Tecogen (TGEN) 10-Q9 May 242024 Q1 Quarterly reportFinancial data

Company Profile

Cover

Cover	3 Months Ended
Cover	Mar. 31, 2024 shares
Document and Entity Information [Abstract]
Document Type	10-Q
Document Quarterly Report	true
Document Period End Date	Mar. 31, 2024
Document Transition Report	false
Entity File Number	001-36103
Entity Registrant Name	TECOGEN INC.
Entity Incorporation, State or Country Code	DE
Entity Tax Identification Number	04-3536131
Entity Address, Address Line One	76 Treble Cove Road
Entity Address, City or Town	North Billerica
Entity Address, State or Province	MA
Entity Address, Postal Zip Code	01862
City Area Code	781
Local Phone Number	466-6402
Entity Current Reporting Status	Yes
Entity Interactive Data Current	Yes
Entity Filer Category	Non-accelerated Filer
Entity Small Business	true
Entity Emerging Growth Company	false
Entity Shell Company	false
Entity Common Stock, Shares Outstanding	24,850,261
Entity Central Index Key	0001537435
Current Fiscal Year End Date	--12-31
Document Fiscal Year Focus	2024
Document Fiscal Period Focus	Q1
Amendment Flag	false

Condensed Consolidated Balance

Condensed Consolidated Balance Sheets - USD ($)	Mar. 31, 2024	Dec. 31, 2023
Current assets:
Cash and cash equivalents	$ 1,510,435	$ 1,351,270
Accounts receivable, net	6,533,130	6,781,484
Inventories, net	10,021,002	10,553,419
Unbilled revenue	1,258,532	1,258,532
Prepaid and other current assets	409,573	360,639
Total current assets	19,732,672	20,305,344
Property, plant and equipment, net	1,147,069	1,162,577
Right of use assets	2,176,264	943,283
Intangible assets, net	2,533,112	2,436,230
Goodwill	2,646,194	2,743,424
Other assets	223,232	201,771
TOTAL ASSETS	28,458,543	27,792,629
Current liabilities:
Related party notes	511,905	505,505
Accounts payable	4,013,899	4,514,415
Accrued expenses	2,682,656	2,504,629
Deferred revenue, current	2,462,570	1,647,206
Lease obligations, current	469,762	289,473
Acquisition liabilities, current	929,411	845,363
Unfavorable contract liability, current	162,822	176,207
Total current liabilities	11,233,025	10,482,798
Lease obligations, current
Deferred revenue, net of current portion	345,427	369,611
Lease obligations, net of current portion	1,725,276	683,307
Acquisition liabilities, net of current portion	1,156,835	1,181,779
Unfavorable contract liability, net of current portion	388,766	422,839
Total liabilities	14,849,329	13,140,334
Commitments and contingencies
Tecogen Inc. shareholders’ equity:
Common stock, $0.001 par value; 100,000,000 shares authorized; 24,850,261 issued and outstanding at March 31, 2024 and December 31, 2023	24,850	24,850
Additional paid-in capital	57,645,937	57,601,402
Accumulated deficit	(43,984,623)	(42,879,656)
Total Tecogen Inc. stockholders’ equity	13,686,164	14,746,596
Non-controlling interest	(76,950)	(94,301)
Tecogen Inc. shareholders’ equity:	13,609,214	14,652,295
TOTAL LIABILITIES AND STOCKHOLDERS’ EQUITY	$ 28,458,543	$ 27,792,629

Condensed Consolidated Balanc_2

Condensed Consolidated Balance Sheets (Parenthetical) - $ / shares	Mar. 31, 2024	Dec. 31, 2023
Statement of Financial Position [Abstract]
Common stock, par value	$ 0.001	$ 0.001
Common stock, shares authorized	100,000,000	100,000,000
Common stock, shares issued		24,850,261
Common stock, shares outstanding	24,850,261	24,850,261

Condensed Consolidated Statemen

Condensed Consolidated Statements of Operations - USD ($)	3 Months Ended
Condensed Consolidated Statements of Operations - USD ($)	Mar. 31, 2024	Mar. 31, 2023
Total revenues	$ 6,186,097	$ 5,379,818
Total cost of sales	3,610,440	3,287,909
Gross profit	2,575,657	2,091,909
Operating expenses:
General and administrative	2,848,568	2,792,483
Selling	529,669	520,070
Research and development	254,696	229,102
Gain on disposition of assets	(7,391)	0
Total operating expenses	3,625,542	3,541,655
Loss from operations	(1,049,885)	(1,449,746)
Other income (expense), net
Other income (expense), net	(15,747)	830
Interest expense	(18,670)	(415)
Unrealized gain on investment securities	18,749	0
Total other income (expense), net	(15,668)	415
Loss before provision for state income taxes	(1,065,553)	(1,449,331)
Provision for state income taxes	22,063	22,638
Consolidated net loss	(1,087,616)	(1,471,969)
Income attributable to the non-controlling interest	(17,351)	(18,060)
Loss attributable to Tecogen Inc.	$ (1,104,967)	$ (1,490,029)
Earnings Per Share [Abstract]
Net income (loss) per share - basic (in USD per share)	$ (0.04)	$ (0.06)
Net income (loss) per share - diluted (in usd per share)	$ (0.04)	$ (0.06)
Weighted average shares outstanding - basic	24,850,261	24,850,261
Weighted average shares outstanding - diluted	24,850,261	24,850,261
Products
Total revenues	$ 1,491,398	$ 1,710,136
Total cost of sales	1,049,543	1,212,568
Services
Total revenues	4,014,310	3,136,173
Total cost of sales	2,092,257	1,737,602
Energy production
Total revenues	680,389	533,509
Total cost of sales	$ 468,640	$ 337,739

Condensed Consolidated Statem_2

Condensed Consolidated Statements of Stockholders' Equity Statement - USD ($)	Total	Common Stock	Additional Paid-In Capital	Accumulated Deficit	Noncontrolling Interest
Beginning balance (shares) at Dec. 31, 2022		24,850,261
Beginning balance at Dec. 31, 2022	$ 18,987,750	$ 24,850	$ 57,351,008	$ (38,281,548)	$ (106,560)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Stock based compensation expense	77,348		77,348
Net income	(18,060)			1,490,029
Net income (loss)	(1,471,969)				18,060
Ending balance (shares) at Mar. 31, 2023		24,850,261
Ending balance at Mar. 31, 2023	17,593,129	$ 24,850	57,428,356	(39,771,577)	(88,500)
Beginning balance (shares) at Dec. 31, 2023		24,850,261
Beginning balance at Dec. 31, 2023	14,652,295	$ 24,850	57,601,402	(42,879,656)	(94,301)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Stock based compensation expense	44,535		44,535
Net income	(17,351)			1,104,967
Net income (loss)	(1,087,616)				17,351
Ending balance (shares) at Mar. 31, 2024		24,850,261
Ending balance at Mar. 31, 2024	$ 13,609,214	$ 24,850	$ 57,645,937	$ (43,984,623)	$ (76,950)

Condensed Consolidated Statem_3

Condensed Consolidated Statements of Cash Flows - USD ($)	3 Months Ended
Condensed Consolidated Statements of Cash Flows - USD ($)	Mar. 31, 2024	Mar. 31, 2023
CASH FLOWS FROM OPERATING ACTIVITIES:
Consolidated net loss	$ (1,087,616)	$ (1,471,969)
Adjustments to Reconcile Net Income (Loss) to Cash Provided by (Used in) Operating Activities [Abstract]
Depreciation and amortization	140,137	105,920
Provision for credit losses	14,258	0
Stock-based compensation	44,535	77,348
Unrealized gain on investment securities	(18,749)	0
Gain on disposition of assets	(7,391)	0
Non-cash interest expense	6,400	0
Increase (Decrease) in Operating Assets [Abstract]
Accounts receivable	234,095	(44,238)
Employee retention credit	0	(667,121)
Inventory	532,418	(1,380,052)
Unbilled revenue	0	16,428
Prepaid assets and other current assets	(48,933)	136,170
Other assets	194,283	161,931
Increase (decrease) in:
Accounts payable	(500,516)	905,509
Accrued expenses and other current liabilities	167,789	(143,923)
Deferred revenue	791,181	852,600
Other liabilities	(213,675)	(167,711)
Net cash provided by (used in) operating activities	248,216	(284,866)
CASH FLOWS FROM INVESTING ACTIVITIES:
Purchases of property and equipment	(104,952)	0
Proceeds from disposition of assets	33,013	0
Net cash used in investing activities	(71,939)	0
CASH FLOWS FROM FINANCING ACTIVITIES:
Finance lease principal payments	(17,112)	0
Net cash used in financing activities	(17,112)	0
Net increase (decrease) in cash and cash equivalents	159,165	(284,866)
Cash and cash equivalents, beginning of the period	1,351,270	1,913,969
Cash and cash equivalents, end of the period	1,510,435	1,629,103
Non-cash investing and financing activities:
Cash paid for interest	11,855	0
Cash paid for taxes	425	22,638
Contingent consideration	$ 92,409	$ 0

Description of business and bas

Description of business and basis of presentation	3 Months Ended
Description of business and basis of presentation	Mar. 31, 2024
Accounting Policies [Abstract]
Description of business and basis of presentation	Description of Business and Basis of Presentation Description of Business Tecogen Inc. (together with its subsidiaries "we", "our", "us" or "Tecogen"), a Delaware Corporation, was incorporated on September 15, 2000, and acquired the assets and liabilities of the Tecogen Products division of Thermo Power Corporation. We produce commercial and industrial, natural-gas-fueled engine-driven, combined heat and power (CHP) products that reduce energy costs, decrease greenhouse gas emissions and alleviate congestion on the national power grid. Our products supply electric power or mechanical power for cooling, while heat from the engine is recovered and purposefully used at a facility. The majority of our customers are located in regions with the highest utility rates, typically California, the Midwest and the Northeast. Our operations are comprised of three business segments. Our Products segment designs, manufactures and sells industrial and commercial cogeneration systems. Our Services segment provides operation and maintenance services to customers for our products. Our Energy Production segment sells energy in the form of electricity, heat, hot water and cooling to our customers under long-term sales agreements. Liquidity, Going Concern and Management's Plans The consolidated financial statements have been prepared in accordance with U.S. generally accepted accounting principles assuming that we will continue as a going concern, which contemplates the realization of assets and the settlement of obligations in the normal course of business. As of March 31, 2024, our cash and cash equivalents were $1,510,435, compared to $1,351,270 at December 31, 2023, an increase of $159,165. For the three months ended March 31, 2024 we generated $248,216 in cash from operations and a net operating loss of $1,049,885, due to a decrease in Products revenue and gross margin, a decrease in Services gross margin percentage due to higher labor and material costs and an increase in operating expenses. Working capital at March 31, 2024 was $8,499,647, compared to $9,822,546 at December 31, 2023, a decrease of $1,322,899 and our accumulated deficit was $43,984,623. As a result of the above factors, management has performed an analysis to evaluate the entity’s ability to continue as a going concern for one year after the financial statements issuance date. Management’s analysis includes forecasting future revenues, expenditures and cash flows, taking into consideration past performance as well as key initiatives recently undertaken. Our forecasts are dependent on our ability to maintain margins based on the Company's ability to close on new and expanded business, leverage existing working capital, and effectively manage expenses. New and expanded business includes the sale and shipment of newly developed hybrid-drive air-cooled chillers and the acquisition of additional maintenance contracts in February 2024. Our backlog at March 31, 2024 was $5,554,599. We may also be required to borrow funds under note subscription agreements with related parties (see Note 11. "Related Party Notes"). Based on management's analysis, we believe that cash flows from operations and the note agreements will be sufficient to fund operations over the next twelve months. There can, however, be no assurance we will be able to do so. Based on our analysis, the consolidated financial statements do not include any adjustments to the carrying amounts and classification of assets, liabilities, and reported expenses that may be necessary if we were unable to continue as a going concern. Our common stock is quoted on OTC Markets Group, Inc.'s OTCQX Best Market tier and trades under the symbol "TGEN." Basis of Presentation The financial statements have been prepared in accordance with accounting standards set by the Financial Accounting Standards Board, or FASB. The FASB sets generally accepted accounting principles, or GAAP, to ensure financial condition, results of operations, and cash flows are consistently reported. References to GAAP issued by the FASB in these footnotes are to the FASB Accounting Standards Codification, or ASC. We adopted the presentation requirements for noncontrolling interests required by ASC 810 Consolidation. Under ASC 810, earnings or losses attributed to the noncontrolling interests are reported as part of the consolidated earnings and not a separate component of income or expense. The accompanying consolidated financial statements include our accounts and the accounts of the entities in which we have a controlling financial interest. Those entities include our wholly-owned subsidiary, American DG Energy Inc. ("ADGE"), Tecogen CHP Solutions, Inc., and a joint venture, American DG New York, LLC, or ADGNY, in which ADGE holds a 51.0% interest. As the controlling partner, all major decisions in respect of ADGNY are made by ADGE in accordance with the joint venture agreement. The interests in the individual underlying energy system projects in ADGNY vary between ADGE and its joint venture partner. The noncontrolling interest and distributions are determined based on economic ownership. The economic ownership is calculated by the amount invested by us and the noncontrolling partner in each site. Each quarter, we calculate a year-to-date profit/loss for each site that is part of ADGNY and the noncontrolling interest percent of economic ownership in each site is applied to determine the noncontrolling interest share in the profit/loss. The same methodology is used to determine quarterly distributions of available cash to the noncontrolling interest partner. On our balance sheet, noncontrolling interest represents the joint venture partner’s investment in ADGNY, plus its share of after-tax profits less any cash distributions. ADGE owned a controlling 51.0% legal and economic interest in ADGNY as of March 31, 2024 and December 31, 2023. Operating results for the three months ended March 31, 2024 are not necessarily indicative of the results that may be expected for the year ending December 31, 2024. All intercompany transactions have been eliminated in consolidation. The condensed consolidated balance sheet at December 31, 2023 has been derived from the audited consolidated financial statements at that date but does not include all of the information and footnotes required by generally accepted accounting principles for complete financial statements. For further information, refer to the consolidated financial statements and footnotes thereto included in Tecogen's Annual Report on Form 10-K for the year ended December 31, 2023. Use of Estimates The preparation of financial statements in conformity with accounting principles generally accepted in the United States of America requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities and disclosure of contingent assets and liabilities at the date of the financial statements and the reported amounts of revenues and expenses during the reporting period. Actual results could differ from those estimates. Income Taxes The provisions for income taxes in the accompanying unaudited consolidated statements of operations differ from that which would be expected by applying the federal statutory tax rate primarily due to losses for which no benefit is recognized.

Revenue

Revenue	3 Months Ended
Revenue	Mar. 31, 2024
Revenue Recognition [Abstract]
Revenue	Revenue Revenue is recognized when performance obligations under the terms of a contract with our customer are satisfied; generally this occurs with the transfer of control of our products, services and energy production. Revenue is measured as the amount of consideration we expect to receive in exchange for transferring goods or providing services or energy to customers. Shipping and handling fees billed to customers in a sales transaction are recorded in revenue and shipping and handling costs incurred are recorded in cost of sales. We have elected to exclude from revenue any value-added sales and other taxes which we collect concurrent with revenue-producing activities. These accounting policy elections are consistent with the manner in which we historically recorded shipping and handling fees and value-added taxes. Incremental costs incurred by us to obtain a contract with a customer are negligible, if any, and are expensed ratably in proportion to the related revenue recognized. Disaggregated Revenue In general, our business segmentation is aligned according to the nature and economic characteristics of our products and customer relationships and provides meaningful disaggregation of each business segment's results of operations. The following table further disaggregates our revenue by major source by segment for the three months ended March 31, 2024 and 2023. Three Months Ended Revenues March 31, 2024 March 31, 2023 Products: Cogeneration $ 774,229 $ 543,693 Chiller 657,061 1,068,934 Engineered Accessories 60,108 97,509 Total Products Revenue 1,491,398 1,710,136 Services 4,014,310 3,136,173 Energy production 680,389 533,509 Total revenues $ 6,186,097 $ 5,379,818 Products Segment Products. Our Product revenues include cogeneration systems that supply electricity and hot water, chillers that provide air-conditioning and hot water and engineered accessories, which consist of ancillary products and parts necessary to install a cogeneration unit including integration into the customers’ existing electrical and mechanical systems. We refer to the package of engineered accessories and engineering and design services necessary for the customers' installation of a cogeneration unit as light installation services. We transfer control and generally recognize a sale when we ship a product from our manufacturing facility at which point the customer takes ownership of the product. Payment terms on product sales are generally 30 days. We recognize revenue in certain circumstances before delivery to the customer has occurred (commonly referred to as bill and hold transactions). We recognize revenue related to such transactions once, among other things, the customer has made a written fixed commitment to purchase the product(s) under normal billing and credit terms, the customer has requested the product(s) be held for future delivery as scheduled and designated by them, risk of ownership has been assumed by the customer, and the product(s) are tagged as sold and segregated for storage awaiting further direction from the customer. Due to the infrequent nature and duration of bill and hold arrangements, the value associated with custodial storage services is deemed immaterial in the context of the contract and in total, and accordingly, none of the transaction price is allocated to such service. Depending on the product and terms of the arrangement, we may defer the recognition of a portion of the transaction price received because we have to satisfy a future obligation (e.g., product start-up service). Amounts allocated to product start-up services are recognized as revenue when the start-up service has been completed. We use an observable selling price to determine standalone selling prices where available and either a combination of an adjusted market assessment approach, an expected cost plus a margin approach, and/or a residual approach to determine the standalone selling prices for separate performance obligations as a basis for allocating contract consideration when an observable selling price is not available. Amounts received but not recognized pending completion of performance are recognized as contract liabilities and are recorded as deferred revenue along with deposits by customers. Services Segment Maintenance Services. Maintenance services are provided under either long-term maintenance contracts or time and material maintenance contracts. Revenue under time and material maintenance contracts is recognized when the maintenance service is completed. Revenue under long-term maintenance contracts is recognized either ratably over the term of the contract where the contract price is fixed or when the periodic maintenance activities are completed and the invoiced cost to the customer is based on run hours or kilowatts produced in a given period. We use an output method to measure progress towards completion of our performance obligation which results in the recognition of revenue on the basis of a direct measurement of the value to the customer of the services transferred to date relative to the remaining services promised under the contract. We use the practical expedient at ASC 606-10-55-18 of recognizing revenue in an amount equal to the amount we have the right to invoice the customer under the contract. Revenues resulting from the Aegis acquisition (see Note 7. Aegis Contract and Related Asset Acquisitions) have been included in our revenue from the Services segment since April 1, 2023. Payment terms for maintenance services are generally 30 days. Energy Production Segment Energy Production. Revenue from energy contracts is recognized when electricity, heat, hot and/or chilled water is produced by our owned on-site cogeneration systems. Each month we bill the customer and recognize revenue for the various forms of energy delivered, based on meter readings which capture the quantity of the various forms of energy delivered in a given month under a contractually defined formula which takes into account the current month's cost of energy from the local power utility. As the various forms of energy delivered by us under energy production contracts are simultaneously delivered and consumed by the customer, our performance obligation under these contracts is considered to be satisfied over time. We use an output method to measure progress towards completion of our performance obligation which results in the recognition of revenue on the basis of a direct measurement of the value to the customer of the services transferred to date relative to the remaining services promised under the contract. We use the practical expedient at ASC 606-10-55-18 of recognizing revenue in an amount equal to that amount to which we have the right to invoice the customer under the contract. Payment terms on invoices under these contracts are generally 30 days. Contract Balances The timing of revenue recognition, billings and cash collections result in billed accounts receivable, unbilled revenue (contract assets) and deferred revenue, consisting of customer deposits and billings in excess of revenue recognized (contract liabilities) on the condensed consolidated balance sheets. We did not recognize any revenue during the three months ended March 31, 2024 that was included in unbilled revenue as of March 31, 2024. Revenue recognized during the three ended months March 31, 2024 that was included in deferred revenue at the beginning of the period was approximately $413,107. Remaining Performance Obligations Remaining performance obligations related to ASC 606 represent the aggregate transaction price allocated to performance obligations with an original contract term of greater than one year, excluding certain maintenance contracts and all energy production contracts where a direct measurement of the value to the customer is used as a method of measuring progress towards completion of our performance obligation. Exclusion of these remaining performance obligations is due in part to the inability to quantify values based on unknown future levels of delivery and in some cases rates used to invoice customers. Remaining performance obligations therefore consist of unsatisfied or partially satisfied performance obligations related to fixed price maintenance contracts and installation contracts.

Income (Loss) Per Common Share

Income (Loss) Per Common Share	3 Months Ended
Income (Loss) Per Common Share	Mar. 31, 2024
Earnings Per Share [Abstract]
Income (Loss) Per Common Share	Income (Loss) Per Common Share Basic and diluted income (loss) per share for the three months ended March 31, 2024 and 2023, respectively, were as follows: Three Months Ended March 31, 2024 March 31, 2023 Numerator: Net loss available to stockholders $ (1,104,967) $ (1,490,029) Denominator: Weighted average shares outstanding - Basic 24,850,261 24,850,261 Effect of dilutive securities: Stock options — — Weighted average shares outstanding - Diluted 24,850,261 24,850,261 Basic loss per share $ (0.04) $ (0.06) Diluted loss per share $ (0.04) $ (0.06) Anti-dilutive shares underlying stock options outstanding 2,081,772 1,744,351

Inventories, net

Inventories, net	3 Months Ended
Inventories, net	Mar. 31, 2024
Inventory Disclosure [Abstract]
Inventories, net	Inventories, net Inventories at March 31, 2024 and December 31, 2023 consisted of the following: March 31, 2024 December 31, 2023 Raw materials, net $ 8,545,175 $ 8,803,054 Work-in-process 460,760 798,522 Finished goods, net 1,015,067 951,843 Total inventories, net $ 10,021,002 $ 10,553,419

Property, Plant and Equipment,

Property, Plant and Equipment, net	3 Months Ended
Property, Plant and Equipment, net	Mar. 31, 2024
Property, Plant and Equipment [Abstract]
Property, Plant and Equipment, net	Property, Plant and Equipment, net Property, plant and equipment at March 31, 2024 and December 31, 2023 consisted of the following: Estimated Useful March 31, 2024 December 31, 2023 Energy systems 1 - 15 years $ 2,810,232 $ 2,810,232 Machinery and equipment 5 - 7 years 1,675,931 1,744,596 Furniture and fixtures 5 years 216,011 212,963 Computer software 3 - 5 years 192,865 192,865 Leasehold improvements * 592,396 466,789 5,487,435 5,427,445 Less - accumulated depreciation and amortization (4,340,366) (4,264,868) Property, plant and equipment, net $ 1,147,069 $ 1,162,577 * Lesser of estimated useful life of asset or lease term

Intangible Assets and Liabiliti

Intangible Assets and Liabilities Other Than Goodwill	3 Months Ended
Intangible Assets and Liabilities Other Than Goodwill	Mar. 31, 2024
Goodwill and Intangible Assets Disclosure [Abstract]
Intangible Assets and Liabilities Other Than Goodwill	Intangible Assets and Liabilities Other Than Goodwill As of March 31, 2024 and December 31, 2023 we had the following amounts related to intangible assets and liabilities other than goodwill: March 31, 2024 December 31, 2023 Intangible assets Cost Accumulated Amortization Total Cost Accumulated Amortization Total Product certifications $ 777,465 $ (675,397) $ 102,068 $ 777,465 $ (658,676) $ 118,789 Patents 888,910 (518,731) 370,179 888,910 (496,807) 392,103 Developed technology 240,000 (176,000) 64,000 240,000 (172,000) 68,000 Trademarks 26,896 — 26,896 26,896 — 26,896 In Process R&D 263,936 (113,115) 150,821 263,936 (103,689) 160,247 Favorable contract asset 384,465 (377,063) 7,402 384,465 (376,138) 8,327 Customer contracts 1,962,298 (150,552) 1,811,746 1,772,659 (110,791) 1,661,868 $ 4,543,970 $ (2,010,858) $ 2,533,112 $ 4,354,331 $ (1,918,101) $ 2,436,230 Intangible liability Unfavorable contract liability $ 2,618,168 $ (2,066,580) $ 551,588 $ 2,618,168 $ (2,019,122) $ 599,046 The aggregate amortization expense related to intangible assets and liabilities exclusive of contract related intangibles for the three months ended March 31, 2024 and 2023 was $92,756 and $49,361. The net credit to cost of sales related to the amortization of the contract related intangible asset and liability for the three months ended March 31, 2024 and 2023 was $47,459 and $60,933, respectively Contract and Non-Contracted Related Intangibles The favorable contract asset and unfavorable contract liability in the foregoing table represent the estimated fair value of American DG Energy's customer contracts (both positive for favorable contracts and negative for unfavorable contracts) which were acquired by us in May 2017. The customer contract asset includes the maintenance contracts acquired by us on April 1, 2023 and February 1, 2024, as part of the Aegis acquisition (see Note 7. "Aegis Contract and Related Asset Acquisition.") Amortization of intangibles including contract related amounts is calculated using the straight-line method over the remaining useful life or contract term, which range from approximately 1-11 years, and is charged against cost of sales and general & administrative expenses in the accompanying consolidated statement of operations. Aggregate future amortization over the next five years and thereafter as of March 31, 2024 is estimated to be as follows: Non-contract Related Intangibles Contract Related Intangibles Total Year 1 $ 183,995 $ 1,883 $ 185,878 Year 2 168,489 67,329 235,818 Year 3 162,381 102,012 264,393 Year 4 138,362 109,678 248,040 Year 5 20,621 113,122 133,743 Thereafter 20,620 866,136 886,756 Total $ 694,468 1,260,160 $ 1,954,628

Sale of Energy Producing Assets

Sale of Energy Producing Assets and Goodwill Impairment	3 Months Ended
Sale of Energy Producing Assets and Goodwill Impairment	Mar. 31, 2024
Discontinued Operations and Disposal Groups [Abstract]
Sale of Energy Producing Assets and Goodwill Impairment	Sale of Energy Producing Assets In connection with these assets sales, we entered into agreements with the purchaser to maintain and operate the assets over the remaining periods of the associated energy production contracts (through August 2033 and January 2034, respectively) in exchange for monthly maintenance and operating fees. These agreements contain provisions whereby we have guaranteed to the purchaser a minimum level or threshold of cash flows from the associated energy production contracts. Actual results are compared to the minimum threshold bi-annually and we are contractually obligated to reimburse any shortfall to the purchaser. To the extent actual cash flow results exceed the minimum threshold, we are entitled to fifty percent of such excess under the agreements. Based upon an analysis of these energy producing assets' expected future performance, as of March 31, 2024, we do not expect to make any material payments under the guarantee. At March 31, 2024, we were due $25,633 under the energy production contracts, representing 50% of the excess cash flows above the minimum threshold for the bi-annual period ended December 31, 2023. We expect to receive these funds in the second quarter of 2024. The foregoing agreements also contain provisions whereby we have agreed to make whole the purchaser in the event the counterparty to the energy production contract(s) defaults on or otherwise terminates before the stated expiration of the energy production contract. Should we be required to make whole the purchaser under such provisions, we would be entitled to seek recovery from the counterparty to the energy production contract(s) under a similar provision contained in those contracts in respect of early termination.

Leases

Leases	3 Months Ended
Leases	Mar. 31, 2024
Leases [Abstract]
Leases	Leases Our leases principally consist of operating leases related to our corporate office, field offices, and our research, manufacturing, and storage facilities. At lease inception, we determine if an arrangement constitutes a lease and whether that lease meets the classification criteria of a finance or operating lease. Some of our lease agreements contain lease components (e.g. minimum rent payments) and non-lease components (e.g. maintenance, labor charges, etc.). We account for each component separately based on the estimated standalone price of each component. Operating Leases Operating leases are included in Right-of-use assets, Lease obligations, current and Long-term liabilities - Lease obligations, net of current portion, on the condensed consolidated balance sheets. These assets and liabilities are recognized at the commencement date based on the present value of remaining lease payments over the lease term and using an incremental borrowing rate consistent with the lease terms or implicit rates when readily determinable. For those leases where it is reasonably certain at the commencement date that we will exercise the option to extend the lease, then the lease term will include the lease extension term. Short-term operating leases, which have an initial term of 12 months or less, are not recorded on the balance sheet. On March 31, 2023, we entered into two lease agreements for two adjoining buildings, located in North Billerica, Massachusetts, containing approximately 26,412 square feet of manufacturing, storage and office space to serve as our headquarters and manufacturing facilities. The lease agreements provide for initial lease terms of five (5) years with two successive options to renew for additional terms of five (5) years. Both leases commence on January 1, 2024 and require payment of the base rent, real estate taxes, common maintenance expenses and aggregate deposits of $38,200. Our costs for initial improvements required to the leased premises is estimated to range between $500,000 and $750,000. The estimated straight-line monthly rent expense for the initial term of the lease is approximately $26,962 per month. In accordance with ASC 842-20-30-1, we recorded the lease liability and right-of-use asset using the discount rate for the lease upon the lease commencement date, January 1, 2024. On January 1, 2024 we extended our lease for the 2,800 square foot Valley Stream, NY service center for an additional three (3) years through December 31, 2026, with an option to renew for an additional term of three (3) years. The straight-line base monthly rent for the extension is $4,560 per month. On February 1, 2024 we entered into a lease agreement for 2,063 square feet of office and storage space in East Syracuse, New York for an initial lease term of three (3) years, expiring on January 31, 2027, with an option for an additional lease term of two (2) years. The straight-line base monthly rent for the initial lease term is $1,891 per month. The lease on our former headquarters located in Waltham, Massachusetts which consists of approximately 43,000 square feet of manufacturing, storage and office space, expired on April 30, 2024. The base monthly rent in 2024 was $44,254. Lease expense for operating leases, which principally consists of fixed payments for base rent, is recognized on a straight-line basis over the lease term. Operating lease expense for the three months ended March 31, 2024 and 2023 was $271,562 and $189,715, respectively. Supplemental information related to operating leases for the three months ended March 31, 2024 and 2023 was as follows: March 31, 2024 March 31, 2023 Cash paid for amounts included in the measurement of operating lease liabilities $ 269,836 $ 184,072 Right-of-use assets obtained in exchange for operating lease liabilities $ 1,429,977 $ — Weighted-average remaining lease term - operating leases 4.7 Years 3.6 Years Weighted-average discount rate - operating leases 7.5 % 6.0 % Supplemental balance sheet information related to operating leases as of March 31, 2024 and December 31, 2023 was as follows: March 31, 2024 December 31, 2023 Operating leases Right-of-use assets $ 1,986,087 $ 743,096 Operating lease liability, current $ 438,334 $ 248,933 Operating lease liability, long-term 1,573,793 523,660 Total operating lease liability $ 2,012,127 $ 772,593 Finance Leases Finance leases are included in Right-of-use assets, Lease obligations, current and Long-term liabilities - Lease obligations, net of current portion, on the condensed consolidated balance sheets. These assets and liabilities are recognized at the commencement date based on the present value of remaining lease payments over the lease term and using an incremental borrowing rate consistent with the lease terms or implicit rates, when readily determinable. For those leases where it is reasonably certain at the commencement date that we will exercise the option to extend the lease, then the lease term will include the lease extension term. Effective December 19, 2023, we entered into a master finance lease agreement for motor vehicles and acquired five (5) service vehicles. Supplemental information for finance leases for the year ended December 31, 2023 is as follows: December 31, 2023 Right-of-use assets obtained in exchange for finance lease liabilities $ 200,187 Weighted-average remaining lease term - finance leases 5.0 years Weighted-average discount rate - finance leases 10.4 % Supplemental balance sheet information related to finance leases as of March 31, 2024 and December 31, 2023 is as follows: March 31, 2024 December 31, 2023 Finance leases Right-of-use assets - motor vehicles $ 190,177 $ 200,187 Finance lease liability, current $ 31,428 $ 40,540 Finance lease liability, long-term 151,483 159,647 Total finance lease liability $ 182,911 $ 200,187 Future minimum lease commitments under non-cancellable operating and finance leases as of March 31, 2024 were as follows: Operating Leases Finance Leases Total Year 1 $ 563,175 $ 48,931 $ 612,106 Year 2 498,686 48,931 547,617 Year 3 472,862 48,931 521,793 Year 4 421,503 48,931 470,434 Year 5 302,960 36,699 339,659 Thereafter 103,230 — 103,230 Total lease payments 2,362,416 232,423 2,594,839 Less: imputed interest 350,289 49,512 399,801 Total $ 2,012,127 $ 182,911 $ 2,195,038

Stock-Based Compensation

Stock-Based Compensation	3 Months Ended
Stock-Based Compensation	Mar. 31, 2024
Equity [Abstract]
Stock-Based Compensation	Stock-Based Compensation We adopted a 2006 Stock Option and Incentive Plan, or the Plan, under which the Board of Directors may grant incentive or non-qualified stock options and stock grants to key employees, directors, advisors and consultants. The Plan was amended at various dates by the Board of Directors to increase the reserved shares of common stock issuable under the Amended Plan to 3,838,750 as of March 31, 2024, and in June 2017 stockholders approved an amendment to extend the termination date of the Plan to January 1, 2026. Stock options vest based upon the terms within the individual option grants, with an acceleration of the unvested portion of such options upon a change in control event, as defined in the Amended Plan. The options are not transferable except by will or domestic relations order. The option price per share under the Amended Plan cannot be less than the fair market value of the underlying shares on the date of the grant. The number of shares remaining available for future issuance under the Amended Plan as of March 31, 2024 was 1,008,368. During the three months ended March 31, 2024, we did not grant any options to purchase shares of common stock under the Amended Plan. We adopted the 2022 Stock Incentive Plan (the "2022 Plan"), under which the Board of Directors may grant incentive or non-qualified stock options and stock grants to key employees, directors, advisors and consultants. We have reserved 3,800,000 shares of our common stock for issuance pursuant to awards under the 2022 Plan. The adoption of the 2022 Plan was approved by our shareholders on June 9, 2022. Under the 2022 Plan, stock options vest based upon the terms within the individual option grants, with an acceleration of the unvested portion of such options upon a change in control event, as defined in the 2022 Plan. The options are not transferable except by will or domestic relations order. The option price per share under the 2022 Plan cannot be less than the fair market value of the underlying shares on the date of the grant. The number of shares remaining available for future issuance under the Plan as of March 31, 2024 was 3,068,750. During the three months ended March 31, 2024, we did not grant any options to purchase shares of common stock under the 2022 Plan. Stock option activity for the three months ended March 31, 2024 was as follows: Common Stock Options Number of Exercise Weighted Average Exercise Price Weighted Aggregate Outstanding, December 31, 2023 3,638,122 $ 0.71 - $ 10.33 $ 1.49 6.70 years $ 127,811 Granted — Exercised — Canceled and forfeited (801,350) $ 0.74 - $ 10.33 $ 2.73 Outstanding, March 31 2024 2,836,772 $ 0.71 - $ 6.74 $ 1.14 7.06 years $ — Exercisable, March 31, 2024 1,643,022 $ 1.28 $ — Vested and expected to vest, March 31, 2024 2,657,710 $ 1.16 $ — Consolidated stock-based compensation expense for the three months ended March 31, 2024 and 2023 was $44,535 and $77,348, respectively. No tax benefit was recognized related to the stock-based compensation recorded during the period.

Fair Value Measurements

Fair Value Measurements	3 Months Ended
Fair Value Measurements	Mar. 31, 2024
Fair Value Disclosures [Abstract]
Fair Value Measurements	The fair value topic of the FASB Accounting Standards Codification defines fair value as the exchange price that would be received for an asset or paid to transfer a liability (an exit price) in the principal or most advantageous market for the asset or liability in an orderly transaction between market participants on the measurement date. The accounting guidance also establishes a fair value hierarchy which requires an entity to maximize the use of observable inputs, where available, and minimize the use of unobservable inputs when measuring fair value. There are three levels of inputs that may be used to measure fair value: Level 1 - Unadjusted quoted prices in active markets for identical assets or liabilities. We currently do not have any Level 1 financial assets or liabilities. Level 2 - Observable inputs other than quoted prices included in Level 1. Level 2 inputs include quoted prices for identical assets or liabilities in non-active markets, quoted prices for similar assets or liabilities in active markets and inputs other than quoted prices that are observable for substantially the full term of the asset or liability. We have Level 2 financial assets as provided below. Level 3 - Unobservable inputs reflecting management’s own assumptions about the input used in pricing the asset or liability. We have Level 3 liabilities as provided below. Available-for-sale equity securities The following tables present the asset reported in "other assets" in the consolidated balance sheet measured at its fair value on a recurring basis as of March 31, 2024 and 2023 by level within the fair value hierarchy. Quoted prices in active markets for identical assets Significant other observable inputs Significant unobservable inputs Total Level 1 Level 2 Level 3 Gains (losses) March 31, 2024 Recurring fair value measurements Available-for-sale equity securities EuroSite Power Inc. $ 112,493 $ — $ 112,493 $ — $ 18,749 Total recurring fair value measurements $ 112,493 $ — $ 112,493 $ — $ 18,749 March 31, 2023 Recurring fair value measurements Available-for-sale equity securities EuroSite Power Inc. $ 93,744 $ — $ 93,744 $ — $ — Total recurring fair value measurements $ 93,744 $ — $ 93,744 $ — $ — We utilize a Level 2 category fair value measurement to value its investment in EuroSite Power, Inc. as a marketable equity security at period end. That measurement is equal to the quoted market closing price at period end. Since this security is not actively traded we classify it as Level 2. The following table summarizes changes in Level 2 assets which are comprised of marketable equity securities for the three months ended March 31, 2024 and 2023: Fair value at December 31, 2023 $ 93,744 Unrealized gains 18,749 Fair value at March 31, 2024 $ 112,493 Fair value at December 31, 2022 $ 93,744 Unrealized gains — Fair value at March 31, 2023 $ 93,744 Contingent Contract Consideration We utilize a Level 3 category fair value measurement to value the contingent contract consideration liability at period end since there are no quoted prices for this liability in non-active markets, there are no quoted prices for similar liabilities in active markets and there are no inputs that are observable for substantially the full term of the the liability. The contingent contract consideration calculation requires management to make estimates and assumptions that affect the reported amount of the liability. The contingent contract consideration is payable each calendar quarter through the earlier of the expiration or termination of the relevant maintenance agreements, or the seventh (7th) anniversary of the acquisition date. The consideration is equal to the product of the revenues collected in a calendar quarter multiplied by an applicable percentage. The agreement stipulates quarterly aggregate revenue targets and an applicable percentage, and provides for a higher applicable percentage if revenues exceed the target revenues. The applicable percentage ranges from 5% to 10% over the agreement term. On the date of acquisition, the fair value of the contingent consideration was calculated using a weighted average cost of capital of 15%, discounting the future cash flows to present value. Quoted prices in active markets for identical assets Significant other observable inputs Significant unobservable inputs Total Level 1 Level 2 Level 3 Total gains (losses) March 31, 2024 Recurring fair value measurements Contingent contract consideration Current $ 237,928 $ — $ — $ 237,928 $ — Long-term 1,016,558 — — 1,016,558 — Total recurring fair value measurements $ 1,254,486 $ — $ — $ 1,254,486 $ —

Related party transactions

Related party transactions	3 Months Ended
Related party transactions	Mar. 31, 2024
Related Party Transactions [Abstract]
Notes Payable	On October 9, 2023, we entered into note subscription agreements with each of John N. Hatsopoulos, a director and principal shareholder of registrant, and Earl R. Lewis, III, a director of registrant, pursuant to which Mr. Hatsopoulos agreed to provide financing to us of up to $1 million, and Mr. Lewis agreed to provide financing to us of $500,000, and potentially, an additional $500,000 at his discretion. We have the right to determine the amount of the loans at the time of a draw down, subject to the conditions in our agreements with each of Mr. Hatsopoulos and Mr. Lewis discussed below. The loans and terms of the loan agreements were unanimously approved by our board of directors. The loans bear interest on the outstanding principal at the Internal Revenue Service’s Applicable Federal Rate to be determined at the time we issue a promissory note in connection with a loan drawdown. The principal amount and accrued interest of each loan is repayable one year from the date of issuance of the applicable promissory note. A note may be prepaid by us at any time. The principal amount of each loan and accrued interest is subject to mandatory prepayment in the event of a change of control of the registrant. The promissory notes are subject to customary events of default and are transferable provided the conditions to transfer set forth in the promissory notes are satisfied by the noteholder. The proceeds of the loans are expected to be used for general working capital purposes. On October 10, 2023, we issued a promissory note and borrowed $500,000 from Mr. Hatsopoulos. The loan bears interest at 5.12% per annum. At March 31, 2024 our obligation to Mr. Hatsopoulos under the promissory note, inclusive of $11,905 of accrued and unpaid interest, was $511,905. On March 21, 2024, John H. Hatsopoulos amended the terms of the promissory note, dated October 10, 2023, extending the maturity date by one year, making the maturity date October 10, 2025, and agreeing to accept payment in cash or Tecogen Inc. common stock.

Segments

Segments	3 Months Ended
Segments	Mar. 31, 2024
Segment Reporting [Abstract]
Segments	As of March 31, 2024, we were organized into three operating segments through which senior management evaluates our business. These segments, as described in more detail in Note 1, are organized around the products and services provided to customers and represent our reportable segments. The following table presents information by reportable segment for the three months ended March 31, 2024 and 2023: Products Services Energy Production Corporate, other and elimination (1) Total Three Months Ended March 31, 2024 Revenue - external customers $ 1,491,398 $ 4,014,310 $ 680,389 $ — $ 6,186,097 Intersegment revenue — 117,348 — (117,348) $ — Total revenue $ 1,491,398 $ 4,131,658 $ 680,389 $ (117,348) $ 6,186,097 Gross profit $ 441,855 $ 1,922,053 $ 211,749 $ — $ 2,575,657 Identifiable assets $ 9,793,634 $ 12,207,675 $ 3,295,316 $ 3,161,918 $ 28,458,543 Three Months Ended March 31, 2023 Revenue - external customers $ 1,710,136 $ 3,136,173 $ 533,509 $ — $ 5,379,818 Intersegment revenue — 88,214 — (88,214) — Total revenue $ 1,710,136 $ 3,224,387 $ 533,509 $ (88,214) $ 5,379,818 Gross profit $ 497,567 $ 1,398,572 $ 195,770 $ — $ 2,091,909 Identifiable assets $ 12,023,164 $ 9,750,153 $ 3,433,439 $ 3,036,675 $ 28,243,431 (1) Corporate, intersegment revenue, other and elimination includes various corporate assets.

Subsequent Events

Subsequent Events	3 Months Ended
Subsequent Events	Mar. 31, 2024
Subsequent Events [Abstract]
Subsequent Events	Subsequent Events We have evaluated events through the date of this filing, and, except as described below, have determined that no material subsequent events occurred that would require recognition in the consolidated financial statements or disclosure in the notes thereto. On May 1, 2024, Tecogen and Aegis amended the Agreement to add thirty-one (31) additional maintenance contracts (the "Amendment"). The Amendment ("Second Amendment") includes an undertaking by Aegis to use commercially reasonable efforts to support and assist our execution of maintenance service agreements for an additional forty-eight (48) cogeneration units sold to customers by Aegis.

Aegis Contract and Related Asse

Aegis Contract and Related Asset Acquisitions	3 Months Ended
Aegis Contract and Related Asset Acquisitions	Mar. 31, 2024
Business Combination and Asset Acquisition [Abstract]
Aegis Contract and Related Asset Acquisitions	Note 7. Aegis Contract and Related Asset Acquisitions On March 15, 2023, we entered into an agreement ("Agreement") with Aegis Energy Services, LLC (“Aegis”) pursuant to which Aegis agreed to assign to us and we agreed to assume certain Aegis maintenance agreements and agreed to purchase certain assets from Aegis, and related matters (“Acquisition”). On April 1, 2023, the Acquisition closed. Under the Agreement, we agreed to acquire from Aegis and assume Aegis’ rights and obligations arising on or after April 1, 2023, under maintenance agreements pursuant to which Aegis provided maintenance services to third parties for approximately 200 cogeneration systems and we agreed to acquire from Aegis certain vehicles and inventory used by Aegis in connection with the performance of its maintenance services. At closing, we acquired eight (8) Aegis vehicles for consideration consisting of $170,000 in cash. Also, we issued credits against outstanding accounts receivable due from Aegis in the amount of $300,000 for the acquisition of inventory that Aegis used to provide maintenance services. At closing, we hired eight (8) Aegis employees who, following the closing, have agreed to continue to provide maintenance services relating to the cogeneration systems covered by the maintenance agreements assumed pursuant to the Agreement. Following the closing and for a period of up to seven (7) years, we agreed to pay Aegis a percentage of the revenue collected for maintenance services provided pursuant to the maintenance agreements acquired from Aegis. The Agreement contained certain indemnification provisions and agreements on the part of Aegis and for each party to cooperate with each other and provide certain transitional assistance. We acquired the Aegis maintenance agreements to expand our Service portfolio and to benefit from the long-term contract revenue stream generated by these agreements. On February 1, 2024, Tecogen and Aegis amended the Agreement to add eighteen (18) additional maintenance contracts (the "Amendment"). The Amendment includes an undertaking by Aegis to use commercially reasonable efforts to support and assist our execution of maintenance service agreements for an additional thirty-six (36) cogeneration units sold to customers by Aegis. No additional maintenance service agreements have been executed as of March 31, 2024. We have determined that the assignment and assumption of the Aegis maintenance agreements, in combination with the related asset acquisition and the retention of the former Aegis employees, constitutes a business and should be accounted for as a business combination under the acquisition method. As of the acquisition date, we recognized, separately from goodwill, the identifiable assets acquired and the liabilities assumed, at fair value. We have applied an interpretation of the guidance in ASC 805, Business Combinations, that allows an entity to combine multiple acquisitions as one single transaction due to the April 1, 2023 and February 1, 2024 acquisitions being executed in contemplation of one another to achieve the same commercial objective for the Company. As a result, we have adjusted the initial accounting for the April 1, 2023 acquisition for the value of net assets acquired from the February 1, 2024 acquisition. We have included the financial results of the Aegis maintenance agreements in our consolidated financial statements from April 1, 2023, and from February 1, 2024, the closing or acquisition dates for the acquisitions. The following table summarizes the consideration paid for the Aegis acquisitions and the fair value of assets acquired and contract-related liabilities assumed as of the respective acquisition date for each acquisition date along with the combined accounting result: April 1, 2023 February 1, 2024 Total Consideration Paid: Cash $ 170,000 $ — $ 170,000 Accounts receivable credit issued 300,000 — 300,000 Account payable due to Aegis 91,048 — 91,048 Contingent consideration 1,256,656 92,409 1,349,065 Total fair value of consideration transferred 1,817,704 92,409 1,910,113 Identifiable assets acquired and liabilities assumed: Assets acquired Property, plant and equipment 170,000 — 170,000 Inventory 391,048 — 391,048 Identifiable intangible asset - customer contracts 1,772,659 189,639 1,962,298 2,333,707 189,639 2,523,346 Acquired contract-related liabilities assumed Deferred maintenance reserve (853,271) — (853,271) Net identifiable assets acquired 1,480,436 189,639 1,670,075 Excess of cost over fair value of net assets acquired (Goodwill) $ 337,268 $ (97,230) $ 240,038 Initial Acquisition - April 1, 2023 The amounts initially recognized for inventory, identifiable intangible assets, contingent consideration and deferred maintenance reserves were provisional pending completion of the necessary valuations and analysis. ASC 805 establishes a measurement period to provide companies with a reasonable amount of time to obtain the information necessary to identify and measure various items in a business combination and cannot extend beyond one year from the acquisition date. As of December 31, 2023, we have completed our analysis and valuation. As of March 31, 2024, we recorded no adjustments to the fair value of the contingent consideration and deferred maintenance reserves given the probability of achieving the revenue estimates and the actual and expected maintenance costs were were consistent with our initial valuation. Second Acquisition - February 1, 2024 The amounts initially recognized for identifiable intangible assets and contingent consideration are provisional pending completion of the necessary valuations and analysis. ASC 805 establishes a measurement period to provide companies with a reasonable amount of time to obtain the information necessary to identify and measure various items in a business combination and cannot extend beyond one year from the acquisition date. As of March 31, 2024, we have not completed our analysis and valuation for the second maintenance service agreement acquisition. Acquisition Valuation The fair value of the identifiable intangible asset was estimated using the income approach. The excess cash flow was discounted to present value using an appropriate rate of return to estimate the market value of the customer identifiable intangible asset and the risks associated with the future revenue forecasts due to potential changes in customer energy requirements or changes in the economic viability of these CHP sites which depend on the spread between natural gas fuel and electricity prices, all of which are not within our control. Key assumptions to value the customer identifiable intangible asset included the discount rate of 15%, profitability assumptions, revenue assumptions, and anticipated existing contract run out were the material assumptions utilized in the discounted cash flow model used to estimate fair value. The discount rate reflects an estimate of our weighted-average cost of capital. On the date of acquisition, the fair value of the contingent consideration and the deferred maintenance reserve were calculated under the income approach using a weighted average cost of capital of 15%, discounting the future cash flows to present value, and are subsequently remeasured to fair value at each reporting date until the fair value contingencies are resolved. Fair value adjustments which may be determined at subsequent reporting dates will be recorded in our consolidated statements of operations and will not impact the goodwill balance after the measurement period. The contingent consideration is payable within forty-five (45) days following the end of each calendar quarter through the earlier of the expiration or termination of the relevant maintenance agreements, or the seventh (7th) anniversary of the acquisition date. The consideration is equal to the product of the revenues collected in a calendar quarter multiplied by an applicable percentage. The agreement stipulates quarterly aggregate revenue targets and an applicable percentage, and provides for a higher applicable percentage if revenues exceed the target revenues. The applicable percentage ranges from 5% to 10% over the agreement term. The deferred maintenance reserve represents costs, which are expected to be incurred over a three-year period from the date of acquisition to repair customer equipment which had not been sufficiently maintained prior to our acquisition of the maintenance service agreements. The purchase price of the acquisition was allocated to the tangible and intangible assets acquired and liabilities assumed and recognized at their fair value based on widely accepted valuation techniques in accordance with ASC 820, "Fair Value Measurement," as of the acquisition date. The process for estimating fair value requires the use of significant assumptions and estimates of future cash flows and developing appropriate discount rates. The excess of the purchase price over fair value of the net identified assets acquired and liabilities assumed was recorded as goodwill. Goodwill is primarily attributable to the going concern element of the Aegis business, including its assembled workforce and the long-term nature of the customer maintenance agreements, as well as anticipated cost synergies due primarily to the elimination of administrative overhead. Goodwill resulting from the Aegis acquisition is not expected to be deductible for income tax purposes. Acquisition-related costs which consisted on recurring internal resources were de minimus and such costs were expensed as incurred (ASC 805-50-30-1). The following table summarizes the contract-related liabilities assumed as of March 31, 2024 and December 31, 2023: March 31, 2024 December 31, 2023 Acquisition liabilities, current Contingent consideration $ 237,928 $ 200,639 Deferred maintenance reserve 691,483 644,724 929,411 845,363 Acquisition liabilities, long-term Contingent consideration 1,016,558 994,743 Deferred maintenance reserve 140,277 187,036 $ 1,156,835 $ 1,181,779 Revenues and gross profit from the Aegis maintenance contracts were $758,762 and $485,044, respectively, for the three months ended March 31, 2024 and are included in our Services segment. We are unable to provide the pro forma information required under ASC 805-10-50-2(h) as the disclosure is impracticable since the required pre-acquisition historical information could not be obtained from Aegis.

Description of business and b_2

Description of business and basis of presentation (Policies)	3 Months Ended
	Mar. 31, 2024
Accounting Policies [Abstract]
Principles of Consolidation and Basis of Presentation	Basis of Presentation The financial statements have been prepared in accordance with accounting standards set by the Financial Accounting Standards Board, or FASB. The FASB sets generally accepted accounting principles, or GAAP, to ensure financial condition, results of operations, and cash flows are consistently reported. References to GAAP issued by the FASB in these footnotes are to the FASB Accounting Standards Codification, or ASC. We adopted the presentation requirements for noncontrolling interests required by ASC 810 Consolidation. Under ASC 810, earnings or losses attributed to the noncontrolling interests are reported as part of the consolidated earnings and not a separate component of income or expense. The accompanying consolidated financial statements include our accounts and the accounts of the entities in which we have a controlling financial interest. Those entities include our wholly-owned subsidiary, American DG Energy Inc. ("ADGE"), Tecogen CHP Solutions, Inc., and a joint venture, American DG New York, LLC, or ADGNY, in which ADGE holds a 51.0% interest. As the controlling partner, all major decisions in respect of ADGNY are made by ADGE in accordance with the joint venture agreement. The interests in the individual underlying energy system projects in ADGNY vary between ADGE and its joint venture partner. The noncontrolling interest and distributions are determined based on economic ownership. The economic ownership is calculated by the amount invested by us and the noncontrolling partner in each site. Each quarter, we calculate a year-to-date profit/loss for each site that is part of ADGNY and the noncontrolling interest percent of economic ownership in each site is applied to determine the noncontrolling interest share in the profit/loss. The same methodology is used to determine quarterly distributions of available cash to the noncontrolling interest partner. On our balance sheet, noncontrolling interest represents the joint venture partner’s investment in ADGNY, plus its share of after-tax profits less any cash distributions. ADGE owned a controlling 51.0% legal and economic interest in ADGNY as of March 31, 2024 and December 31, 2023. Operating results for the three months ended March 31, 2024 are not necessarily indicative of the results that may be expected for the year ending December 31, 2024. All intercompany transactions have been eliminated in consolidation. The condensed consolidated balance sheet at December 31, 2023 has been derived from the audited consolidated financial statements at that date but does not include all of the information and footnotes required by generally accepted accounting principles for complete financial statements. For further information, refer to the consolidated financial statements and footnotes thereto included in Tecogen's Annual Report on Form 10-K for the year ended December 31, 2023.
Use of Estimates	Use of Estimates
Income Taxes	Income Taxes The provisions for income taxes in the accompanying unaudited consolidated statements of operations differ from that which would be expected by applying the federal statutory tax rate primarily due to losses for which no benefit is recognized.

Revenue (Tables)

Revenue (Tables)	3 Months Ended
Revenue (Tables)	Mar. 31, 2024
Revenue Recognition [Abstract]
Disaggregation of Revenue	The following table further disaggregates our revenue by major source by segment for the three months ended March 31, 2024 and 2023. Three Months Ended Revenues March 31, 2024 March 31, 2023 Products: Cogeneration $ 774,229 $ 543,693 Chiller 657,061 1,068,934 Engineered Accessories 60,108 97,509 Total Products Revenue 1,491,398 1,710,136 Services 4,014,310 3,136,173 Energy production 680,389 533,509 Total revenues $ 6,186,097 $ 5,379,818

Income (Loss) Per Common Share

Income (Loss) Per Common Share (Tables)	3 Months Ended
Income (Loss) Per Common Share (Tables)	Mar. 31, 2024
Earnings Per Share [Abstract]
Schedule of Income (Loss) Per Common Share, Basic and Diluted	Basic and diluted income (loss) per share for the three months ended March 31, 2024 and 2023, respectively, were as follows: Three Months Ended March 31, 2024 March 31, 2023 Numerator: Net loss available to stockholders $ (1,104,967) $ (1,490,029) Denominator: Weighted average shares outstanding - Basic 24,850,261 24,850,261 Effect of dilutive securities: Stock options — — Weighted average shares outstanding - Diluted 24,850,261 24,850,261 Basic loss per share $ (0.04) $ (0.06) Diluted loss per share $ (0.04) $ (0.06) Anti-dilutive shares underlying stock options outstanding 2,081,772 1,744,351

Inventory (Tables)

Inventory (Tables)	3 Months Ended
Inventory (Tables)	Mar. 31, 2024
Inventory Disclosure [Abstract]
Schedule of Inventory	Inventories at March 31, 2024 and December 31, 2023 consisted of the following: March 31, 2024 December 31, 2023 Raw materials, net $ 8,545,175 $ 8,803,054 Work-in-process 460,760 798,522 Finished goods, net 1,015,067 951,843 Total inventories, net $ 10,021,002 $ 10,553,419

Property, Plant and Equipment (

Property, Plant and Equipment (Tables)	3 Months Ended
Property, Plant and Equipment (Tables)	Mar. 31, 2024
Property, Plant and Equipment [Abstract]
Summary of Property, Plant and Equipment	Property, plant and equipment at March 31, 2024 and December 31, 2023 consisted of the following: Estimated Useful March 31, 2024 December 31, 2023 Energy systems 1 - 15 years $ 2,810,232 $ 2,810,232 Machinery and equipment 5 - 7 years 1,675,931 1,744,596 Furniture and fixtures 5 years 216,011 212,963 Computer software 3 - 5 years 192,865 192,865 Leasehold improvements * 592,396 466,789 5,487,435 5,427,445 Less - accumulated depreciation and amortization (4,340,366) (4,264,868) Property, plant and equipment, net $ 1,147,069 $ 1,162,577 * Lesser of estimated useful life of asset or lease term

Intangible Assets and Liabili_2

Intangible Assets and Liabilities Other Than Goodwill (Tables)	3 Months Ended
	Mar. 31, 2024
Goodwill and Intangible Assets Disclosure [Abstract]
Schedule of Intangible Assets	As of March 31, 2024 and December 31, 2023 we had the following amounts related to intangible assets and liabilities other than goodwill: March 31, 2024 December 31, 2023 Intangible assets Cost Accumulated Amortization Total Cost Accumulated Amortization Total Product certifications $ 777,465 $ (675,397) $ 102,068 $ 777,465 $ (658,676) $ 118,789 Patents 888,910 (518,731) 370,179 888,910 (496,807) 392,103 Developed technology 240,000 (176,000) 64,000 240,000 (172,000) 68,000 Trademarks 26,896 — 26,896 26,896 — 26,896 In Process R&D 263,936 (113,115) 150,821 263,936 (103,689) 160,247 Favorable contract asset 384,465 (377,063) 7,402 384,465 (376,138) 8,327 Customer contracts 1,962,298 (150,552) 1,811,746 1,772,659 (110,791) 1,661,868 $ 4,543,970 $ (2,010,858) $ 2,533,112 $ 4,354,331 $ (1,918,101) $ 2,436,230 Intangible liability Unfavorable contract liability $ 2,618,168 $ (2,066,580) $ 551,588 $ 2,618,168 $ (2,019,122) $ 599,046
Schedule of Future Amortization Expense	Aggregate future amortization over the next five years and thereafter as of March 31, 2024 is estimated to be as follows: Non-contract Related Intangibles Contract Related Intangibles Total Year 1 $ 183,995 $ 1,883 $ 185,878 Year 2 168,489 67,329 235,818 Year 3 162,381 102,012 264,393 Year 4 138,362 109,678 248,040 Year 5 20,621 113,122 133,743 Thereafter 20,620 866,136 886,756 Total $ 694,468 1,260,160 $ 1,954,628

Leases (Tables)

Leases (Tables)	3 Months Ended
Leases (Tables)	Mar. 31, 2024
Leases [Abstract]
Supplemental Information Related to Leases	Supplemental information related to operating leases for the three months ended March 31, 2024 and 2023 was as follows: March 31, 2024 March 31, 2023 Cash paid for amounts included in the measurement of operating lease liabilities $ 269,836 $ 184,072 Right-of-use assets obtained in exchange for operating lease liabilities $ 1,429,977 $ — Weighted-average remaining lease term - operating leases 4.7 Years 3.6 Years Weighted-average discount rate - operating leases 7.5 % 6.0 % Supplemental information for finance leases for the year ended December 31, 2023 is as follows: December 31, 2023 Right-of-use assets obtained in exchange for finance lease liabilities $ 200,187 Weighted-average remaining lease term - finance leases 5.0 years Weighted-average discount rate - finance leases 10.4 %
Future Minimum Lease Commitments	Future minimum lease commitments under non-cancellable operating and finance leases as of March 31, 2024 were as follows: Operating Leases Finance Leases Total Year 1 $ 563,175 $ 48,931 $ 612,106 Year 2 498,686 48,931 547,617 Year 3 472,862 48,931 521,793 Year 4 421,503 48,931 470,434 Year 5 302,960 36,699 339,659 Thereafter 103,230 — 103,230 Total lease payments 2,362,416 232,423 2,594,839 Less: imputed interest 350,289 49,512 399,801 Total $ 2,012,127 $ 182,911 $ 2,195,038
Assets and Liabilities, Lessee	Supplemental balance sheet information related to operating leases as of March 31, 2024 and December 31, 2023 was as follows: March 31, 2024 December 31, 2023 Operating leases Right-of-use assets $ 1,986,087 $ 743,096 Operating lease liability, current $ 438,334 $ 248,933 Operating lease liability, long-term 1,573,793 523,660 Total operating lease liability $ 2,012,127 $ 772,593 Supplemental balance sheet information related to finance leases as of March 31, 2024 and December 31, 2023 is as follows: March 31, 2024 December 31, 2023 Finance leases Right-of-use assets - motor vehicles $ 190,177 $ 200,187 Finance lease liability, current $ 31,428 $ 40,540 Finance lease liability, long-term 151,483 159,647 Total finance lease liability $ 182,911 $ 200,187

Stock-Based Compensation (Table

Stock-Based Compensation (Tables)	3 Months Ended
Stock-Based Compensation (Tables)	Mar. 31, 2024
Tecogen
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Schedule of Stock Option Activity	Stock option activity for the three months ended March 31, 2024 was as follows: Common Stock Options Number of Exercise Weighted Average Exercise Price Weighted Aggregate Outstanding, December 31, 2023 3,638,122 $ 0.71 - $ 10.33 $ 1.49 6.70 years $ 127,811 Granted — Exercised — Canceled and forfeited (801,350) $ 0.74 - $ 10.33 $ 2.73 Outstanding, March 31 2024 2,836,772 $ 0.71 - $ 6.74 $ 1.14 7.06 years $ — Exercisable, March 31, 2024 1,643,022 $ 1.28 $ — Vested and expected to vest, March 31, 2024 2,657,710 $ 1.16 $ —

Fair Value Measurements (Tables

Fair Value Measurements (Tables)	3 Months Ended
Fair Value Measurements (Tables)	Mar. 31, 2024
Fair Value Disclosures [Abstract]
Schedule of Fair Value, Assets and Liabilities Measured on Recurring Basis	The following tables present the asset reported in "other assets" in the consolidated balance sheet measured at its fair value on a recurring basis as of March 31, 2024 and 2023 by level within the fair value hierarchy. Quoted prices in active markets for identical assets Significant other observable inputs Significant unobservable inputs Total Level 1 Level 2 Level 3 Gains (losses) March 31, 2024 Recurring fair value measurements Available-for-sale equity securities EuroSite Power Inc. $ 112,493 $ — $ 112,493 $ — $ 18,749 Total recurring fair value measurements $ 112,493 $ — $ 112,493 $ — $ 18,749 March 31, 2023 Recurring fair value measurements Available-for-sale equity securities EuroSite Power Inc. $ 93,744 $ — $ 93,744 $ — $ — Total recurring fair value measurements $ 93,744 $ — $ 93,744 $ — $ —
Schedule of Fair Value, Measured on Recurring Basis, Gain (Loss) Included in Earnings	The following table summarizes changes in Level 2 assets which are comprised of marketable equity securities for the three months ended March 31, 2024 and 2023: Fair value at December 31, 2023 $ 93,744 Unrealized gains 18,749 Fair value at March 31, 2024 $ 112,493 Fair value at December 31, 2022 $ 93,744 Unrealized gains — Fair value at March 31, 2023 $ 93,744 Contingent Contract Consideration We utilize a Level 3 category fair value measurement to value the contingent contract consideration liability at period end since there are no quoted prices for this liability in non-active markets, there are no quoted prices for similar liabilities in active markets and there are no inputs that are observable for substantially the full term of the the liability. The contingent contract consideration calculation requires management to make estimates and assumptions that affect the reported amount of the liability. The contingent contract consideration is payable each calendar quarter through the earlier of the expiration or termination of the relevant maintenance agreements, or the seventh (7th) anniversary of the acquisition date. The consideration is equal to the product of the revenues collected in a calendar quarter multiplied by an applicable percentage. The agreement stipulates quarterly aggregate revenue targets and an applicable percentage, and provides for a higher applicable percentage if revenues exceed the target revenues. The applicable percentage ranges from 5% to 10% over the agreement term. On the date of acquisition, the fair value of the contingent consideration was calculated using a weighted average cost of capital of 15%, discounting the future cash flows to present value. Quoted prices in active markets for identical assets Significant other observable inputs Significant unobservable inputs Total Level 1 Level 2 Level 3 Total gains (losses) March 31, 2024 Recurring fair value measurements Contingent contract consideration Current $ 237,928 $ — $ — $ 237,928 $ — Long-term 1,016,558 — — 1,016,558 — Total recurring fair value measurements $ 1,254,486 $ — $ — $ 1,254,486 $ —

Segments (Tables)

Segments (Tables)	3 Months Ended
Segments (Tables)	Mar. 31, 2024
Segment Reporting [Abstract]
Schedule of Segment Reporting Information	The following table presents information by reportable segment for the three months ended March 31, 2024 and 2023: Products Services Energy Production Corporate, other and elimination (1) Total Three Months Ended March 31, 2024 Revenue - external customers $ 1,491,398 $ 4,014,310 $ 680,389 $ — $ 6,186,097 Intersegment revenue — 117,348 — (117,348) $ — Total revenue $ 1,491,398 $ 4,131,658 $ 680,389 $ (117,348) $ 6,186,097 Gross profit $ 441,855 $ 1,922,053 $ 211,749 $ — $ 2,575,657 Identifiable assets $ 9,793,634 $ 12,207,675 $ 3,295,316 $ 3,161,918 $ 28,458,543 Three Months Ended March 31, 2023 Revenue - external customers $ 1,710,136 $ 3,136,173 $ 533,509 $ — $ 5,379,818 Intersegment revenue — 88,214 — (88,214) — Total revenue $ 1,710,136 $ 3,224,387 $ 533,509 $ (88,214) $ 5,379,818 Gross profit $ 497,567 $ 1,398,572 $ 195,770 $ — $ 2,091,909 Identifiable assets $ 12,023,164 $ 9,750,153 $ 3,433,439 $ 3,036,675 $ 28,243,431 (1) Corporate, intersegment revenue, other and elimination includes various corporate assets.

Aegis Contract and Related As_2

Aegis Contract and Related Asset Acquisitions (Tables)	3 Months Ended
Aegis Contract and Related Asset Acquisitions (Tables)	Mar. 31, 2024
Business Combination and Asset Acquisition [Abstract]
Asset Acquisition	The following table summarizes the consideration paid for the Aegis acquisitions and the fair value of assets acquired and contract-related liabilities assumed as of the respective acquisition date for each acquisition date along with the combined accounting result: April 1, 2023 February 1, 2024 Total Consideration Paid: Cash $ 170,000 $ — $ 170,000 Accounts receivable credit issued 300,000 — 300,000 Account payable due to Aegis 91,048 — 91,048 Contingent consideration 1,256,656 92,409 1,349,065 Total fair value of consideration transferred 1,817,704 92,409 1,910,113 Identifiable assets acquired and liabilities assumed: Assets acquired Property, plant and equipment 170,000 — 170,000 Inventory 391,048 — 391,048 Identifiable intangible asset - customer contracts 1,772,659 189,639 1,962,298 2,333,707 189,639 2,523,346 Acquired contract-related liabilities assumed Deferred maintenance reserve (853,271) — (853,271) Net identifiable assets acquired 1,480,436 189,639 1,670,075 Excess of cost over fair value of net assets acquired (Goodwill) $ 337,268 $ (97,230) $ 240,038 The following table summarizes the contract-related liabilities assumed as of March 31, 2024 and December 31, 2023: March 31, 2024 December 31, 2023 Acquisition liabilities, current Contingent consideration $ 237,928 $ 200,639 Deferred maintenance reserve 691,483 644,724 929,411 845,363 Acquisition liabilities, long-term Contingent consideration 1,016,558 994,743 Deferred maintenance reserve 140,277 187,036 $ 1,156,835 $ 1,181,779

Description of business and b_3

Description of business and basis of presentation - Additional Information (Details) - USD ($)	3 Months Ended
	Mar. 31, 2024	Mar. 31, 2023	Dec. 31, 2023
Business Acquisition [Line Items]
Ownerhsip interest in American DG New York, LLC (percent)	51%
Employee retention credit	$ 0	$ (667,121)
Backlog	5,554,599
Increase (Decrease) in Working Capital	(1,322,899)
Working Capital, Net	$ 8,499,647		$ 9,822,546

Revenue - Disaggregation of Rev

Revenue - Disaggregation of Revenue (Details) - USD ($)	3 Months Ended
Revenue - Disaggregation of Revenue (Details) - USD ($)	Mar. 31, 2024	Mar. 31, 2023
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax	$ 6,186,097	$ 5,379,818
Products
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax	1,491,398	1,710,136
Energy production
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax	680,389	533,509
Products Segment
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax	1,491,398	1,710,136
Products Segment \| Cogeneration
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax	774,229	543,693
Products Segment \| Chiller
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax	657,061	1,068,934
Products Segment \| Engineered Accessories
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax	60,108	97,509
Services \| Installation Services [Member]
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax	4,014,310	3,136,173
Services \| Energy Production [Member]
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax	680,389	533,509
Energy Production [Member]
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax	680,389	533,509
Operating Segments
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax		5,379,818
Operating Segments \| Products Segment
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax	1,491,398	1,710,136
Operating Segments \| Energy Production [Member]
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax	$ 680,389	$ 533,509

Revenue - Additional Informatio

Revenue - Additional Information (Details)	3 Months Ended
Revenue - Additional Information (Details)	Mar. 31, 2024 USD ($)
Revenue Recognition [Abstract]
Deferred revenue recognized	$ 413,107
Remaining performance obligations	$ 2,807,997
Performance obligation revenue expected to be recognized over the next 24 months (percent)	74.30%
Performance obligation revenue to be recognized in first 12 months (percent)	62%
Performance obligation revenue to be recognized over the subsequent 12 months (percent)	12.30%

Income (Loss) Per Common Shar_2

Income (Loss) Per Common Share - Schedule of Income (Loss) Per Common Share, Basic and Diluted (Details) - USD ($)	3 Months Ended
	Mar. 31, 2024	Mar. 31, 2023
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Net loss available to stockholders	$ (1,104,967)	$ (1,490,029)
Weighted average shares outstanding - basic	24,850,261	24,850,261
Effect of dilutive securities:
Weighted average shares outstanding - Diluted	24,850,261	24,850,261
Net income (loss) per share - basic (in USD per share)	$ (0.04)	$ (0.06)
Net income (loss) per share - diluted (in usd per share)	$ (0.04)	$ (0.06)
Stock Options
Effect of dilutive securities:
Stock options	0	0
Anti-dilutive shares underlying stock options outstanding	2,081,772	1,744,351

Inventory (Details)

Inventory (Details) - USD ($)	Mar. 31, 2024	Dec. 31, 2023
Inventory Disclosure [Abstract]
Inventory, Raw Materials, Net of Reserves	$ 8,545,175	$ 8,803,054
Inventory, Work in Process, Net of Reserves	460,760	798,522
Inventory, Finished Goods, Net of Reserves	1,015,067	951,843
Inventories, net	$ 10,021,002	$ 10,553,419

Property, Plant and Equipment -

Property, Plant and Equipment - Summary of Property and Equipment (Details) - USD ($)	Mar. 31, 2024	Dec. 31, 2023
Property, Plant and Equipment [Line Items]
Property and equipment, gross	$ 5,487,435	$ 5,427,445
Accumulated Depreciation, Depletion and Amortization, Property, Plant, and Equipment	(4,340,366)	(4,264,868)
Property, plant and equipment, net	1,147,069	1,162,577
Energy Equipment [Member]
Property, Plant and Equipment [Line Items]
Property and equipment, gross	2,810,232	2,810,232
Machinery and Equipment [Member]
Property, Plant and Equipment [Line Items]
Property and equipment, gross	1,675,931	1,744,596
Furniture and Fixtures [Member]
Property, Plant and Equipment [Line Items]
Property and equipment, gross	216,011	212,963
Computer Software, Intangible Asset [Member]
Property, Plant and Equipment [Line Items]
Property and equipment, gross	192,865	192,865
Leasehold Improvements [Member]
Property, Plant and Equipment [Line Items]
Property and equipment, gross	$ 592,396	$ 466,789

Property, Plant and Equipment_2

Property, Plant and Equipment - Depreciation (Details) - USD ($)	3 Months Ended
	Mar. 31, 2024	Mar. 31, 2023
Property, Plant and Equipment [Abstract]
Depreciation and amortization expense	$ 94,838	$ 117,492

Intangible Assets and Liabili_3

Intangible Assets and Liabilities Other Than Goodwill -Amounts related to intangible assets (Details) - USD ($)	Mar. 31, 2024	Dec. 31, 2023
Finite-Lived Intangible Assets [Line Items]
Intangible assets	$ 4,543,970	$ 4,354,331
Less - accumulated amortization	(2,010,858)	(1,918,101)
Intangible assets, net	2,533,112	2,436,230
Unfavorable Contract Liability
Finite-Lived Intangible Assets [Line Items]
Unfavorable contract liability	2,618,168	2,618,168
Less - accumulated amortization	(2,066,580)	(2,019,122)
Unfavorable contract liability, net	551,588	599,046
Product Certifications
Finite-Lived Intangible Assets [Line Items]
Intangible assets	777,465	777,465
Less - accumulated amortization	(675,397)	(658,676)
Intangible assets, net	102,068	118,789
Patents
Finite-Lived Intangible Assets [Line Items]
Intangible assets	888,910	888,910
Less - accumulated amortization	(518,731)	(496,807)
Intangible assets, net	370,179	392,103
Developed Technology
Finite-Lived Intangible Assets [Line Items]
Intangible assets	240,000	240,000
Less - accumulated amortization	(176,000)	(172,000)
Intangible assets, net	64,000	68,000
Favorable Contract Asset
Finite-Lived Intangible Assets [Line Items]
Intangible assets	384,465	384,465
Less - accumulated amortization	(377,063)	(376,138)
Intangible assets, net	7,402	8,327
Customer Contracts
Finite-Lived Intangible Assets [Line Items]
Intangible assets	1,962,298	1,772,659
Less - accumulated amortization	(150,552)	(110,791)
Intangible assets, net	1,811,746	1,661,868
Trademarks
Finite-Lived Intangible Assets [Line Items]
Intangible assets	26,896	26,896
Less - accumulated amortization	0	0
Intangible assets, net	26,896	26,896
In Process Research and Development [Member]
Finite-Lived Intangible Assets [Line Items]
Intangible assets	263,936	263,936
Less - accumulated amortization	(113,115)	(103,689)
Intangible assets, net	$ 150,821	$ 160,247

Intangible Assets and Liabili_4

Intangible Assets and Liabilities Other Than Goodwill (Details) - USD ($)	3 Months Ended
	Mar. 31, 2024	Mar. 31, 2023
Goodwill and Intangible Assets Disclosure [Abstract]
Amortization of intangible assets	$ (92,756)	$ (49,361)
Net credit to cost of sales for amortization of contract related intangible assets and liabilities	$ 47,459	$ 60,933

Intangible Assets and Liabili_5

Intangible Assets and Liabilities Other Than Goodwill - Future Amortization of Customer Contracts (Details) - USD ($)	Mar. 31, 2024	Dec. 31, 2023
Non-contract Related Intangibles [Abstract]
Finite-Lived Intangible Assets, Net, Total	$ 2,533,112	$ 2,436,230
Contract Asset and Liability
Contract-related Intangibles [Abstract]
Finite-Lived Intangible Liability, Expected Amortization, Year One	185,878
Finite-Lived Intangible Liability, Expected Amortization, Year Two	235,818
Finite-Lived Intangible Liability, Expected Amortization, Year Three	264,393
Finite-Lived Intangible Liability, Expected Amortization, Year Four	248,040
Finite-Lived Intangible Liabilities, Net	1,954,628
Finite-Lived Intangible Asset, Expected Amortization, Year Five	133,743
Finite-Lived Intangible Liability, Expected Amortization, after Year Five	(886,756)
Non-contract Related Intangible Assets \| Contract Asset and Liability
Non-contract Related Intangibles [Abstract]
Finite-Lived Intangible Asset, Expected Amortization, Year One	183,995
Finite-Lived Intangible Asset, Expected Amortization, Year Two	168,489
Finite-Lived Intangible Asset, Expected Amortization, Year Three	162,381
Finite-Lived Intangible Asset, Expected Amortization, Year Four	138,362
Finite-Lived Intangible Assets, Net, Total	694,468
Contract-related Intangibles [Abstract]
Finite-Lived Intangible Asset, Expected Amortization, Year Five	20,621
Finite-Lived Intangible Asset, Expected Amortization, after Year Five	20,620
Contract-Based Intangible Assets [Member] \| Contract Asset and Liability
Contract-related Intangibles [Abstract]
Finite-Lived Intangible Liability, Expected Amortization, Year One	1,883
Finite-Lived Intangible Liability, Expected Amortization, Year Two	67,329
Finite-Lived Intangible Liability, Expected Amortization, Year Three	102,012
Finite-Lived Intangible Liability, Expected Amortization, Year Four	109,678
Finite-Lived Intangible Liabilities, Net	1,260,160
Finite-Lived Intangible Liability, Expected Amortization, Year Five	113,122
Finite-Lived Intangible Liability, Expected Amortization, after Year Five	$ 866,136

Sale of Energy Producing Asse_2

Sale of Energy Producing Assets and Goodwill Impairment (Details) $ in Millions	3 Months Ended
	Dec. 31, 2021 USD ($) site sale
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Number of sales of energy producing assets \| sale	2
Number of energy producing sites sold \| site	8
Consideration received \| $	$ 7

Leases (Details)

Leases (Details)		3 Months Ended		12 Months Ended
Leases (Details)	Jan. 01, 2024 USD ($)	Mar. 31, 2024 USD ($) ft²	Mar. 31, 2023 USD ($) ft²	Dec. 31, 2023 USD ($)
Lessee, Lease, Description [Line Items]
Lease cost	$ 38,200
Operating Lease, Payments		$ 269,836	$ 184,072
Right-of-Use Asset Obtained in Exchange for Operating Lease Liability		$ 1,429,977	$ 0
Weighted-average discount rate - operating leases (percent)		7.50%	6%
Square feet of lease \| ft²			26,412
Monthly base rent	$ 26,962	$ 44,254
Initial lease term			5 years
Operating Lease, Right-of-Use Asset		1,986,087		$ 743,096
Operating Lease, Liability, Current		438,334		248,933
Operating Lease, Liability, Noncurrent		1,573,793		523,660
Operating Lease, Liability		$ 2,012,127		$ 772,593
Operating Lease, Right-of-Use Asset, Statement of Financial Position [Extensible Enumeration]		Right of use assets		Right of use assets
Operating Lease, Liability, Current, Statement of Financial Position [Extensible Enumeration]		Lease obligations, current		Lease obligations, current
Operating Lease, Liability, Noncurrent, Statement of Financial Position [Extensible Enumeration]		Lease obligations, net of current portion		Lease obligations, net of current portion
Vehicles Acquired Under Finance Leases		$ 190,177		$ 200,187
Finance Lease, Weighted Average Remaining Lease Term				5 years
Finance Lease, Weighted Average Discount Rate, Percent				10.40%
Minimum
Lessee, Lease, Description [Line Items]
Payments for Leasing Costs, Commissions, and Tenant Improvements		500,000
Maximum
Lessee, Lease, Description [Line Items]
Payments for Leasing Costs, Commissions, and Tenant Improvements		$ 750,000
Manufacturing, Storage and Office Space
Lessee, Lease, Description [Line Items]
Square feet of lease \| ft²		43,000

Leases - Assets and Liabilities

Leases - Assets and Liabilities, Lessee (Details) - USD ($)	3 Months Ended	12 Months Ended
Leases - Assets and Liabilities, Lessee (Details) - USD ($)	Mar. 31, 2024	Dec. 31, 2023
Leases [Abstract]
Operating Lease, Liability, Current, Statement of Financial Position [Extensible Enumeration]	Lease obligations, current	Lease obligations, current
Operating Lease, Liability, Noncurrent, Statement of Financial Position [Extensible Enumeration]	Lease obligations, net of current portion	Lease obligations, net of current portion
Operating Lease, Right-of-Use Asset, Statement of Financial Position [Extensible Enumeration]	Right of use assets	Right of use assets
Vehicles Acquired Under Finance Leases	$ 190,177	$ 200,187
Finance Lease, Liability, Current	31,428	40,540
Finance Lease, Liability, Noncurrent	151,483	159,647
Finance Lease, Liability	$ 182,911	$ 200,187

Leases - Future Minimum Lease C

Leases - Future Minimum Lease Commitments (Details) - USD ($)	Mar. 31, 2024	Dec. 31, 2023
Leases [Abstract]
Lessee, Operating Lease, Liability, to be Paid, Year One	$ 563,175
Lessee, Operating Lease, Liability, to be Paid, Year Two	498,686
Lessee, Operating Lease, Liability, to be Paid, Year Three	472,862
Lessee, Operating Lease, Liability, to be Paid, Year Four	421,503
Lessee, Operating Lease, Liability, to be Paid, Total	2,362,416
Lessee, Operating Lease, Liability, Undiscounted Excess Amount	350,289
Operating Lease, Liability	2,012,127	$ 772,593
Finance Lease, Liability, to be Paid, Year One	48,931
Operating and Finance Lease, Liability, to be Paid, Year One	612,106
Finance Lease, Liability, to be Paid, Year Two	48,931
Operating and Finance Lease, Liability, to be Paid, Year Two	547,617
Finance Lease, Liability, to be Paid, Year Three	48,931
Operating and Finance Lease, Liability, to be Paid, Year Three	521,793
Finance Lease, Liability, to be Paid, Year Four	48,931
Operating and Finance Lease, Liability, to be Paid, Year Four	470,434
2024	302,960
Finance Lease, Liability, to be Paid, Year Five	36,699
Operating and Finance Lease, Liability, to be Paid, Year Five	339,659
Lessee, Operating Lease, Liability, to be Paid, after Year Five	103,230
Finance Lease, Liability, to be Paid, after Year Five	0
Operating and Finance Lease, Liability, to be Paid, After Year Five	103,230
Finance Lease, Liability, to be Paid	232,423
Operating and Finance Lease, Liability, to be Paid	2,594,839
Finance Lease, Liability, Undiscounted Excess Amount	49,512
Operating and Finance Lease, Liability, Undiscounted Excess Amount	399,801
Finance Lease, Liability	182,911	$ 200,187
Operating and Finance Lease, Liability	$ 2,195,038

Stock-Based Compensation - Stoc

Stock-Based Compensation - Stock-Based Compensation (Details) - USD ($)	3 Months Ended
	Mar. 31, 2024	Mar. 31, 2023	Jun. 09, 2022
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based Payment Arrangement, Noncash Expense	$ 44,535	$ 77,348
Amended Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares of common stock reserved for future issuance			3,800,000
Tecogen
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Compensation cost not yet recognized, amount	$ 362,187
Compensation cost not yet recognized, period for recognition	2 years 5 months 8 days
Share-Based Payment Arrangement, Expense	$ 44,535	$ 77,348

Stock-Based Compensation - St_2

Stock-Based Compensation - Stock Option Activity (Details) - USD ($)	3 Months Ended	12 Months Ended
	Mar. 31, 2024	Dec. 31, 2023
Exercise Price Per Share [Abstract]
Exercise Price Per Share, Outstanding, Minimum (per share)	$ 0.71	$ 0.71
Exercise Price Per Share, Outstanding, Maximum (dollars per share)	6.74
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Additional Disclosures [Abstract]
Share Based Compensation Shares Authorized Under Stock Option Plans, Granted, Exercise Price Range, Upper Range Limit		$ 10.33
Share Based Compensation Shares Authorized Under Stock Option Plans, Cancelled and Forfeited, Exercise Price Range, Lower Range Limit	0.74
Share Based Compensation Shares Authorized Under Stock Option Plans, Cancelled and Forfeited, Exercise Price Range, Upper Range Limit	$ 10.33
Tecogen
Stock Options Outstanding [Roll Forward]
Beginning (shares)	3,638,122
Canceled and forfeited (shares)	(801,350)
Ending (shares)	2,836,772	3,638,122
Exercisable (shares)	1,643,022
Vested and expected to vest (shares)	2,657,710
Weighted Average Exercise Price [Roll Forward]
Beginning (usd per share)	$ 1.49
Canceled and forfeited (usd per share)	2.73
Ending (usd per share)	1.14	$ 1.49
Exercisable (usd per share)	1.28
Vested and expected to vest (usd per share)	$ 1.16
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Additional Disclosures [Abstract]
Outstanding, Aggregate Intrinsic Value		$ 127,811
Vested and expected to vest, Aggregate Intrinsic Value	$ 0
Tecogen \| Stock Options
Weighted Average Exercise Price [Roll Forward]
Weighted Average Remaining Life	7 years 21 days	6 years 8 months 12 days

Fair Value Measurements - Fair

Fair Value Measurements - Fair Value on a Recurring Basis (Details) - USD ($)	3 Months Ended
	Mar. 31, 2024	Mar. 31, 2023	Dec. 31, 2023	Dec. 31, 2022
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Unrealized gain (loss) on investment securities	$ 18,749	$ 0
Fair Value, Measurements, Recurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Unrealized gain (loss) on investment securities	18,749	0
Fair Value, Measurements, Recurring \| Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets, Fair Value Disclosure	0	0
Fair Value, Measurements, Recurring \| Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets, Fair Value Disclosure	112,493	93,744
Fair Value, Measurements, Recurring \| Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets, Fair Value Disclosure	0	0
Estimate of Fair Value Measurement \| Fair Value, Measurements, Recurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets, Fair Value Disclosure	112,493	93,744	$ 93,744	$ 93,744
Eurosite Power, Inc. \| Fair Value, Measurements, Recurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Unrealized gain (loss) on investment securities	18,749	0
Eurosite Power, Inc. \| Fair Value, Measurements, Recurring \| Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale equity securities	0	0
Eurosite Power, Inc. \| Fair Value, Measurements, Recurring \| Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale equity securities	112,493	93,744
Eurosite Power, Inc. \| Fair Value, Measurements, Recurring \| Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale equity securities	0	0
Eurosite Power, Inc. \| Estimate of Fair Value Measurement \| Fair Value, Measurements, Recurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale equity securities	$ 112,493	$ 93,744

Fair Value Measurements - Chang

Fair Value Measurements - Change in Level 2 Assets (Details) - USD ($)	3 Months Ended
	Mar. 31, 2024	Mar. 31, 2023	Dec. 31, 2023	Dec. 31, 2022
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Gain (Loss) Included in Earnings	$ 18,749	$ 0
Fair Value, Asset, Recurring Basis, Unobservable Input Reconciliation, Gain (Loss), Statement of Income or Comprehensive Income [Extensible Enumeration]	Unrealized gain on investment securities
Fair Value, Measurements, Recurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Asset Acquisition, Contingent Consideration, Liability, Current	$ 237,928
Asset Acquisition, Contingent Consideration, Liability, Noncurrent	1,016,558
Liabilities, Fair Value Disclosure	1,254,486
Fair Value, Measurements, Recurring \| Estimate of Fair Value Measurement
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets, Fair Value Disclosure	112,493	93,744	$ 93,744	$ 93,744
Fair Value, Measurements, Recurring \| Eurosite Power, Inc. \| Estimate of Fair Value Measurement
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value, ending	112,493	93,744
Fair Value, Measurements, Recurring \| Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets, Fair Value Disclosure	112,493	93,744
Asset Acquisition, Contingent Consideration, Liability, Current	0
Asset Acquisition, Contingent Consideration, Liability, Noncurrent	0
Liabilities, Fair Value Disclosure	0
Fair Value, Measurements, Recurring \| Level 2 \| Eurosite Power, Inc.
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value, ending	112,493	93,744
Fair Value, Measurements, Recurring \| Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets, Fair Value Disclosure	0	0
Asset Acquisition, Contingent Consideration, Liability, Current	0
Asset Acquisition, Contingent Consideration, Liability, Noncurrent	0
Liabilities, Fair Value Disclosure	0
Fair Value, Measurements, Recurring \| Level 1 \| Eurosite Power, Inc.
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value, ending	0	0
Fair Value, Measurements, Recurring \| Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets, Fair Value Disclosure	0	0
Asset Acquisition, Contingent Consideration, Liability, Current	237,928
Asset Acquisition, Contingent Consideration, Liability, Noncurrent	1,016,558
Liabilities, Fair Value Disclosure	1,254,486
Fair Value, Measurements, Recurring \| Level 3 \| Eurosite Power, Inc.
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value, ending	$ 0	$ 0

Related party transactions (Det

Related party transactions (Details) - USD ($)	Mar. 31, 2024	Dec. 31, 2023	Oct. 09, 2023
Schedule of Equity Method Investments [Line Items]
Related party notes	$ 511,905	$ 505,505
John N. Hatsopoulos and Earl R. Lewis, III \| Related Party
Schedule of Equity Method Investments [Line Items]
Related party notes			$ 1,000,000
Earl R. Lewis, III \| Related Party
Schedule of Equity Method Investments [Line Items]
Related party notes			$ 500,000

Segments (Details)

Segments (Details) - USD ($)	3 Months Ended
Segments (Details) - USD ($)	Mar. 31, 2024	Mar. 31, 2023	Dec. 31, 2023
Segment Reporting Information [Line Items]
Revenue	$ 6,186,097	$ 5,379,818
Gross profit	2,575,657	2,091,909
Assets	28,458,543	28,243,431	$ 27,792,629
Energy Production [Member]
Segment Reporting Information [Line Items]
Revenue	680,389	533,509
Gross profit	211,749	195,770
Assets	3,295,316	3,433,439
Corporate, other and elimination
Segment Reporting Information [Line Items]
Revenue	(117,348)	(88,214)
Gross profit	0	0
Assets	3,161,918	3,036,675
Products Segment
Segment Reporting Information [Line Items]
Revenue	1,491,398	1,710,136
Gross profit	441,855	497,567
Assets	9,793,634	12,023,164
Services and Other Segment
Segment Reporting Information [Line Items]
Revenue	4,131,658	3,224,387
Gross profit	1,922,053	1,398,572
Assets	12,207,675	9,750,153
Operating Segments
Segment Reporting Information [Line Items]
Revenue		5,379,818
Operating Segments \| Energy Production [Member]
Segment Reporting Information [Line Items]
Revenue	680,389	533,509
Operating Segments \| Corporate, other and elimination
Segment Reporting Information [Line Items]
Revenue	0	0
Operating Segments \| Products Segment
Segment Reporting Information [Line Items]
Revenue	1,491,398	1,710,136
Operating Segments \| Services and Other Segment
Segment Reporting Information [Line Items]
Revenue	4,014,310	3,136,173
Intersegment Eliminations
Segment Reporting Information [Line Items]
Revenue		0
Intersegment Eliminations \| Energy Production [Member]
Segment Reporting Information [Line Items]
Revenue	0	0
Intersegment Eliminations \| Corporate, other and elimination
Segment Reporting Information [Line Items]
Revenue	(117,348)	(88,214)
Intersegment Eliminations \| Products Segment
Segment Reporting Information [Line Items]
Revenue	0	0
Intersegment Eliminations \| Services and Other Segment
Segment Reporting Information [Line Items]
Revenue	$ 117,348	$ 88,214

Aegis Contract and Related As_3

Aegis Contract and Related Asset Acquisitions (Details) - Aegis Energy Services, LLC				3 Months Ended	12 Months Ended
	Mar. 31, 2024 USD ($)	Feb. 01, 2024 USD ($)	Mar. 15, 2023 USD ($) vehicle employee	Mar. 31, 2024 USD ($)	Dec. 31, 2023 USD ($)
Business Acquisition, Equity Interests Issued or Issuable [Line Items]
Number of Assets Acquired \| vehicle			8
Payments for Asset Acquisitions	$ 170,000		$ 170,000
Consideration transferred, credits	300,000		$ 300,000
Number of Employees Acquired \| employee			8
Asset Acquisition, Consideration Transferred, Accounts Payable	91,048		$ 91,048
Asset Acquisition, Consideration Transferred, Contingent Consideration	1,349,065	$ 92,409	1,256,656
Consideration transferred	1,910,113	92,409	1,817,704
Asset Acquisition, Property, Plant and Equipment	170,000		170,000
Asset Acquisition, Inventory	391,048		391,048
Finite-Lived Intangible Assets Acquired	1,962,298	189,639	1,772,659
Asset Acquisition, Assets Acquired	2,523,346	189,639	2,333,707
Asset Acquisition, Reserves	(853,271)		(853,271)
Asset Acquisition, Assets Acquired and Liabilities Assumed, Net	1,670,075	189,639	1,480,436
Goodwill, Acquired During Period	$ (240,038)	$ (97,230)	$ (337,268)
Asset Acquisition, Consideration Transferred, Contingent Consideration, Current				$ 237,928	$ 200,639
Asset Acquisition, Reserves, Current				691,483	644,724
Asset Acquisition, Liabilities Assumed, Current				929,411	845,363
Asset Acquisition, Consideration Transferred, Contingent Consideration, Noncurrent				1,016,558	994,743
Asset Acquisition, Reserves, Noncurrent				140,277	187,036
Asset Acquisition, Liabilities Assumed, Noncurrent				$ 1,156,835	$ 1,181,779
Measurement Input, Discount Rate
Business Acquisition, Equity Interests Issued or Issuable [Line Items]
Intangible Assets, Measurement Input			15%