RESOURCE ADEQUACY MODELLING AND REGULATION

1. Meaning and Purpose

Resource adequacy modelling determines whether an electricity system possesses sufficient dependable generation, storage, interconnection and demand-side flexibility to satisfy demand across a range of future conditions. It differs from short-term balancing because it addresses whether enough resources will be available over months and years, including during periods of high demand, renewable intermittency, generator outages or interconnector constraints.

In Great Britain, resource adequacy is closely linked to the Capacity Market, the statutory reliability standard and the National Energy System Operator’s modelling functions. NESO defines resource adequacy as assessing risks to security of supply and determining whether sufficient resources are available to meet demand throughout the year.

2. Reliability Standard

The principal regulatory benchmark is Loss of Load Expectation (LOLE). LOLE measures the expected number of hours in a year during which available electricity resources may be insufficient to meet demand.

Great Britain’s Capacity Market currently applies a reliability standard of 3 hours LOLE per year. NESO uses this standard when recommending how much capacity should be procured through the Capacity Market.

LOLE is probabilistic rather than an absolute guarantee. A three-hour standard does not mean that consumers will necessarily suffer three hours of disconnection every year. Instead, it represents an expected statistical level of adequacy across numerous possible system conditions.

3. Modelling Methodology

Resource adequacy models normally combine:

Forecast electricity demand;

Conventional generator availability and forced-outage rates;

Wind and solar production patterns;

Battery duration and discharge capability;

Interconnector availability;

Demand-side response;

weather uncertainty; and

correlations between simultaneous system stresses.

Different technologies are assigned de-rating factors, reflecting their expected contribution during scarcity periods. NESO expressly models technology-specific de-rating factors when assessing Capacity Market requirements.

This is particularly important for storage and variable renewables. Installed megawatts do not necessarily equal dependable megawatts during prolonged scarcity.

4. Capacity Market Regulation

The Capacity Market provides payments to eligible resources in return for being available when the electricity system requires capacity. The detailed operational regime is contained in the Capacity Market Rules, most recently consolidated in July 2026.

NESO prepares an annual Electricity Capacity Report assessing future adequacy and recommending auction parameters. The Secretary of State then determines target capacity for T-1 and T-4 auctions.

For the July 2026 parameters, government set target capacity at 5.0 GW for the 2027/28 T-1 auction and 40.9 GW for the 2030/31 T-4 auction, while retaining the three-hour LOLE standard.

Independent scrutiny is provided by the Panel of Technical Experts, which reviews NESO's modelling and advises government on its assumptions and methodology.

5. Regulatory Challenges

Adequacy regulation must address considerable uncertainty. Climate change can alter demand and renewable-output patterns, while electrification of heating and transport can increase peak demand. Large quantities of storage, distributed resources and interconnection also make traditional capacity calculations more complex.

Regulators therefore need scenario analysis, probabilistic modelling, sensitivity testing and transparent assumptions. Excessive procurement can unnecessarily increase consumer costs, whereas under-procurement can increase security-of-supply risks.

Resource adequacy regulation must consequently balance reliability, affordability and decarbonisation.

6. Case Law

Case Name/Citation: Tempus Energy Ltd v European Commission, Case T-793/14, EU:T:2018:790

Facts: Tempus Energy challenged European Commission approval of the UK Capacity Market, arguing that the scheme inadequately considered demand-side response.

Legal Issue: Whether the Commission should have undertaken a formal investigation before approving the capacity mechanism.

Judgment: The General Court annulled the Commission's approval.

Legal Principle/Ratio: Capacity mechanisms must be assessed carefully where technological neutrality, competition and security-of-supply assumptions materially affect market participation.

Significance: Resource adequacy models should recognise genuine contributions from demand response and alternative flexibility rather than automatically privileging conventional generation.

Case Name/Citation: Commission v Tempus Energy Ltd, Case C-57/19 P, EU:C:2021:663

Facts: The Commission appealed the General Court decision relating to approval of the UK Capacity Market.

Legal Issue: Whether the evidence demonstrated sufficient doubts requiring a formal State-aid investigation.

Judgment: The Court of Justice allowed the Commission's appeal and set aside the General Court judgment.

Legal Principle/Ratio: Complex capacity-market modelling does not itself establish legal inadequacy; challenges must satisfy the applicable evidential and procedural standards.

Significance: Regulators retain substantial technical discretion in adequacy modelling, but their methodologies remain subject to legal scrutiny concerning evidence, procedure and equal treatment.

7. Conclusion

Resource adequacy modelling converts uncertain future electricity conditions into legally significant procurement decisions. The UK framework combines LOLE modelling, de-rating factors, Capacity Market auctions, NESO analysis and independent technical scrutiny. Effective regulation requires technologically neutral modelling, transparent assumptions and an appropriate balance between security of supply, consumer cost and the transition to a low-carbon electricity system.