1. Introduction

Curtailment risk arises when a power generator is technically capable of producing electricity but is prevented from delivering some or all of that electricity to the grid because of transmission congestion, system-security requirements, oversupply, negative prices, or other network constraints. It is particularly important for wind, solar and other variable renewable-energy projects.

Investment decisions in electricity markets depend heavily on expected revenues. Investors generally consider expected energy prices, capacity revenues, renewable-energy certificates, subsidies, congestion costs, balancing costs and the probability that generated electricity will actually be dispatched. When curtailment is uncertain or inadequately priced, the resulting investment signal may become distorted.

The central legal and regulatory issue is therefore:

Who should bear the economic risk when a renewable project cannot deliver electricity because the electricity network cannot accommodate its output?

This question affects project finance, transmission planning, grid connection, power-purchase agreements (PPAs), tariff design and the legal allocation of risks between generators, network operators, consumers and governments.

2. Meaning of Curtailment Risk

Curtailment can occur for several reasons:

Transmission congestion – the local transmission network cannot transport all available generation.

System-security constraints – the system operator reduces generation to maintain stability.

Excess renewable generation – available renewable output exceeds demand or network capability.

Interconnection limitations – the project has limited grid-export capability.

Economic curtailment – generation is reduced because market prices make production uneconomic.

Administrative curtailment – regulators or system operators impose restrictions under statutory or contractual authority.

For an investor, the critical distinction is between installed capacity and revenue-generating output.

A 100-MW solar plant does not necessarily have the economic value of 100 MW of continuously dispatchable capacity. If grid constraints regularly prevent 15% of potential generation from being delivered, the investor's effective revenue-producing capacity is materially lower.

3. How Curtailment Distorts Investment Signals

Investment signals are supposed to communicate where, when and in what technology investment is economically valuable.

Normally:

High demand + high prices + available transmission → investment incentive

But curtailment can produce:

High renewable resource + apparent low generation cost + inadequate transmission → apparent investment opportunity that may not produce expected revenues

This creates several distortions.

A. Geographic distortion

Investors may locate projects in areas with excellent solar or wind resources even when those areas have inadequate transmission capacity.

The resource signal therefore says:

"Build here."

The transmission constraint says:

"The electricity cannot reliably leave this location."

If the second signal is not properly incorporated into project economics, capital can become concentrated in already-congested regions.

B. Technology distortion

Curtailment can also alter the relative attractiveness of technologies.

For example:

solar may experience high midday curtailment;

wind may experience curtailment during periods of strong production;

batteries may benefit because they can absorb otherwise curtailed electricity;

flexible generation may receive greater value during constrained periods.

Thus, poorly designed curtailment rules may encourage additional generation capacity while failing to encourage storage and transmission capacity, even though the latter may provide greater system value.

C. Revenue distortion

Suppose a renewable project expects:

annual potential production = 100,000 MWh;

expected electricity price = ₹4/MWh-equivalent;

expected revenue = ₹400,000.

If 20% of output is curtailed, only 80,000 MWh may be delivered.

The actual revenue becomes approximately:

80,000 × ₹4 = ₹320,000

The investment model has therefore overstated revenue by approximately ₹80,000.

If investors systematically underestimate this risk, the market may attract excessive investment into generation and insufficient investment into transmission.

4. Curtailment and Transmission Investment

One of the most important legal-economic relationships is between generation investment and transmission investment.

Electricity cannot ordinarily be stored economically in unlimited quantities. Consequently, generation and transmission must be coordinated.

A transmission network that is unable to carry renewable output creates a phenomenon sometimes described as stranded generation capacity.

The legal framework should therefore answer:

Who determines available transmission capacity?

Who pays for network reinforcement?

Who bears curtailment losses?

Is curtailment compensated?

Does a generator have priority dispatch?

Can the system operator curtail generation without compensation?

Are congestion costs reflected in locational prices?

Can investors challenge discriminatory or arbitrary curtailment?

These questions directly affect the investment signal.

5. Priority Dispatch and Curtailment

Renewable-energy laws sometimes provide renewable generators with priority or preferential dispatch.

The rationale is straightforward: renewable generation has environmental and policy benefits, and governments may wish to ensure that renewable electricity is not routinely displaced by conventional generation.

However, priority dispatch cannot necessarily eliminate physical grid constraints.

Where the network itself is incapable of carrying the electricity safely, the system operator may have to curtail generation.

This creates an important legal distinction:

Economic curtailment may be a consequence of market design, while

technical curtailment may be necessary for system security.

Investment law and energy regulation must therefore distinguish legitimate grid-management decisions from arbitrary or discriminatory treatment of generators.

6. Curtailment Risk in Renewable PPAs

Curtailment risk is especially important in long-term PPAs.

A PPA may specify:

minimum purchase obligations;

deemed generation;

must-run status;

priority dispatch;

force-majeure provisions;

grid-availability obligations;

compensation for transmission-related curtailment;

termination rights.

The contractual allocation of curtailment risk can substantially change the project's bankability.

Example

If the buyer must pay for electricity that could have been generated but was curtailed because of transmission congestion, the buyer or network system may bear the risk.

If payment is made only for electricity actually delivered, the generator bears more of the risk.

Therefore:

The same physical grid constraint can produce completely different investment signals depending on the contractual allocation of curtailment risk.

7. Regulatory Treatment of Curtailment

A well-designed regulatory framework generally needs to distinguish between:

(i) Generator-caused curtailment

For example, failure to satisfy technical grid requirements.

The generator may reasonably bear the associated risk.

(ii) Network-caused curtailment

For example, inadequate transmission capacity.

Placing the entire risk on the generator can discourage investment even where the project itself is efficient.

(iii) System-security curtailment

Temporary curtailment necessary to preserve grid stability.

Some level of generator risk may be unavoidable.

(iv) Policy-driven curtailment

Where government policy or regulatory decisions cause generation to be reduced.

This can raise more significant questions concerning legitimate expectations, regulatory stability and investment protection.

8. Case Law: Eiser Infrastructure Ltd. v. Spain

A significant international investment-law case involving renewable-energy investment is Eiser Infrastructure Limited and Energía Solar Luxembourg S.à r.l. v. Kingdom of Spain, ICSID Case No. ARB/13/36.

The dispute concerned investments in Spanish concentrated solar-power plants and changes to Spain's renewable-energy regulatory regime. The investors alleged that subsequent regulatory measures undermined the economic basis on which their investments had been made.

The original 2017 tribunal found a violation of the fair-and-equitable-treatment standard and awarded compensation. However, the original award was subsequently annulled, and a resubmission proceeding produced a later award in 2025. Therefore, the procedural history must be treated carefully rather than citing the 2017 award as the final word on the dispute. (ICSID)

Relevance to curtailment risk

Eiser was not principally a curtailment case. Its importance is broader: it demonstrates how changes to the economic and regulatory conditions governing renewable-energy investments can become relevant to investment-protection claims.

The case illustrates a fundamental principle for curtailment-risk analysis:

An investor's expected return depends not merely on physical generation potential, but also on the legal and regulatory framework governing access to the electricity market.

This is particularly relevant where renewable projects were encouraged through long-term regulatory guarantees or preferential treatment. (Investment Policy Hub)

9. Case Law: Citadel FNGE Ltd. v. FERC

The U.S. case Citadel FNGE Ltd. v. Federal Energy Regulatory Commission, D.C. Circuit, 2023, provides a useful example of the relationship between congestion and investment signals.

The case concerned PJM's treatment of transmission congestion and a transmission constraint penalty factor.

The court described the purpose of the relevant pricing mechanism as providing transparent signals concerning transmission constraints and encouraging investment capable of resolving those constraints. (Justia Law)

The underlying principle is highly relevant to curtailment:

Persistent congestion → price signal → investment in transmission or generation/storage that relieves the constraint.

If regulatory intervention suppresses that signal without replacing it with another mechanism, investment incentives can become distorted.

10. Case Law: Advanced Energy United v. FERC

The 2026 D.C. Circuit decision in Advanced Energy United v. FERC is also relevant to the investment-signal problem.

The court considered FERC's Order 2023 reforms concerning generator interconnection.

The court noted that, at the end of 2023, approximately 2,600 GW of proposed generation and storage capacity was waiting in interconnection queues, with solar, wind and storage representing approximately 95% of that capacity. (Justia Law)

The court upheld FERC's approach to addressing speculative interconnection requests, including measures intended to make project developers demonstrate greater commercial viability before entering or remaining in the queue.

This is relevant because:

An apparently attractive renewable investment signal can become misleading when the physical grid connection required to monetize the investment is uncertain.

Interconnection rules therefore form part of the investment-signal architecture.

11. Transmission Investment as a Remedy

One solution to curtailment-induced investment distortion is to strengthen transmission infrastructure.

The U.S. regulatory framework explicitly recognizes transmission investment as a means of reducing congestion and improving reliability. FERC states that its transmission policies are designed to promote investment in transmission infrastructure and reduce transmission congestion. (Federal Energy Regulatory Commission)

This produces an important regulatory feedback mechanism:

Renewable investment → increased congestion → transmission investment → reduced curtailment → improved renewable investment conditions.

But if transmission planning occurs too slowly, the cycle breaks down.

12. Curtailment and Locational Investment Signals

A sophisticated electricity market should ideally communicate that the value of generation differs by location.

Consider two locations:

If investors receive only a uniform renewable tariff without adequate locational information, they may disproportionately invest in Location A.

The result may be:

Excess generation + insufficient transmission + rising curtailment.

Locational pricing, congestion pricing, transmission planning and transparent curtailment data can therefore improve investment decisions.

13. Curtailment Risk and Energy Storage

Storage changes the economics considerably.

Suppose renewable electricity is curtailed during midday because demand and transmission capacity are insufficient.

A battery can:

absorb excess generation;

prevent or reduce curtailment;

discharge during peak demand;

provide ancillary services;

reduce congestion-related losses.

Therefore, predictable curtailment can itself become an investment signal for storage.

However, if market rules do not allow storage to capture sufficient value, the signal becomes distorted again.

For example:

High curtailment + no storage compensation → underinvestment in storage.

Thus, effective regulation should consider generation, transmission and storage as interconnected investments.

14. Regulatory Risk versus Physical Curtailment Risk

These should not be confused.

Physical curtailment risk

Results from:

congestion;

inadequate grid capacity;

system stability;

demand fluctuations.

Regulatory curtailment risk

Results from:

changes in dispatch rules;

changes in renewable priority;

changes in compensation;

changes in market access;

regulatory restrictions on generation.

The second category may be particularly important for investment-law analysis because investors may argue that government measures have fundamentally altered the conditions under which investment was made.

The Spanish renewable-energy arbitration cases demonstrate the broader importance of regulatory stability to renewable-energy investment. UNCTAD records numerous investment disputes concerning Spain's renewable-energy reforms, including Eiser, Green Power and SCE, and EDF. (Investment Policy Hub)

15. Legal Principles Governing Curtailment Risk

Several legal principles can be applied.

A. Non-discrimination

Curtailment rules should not arbitrarily discriminate between similarly situated generators.

B. Transparency

Generators should be able to understand:

when curtailment can occur;

who orders it;

how it is prioritized;

how compensation is calculated.

C. Regulatory certainty

Investors require reasonable visibility concerning the rules governing grid access and dispatch.

D. Proportionality

Curtailment should ordinarily be connected to a legitimate system objective, particularly where it materially affects property or investment value.

E. Due process

Generators may require mechanisms to challenge or review curtailment decisions.

F. Cost allocation

The regulatory framework should clearly establish who bears the financial consequences of network constraints.

16. Indian Legal Context

In India, curtailment issues are closely connected with the Electricity Act, 2003, renewable-energy policy, grid-code requirements, open access, transmission planning and regulatory tariff arrangements.

The basic legal challenge is to reconcile renewable-energy promotion with the physical requirements of grid operation.

Indian renewable projects often depend on:

long-term PPAs;

state-level renewable policies;

transmission connectivity;

scheduling and forecasting rules;

renewable purchase obligations;

electricity-market regulations.

A particularly important recent Indian case is Southern Power Distribution Company of Andhra Pradesh Ltd. v. Green Infra Wind Solutions Ltd., decided in March 2026. The Supreme Court considered whether a State Electricity Regulatory Commission could take a Generation Based Incentive into account in tariff determination. The case illustrates the broader principle that renewable-investment economics can be affected by the interaction between executive incentive schemes and the statutory powers of electricity regulators. (Indian Kanoon)

Although this case is not a direct curtailment case, it is relevant to the larger question of how regulatory design affects expected renewable-project revenues.

17. Investment Distortion Through Poor Risk Allocation

Curtailment creates the greatest investment distortion when risk is allocated without reference to its cause.

For example:

Scenario 1: Generator bears all curtailment risk

Investors may avoid renewable projects in locations where the grid is constrained.

Scenario 2: Network bears all risk

Investors may build excessively in attractive renewable-resource areas because they are protected from congestion losses.

Scenario 3: Shared risk

The investor bears ordinary operational risk while the network or buyer bears extraordinary network-caused curtailment.

The third approach can produce more balanced investment incentives, provided the rules are transparent.

18. Deemed Generation Compensation

One regulatory solution is deemed generation compensation.

Under such a mechanism, if a renewable generator could have produced electricity but was curtailed for reasons outside its control, compensation is calculated based on the electricity that would reasonably have been generated.

This protects the investment from some forms of network-related risk.

However, excessive compensation can create another distortion: developers may have insufficient incentive to consider network constraints when choosing project locations.

Therefore, compensation mechanisms should be carefully designed.

19. Importance of Curtailment Forecasting

Investment decisions improve when investors have access to reliable information concerning:

historical curtailment;

expected transmission upgrades;

interconnection queue positions;

congestion forecasts;

renewable build-out;

demand forecasts;

storage deployment;

transmission availability.

A project with a 5% expected curtailment rate and a project with a 30% expected curtailment rate should not appear economically identical simply because both receive the same renewable tariff.

20. Broader Investment-Law Significance

Curtailment risk can become relevant to investment protection where government action fundamentally affects the economic value of an investment.

Potential legal claims may involve:

fair and equitable treatment;

legitimate expectations;

indirect expropriation;

discrimination;

arbitrary or unreasonable governmental action;

contractual protection;

stabilization commitments.

However, ordinary grid management does not automatically constitute a breach of investment law.

States generally retain regulatory authority to maintain electricity-system reliability and public welfare.

The legal question is therefore highly fact-specific.

21. Policy and Regulatory Solutions

A robust regulatory framework can reduce distorted investment signals through:

Transparent curtailment rules

Locational transmission pricing

Long-term transmission planning

Transparent interconnection queues

Curtailment compensation rules

Storage incentives

Congestion forecasting

Firm and non-firm grid-access classifications

Deemed-generation provisions

Independent dispute-resolution mechanisms

Transparent renewable dispatch protocols

Integrated generation-transmission planning

The objective should not necessarily be to eliminate all curtailment. Some curtailment is economically efficient.

The objective is to ensure that investors receive an accurate signal about the probability and economic consequences of curtailment.

22. Conclusion

Investment signals are distorted by curtailment risk when investors cannot accurately determine whether electricity-generating capacity can be converted into delivered and remunerated electricity.

The distortion operates through several channels:

Renewable resource quality → project investment → grid congestion → curtailment → lower realized output → lower revenue → altered investment incentives.

Where curtailment risk is hidden or inadequately allocated, capital may flow excessively into generation while insufficient capital flows into transmission, storage and flexible resources.

The legal framework therefore has a central role in determining whether curtailment becomes a legitimate market signal or an investment distortion. Cases such as Eiser v. Spain demonstrate the importance of regulatory stability for renewable investment, while Citadel FNGE v. FERC illustrates how congestion-pricing mechanisms can be designed to communicate investment signals. Advanced Energy United v. FERC further demonstrates the importance of interconnection rules in determining whether proposed generation can realistically reach the electricity network. (Investment Policy Hub)

Ultimately, effective energy law should seek to align generation investment, transmission expansion, storage deployment and system-operation rules so that the financial consequences of curtailment are predictable, transparent and allocated according to the source of the risk.