Exhibit 4.15

Fifth Supplemental Indenture

FIFTH SUPPLEMENTAL INDENTURE (this “Supplemental Indenture”), dated as of November 29, 2012, among Atlantic Ridgeline Holdings, LLC, a Delaware limited liability company (the “New Guarantor”), a subsidiary of Atlantic Power Corporation (or its successor), a British Columbia corporation (“Atlantic Power”), the Guarantors (the “Existing Guarantors”) under the Indenture referred to below, and Wilmington Trust, National Association, as trustee under the Indenture referred to below (the “Trustee”).

WITNESSETH:

WHEREAS Atlantic Power has heretofore executed and delivered to the Trustee an Indenture (as such may be amended from time to time, the “Indenture”), dated as of November 4, 2011, providing for the issuance of its 9% Senior Notes due 2018 (the “Notes”);

WHEREAS under certain circumstances Atlantic Power is required (or permitted) to cause the New Guarantor to execute and deliver to the Trustee a supplemental indenture pursuant to which the New Guarantor shall unconditionally guarantee all of Atlantic Power’s obligations under the Notes pursuant to a Guarantee on the terms and conditions set forth herein; and

WHEREAS pursuant to Section 8.01 of the Indenture, the Trustee, Atlantic Power and the Existing Guarantors are authorized to execute and deliver this Supplemental Indenture;

NOW THEREFORE, in consideration of the foregoing and for other good and valuable consideration, the receipt of which is hereby acknowledged, the New Guarantor, Atlantic Power, the Existing Guarantors and the Trustee mutually covenant and agree for the equal and ratable benefit of the Holders as follows:

1. Definitions.

(a) Capitalized terms used herein without definition shall have the meanings assigned to them in the Indenture.

(b) For all purposes of this Supplemental Indenture, except as otherwise herein expressly provided or unless the context otherwise requires: (i) the terms and expressions used herein shall have the same meanings as corresponding terms and expressions used in the Indenture; and (ii) the words “herein,” “hereof” and “hereby” and other words of similar import used in this Supplemental Indenture refer to this Supplemental Indenture as a whole and not to any particular section hereof.

2. Agreement to Guarantee. The New Guarantor hereby agrees, jointly and severally with all other Guarantors, to guarantee Atlantic Power’s obligations under the Notes and the Indenture on the terms and subject to the conditions set forth in Article 10 of the Indenture and to be bound by all other applicable provisions of the Indenture. From and after the date hereof, the New Guarantor shall be a Guarantor for all purposes under the Indenture and the Notes.

3. Ratification of Indenture; Supplemental Indentures Part of Indenture. Except as expressly amended hereby, the Indenture is in all respects ratified and confirmed and all the terms, conditions and provisions thereof shall remain in full force and effect. This Supplemental Indenture shall form a part of the Indenture for all purposes, and every Holder heretofore or hereafter authenticated and delivered shall be bound hereby.

4. Governing Law. THIS SUPPLEMENTAL INDENTURE SHALL BE GOVERNED BY AND CONSTRUED IN ACCORDANCE WITH THE LAWS OF THE STATE OF NEW YORK, AS APPLIED TO CONTRACTS MADE AND PERFORMED WITHIN THE STATE OF NEW YORK (INCLUDING, WITHOUT LIMITATION, SECTION 5-1401 OF THE NEW YORK GENERAL OBLIGATIONS LAW OR ANY SUCCESSOR STATUTE). EACH OF THE PARTIES HERETO AGREES TO SUBMIT TO THE JURISDICTION OF THE COURTS OF THE STATE OF NEW YORK IN ANY ACTION OR PROCEEDING ARISING OUT OF OR RELATING TO THIS SUPPLEMENTAL INDENTURE.

5. Trustee Makes No Representation. The Trustee shall not be responsible in any manner whatsoever for or in respect of the validity or sufficiency of this Supplemental Indenture or for or in respect of the recitals contained herein, all of which are made solely by Atlantic Power.

6. Multiple Counterparts. The parties may sign multiple counterparts of this Supplemental Indenture. Each signed counterpart shall be deemed an original, but all of them together represent one and the same agreement.

7. Headings. The headings of this Supplemental Indenture have been inserted for convenience of reference only, are not to be considered a part hereof, and shall in no way modify or restrict any of the terms or provisions hereof.

[Signature Pages Follow]

2

IN WITNESS WHEREOF, the parties have caused this Supplemental Indenture to be duly executed all as of the date and year first written above.

| ATLANTIC POWER CORPORATION
| By: | /s/ Barry E. Welch
|  | Name: | Barry E. Welch
|  | Title: | President and Chief Executive Officer
| GUARANTORS
| ATLANTIC AUBURNDALE, LLC
| By: | /s/ Barry E. Welch
|  | Name: | Barry E. Welch
|  | Title: | President
| ATLANTIC CADILLAC HOLDINGS, INC.
| By: | /s/ Barry E. Welch
|  | Name: | Barry E. Welch
|  | Title: | President
| ATLANTIC IDAHO WIND C, LLC
| By: | /s/ Barry E. Welch
|  | Name: | Barry E. Welch
|  | Title: | President
| ATLANTIC IDAHO WIND HOLDINGS, LLC
| By: | /s/ Barry E. Welch
|  | Name: | Barry E. Welch
|  | Title: | President

Signature Page 1 to Fifth Supplemental Indenture

| ATLANTIC OKLAHOMA WIND, LLC
| By: | /s/ Barry E. Welch
|  | Name: | Barry E. Welch
|  | Title: | President
| ATLANTIC PIEDMONT HOLDINGS, LLC
| By: | /s/ Barry E. Welch
|  | Name: | Barry E. Welch
|  | Title: | President
| ATLANTIC POWER GENERATION, INC.
| By: | /s/ Barry E. Welch
|  | Name: | Barry E. Welch
|  | Title: | President
| ATLANTIC POWER HOLDINGS, INC.
| By: | /s/ Barry E. Welch
|  | Name: | Barry E. Welch
|  | Title: | President
| ATLANTIC POWER SERVICES, INC.
| By: | /s/ Barry E. Welch
|  | Name: | Barry E. Welch
|  | Title: | President
| ATLANTIC POWER SERVICES CANADA GP INC.
| By: | /s/ Barry E. Welch
|  | Name: | Barry E. Welch
|  | Title: | President

Signature Page 2 to Fifth Supplemental Indenture

| ATLANTIC POWER SERVICES CANADA LP
| By: ATLANTIC POWER SERVICES
| CANADA GP INC.,
| ITS GENERAL PARTNERS
| By: | /s/ Barry E. Welch
|  | Name: | Barry E. Welch
|  | Title: | President
| ATLANTIC POWER TRANSMISSION, INC.
| By: | /s/ Barry E. Welch
|  | Name: | Barry E. Welch
|  | Title: | President
| ATLANTIC RENEWABLES HOLDINGS, LLC
| By: | /s/ Barry E. Welch
|  | Name: | Barry E. Welch
|  | Title: | President
| ATLANTIC RIDGELINE HOLDINGS, LLC
| By: | /s/ Barry E. Welch
|  | Name: | Barry E. Welch
|  | Title: | President
| ATLANTIC ROCKLAND HOLDINGS, LLC
| By: | /s/ Barry E. Welch
|  | Name: | Barry E. Welch
|  | Title: | President

Signature Page 3 to Fifth Supplemental Indenture

| AUBURNDALE GP, LLC
| By: AUBURNDALE LP, LLC,
| ITS SOLE MEMBER
| By: ATLANTIC AUBURNDALE, LLC,
| ITS SOLE MEMBER
| By: | /s/ Barry E. Welch
|  | Name: | Barry E. Welch
|  | Title: | President
| AUBURNDALE LP, LLC
| By: ATLANTIC AUBURNDALE, LLC,
| ITS SOLE MEMBER
| By: | /s/ Barry E. Welch
|  | Name: | Barry E. Welch
|  | Title: | President
| BAKER LAKE HYDRO LLC
| By: | /s/ Barry E. Welch
|  | Name: | Barry E. Welch
|  | Title: | President
| DADE INVESTMENT, L.P.
| By: NCP DADE POWER, LLC,
| ITS GENERAL PARTNER
| By: | /s/ Barry E. Welch
|  | Name: | Barry E. Welch
|  | Title: | President

Signature Page 4 to Fifth Supplemental Indenture

| EPSILON POWER FUNDING, LLC
| By: | /s/ Barry E. Welch
|  | Name: | Barry E. Welch
|  | Title: | President
| HARBOR CAPITAL HOLDINGS, LLC
| By: ATLANTIC POWER HOLDINGS, INC.,
| ITS SOLE MEMBER
| By: | /s/ Barry E. Welch
|  | Name: | Barry E. Welch
|  | Title: | President
| LAKE COGEN LTD.
| By: NCP LAKE POWER LLC
| ITS GENERAL PARTNER
| By: | /s/ Barry E. Welch
|  | Name: | Barry E. Welch
|  | Title: | President
| LAKE INVESTMENT, L.P.
| By: NCP LAKE POWER LLC
| ITS GENERAL PARTNER
| By: | /s/ Barry E. Welch
|  | Name: | Barry E. Welch
|  | Title: | President
| NCP DADE POWER LLC
| By: | /s/ Barry E. Welch
|  | Name: | Barry E. Welch
|  | Title: | President

Signature Page 5 to Fifth Supplemental Indenture

| NCP GEM LLC
| By: | /s/ Barry E. Welch
|  | Name: | Barry E. Welch
|  | Title: | President
| NCP LAKE POWER LLC
| By: | /s/ Barry E. Welch
|  | Name: | Barry E. Welch
|  | Title: | President
| NCP PASCO LLC
| By: | /s/ Barry E. Welch
|  | Name: | Barry E. Welch
|  | Title: | President
| OLYMPIA HYDRO LLC
| By: | /s/ Barry E. Welch
|  | Name: | Barry E. Welch
|  | Title: | President
| ORLANDO POWER GENERATION I LLC
| By: | /s/ Barry E. Welch
|  | Name: | Barry E. Welch
|  | Title: | President

Signature Page 6 to Fifth Supplemental Indenture

| ORLANDO POWER GENERATION II LLC
| By: | /s/ Barry E. Welch
|  | Name: | Barry E. Welch
|  | Title: | President
| PASCO COGEN, LTD.
| By: NCP DADE POWER LLC
| ITS GENERAL PARTNER
| By: | /s/ Barry E. Welch
|  | Name: | Barry E. Welch
|  | Title: | President
| TETON EAST COAST GENERATION LLC
| By: | /s/ Barry E. Welch
|  | Name: | Barry E. Welch
|  | Title: | President
| TETON NEW LAKE, LLC
| By: | /s/ Barry E. Welch
|  | Name: | Barry E. Welch
|  | Title: | President
| TETON OPERATING SERVICES, LLC
| By: | /s/ Barry E. Welch
|  | Name: | Barry E. Welch
|  | Title: | President

Signature Page 7 to Fifth Supplemental Indenture

| TETON POWER FUNDING, LLC
| By: | /s/ Barry E. Welch
|  | Name: | Barry E. Welch
|  | Title: | President
| TETON SELKIRK LLC
| By: | /s/ Barry E. Welch
|  | Name: | Barry E. Welch
|  | Title: | President

Signature Page 8 to Fifth Supplemental Indenture

| WILMINGTON TRUST, NATIONAL ASSOCIATION, AS Trustee
| By: | /s/ Joseph P. O’Donnell
|  | Name: | Joseph P. O’Donnell
|  | Title: | Vice President

Signature Page 9 to Fifth Supplemental Indenture