American DG Energy Inc. 6% Senior Unsecured Convertible DebentureDue 2018

Exhibit 4.1

THE 6% SENIOR UNSECURED CONVERTIBLE DEBENTURE DUE 2018 REPRESENTED BY THIS CERTIFICATE AND THE SECURITIES INTO WHICH IT MAY BE CONVERTED HAVE NOT BEEN REGISTERED UNDER THE U.S. SECURITIES ACT OF 1933, AS AMENDED (“SECURITIES ACT”) OR ANY STATE SECURITIES LAWS, AND NEITHER SUCH SECURITIES NOR ANY INTEREST THEREIN MAY BE OFFERED FOR SALE, SOLD, PLEDGED, ASSIGNED OR OTHERWISE TRANSFERRED UNLESS (1) A REGISTRATION STATEMENT WITH RESPECT THERETO IS EFFECTIVE UNDER THE SECURITIES ACT AND ANY APPLICABLE SECURITIES LAWS OR (2) THE COMPANY RECEIVES AN OPINION OF COUNSEL TO THE HOLDERS OF SUCH SECURITIES, WHICH COUNSEL AND OPINION ARE REASONABLY SATISFACTORY TO THE COMPANY, THAT SUCH SECURITIES MAY BE OFFERED, SOLD, PLEDGED, ASSIGNED OR TRANSFERRED IN THE MANNER CONTEMPLATED WITHOUT AN EFFECTIVE REGISTRATION STATEMENT UNDER THE SECURITIES ACT OR APPLICABLE STATE SECURITIES LAWS.

American DG Energy Inc.

6% Senior Unsecured Convertible Debenture Due 2018

This Debenture (the “Debenture”) is one of a duly authorized issue of Debentures of American DG Energy Inc., a corporation duly incorporated under the laws of the State of Delaware, and having its principal address at 45 First Avenue, Waltham, Massachusetts 02451 (the “Company”), designated as its 6% Senior Unsecured Convertible Debentures due 2018 (the “Debentures”) in an aggregate principal amount of up to $[__]. This Debenture replaces the 6% Senior Unsecured Convertible Debenture due 2018, dated as of [__], 2011, as amended, originally issued in the aggregate principal amount of $[__] (the “Original Debenture”).

FOR VALUE RECEIVED, the Company promises to pay to the order of the [__], or its registered assigns (the “Holder”), the principal sum of [__] United States Dollars (U.S. $[__]) (the “Principal Amount”) on May 25, 2018, subject to earlier payment as otherwise provided herein (the “Maturity Date”). All interest previously accrued under this Debenture, together with all future interest payable through the scheduled Maturity Date, has been prepaid in shares of common stock of EuroSite Power Inc. (“EuroSite”) previously owned by the Company pursuant to the Convertible Note Amendment Agreement, dated October 3, 2014, by and among the Company, EuroSite and the Holder.

On the Maturity date, the Company will pay, in cash, the Principal Amount outstanding under this Debenture (the “Outstanding Principal Amount”).

This Debenture is subject to the following additional provisions:

1. Exchange. This Debenture is exchangeable for an equal aggregate principal amount of Debentures of different denominations as requested by the Holder surrendering the same. No fees will be charged for such exchange. Notwithstanding the foregoing, the Company shall have no obligation to issue new Debentures unless and until requested by the Holders thereof.

2. Transfers. This Debenture has been issued subject to investment representations of the original purchaser hereof and may be transferred or exchanged only (a) in compliance with the Exchange Act, and applicable state securities laws, and (b) in accordance with applicable provisions hereof. Prior to due presentment for transfer of this Debenture, the Company may treat the person in whose name this Debenture is duly registered on the Company’s debenture register as the owner hereof for the purpose of receiving payment as herein provided and all other purposes, whether or not this Debenture is then overdue, and the Company shall not be affected by notice to the contrary.

3. Definitions. For purposes hereof the following definitions shall apply:

“2011 Private Placement” The Company’s private placement of up to $[__] of Debentures.

“Acquisition” shall have the meaning set forth in Paragraph 16(a).

“Callable Date” shall have the meaning set forth in Paragraph 6(a)(ii).

“Common Stock” shall mean the Common Stock, $.001 par value per share, of the Company.

“Company” shall have the meaning set forth in the first introductory paragraph.

“Conversion Notice” shall have the meaning set forth in Paragraph 5(c).

“Conversion Price” shall mean $2.11, subject to adjustment from time to time as set forth in Paragraph 7 hereof.

“Debenture” shall have the meaning set forth in the first introductory paragraph.

“Debentures” shall have the meaning set forth in the first introductory paragraph.

“EuroSite” shall have the meaning set forth in the second introductory paragraph.

“Events of Default” shall have the meaning set forth in Paragraph 15.

“Exchange Act” shall mean the Securities Exchange Act of 1934, as amended.

“Holder” shall have the meaning set forth in the second introductory paragraph.

“Holder Conversion Date” shall have the meaning set forth in Paragraph 5(c).

“Maturity Date” shall have the meaning set forth in the second introductory paragraph.

“Original Debenture” shall have the meaning set forth in the first introductory paragraph.

“Outstanding Principal Amount” shall have the meaning set forth in the third introductory paragraph.

“Principal Amount” shall have the meaning set forth in the second introductory paragraph.

“Redemption Date” shall have the meaning set forth in Paragraph 6(a)(iii).

“Redemption Debentures” shall have the meaning set forth in Paragraph 6(c).

“Redemption Price” shall have the meaning set forth in Paragraph 6(b).

“Redemption Notice” shall have the meaning set forth in Paragraph 6(a).

“Securities Act” means the Securities Act of 1933, as amended.

“Subscription Agreement” shall mean the agreement entered into by and between the Company and the Holder for the purchase of the Original Debenture.

“Underlying Shares” shall mean the shares of Common Stock into which this Debenture is convertible.

In addition, other terms defined in the Subscription Agreement and not otherwise defined herein shall have the same meanings herein as are set forth for such terms in the Subscription Agreement.

4. Maturity. On the Maturity Date, the Outstanding Principal Amount of this Debenture shall be payable in cash.

5. Conversion. This Debenture is subject to conversion as follows:

(ii) Issuance of Certificates. In the case of any Conversion Notice given by the Holder to the Company, the Company shall issue and deliver as promptly as practicable and in no event later than five (5) business days after delivery to the Company of the Debenture, or after receipt of such agreement and indemnification, to such Holder or to its designee, a certificate or certificates for the number of shares of Common Stock to which the Holder shall be entitled, together with a Debenture for the Outstanding Principal Amount not submitted for conversion, if any. The person or persons entitled to receive the shares of Common Stock issuable upon conversion shall be treated for all purposes as the record holder or holders of such shares of Common Stock on the Holder Conversion Date.

6. Redemption.

Notwithstanding anything to the contrary contained herein, the Holder’s rights of conversion pursuant to Paragraph 5 hereof shall expire at the close of business on the 15th day prior to the Redemption Date.

7. Adjustments to the Conversion Price.

8. Limitations on Conversion. The Holder shall not have the right to convert any portion of this Debenture to the extent that such conversion right would cause the Company to be in violation of any regulation of a national securities exchange limiting the number or amount of securities that an issuer subject to such regulation is able to issue without prior registration under the Securities Act or stockholder approval, including without limitation, Rule 312.03 set forth in the NYSE Listed Company Manual.

9. Fractional Shares. No fractional shares of Common Stock or scrip representing fractional shares of Common Stock shall be issuable hereunder. The number of shares of Common Stock that are issuable upon any conversion shall be rounded up or down to the nearest whole share.

10. Reservation of Stock Issuable Upon Conversion. The Company has reserved and the Company shall continue to reserve and keep available at all times, free of preemptive rights, shares of Common Stock (or other securities issuable upon conversion hereof) for the purpose of enabling the Company to satisfy any obligation to issue shares of its Common Stock or such other securities upon conversion of the Debentures.

11. Other Covenants of the Company.

12. Obligations Absolute. No provision of this Debenture, other than conversion as provided herein, shall alter or impair the obligation of the Company, which is absolute and unconditional, to pay the principal of, and interest on, this Debenture at the time, place and rate, and in the manner, herein prescribed.

13. Waivers of Demand, Etc. The Company hereby expressly waives demand and presentment for payment, notice of nonpayment, protest, notice of protest, notice of dishonor, notice of intent to accelerate, prior notice of bringing of suit and diligence in taking any action to collect amounts called for hereunder and will be directly and primarily liable for the payments of all sums owing and to be owing hereon, regardless of and without any notice (except as required by law), diligence, act or omission as or with respect to the collection of any amount called for hereunder.

14. Replacement Debentures. In the event that the Holder notifies the Company that its Debenture has been lost, stolen or destroyed, a replacement Debenture identical in all respects to the original Debenture (except for registration number and Outstanding Principal Amount, if different than that shown on the original Debenture) shall be issued to the Holder, provided that the Holder executes and delivers to the Company an agreement reasonably satisfactory to the Company to indemnify the Company from any loss incurred by it in connection with the Debenture and provided that the Company is provided a form of Debenture for such replacement purposes.

15. Defaults. If one or more of the following described “Events of Default” shall occur:

then, or at any time thereafter prior to the date on which all continuing Events of Default have been cured, and in each and every such case, unless such Event of Default shall have been waived in writing by the Holder (which waiver shall not be deemed to be a waiver of any subsequent default), at the option of the Holder and in the Holder’s sole discretion, the Holder may, by notice to the Company declare this Debenture immediately due and payable, and the Holder may immediately, and without expiration of any period of grace, enforce any and all of the Holder’s rights and remedies provided herein or any other rights or remedies afforded by law. In such event, the Debenture shall be redeemed at a redemption price per Debenture equal to the Redemption Price provided in Paragraph 6(b).

16. Special Treatment on an Acquisition.

17. Extension. At the election of the Holder, if the Outstanding Principal Amount of this Debenture remains unpaid after the Maturity Date, this Debenture and the aggregate Outstanding Principal Amount shall remain an outstanding obligation of the Company, payable on the demand of the Holder, and the Company promises to pay to the Holder interest on the Outstanding Principal Amount, at the rate of 6% per annum, due and payable on demand. Interest shall be calculated based on a 360-day year. Interest shall accrue from the Maturity Date.

18. Savings Clause. In case any provision of this Debenture is held by a court of competent jurisdiction to be excessive in scope or otherwise invalid or unenforceable, such provision shall be adjusted rather than voided, if possible, so that it is enforceable to the maximum extent possible, and the validity and enforceability of the remaining provisions of this Debenture will not in any way be affected or impaired thereby.

19. Entire Agreement. This Debenture and the agreements referred to in this Debenture constitute the full and entire understanding and agreement between the Company and the Holder with respect to the subject hereof. Neither this Debenture nor any term hereof may be amended, waived, discharged or terminated other than by a written instrument signed by the Company and a majority of the Outstanding Principal Amount of the Debentures. By countersigning this Debenture below, the Holder consents to the amending and restating of the Original Debenture, in a manner similar to as provided for herein.

20. Assignment, Etc. Subject to any applicable law and the requirements set forth in the legend set forth hereon, any Holder may, without notice, transfer or assign this Debenture. The Company agrees that, subject to compliance with the applicable law, after receipt by the Company of written notice of assignment from the Holder or from the Holder’s assignee, all principal, interest, and other amounts which are then due and thereafter become due under this Debenture shall be paid to such assignee at the place of payment designated in such notice. This Debenture shall be binding upon the Company and its successors and shall inure to the benefit of the Holder and its successors and assigns.

21. No Waiver. No failure on the part of the Holder to exercise, and no delay in exercising any right, remedy or power hereunder shall operate as a waiver thereof, nor shall any single or partial exercise by the Holder of any right, remedy or power hereunder preclude any other or future exercise of any other right, remedy or power. Each and every right, remedy or power hereby granted to the Holder or allowed it by law or other agreement shall be cumulative and not exclusive of any other, and may be exercised by the Holder from time to time.

22. Miscellaneous. Unless otherwise provided herein, any notice or other communication to a party hereunder shall be deemed to have been duly given if personally delivered or sent by registered or certified mail, return receipt requested, postage prepaid with a copy in each case sent on the same day to the party by facsimile, FedEx or other overnight delivery service to said party at its address set forth herein or such other address as either may designate for itself in such notice to the other and communications shall be deemed to have been received when delivered personally or, if sent by mail, when actually received by the party to whom it is addressed.

Copies of all notices to the Company shall be sent to: American DG Energy Inc., 45 First Avenue, Waltham, Massachusetts 02451, attention Chief Financial Officer. Whenever the sense of this Debenture requires, words in the singular shall be deemed to include the plural and words in the plural shall be deemed to include the singular. Paragraph headings are for convenience only and shall not affect the meaning of this document.

23. Choice of Law and Consent to Jurisdiction. This Debenture shall be governed by, and construed in accordance with, the internal laws of the State of New York and, to the extent it involves any United States federal statute or regulations, in accordance therewith. The parties hereby consent and submit to the exclusive jurisdiction of the state and federal courts in New York City with respect to all disputes arising in connection with this Debenture.

[Remainder of this page intentionally left blank; signature page follows.]

IN WITNESS WHEREOF, the Company has caused this instrument to be duly executed by an officer thereunto duly authorized.

ACKNOWLEDGEMENT

[Holder]

By:__________________________

Name:

Title: 

EXHIBIT 1

Conversion Notice

6% Senior Unsecured Convertible Debenture Due 2018

The undersigned, as Holder of the 6% Senior Unsecured Convertible Debenture due 2018 of American DG Energy Inc. (“Company”), No. [__], in the Outstanding Principal Amount of U.S.$[__] (the “Debenture”), hereby irrevocably elects to convert U.S.$_______________ of the Outstanding Principal Amount of the Debenture and U.S.$______________ of interest accrued but unpaid under the Debenture, into shares of Common Stock, par value $.001 per share (the “Common Stock”), of Company according to the conditions of the Debenture, as of the date written below. The undersigned hereby requests that share certificates for the Common Stock to be issued to the undersigned pursuant to this Conversion Notice be issued in the name of, and delivered to, the undersigned or its designee as indicated below. If shares are to be issued in the name of a person other than the undersigned, the undersigned will pay all transfer taxes payable with respect thereto. No fee will be charged to the Holder for any conversion, except for transfer taxes, if any.