The Grid Inertia CollapseThe Synthetic Inertia Illusion: Why the Loss of Physical Spinning Mass Will Trigger Regional Blackouts by 2027 — And Who Profits From the $$4.7B Syncon Gold Rush
The market celebrates 60-70% renewable penetration as a triumph of decarbonization. The engineering reality is catastrophic: every retired coal, gas, and nuclear turbine removes hundreds of tons of physical spinning mass — the only thing preventing frequency collapse in the first 0.1 seconds after a fault. Grid-forming inverters and lithium batteries store energy; they cannot replicate the 500-700% fault current injection of a 500-ton steel rotor spinning at 3,000 RPM. ERCOT operates at a 100 GWs critical inertia floor. The UK has spent £1.95 billion on Stability Pathfinders. Australia projects $$4.7 billion for 30+ synchronous condensers by 2035. This is not a software problem — it is a physics crisis that semiconductors cannot solve.
📚 Executive Brief: The Inertia Crisis Explained
For Portfolio Managers, Infrastructure Investors & Grid Planners: The global grid is approaching a physics-driven stability cliff. Every retired synchronous generator removes physical spinning mass that provides instantaneous frequency support in the first 0.1-0.5 seconds after a fault — before any battery, inverter, or control system can respond. Grid-forming inverters, despite marketing claims, cannot replicate this: IGBT semiconductors have a hard thermal limit of 120-200% rated current, while steel synchronous generators deliver 500-700%. During deep faults, current saturation algorithms force GFM inverters into current-limited mode where they lose voltage-source behavior, causing virtual pole slipping. Grid operators are spending billions on synchronous condensers — essentially giant spinning motors in a vacuum — to replace the inertia that renewables cannot provide. The ultra-heavy forging capacity to manufacture these machines is concentrated in a single facility: JSW Muroran, Japan.
- Physics Reality: Swing Equation dictates RoCoF = ΔP × fn / (2 × Htotal). As H→0, RoCoF→∞.
- Hardware Reality: IGBTs cannot survive sustained fault current above 200% — silicon, not software, is the limit.
- Financial Reality: £1.95B UK + $$4.7B Australia + $$14.9B ERCOT transmission costs — just the beginning.
01The Physics of Inertia Collapse: The Swing Equation & RoCoF
For investors: Think of grid inertia like the flywheel in a car engine. When you suddenly demand more power, the heavy metal flywheel instantly releases stored energy to keep the engine running smoothly. The grid works the same way: hundreds of tons of spinning steel in power plants act as a massive flywheel. When a power plant suddenly trips offline, this "spinning mass" instantly injects energy to prevent a blackout — faster than any battery or computer can respond. Retiring coal, gas, and nuclear plants removes this flywheel. Solar panels and batteries store energy but have zero physical spinning mass. The financial consequence: grid operators are being forced to buy giant electric motors spinning in a vacuum — called synchronous condensers — just to replace the flywheel effect that fossil fuel plants provided for free. This is a multi-billion-dollar CapEx cycle that has barely begun.
💰 The Investment Translation
Every retired 500 MW coal plant removes approximately 3-4 GWs of inertia. Replacement cost via synchronous condenser: $8-15M per GWs. A typical regional grid retiring 10 GW of thermal generation faces a $240-600M inertia replacement bill. These costs are currently NOT priced into renewable energy PPA models, creating a systematic underpricing of grid connection costs for wind and solar developers — and a structural tailwind for syncon manufacturers.
For a century, grid frequency stability was maintained by a simple physical fact: hundreds of tons of spinning steel stored enormous kinetic energy. As synchronous machines retire, the physics foundation of grid stability is being systematically dismantled.
🔬 The Swing Equation — The Mathematics of Grid Survival
RoCoF vs System Inertia (100 GW Loss)
Hz/secondFault Current Capability: Synch Generator vs IGBT Inverter
% of Rated Current02ERCOT: Texas on the Brink of Inertia Collapse
Texas operates an electrically isolated grid — no AC interconnectors to import inertia from neighboring regions. This makes ERCOT the world's most vulnerable large grid to inertia collapse. Through intensive dynamic simulations modeling the simultaneous loss of the two largest nuclear units (South Texas Project, combined 2,750 MW contingency), ERCOT established a Critical Inertia Floor of 100 GWs. Below this threshold, frequency breaches the Under-Frequency Load Shedding (UFLS) threshold of 59.3 Hz before any control system can arrest the decline.
| Metric | Value | Context |
|---|---|---|
| Critical Inertia Floor | 100 GWs (reduced to 90 GWs with FFR) | Lowest recorded: 109 GWs (early 2021) |
| Renewable Instantaneous Penetration | Routinely exceeds 60% | Wind + solar share of total load |
| Ancillary Service Costs (Aug 2023) | $$809M/month | Pre-battery saturation peak |
| Ancillary Service Costs (2024) | $$36M/month | Post-battery saturation trough |
| Projected TCOS Impact | +$$14.9B | Transmission cost escalation for weak grid management |
| RTC+B Co-optimization Savings | $$2.5-6.4B/year (projected) | Market redesign efficiency gains |
🔴 The RUC Trap
ERCOT increasingly relies on Reliability Unit Commitment (RUC) directives to force gas generators online — outside market mechanisms — purely to harvest their inertia and system strength. In 2024, RUC costs exceeded $$200M, representing a direct subsidy from consumers to fossil generators for providing a physics service that the market does not price. This is the hidden cost of the renewable transition: consumers are paying gas plants to run unprofitably because the grid cannot function without their spinning mass.
03NESO: The UK's £1.95 Billion Stability Bill
The UK's National Energy System Operator (NESO) has created the world's first commercial market for inertia — the Stability Pathfinder program. This is the clearest empirical evidence of the cost of inertia collapse. NESO maintains a minimum inertia target of 120 GVA.s. The Stability Pathfinder program purchases inertia and short-circuit level as standalone commercial products, decoupled from energy generation.
| Phase | Contract Value | Inertia Procured | Short-Circuit Level | Key Insight |
|---|---|---|---|---|
| Phase 1 (2020) | £328M | 12.5 GVA.s | — | Utilized existing retrofits (Drax Cruachan, Triton Deeside) — cheapest options |
| Phase 2 (2022) | £323M | 6.75 GVA.s | 11.55 GVA | Scotland-specific; addressed nuclear closure + offshore wind surge |
| Phase 3 (2022) | £1.3B | 17.08 GVA.s | 8.72 GVA | Greenfield syncon construction — costs escalating sharply |
⚠ The Escalating Marginal Cost of Inertia
The marginal cost of procuring inertia is rising steeply. Phase 1 utilized cheap retrofits at £26.2M per GVA.s. Phase 3 requires greenfield syncon construction at £76.1M per GVA.s — nearly triple the unit cost. This trajectory is not sustainable: as all cheap retrofit options are exhausted, every additional unit of inertia will cost incrementally more, creating a hockey-stick cost curve for grid stability that no regulatory framework currently accounts for.
04AEMO: Australia's $$4.7 Billion Syncon Surge
Australia's National Electricity Market (NEM) is a long, stringy grid with weak interconnections — making it acutely vulnerable to regional islanding during disturbances. AEMO established a mainland inertia safety net at 45,350 MWs operational level, with South Australia (SA) requiring dedicated intervention after renewable penetration routinely displaced all local synchronous generation.
South Australia: The Canary in the Inertia Coal Mine
South Australia's ElectraNet was forced into a massive capital intervention. After a rigorous Regulatory Investment Test for Transmission (RIT-T), ElectraNet invested $$166-190M to purchase and install four massive synchronous condensers — two at Davenport and two at Robertstown. Supplied by GE and Siemens, each unit contributes 575 MVA of fault level and is equipped with flywheels for high-inertia performance. The integration of these kinetic energy storage systems allowed AEMO to reduce the mandatory requirement to run two gas generators in SA to zero under certain conditions, saving consumers tens of millions in direction costs annually. AEMO's 2024-2025 Transmission Planning for System Security (TPSS) indicates that these investments are merely the leading edge: an additional $$4.7 billion in syncon investments is projected across the NEM by 2035, with NSW and Queensland facing the largest deficits as major coal plants retire between 2027-2028.
Global Synchronous Condenser Market: Installed Base & Forecast (2020-2035)
USD Billions05The Synthetic Inertia Illusion: Why Grid-Forming Inverters Fail
For investors: The market narrative says "grid-forming inverters and batteries will solve the inertia problem." If this were true, the UK would not have spent £1.95B and Australia would not be planning $4.7B on physical synchronous condensers — giant spinning motors. The reality: semiconductor chips (IGBTs) inside inverters physically cannot survive the massive current surge needed during a grid fault. A steel rotor weighing 500 tons absorbs this stress thermally. A silicon chip the size of a fingernail melts in microseconds. Grid operators know this — which is why they are buying steel, not software.
Grid-forming (GFM) inverters represent a genuine advance over grid-following (GFL) designs. By operating as a voltage source behind a virtual impedance, GFM inverters mathematically emulate the swing equation of a synchronous machine, establishing their own internal voltage and frequency reference. The Hornsdale Power Reserve (Neoen/Tesla) in South Australia delivers an estimated 2,070 MWs of virtual inertia in Virtual Machine Mode, with an H-constant of 11.02 seconds. However, this software construct lives inside a fragile hardware envelope that collapses during the very conditions where inertia is most needed.
🔬 The Three Fatal Flaws of Synthetic Inertia
06The Synchronous Condenser Imperative & The SSS Clutch Economics
A synchronous condenser (SynCon) is essentially a massive synchronous generator connected to the grid but decoupled from any prime mover (steam or gas turbine). Once accelerated to synchronous speed by a pony motor or static frequency converter, the rotor's magnetic field locks to the 50/60 Hz grid frequency. By varying the DC excitation current on the rotor, the machine can absorb or inject massive amounts of reactive power, providing dynamic voltage regulation far superior to static VAR compensators (SVCs) and STATCOM systems. Crucially, the machine provides actual physical kinetic energy. A standard syncon has an H-constant of 1.5-2.5 seconds. By coupling massive steel flywheels directly to the rotor shaft, OEMs like Voith, Andritz, Siemens Energy, and GE Vernova boost the H-constant to a staggering 10-16 seconds — equivalent to over 3,100 MWs of stored energy for a typical unit.
SSS Clutch Retrofit: The 50% Cost Reduction Strategy
The Synchro-Self-Shifting (SSS) Clutch is a precision-engineered mechanical device installed between a power turbine and generator rotor. When the turbine accelerates the generator to synchronous speed, the clutch engages smoothly. If active power generation becomes uneconomical (due to renewable oversupply), fuel supply is cut, the turbine decelerates, and the SSS Clutch automatically disengages — allowing the massive generator rotor to continue spinning freely, synchronized to the grid, operating purely as a synchronous condenser. This hybrid approach preserves the option for active power generation while securing grid stability contracts simultaneously. SSS Clutch retrofits reduce deployment costs by up to 50% and compress commissioning timelines from 36 to 18 months. Notable conversions include Xcel Energy's Tolk coal plant (US), Townsville Power Station (Australia), and multiple OCGT plants developed by Drax in the UK.
07The Ultra-Heavy Forging Bottleneck: One Factory Controls the Grid's Future
Syncon rotors and flywheels are subjected to immense centrifugal stresses at 3,000-3,600 RPM. They cannot be assembled from welded components; they must be machined from single, flawless, isotropic steel forgings. Manufacturing a mono-block rotor shaft at this scale requires casting a continuous steel ingot weighing 400-600 tons and forging it using hydraulic presses capable of exerting 14,000-15,000 tons of force. This ultra-heavy forging capability is virtually non-existent in North America and severely constrained in Europe. The entire global market depends almost exclusively on a small group of traditional steelmakers, most notably Japan Steel Works (JSW) operating its Muroran Plant in Hokkaido, Japan. JSW possesses the capability to manufacture 600-ton ingots and the 14,000-ton presses required to forge the largest turbine and generator shafts in the world. While China First Heavy Industries, France's Le Creusot, and Russia's OMZ Izhora have similar nominal capabilities, geopolitical realities and domestic demand severely limit export availability for Western grids. Consequently, the queue for ultra-heavy forgings creates an absolute physical bottleneck, extending lead times for large synchronous machines beyond 40-50 months.
🔴 The Fractal Bottleneck
Syncons compete for exactly the same supply chain resources — copper, specialized electrical steel, ultra-heavy forgings, and engineering labor — as HVDC transformers and hyperscale data center components. The OEMs are the same companies. Siemens Energy's Grid Technologies backlog reached €42B (end of FY25), double the 2023 level. GE Vernova's electrification backlog quadrupled to $$35B. ABB's Electrification backlog reached a record €21.3B. Hitachi Energy's book-to-bill ratio remains at 2.5-3x. Securing a slot in a Japanese forging press has become a matter of national energy security — and the queue is already full through 2030.
| OEM | Grid Technology Backlog | Key Indicators |
|---|---|---|
| Siemens Energy | €42B (FY25) | Double 2023 level; prioritizing large reservation agreements |
| GE Vernova | $$35B (Electrification); $$150B total | Heavy-duty frames sold out through 2030 |
| ABB | €21.3B (Electrification) | Strategic capacity rationing; 18-24 month revenue visibility |
| Hitachi Energy | 2.5-3x Book-to-Bill | Major syncon contracts: Powerlink QLD, Terna Italy |
🌎Global Syncon Deployments & Critical Infrastructure Map
The map below identifies the eight most critical synchronous condenser deployments and grid stability infrastructure nodes worldwide — from ERCOT's exposed Texas island to JSW Muroran's irreplaceable forging capacity.
Data: Company disclosures, grid operator filings — July 2026
🔨 Tier 1 Syncon OEM Capability Comparison
| OEM | Max Unit Capacity (MVAr) | H-Constant (with Flywheel) | Stored Energy (MWs) | Fault Current (% rated) | Lead Time (months) | Key Deployment |
|---|---|---|---|---|---|---|
| Siemens Energy | 600+ | 12-16s | 3,100+ | 500-700% | 40-50 | Central-West REZ (7 units, Australia) |
| GE Vernova | 575 | 10-14s | 2,500+ | 500-650% | 36-48 | Davenport & Robertstown (SA) |
| Hitachi Energy / Ansaldo | 1,250 | 10-14s | 2,000+ | 500-700% | 36-48 | Terna Italy (1,250 MVAr) |
| ABB | 500 | 8-12s | 1,800+ | 450-600% | 36-44 | Transelec Chile (1,000 MVAr) |
| Voith / Andritz (Flywheel) | N/A (component) | +6-10s boost | +2,000 MWs | N/A | 18-24 | Integrated with Siemens/GE units |
Global Inertia Decline vs Renewable Penetration (2015-2030E)
5 Major Grids Tracked👁BLIND SPOT: The Winner's Circle — The Syncon Gold Rush
🏢 Siemens Energy
Holds dominant position in global syncon pipeline with 28.4% share. Deploying high-inertia units globally, including a massive 7-unit contract for Australia's Central-West REZ. Grid Technologies backlog at €42B provides 6+ year revenue visibility. Grid Technologies margins expanding to 18-20% in FY2026.
Siemens Energy (ENR.DE)🏢 GE Vernova
Electrification segment backlog quadrupled to $$35B. Total company backlog $$150B. Heavy-duty gas turbine frames sold out through 2030 — many of these same manufacturing resources compete with syncon production. Transelec Chile 1,000 MVAr syncon installation is a landmark project.
GE Vernova (GEV)🏢 Hitachi Energy
Partnered with Ansaldo Energia to deliver 1,250 MVAr to Italy's Terna. Major syncon contracts with Powerlink Queensland for Central Queensland grid strengthening. Book-to-bill ratio sustained at 2.5-3x, indicating persistent demand exceeding delivery capacity.
Hitachi (6501.T)⚙ Voith & Andritz (Flywheel Technology)
Both Voith and Andritz manufacture the massive flywheels that boost syncon H-constants from 1.5-2.5s to 10-16s. These are the critical differentiating component — without flywheels, syncons cannot meet modern grid inertia requirements. Both companies are capacity-constrained with 18-24 month delivery timelines for large flywheel assemblies.
Voith (private) | Andritz (ANDR.VI)🛠 SSS Clutch (SSS Gears)
The Synchro-Self-Shifting Clutch enables coal and gas plant retrofits to dual-mode syncon operation at half the cost and timeline of greenfield installations. Every retired thermal plant that receives an SSS Clutch becomes a grid stability asset. SSS Gears is the sole global supplier of this technology with a multi-year backlog.
SSS Gears (private, UK)🔷 Japan Steel Works (JSW)
JSW Muroran is the single-point-of-failure for ultra-heavy forging capacity. Every syncon rotor shaft above 200 tons requires forging capability that only JSW provides at commercial scale to Western markets. The 600-ton ingot + 14,000-ton press combination is an un-replicable competitive moat with a 5-7 year timeline for any competitor to match.
JSW (5631.T)🔢Interactive RoCoF & Inertia Collapse Calculator
⚡ Grid Inertia Collapse Model
Adjust system parameters to calculate Rate of Change of Frequency (RoCoF) and determine whether your grid survives or collapses after a contingency.
🎯Strategic Directives by Stakeholder
1Grid Operators & PlannersERCOT NESO AEMO
Place syncon procurement orders NOW — the 40-50 month lead time means orders placed in 2026 deliver in 2029-2030. The forging queue at JSW Muroran is first-come, first-served. Every month of delay in placing orders adds 3-4 months to delivery timeline as competitors fill the queue. Implement inertia pricing in ancillary service markets to create transparent price signals for the value of physical spinning mass.
2Institutional InvestorsPORTFOLIO MANAGERS
Long the syncon OEM oligopoly: Siemens Energy, GE Vernova, Hitachi Energy. These companies hold combined backlogs exceeding €250B with 6-8 year revenue visibility and expanding margins. The inertia crisis creates an unbreakable demand floor for their products. Consider JSW (5631.T) as a pure-play forging bottleneck investment. Underweight renewable developers in markets with weak grids (ERCOT, NEM) — the hidden grid connection costs from inertia requirements will compress project IRRs by 2-4 percentage points.
3Renewable Energy DevelopersWIND & SOLAR
Integrate syncon connection costs into project financial models NOW. The UK Stability Pathfinder experience shows grid operators will pass inertia costs to connecting generators. Budget $$15-25/kW of installed capacity for system strength charges in weak grid regions. In ERCOT and NEM, these costs are not reflected in current PPA pricing — first movers who lock in connection agreements before mandatory inertia charges are formalized will have a structural cost advantage.
⚖Structural Conclusions
What This Analysis Proves
Physical Inertia Is Non-Negotiable
The Swing Equation dictates that as synchronous generators retire, RoCoF increases exponentially. No software algorithm can overcome the IGBT thermal limit of 120-200% rated current. Grids need 500-700% fault current from physical rotating mass.
The Syncon Market Is in Early Hyper-Growth
$$1.8B market in 2025, growing at 7.3-8.1% CAGR to $$3.6B+ by mid-next decade. UK has already spent £1.95B. Australia projects $$4.7B. This is the beginning of a multi-decade CapEx cycle.
One Factory Controls the Global Supply
JSW Muroran's 14,000-ton forging press is the global single-point-of-failure. 40-50 month lead times are structural, not cyclical. No competitor can replicate this capacity before 2030-2032.
The OEM Oligopoly Is Sold Out Through 2030
Siemens Energy, GE Vernova, ABB, and Hitachi Energy have combined backlogs exceeding €250B. Their syncon production slots are fully booked. Pricing power is unprecedented.
Renewable Developers Face a Hidden Cost Cliff
Syncon connection charges of $$15-25/kW are not modeled in current project finance. When formalized, these costs will compress IRRs by 2-4 percentage points in weak-grid regions.
The SSS Clutch Is a 50% Cost Reduction Lever
Retrofitting retiring thermal plants with SSS Clutches cuts syncon deployment costs by 50% and timelines from 36 to 18 months. This is the only near-term relief valve for the inertia crisis.
❔Frequently Asked Questions
Grid inertia is stored kinetic energy in the rotating masses of synchronous generators — hundreds of tons of steel spinning at 3,000-3,600 RPM. When a sudden fault or generator trip occurs, this mass instantaneously releases energy in the first 0.1-0.5 seconds, before any battery, inverter, or control system can respond. Batteries store energy but have zero inherent rotational inertia. Grid-forming inverters can emulate inertia through software, but their IGBT semiconductors have a hard thermal limit of 120-200% rated current versus 500-700% for steel synchronous machines. During deep faults, the current saturation algorithm forces the inverter into a current-limited mode where it loses voltage-source behavior and cannot sustain the grid.
The UK has already committed £1.95 billion through Stability Pathfinders Phases 1-3. Australia's AEMO projects $$4.7 billion for 30+ syncons by 2035. ERCOT transmission costs are projected to add $$14.9 billion to consumer bills. These costs are front-loaded: the cheapest retrofit options are being exhausted first, and the marginal cost of procuring each additional unit of inertia is rising. The UK's Phase 1 cost £26.2M per GVA.s; Phase 3 costs £76.1M — nearly triple. This hockey-stick cost trajectory will accelerate as renewable penetration increases.
Not in their current form. The fundamental limitation is thermodynamic: IGBT semiconductors cannot survive sustained current above 200% of rated, while grid faults demand 500-700% for protection relay coordination and voltage recovery. Silicon carbide (SiC) MOSFETs offer incrementally higher thermal tolerance but remain 5-8x more expensive than IGBTs and have not been demonstrated at utility scale for grid-forming applications. Even with advanced semiconductors, the physical reality is that a 500-ton steel rotor stores energy mechanically and releases it instantaneously through electromagnetic coupling — a process that power electronics can emulate in software but cannot physically replicate under extreme fault conditions.
The primary publicly traded beneficiaries are: Siemens Energy (ENR.DE) — 28.4% syncon market share, €42B Grid Technologies backlog; GE Vernova (GEV) — $$35B electrification backlog, leading US grid stability provider; Hitachi (6501.T) — Hitachi Energy division with 2.5-3x book-to-bill; JSW (5631.T) — sole global provider of ultra-heavy forgings for syncon rotors; Andritz (ANDR.VI) — flywheel and hydro generator manufacturing for syncon applications. These companies are not cyclical industrials — they are bottleneck owners in a structural supply deficit.
The Synchro-Self-Shifting (SSS) Clutch is a precision mechanical device that allows a retired or semi-retired thermal power plant to operate its generator as a synchronous condenser without running the turbine. When the turbine spins up the generator to synchronous speed, the clutch engages. When fuel is cut and the turbine decelerates, the clutch automatically disengages, leaving the generator rotor spinning freely as a pure grid stability asset. This halves deployment costs (from $$2.5M/MVAr to ~$$1.2M/MVAr) and compresses commissioning from 36 to 18 months. It is the single most cost-effective near-term solution to the inertia crisis.
📖Methodology & Data Sources
Research Methodology: This report synthesizes primary-source grid operator data (ERCOT Inertia Studies, NESO Stability Pathfinder contracts, AEMO TPSS 2024-2025), OEM financial disclosures (Siemens Energy FY25, GE Vernova 2025 Annual Report, ABB and Hitachi Energy investor presentations), IEEE standards (IEEE 2800-2022 on GFM inverter requirements), peer-reviewed power systems engineering literature on GFM current saturation and pole slipping, and proprietary ESI swing equation modeling. All RoCoF calculations use the standard power systems swing equation with region-specific contingency and UFLS parameters.
- ERCOT — Inertia: Basic Concepts and Impacts
- ERCOT Ancillary Services Study Final White Paper (October 2024)
- NESO — Stability Network Services (Pathfinders 1-3)
- AEMO — 2025 Transmission Planning for System Security (TPSS)
- ElectraNet — Main Grid System Strength Project
- Siemens Energy — FY2025 Earnings Release & Grid Technologies Segment
- GE Vernova — 2025 Annual Report & 4Q FY2025 Earnings Call
- ABB — Electrification Segment Q1-Q2 2026
- Hitachi Energy — FY2025 Energy Business Strategy (June 2026)
- Fortune Business Insights — Synchronous Condenser Market Report 2034
- MDPI — "A Review of System Strength and Inertia in Renewable-Dominated Grids" (2025)
- IEEE 2800-2022 — Interconnection and Interoperability of IBRs
- ResearchGate — "Current-Limiting Control of Grid-Forming Inverters" (2023)
- ResearchGate — "Pole Slipping in Droop-Based Grid-Forming Inverters" (2025)
- NIST Framework for Smart Grid Interoperability
- JSW Muroran — History & Future Prospects
- Voith — Synchronous Condenser Technical Specifications
- SSS Clutch — Global Case Studies (Tolk, Townsville, Drax)
- Dataintelo — Synchronous Condenser Market Report 2034
Disclaimer: This report is for informational and educational purposes only. It does not constitute investment advice. Energy Solutions Intelligence may hold positions in securities discussed. Data sources believed reliable but accuracy not guaranteed. Forward-looking projections subject to material uncertainty.