What Happened
- India has delayed its coal flexibility plan by one year, pushing back the timeline for requiring thermal power plants to operate at lower minimum loads to accommodate rising solar generation
- The delay is attributed primarily to the absence of a clear compensation framework for thermal generators who lose revenue when they reduce output to make room for solar
- Solar curtailment in India reached 2.3 TWh between May and December 2025 — energy that was generated but not absorbed by the grid, largely because coal plants could not ramp down fast enough
- The Central Electricity Authority (CEA) had issued regulations in 2023 requiring coal plants to progressively lower their Minimum Technical Load (MTL) from 55% to 40% of installed capacity, but implementation has been delayed
- The lack of compensation rules means coal plant operators have little financial incentive to undertake costly retrofits needed for flexible operation
Static Topic Bridges
Minimum Technical Load (MTL) and Coal Plant Inflexibility
The Minimum Technical Load (MTL) is the lowest level at which a coal-fired thermal power plant can safely and stably operate without shutting down. In India, most coal plants have an MTL of 55% — meaning they cannot generate less than 55% of their rated capacity even when power demand or grid conditions would require lower output. This creates a structural barrier to integrating variable renewable energy (solar, wind).
- Current MTL in India: 55% (formalised in the Grid Code 2023 by CEA)
- Target MTL (CEA 2023 regulations): 40% — to be achieved progressively through retrofits, advanced control systems, and OEM consultation
- Why MTL matters: During midday hours when solar generation peaks, total supply can exceed demand. If coal plants cannot reduce output below 55%, the excess supply must be absorbed by curtailing (wasting) solar energy
- Implementation delay: Nominated pilot units for testing 40% MTL have not been fully identified; tariff implications and life-consumption effects on plant hardware remain unresolved
- Ramping requirement: Flexible operation also requires faster ramp rates — the speed at which a plant can increase or decrease output. Current coal plants ramp slowly (~1–3% of capacity per minute)
Connection to this news: The one-year delay in the coal flexibility plan directly means continued high MTL limits, making solar curtailment worse. Every GWh of curtailed solar is a GWh that coal must keep running to fill — an inefficiency that costs money and carbon.
Solar Curtailment — Causes, Scale, and Economic Impact
Solar curtailment refers to the deliberate reduction of solar power output below what the panels could generate, typically for grid stability reasons. Curtailment occurs when supply exceeds demand and the grid cannot safely absorb all available generation.
- India's 2025 curtailment: 2.3 TWh of solar curtailed between May–December 2025 (Ember report), equivalent to powering ~14 lakh households for a year
- Monthly distribution: Nearly 40% of 2025 curtailment occurred in October alone — reflecting seasonal solar peaks and post-monsoon demand drops
- Root cause: Coal plants operating above 55% MTL could not ramp down during midday solar surplus; grid operator had no alternative but to curtail solar
- Compensation paid (TRAS mechanism): Affected solar generators received INR 5,750–6,900 million (~USD 63–76 million) via emergency Tertiary Reserve Ancillary Service (TRAS) payments
- Environmental cost: Curtailed 2.3 TWh could have avoided ~2.1 million tonnes of CO₂ emissions if it had displaced coal generation
- Solar capacity added in 2025: India added a record ~38 GW of solar in 2025, pushing non-fossil installed capacity to 50% — making the curtailment problem more acute
Connection to this news: The coal flexibility delay directly worsens the curtailment problem. Without lower MTL for coal plants, India's rapidly expanding solar capacity will face increasing curtailment as midday solar peaks grow larger relative to demand.
Renewable Energy Integration — Grid Flexibility Framework
Integrating large shares of variable renewable energy (VRE) — solar and wind — requires the entire power system to become more flexible. Grid flexibility refers to the ability of the power system to rapidly adjust supply and demand balance despite variability in generation and load.
- Sources of flexibility: Coal/gas plant flexibility (MTL reduction, faster ramping); hydropower (highly flexible, rapid dispatch); pumped storage hydro (PSH — stores energy by pumping water uphill, releases on demand); battery energy storage systems (BESS); demand response (shifting industrial/commercial loads)
- India's Grid Code 2023: Issued by CEA; governs operation of the national and regional grids; includes provisions for ancillary services, reactive power, and frequency regulation
- Pumped Hydro Storage (PHS): India targets 18,771 MW of new PHS capacity by 2032; only ~4,745 MW currently operational
- Duck Curve problem: As solar penetration rises, the net demand curve (total demand minus solar) dips deeply in midday then spikes sharply at sunset — resembling a duck shape. Managing this spike requires fast-ramping resources
- Tertiary Reserve Ancillary Service (TRAS): An emergency grid balancing mechanism in India; currently used to compensate curtailed solar generators — a temporary fix, not a structural solution
Connection to this news: The delay in coal flexibility implementation means India is patching the curtailment problem through expensive TRAS payments rather than solving it structurally. The longer the delay, the greater the mismatch between India's solar ambitions and its grid's actual absorption capacity.
Key Facts & Data
- Solar curtailed in 2025: 2.3 TWh (May–December); equivalent to ~14 lakh households for a year
- October 2025: ~40% of annual curtailment in a single month
- TRAS compensation paid to curtailed solar generators: INR 5,750–6,900 million (~USD 63–76 million)
- CO₂ avoided if curtailment had not occurred: ~2.1 million tonnes
- Coal MTL (current): 55%; CEA target: 40% (per 2023 regulations)
- Solar capacity added in 2025: Record ~38 GW
- India's total installed power capacity (2025): ~460 GW; ~50% non-fossil
- Pumped Hydro Storage target (India): 18,771 MW by 2032; operational capacity ~4,745 MW
- India's renewable energy target: 500 GW non-fossil capacity by 2030
- Coal's share of actual electricity generation: ~70% despite 50% non-fossil installed capacity