Document and Entity Information Document Type Document Type Document Quarterly Report Document Quarterly Report Document Period End Date Document Period End Date Document Transition Report Document Transition Report Securities Act File Number Entity File Number Entity Registrant Name Entity Registrant Name Entity Incorporation, State or Country Code Entity Incorporation, State or Country Code Entity Tax Identification Number Entity Tax Identification Number Entity Address, Address Line One Entity Address, Address Line One Entity Address, City or Town Entity Address, City or Town Entity Address, State or Province Entity Address, State or Province Entity Address, Postal Zip Code Entity Address, Postal Zip Code Country Region City Area Code City Area Code Local Phone Number Local Phone Number Title of 12(b) Security Title of 12(b) Security Trading Symbol Trading Symbol Security Exchange Name Security Exchange Name Entity Current Reporting Status Entity Current Reporting Status Entity Interactive Data Current Entity Interactive Data Current Entity Filer Category Entity Filer Category Entity Small Business Entity Small Business Entity Emerging Growth Company Entity Emerging Growth Company Entity Shell Company Entity Shell Company Entity Common Stock, Shares Outstanding Entity Common Stock, Shares Outstanding Entity Central Index Key Entity Central Index Key Amendment Flag Amendment Flag Current Fiscal Year End Date Current Fiscal Year End Date Document Fiscal Year Focus Document Fiscal Year Focus Document Fiscal Period Focus Document Fiscal Period Focus Consolidated Balance Sheets Statement [Table] Statement [Table] Statement [Line Items] Statement [Line Items] Assets [Abstract] ASSETS Assets, Current [Abstract] Current assets: Cash and Cash Equivalents, at Carrying Value Cash and cash equivalents, unrestricted Cash Restricted Cash and Cash Equivalents, Current Restricted Cash and Cash Equivalents - Short-Term Restricted cash and cash equivalents - short-term Short-Term Investments Investments - short-term Accounts Receivable, after Allowance for Credit Loss, Current Accounts receivable, net Unbilled Receivables, Current Unbilled receivables Inventory, Net Inventories - current Inventories Other Assets, Current Other current assets Assets, Current Total current assets Restricted Cash and Cash Equivalents, Noncurrent Restricted cash and cash equivalents - long-term Restricted Cash and Cash Equivalents - Long-Term Inventory, Noncurrent Inventories - long-term Inventories - long-term Long-term project assets. Long Term Project Assets Project assets, net Project Assets, net Property, Plant and Equipment, Net Property, plant and equipment, net Operating Lease, Right-of-Use Asset Operating lease right-of-use assets, net Intangible Assets, Net (Excluding Goodwill) Intangible assets, net Other Assets, Noncurrent Other assets Assets Assets Total assets Liabilities and Equity [Abstract] LIABILITIES AND STOCKHOLDERS' EQUITY Liabilities, Current [Abstract] Current liabilities: Debt, Current Current portion of long-term debt Operating Lease, Liability, Current Current portion of operating lease liabilities Accounts Payable, Current Accounts payable Accrued Liabilities, Current Accrued liabilities Accrued liabilities Contract with Customer, Liability, Current Deferred revenue Liabilities, Current Total current liabilities Contract with Customer, Liability, Noncurrent Long-term deferred revenue Operating Lease, Liability, Noncurrent Long-term operating lease liabilities Other Liabilities, Noncurrent Long-term debt and other liabilities Other non-current liabilities Liabilities Total liabilities Temporary Equity, Carrying Amount, Attributable to Parent Redeemable Series B preferred stock (liquidation preference of $64,020 as of April 30, 2026 and October 31, 2025) Temporary equity, carrying amount, attributable to parent Stockholders' Equity Total equity: Equity, Attributable to Parent [Abstract] Stockholders' equity: Common Stock, Value, Issued Common stock ($0.0001 par value); 1,000,000,000 shares authorized as of April 30, 2026 and October 31, 2025; 63,549,362 and 46,075,237 shares issued and outstanding as of April 30, 2026 and October 31, 2025, respectively Additional Paid in Capital, Common Stock Additional paid-in capital Retained Earnings (Accumulated Deficit) Accumulated deficit Accumulated Other Comprehensive Income (Loss), Net of Tax Accumulated other comprehensive loss Treasury Stock, Common, Value Treasury stock, Common, at cost (57,681 and 44,913 shares as of April 30, 2026 and October 31, 2025, respectively) Deferred Employee Stock Ownership Plan, Issuance of Shares or Sale of Treasury Shares Deferred compensation Equity, Attributable to Parent Total stockholders' equity Equity, Attributable to Noncontrolling Interest Noncontrolling interests Equity, Including Portion Attributable to Noncontrolling Interest Ending Balance Beginning Balance Total equity Liabilities and Equity Total liabilities, redeemable Series B preferred stock and total equity Class of Stock [Axis] Class of Stock [Domain] Series B Preferred Stock [Member] Series B Preferred Stock Consolidated Entities [Axis] Consolidated Entities [Domain] Variable Interest Entity, Primary Beneficiary [Member] Variable interest entity ("VIE") Preferred Stock, Liquidation Preference, Value Preferred stock, liquidation preference value Common Stock, Par or Stated Value Per Share Common stock, par value (in dollars per share) Common Stock, Shares Authorized Common stock, shares authorized (in shares) Common Stock, Shares, Issued Common stock, shares issued (in shares) Common Stock, Shares, Outstanding Ending Balance at (in shares) Beginning Balance at (in shares) Common stock, shares outstanding (in shares) Treasury Stock, Common, Shares Treasury stock, common shares (in shares) Derivative Asset, Noncurrent Derivative asset Derivative Liability, Noncurrent Derivative liabilities Consolidated Statements of Operations and Comprehensive Loss Product and Service [Axis] Product and Service [Domain] Product [Member] Product Service [Member] Service Electricity, Generation [Member] Generation Advanced technologies. Advanced Technologies [Member] Advanced Technologies Revenues [Abstract] Revenues: Revenue from Contract with Customer, Excluding Assessed Tax Total revenues Cost of Goods and Services Sold [Abstract] Costs of revenues: Cost of Goods and Services Sold Total costs of revenues Aggregate revenue less cost of goods and services sold or operating expenses directly attributable to the revenue generation activity. Gross Profit Loss Gross loss Operating Expenses [Abstract] Operating expenses: Selling, General and Administrative Expense Administrative and selling expenses Research and Development Expense Research and development expenses Restructuring Costs Restructuring expense relating to eliminated positions Restructuring expense Asset Impairment Charges Impairment expense Operating Expenses Total costs and expenses Operating Income (Loss) Loss from operations Interest Expense, Operating and Nonoperating Interest expense Investment Income, Interest Interest income Other Nonoperating Income (Expense) Other income (expense), net Income (Loss) from Continuing Operations before Income Taxes, Noncontrolling Interest Loss before provision for income taxes Income Tax Expense (Benefit) Benefit from (provision for) income taxes Income (Loss) from Continuing Operations, Net of Tax, Including Portion Attributable to Noncontrolling Interest Net loss Net Loss Net Income (Loss) Attributable to Noncontrolling Interest Net income attributable to noncontrolling interests Net income (loss) attributable to noncontrolling interests Net loss attributable to FuelCell Energy, Inc. Net loss attributable to FuelCell Energy, Inc. Dividends, Preferred Stock Series B preferred stock dividends Net Income (Loss) Available to Common Stockholders, Basic Net loss attributable to common stockholders Loss Per Share Loss per share basic and diluted: Earnings Per Share, Basic Net loss per share attributable to common stockholders, basic (in dollars per share) Net loss to common stockholders per share - basic Earnings Per Share, Diluted Net loss per share attributable to common stockholders, diluted (in dollars per share) Net loss to common stockholders per share - diluted Weighted Average Number of Shares Outstanding, Basic Basic weighted average shares outstanding (in shares) Weighted average common shares outstanding - basic Weighted Average Number of Shares Outstanding, Diluted Diluted weighted average shares outstanding (in shares) Weighted average common shares outstanding - diluted Net Income (Loss), Including Portion Attributable to Noncontrolling Interest Net loss Other comprehensive loss: Other Comprehensive Income (Loss), Foreign Currency Transaction and Translation Gain (Loss) Arising During Period, Net of Tax Foreign currency translation adjustments Effect of foreign currency translation Comprehensive Income (Loss), Net of Tax, Including Portion Attributable to Noncontrolling Interest Total comprehensive loss Comprehensive Income (Loss), Net of Tax, Attributable to Noncontrolling Interest Comprehensive loss attributable to noncontrolling interests Comprehensive Income (Loss), Net of Tax, Attributable to Parent Comprehensive loss attributable to FuelCell Energy, Inc. Consolidated Statements of Changes in Equity Equity Components [Axis] Equity Component [Domain] Parent [Member] Total Stockholder's Equity Common Stock [Member] Common Stock Additional Paid-in Capital [Member] Additional Paid-in Capital Retained Earnings [Member] Accumulated Deficit AOCI Attributable to Parent [Member] Accumulated Other Comprehensive Loss Treasury Stock, Common [Member] Treasury Stock Deferred Compensation, Share-Based Payments [Member] Deferred Compensation Noncontrolling Interest [Member] Noncontrolling Interests Stock Issued During Period, Value, New Issues Sale of common stock, net of fees Stock issued share value Stock Issued During Period, Shares, New Issues Sale of common stock, net of fees (in shares) Shares sold during the period Stock Issued During Period, Value, Issued for Services Common stock issued, non-employee compensation Stock Issued During Period, Shares, Issued for Services Common stock issued, non-employee compensation (in shares) Unrestricted common stock Stock Issued During Period, Value, Restricted Stock Award, Net of Forfeitures Stock issued under benefit plans, net of taxes paid upon vesting of restricted stock awards Stock Issued During Period, Shares, Restricted Stock Award, Net of Forfeitures Stock issued under benefit plans, net of taxes paid upon vesting of restricted stock awards (in shares) APIC, Share-Based Payment Arrangement, Increase for Cost Recognition Share based compensation Amount of stock-based compensation previously recorded as a liability that is reclassified into equity during the reporting period. Reclassification Of Stock-Based Compensation Liability To Equity Reclassification of stock-based compensation liability to equity Adjustments to Additional Paid in Capital, Dividends in Excess of Retained Earnings Preferred dividends - Series B Treasury Stock, Value, Acquired, Cost Method Adjustment for deferred compensation Stock Issued During Period, Shares, Treasury Stock Reissued Adjustment for deferred compensation (in shares) The amount of increase in equity from contributions received for the sale of noncontrolling interest. Contributions Received for the Sale of Noncontrolling Interest Contributions received for the sale of noncontrolling interest Noncontrolling Interest, Decrease from Distributions to Noncontrolling Interest Holders Distribution to noncontrolling interest Consolidated Statements of Cash Flows Net Cash Provided by (Used in) Operating Activities [Abstract] Cash flows from operating activities: Adjustments to Reconcile Net Income (Loss) to Cash Provided by (Used in) Operating Activities [Abstract] Adjustments to reconcile net loss to net cash used in operating activities: Share-Based Payment Arrangement, Noncash Expense Share-based compensation Depreciation, Depletion and Amortization Depreciation and amortization Amortization of bond premium and interest expense on Series 1 Preferred Amortization Of Bond Premium Non-cash interest expense on finance obligations Unrealized Gain (Loss) on Derivatives Unrealized loss (gain) on derivative contracts Operating Lease, Expense Operating lease costs Operating lease expense Operating Lease, Payments Operating lease payments Operating lease, payments Other Noncash Income (Expense) Other, net Increase (Decrease) in Operating Assets [Abstract] (Increase) decrease in operating assets: Increase (Decrease) in Accounts Receivable Accounts receivable Increase decrease in contract with customer unbilled receivables. Increase Decrease In Contract With Customer Unbilled Receivables Unbilled receivables Increase (Decrease) in Inventories Inventories Increase (Decrease) in Other Operating Assets Other assets Increase (Decrease) in Operating Liabilities [Abstract] (Decrease) increase in operating liabilities: Increase (Decrease) in Accounts Payable Accounts payable Increase (Decrease) in Accrued Liabilities Accrued liabilities Increase (Decrease) in Contract with Customer, Liability Deferred revenue Net Cash Provided by (Used in) Operating Activities Net cash used in operating activities Net Cash Provided by (Used in) Investing Activities [Abstract] Cash flows from investing activities: Payments to Acquire Productive Assets Capital expenditures Investment in long term project assets. Investment In Long Term Project Assets Project asset expenditures Proceeds from Sale of Held-to-Maturity Securities Maturity of held-to-maturity debt securities Payments to Acquire Held-to-Maturity Securities Purchases of held-to-maturity debt securities Net Cash Provided by (Used in) Investing Activities Net cash (used in) provided by investing activities Net Cash Provided by (Used in) Financing Activities [Abstract] Cash flows from financing activities: Repayments of Long-Term Debt Repayment of debt and finance obligations Proceeds from Issuance of Debt Proceeds from the issuance of debt Payments of Debt Issuance Costs Payment for deferred financing costs Payments of debt issuance costs Proceeds From Issuance Of Common Stock Issued For Stock Plans And Related Expenses Proceeds From Issuance Of Common Stock Issued For Stock Plans And Related Expenses Common stock issued for stock plans and related expenses Proceeds from Noncontrolling Interests Contributions received from sale of noncontrolling interest Payments of Ordinary Dividends, Noncontrolling Interest Distribution to noncontrolling interest Payment, Tax Withholding, Share-Based Payment Arrangement Payments for taxes related to net share settlement of equity awards Proceeds, Issuance of Shares, Share-Based Payment Arrangement, Including Option Exercised Common stock issuance, net of fees Payment of preferred dividends and return of capital. Payment Of Preferred Dividends And Return Of Capital Payment of preferred dividends Net Cash Provided by (Used in) Financing Activities Net cash provided by financing activities Effect of Exchange Rate on Cash, Cash Equivalents, Restricted Cash, and Restricted Cash Equivalents, Continuing Operations Effects on cash from changes in foreign currency rates Cash, Cash Equivalents, Restricted Cash, and Restricted Cash Equivalents, Period Increase (Decrease), Including Exchange Rate Effect Net increase (decrease) in cash, cash equivalents and restricted cash Cash, Cash Equivalents, Restricted Cash, and Restricted Cash Equivalents Cash, cash equivalents and restricted cash-end of period Cash, cash equivalents and restricted cash-beginning of period Total cash, cash equivalents and restricted cash Supplemental cash flow disclosures: Interest Paid, Excluding Capitalized Interest, Operating Activities Cash interest paid