. (Eur-Lex)

7. Relevant Case Laws

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

The General Court's 2024 judgment concerned the EU methodology for allocating redispatching and countertrading costs. The case is relevant because it demonstrates the importance of regulatory methodologies for determining how congestion-management costs are distributed between transmission-system operators. (Eur-Lex)

TransnetBW GmbH v ACER, Case T-476/21

This case also concerned the allocation methodology for redispatching and countertrading costs. It illustrates how regulatory decisions concerning network congestion can have significant financial consequences and therefore require a clear legal methodology.

These cases are relevant to forecasting because forecasting, congestion identification, redispatch and cost allocation form interconnected parts of modern electricity regulation.

8. Conclusion

Curtailment forecasting is becoming an important part of renewable-energy governance. Accurate forecasts allow system operators to anticipate congestion and use storage, demand response, interconnection and redispatch more efficiently. Regulatory oversight ensures that forecasting and curtailment decisions are not arbitrary.

A strong legal framework should therefore require accurate data, transparent forecasting methodologies, regular reporting, independent regulatory supervision, non-discriminatory redispatch and proper justification of renewable curtailment. This approach can reduce unnecessary renewable-energy losses while maintaining electricity-system security.