Quick Facts
What curtailment is
Curtailment is the reduction of power generation below the available capacity. For solar plants, this means the plant could generate more electricity given the available sunlight, but is restricted from doing so. Curtailment can occur for technical reasons (grid limitations) or commercial reasons (DISCOM economics).
For solar developers, curtailment is a critical risk factor. Generation that doesn’t reach the grid is revenue lost. India’s must-run status for renewables provides legal protection against curtailment, with compensation provisions when curtailment does occur.
As Indian solar capacity grows past 30 percent of total grid generation during peak hours, curtailment risk grows. Grid investments, storage deployment, and demand-side flexibility are needed to absorb increasing renewable generation without curtailment.
Causes of curtailment
Several factors cause curtailment:
Grid evacuation constraints:
Transmission capacity inadequate for solar generation.
Substation capacity limits.
Inter-state transmission bottlenecks.
Localized congestion.
Oversupply:
Solar peak coincides with low demand.
Renewable share exceeds demand at certain hours.
Particularly in solar-heavy states.
Grid stability:
Frequency or voltage management requires generation reduction.
Backup generation prioritised for stability.
Solar variability creates dispatch challenges.
Scheduled maintenance:
Transmission line maintenance.
Substation upgrades.
Generation impossible during maintenance.
Commercial dispatch:
DISCOM economic dispatch (despite must-run).
Cost optimization decisions.
This category should be prohibited under must-run status.
Force majeure:
Natural disasters, fires, grid faults.
Curtailment patterns vary by state and project. Identifying causes is essential for mitigation.
Must-run status protection
Indian renewables generally have must-run status under MNRE/CERC guidelines:
Legal protection: Curtailment of must-run plants is restricted.
Curtailment compensation: When curtailment occurs, developer is compensated as if generation had happened.
State Grid Code: State regulations implement must-run.
State Electricity Regulatory Commissions: Enforce must-run.
Despite must-run protection, curtailment events have occurred, often without full compensation. Litigation and regulatory orders have been needed to enforce protection in specific cases.
Deemed generation compensation
When curtailment occurs despite must-run status:
Calculation methodology:
Generation forecast versus actual delivery.
Comparable plant performance.
Pyranometer-based generation calculation.
Per-hour curtailment quantification.
Compensation:
Developer paid as if curtailed energy had been delivered.
At the contracted PPA tariff.
Bills include curtailment compensation.
Dispute resolution:
State regulatory commissions hear disputes.
Tribunal of electricity for appeals.
Often involves legal proceedings.
Deemed generation provisions are essential to project economics for lenders and developers.
Historical curtailment incidents
Notable curtailment in India:
Rajasthan: Solar parks experienced curtailment during peak hours; compensation disputes.
Tamil Nadu: Wind and solar curtailment during high renewable hours; regulatory orders required.
Andhra Pradesh: Renewable curtailment under specific policy reversals.
Karnataka: Some curtailment events.
Recent regulatory clarifications and grid strengthening have reduced curtailment frequency, but ongoing vigilance remains important.
Curtailment mitigation strategies
Several strategies reduce curtailment risk:
Grid infrastructure:
More transmission capacity.
Substation upgrades.
Inter-state evacuation.
Storage deployment:
Battery storage time-shifts generation.
Reduces midday surplus.
Allows evening dispatch.
Demand-side flexibility:
EV charging during solar peak.
Industrial demand response.
Time-of-use tariffs aligning demand with solar.
Inter-state coordination:
Renewable energy certificates.
Real-time market.
Inter-state energy markets.
Forecasting improvements:
Better solar forecasting.
Helps grid operators prepare.
Reduces grid stability concerns.
These strategies require investment and policy support but are essential for high-renewable grids.
Curtailment in PPA terms
PPAs typically address curtailment:
Must-run provisions: Reference to applicable regulations.
Deemed generation: Calculation methodology.
Compensation: Payment terms for curtailment.
Force majeure: Exclusion of force majeure events.
Dispute resolution: Regulatory forum or arbitration.
For lender-grade PPAs, curtailment risk allocation is carefully drafted to protect developer revenue.
Common curtailment mistakes
Underestimating curtailment risk. Particularly in solar-heavy states.
Inadequate PPA provisions. Weak deemed generation clauses.
Poor data infrastructure. Inability to quantify curtailment events.
Slow dispute resolution. Curtailment compensation often delayed.
Ignoring grid capacity. Site selection without grid evacuation assessment.
Missing storage opportunities. Storage reduces curtailment loss.
Best practices
For developers:
Detailed grid evacuation assessment in site selection.
Strong deemed generation provisions in PPAs.
Robust data infrastructure for curtailment quantification.
Engage with grid operators and regulators.
Plan storage if curtailment risk high.
For lenders:
Curtailment risk in financial models.
Strong PPA provisions.
Curtailment compensation track record review.
For grid operators:
Transparent curtailment causes and compensation.
Investment in grid strengthening.
Renewable forecasting capabilities.
For regulators:
Clear must-run guidelines.
Effective compensation enforcement.
Grid investment incentives.
Standards and references
Curtailment management is governed by MNRE must-run guidelines, CERC regulations, State Grid Code, and State Electricity Regulatory Commission orders. PPA documents implement these regulations in specific projects. Lender’s diligence frameworks address curtailment risk.
Related glossary terms
Key takeaways
Curtailment is the reduction of solar generation below available capacity, typically due to grid constraints, oversupply, or commercial reasons. Indian solar plants have must-run status under MNRE/CERC guidelines, providing legal protection against curtailment with deemed generation compensation when curtailment occurs. Notable curtailment events have occurred in Rajasthan, Tamil Nadu, and other solar-heavy states. As Indian solar grows toward 280 GW by 2030, curtailment risk grows; mitigation requires grid strengthening, storage deployment, demand-side flexibility, and effective regulatory enforcement of must-run status.