NASDAQ: TGEN FIRST QUARTER 2020 Earnings Call May 14, 2020

Participants Benjamin Locke Chief Executive Officer President & Chief Operating Robert Panora Officer Bonnie Brown Chief Accounting Officer Jack Whiting General Counsel & Secretary 2

Safe Harbor Statement This presentation and accompanying documents contain “forward-looking statements” which may describe strategies, goals, outlooks or other non- historical matters, or projected revenues, income, returns or other financial measures, that may include words such as "believe," "expect," "anticipate," "intend," "plan," "estimate," "project," "target," "potential," "will," "should," "could," "likely," or "may" and similar expressions intended to identify forward-looking statements. These statements are only predictions and involve known and unknown risks, uncertainties, and other factors that may cause our actual results to differ materially from those expressed or implied by such forward-looking statements. Given these uncertainties, you should not place undue reliance on these forward-looking statements. Forward-looking statements speak only as of the date on which they are made, and we undertake no obligation to update or revise any forward-looking statements. In addition to those factors described in our Annual Report on Form 10-K and our Quarterly Reports on Form 10-Q under “Risk Factors”, among the factors that could cause actual results to differ materially from past and projected future results are the following: fluctuations in demand for our products and services, competing technological developments, issues relating to research and development, the availability of incentives, rebates, and tax benefits relating to our products and services, changes in the regulatory environment relating to our products and services, integration of acquired business operations, and the ability to obtain financing on favorable terms to fund existing operations and anticipated growth. In addition to GAAP financial measures, this presentation includes certain non-GAAP financial measures, including adjusted EBITDA which excludes certain expenses as described in the presentation. We use Adjusted EBITDA as an internal measure of business operating performance and believe that the presentation of non-GAAP financial measures provides a meaningful perspective of the underlying operating performance of our current business and enables investors to better understand and evaluate our historical and prospective operating performance by eliminating items that vary from period to period without correlation to our core operating performance and highlights trends in our business that may not otherwise be apparent when relying solely on GAAP financial measures. 3

Earnings Call Agenda Benjamin Locke Tecogen Overview Q1 2020 Results Overview Bonnie Brown Q1 2020 Financial Review Benjamin Locke Market Update Robert Panora Emissions & Technology Update Benjamin Locke 2020 Outlook Q&A 4

Advanced Modular Cogeneration Systems Heat, Power, and/or Cooling that is: Efficient Industry leading efficiency and reduced exposure to expensive electricity Clean Proprietary near-zero emissions technology, GHG reductions Reliable Real-time monitoring, blackout protection, and improved grid resiliency All of Tecogen’s equipment is equipped with Tecogen’s patented Ultera Emission Control Technology 5

1st Qtr 2020 Results YoY $ in thousands 1Q'20 1Q'19 % Chg Change Revenues = $7.9 million Revenue • Compared to $8.2 million in 1Q’19, 3% decrease Products $ 2,750 $ 3,025 $ (274) • Product revenue down 9%, Service up 14% Service 4,461 3,911 550 Energy Production 751 1,241 (490) • Includes return of ($655k) chillers shipped in Q4 Total Revenue 7,963 8,177 (214) -2.6% • Energy production down 40% from sale of assets Gross Profit Products $ 1,083 $ 1,081 $ 2 Gross Margin = 35.1% Service 1,443 1,437 6 Energy Production 266 441 (174) • Compared to 36.2% in 1Q’19 Total Gross Profit 2,792 2,959 (167) -5.6% • Product margins improved to 39.4% compared to 35.7% in Gross Margin: % Products 39% 36% 4% 1Q’19 Service 32% 37% -4% • Service margins declined to 32.3% compared to 36.7% in Energy Production 35% 36% -1% Total Gross Margin 35% 36% -1% 1Q’19 Operating Expenses General & administrative $ 2,689 $ 2,655 $ 34 1.3% Op Ex Selling 856 693 163 23.4% • Includes a non-cash abandonment of intangible assets of ~ Research and development 364 345 19 5.6% Sub-total 3,910 3,694 216 5.8% $180K Gain on sale of assets - (1,081) Goodwill impairment - 3,693 Net loss of $1.2 million Net income (loss) $ (1,202) $ (3,280) $ 2,078 • Compared to $3.3 million loss for 1Q ’19 (1Q ‘19 included $ (817) $ 678 $ (1,495) Adjusted EBITDA* $3.7 million goodwill impairment) *Adjusted EBITDA is defined as net income (loss) attributable to Tecogen Adjusted EBITDA = negative $817K Inc, adjusted for interest, depreciation and amortization, stock based compensation expense, unrealized loss on investment securities, non- • Compared to positive $678K 1Q ’19 (1Q ‘19 included cash adjustment and goodwill impairment. $1,081K gain on sale of assets) 6

Q1 2020 Financial Results: Revenues, Margins, and Profitability Quarter Ended March 31, YoY % of Total $ in thousands 2020 2019 Increase in combined product and service revenue Growth Rev of 4% Revenue Cogeneration $ 3,236 $ 1,819 78% 41% Chiller (486) 1,205 -140% -6% Decrease in overall revenue, a result of the $655K Total Product Revenue 2,750 3,025 -9% 35% sale return and sale of energy producing assets Service Contracts and Parts 2,466 2,355 5% 31% Installation Services 1,995 1,556 28% 25% Total Service Revenue 4,461 3,911 14% 56% Four diverse revenue streams Combined Product & Service Revenue 7,211 6,936 4% 91% Energy Production 751 1,241 -39% 9% • 78% growth in cogeneration sales; slowdown in Total Revenue 7,963 8,177 -3% 100% chiller sales Cost of Sales Products $ 1,667 $ 1,943 -14% • Long term service contracts provide steady cash Services 3,019 2,475 22% Energy Production 484 800 -39% flow, growing 5% Total Cost of Sales $ 5,171 $ 5,218 -1% • Turnkey installation revenue, increased by 28%, Gross Profit $ 2,792 $ 2,959 -6% 35% facilitating both Product sales and Service revenue Net loss attributable to Tecogen Inc. $ (1,202) $ (3,280) Gross Margin • Energy Production decreased year over year due to Products 39% 36% the sale of energy producing assets Services 32% 37% Aggregate Products and Services 35% 36% Energy Production 35% 36% Maintained 35% overall gross margin Overall 35% 36% Product & Services revenue Strong cogeneration sales; Service revenue increase of increase of 4% YoY slowdown in chiller sales 14% YoY 7

Adjusted EBITDA Reconciliation Quarter Ended, March 31, Reconciliation of Q1 2020 and 2019 Net loss to Non-GAAP financial disclosure 2020 2019 Net loss attributable to Tecogen Inc. $ (1,202,387) $ (3,280,077) Adjusted EBITDA Interest expense, net 48,258 27,494 Depreciation & amortization, net 90,152 168,244 EBITDA: Interest, taxes, depreciation & Income tax expense 5,222 (8,169) EBITDA (1,058,755) (3,092,508) amortization Stock based compensation 42,236 38,035 Non-cash adjustments Unrealized loss on investment securities 19,681 39,361 Non-recurring, non-cash adjustment 179,944 - • Stock based compensation Goodwill impairment - 3,693,198 • Unrealized loss on investment securities Adjusted EBITDA* $ (816,894) $ 678,086 • Non-cash abandonment of intangible assets • Goodwill impairment *Adjusted EBITDA is defined as net income (loss) attributable to Tecogen Inc, adjusted for interest, depreciation and amortization, stock based compensation expense, unrealized loss on investment securities, non-cash adjustment and goodwill impairment. 8

Earnings Takeaways Core Business is Stable • Shipped $3.4 million of Products in Q1 (revenue impacted by product return) Core Business is Stable • Energy Production assets produce consistent revenues (revenue drop from previous asset sales expected) • Service revenue continues to grow as increase Service contracts 2020 Business Planning – COVID update • COVID pandemic interrupted 2020 business plan, including delays in marketing activities and some sales Overcoming COVID Challenges • We continue to anticipate profitability in 2020 • Product backlog is strong; focus on improving Service margins • Toronto Service Center will add additional Service revenue • Corporate cost reductions, eliminated LOC Growth Opportunities Strong, although Delayed • Ultera Forklift Program • Expand Cooling Product Segment / Partnership Opportunities Prospects For Growth • Expand to New Geographies 9

Product and Installation Backlog Customer Segment Backlog - Product and Installation Services 14.1% $ Millions Indoor Growing $35.0 18.5% $30.0 Office Building 39.7% Multi-Unit 1.3% Residential $25.0 Recreation $20.0 5.0% $15.0 Health Care $10.0 $5.0 $- 12.6% Education Jul-15 Jul-16 Jul-17 Jul-18 Jul-19 Jan-15 Jan-16 Jan-17 Jan-18 Jan-19 Jan-20 Sep-15 Sep-16 Sep-17 Sep-18 Sep-19 Nov-15 Nov-16 Nov-17 Nov-18 Nov-19 Mar-15 Mar-16 Mar-17 Mar-18 Mar-19 Mar-20 May-15 May-16 May-17 May-18 May-19 May-20 7.2% Industrial & Manufacturing Current Backlog of $12.7 million Product backlog: $10.2 million, Installation backlog $2.5 million 10

Emissions Technology Update MCFA (Mitsubishi Caterpillar Forklift America) Program Precertification Testing of MCFA engine was planned for mid-May by SwRI (Southwest Research Institute) Objective was to demonstrate revised Ultera engine tuning in certification test cycle Project remains on hold until travel restrictions lifted from Japan to United States Mitsubishi engineer oversight required PERC (Propane Education and Research Council) funding commitment remains Municipal water pumping order (California) Project proceeding Installation contractors bidding project with our latest pricing Order anticipated in August Ultera IP Core Ultera patent confirmed in 19 EU countries including United Kingdom, Germany and France Some Overseas Ultera-related patent applications abandoned Further pursuit costly, not of significant value Continue effort with most in the US

2020 Business Outlook Growth in Product Revenue • Steady demand for Tecogen products despite COVID pandemic • Expanding sales geography in North America (e.g. Toronto) • Expanding sales of chiller products through partnerships (e.g. Vilter) • Focus on improving overall margins Growth in Service Revenues • Service center expansion leads to revenue growth • Improved remote monitoring helps increase unit runtime, revenues Scaling back large turnkey installation projects • Gradually winding down large turnkey jobs • “Turnkey light” option includes engineered accessories that makes installations simpler for contractors Resume Ultera development • Resume work with Mitsubishi to certify a near-zero emission engine for forktrucks using Ultera • Develop additional opportunities for Ultera retrofits 12

Q&A Company Information Tecogen, Inc 45 First Ave Waltham, MA 02451 www.Tecogen.com Contact information Benjamin Locke, CEO 781.466.6402 Benjamin.Locke@Tecogen.com 13