PURSUANT TO 44-14-35.1 OF OFFICIAL CODE OF GEORGIA ANNOTATED, THIS INSTRUMENT EMBRACES, COVERS AND CONVEYS SECURITY TITLE TO AFTER-ACQUIRED PROPERTY OF THE GRANTOR OGLETHORPE POWER CORPORATION (AN ELECTRIC MEMBERSHIP CORPORATION), GRANTOR, to U.S. BANK NATIONAL ASSOCIATION, TRUSTEE SEVENTY-THIRD SUPPLEMENTAL INDENTURE Relating to Confirming the Lien of the Indenture with respect to certain Agreements and Licenses Dated as of July 26, 2017 FIRST MORTGAGE OBLIGATIONS

THIS SEVENTY-THIRD SUPPLEMENTAL INDENTURE, dated as of July 26, 2017, is between OGLETHORPE POWER CORPORATION (AN ELECTRIC MEMBERSHIP CORPORATION), formerly known as Oglethorpe Power Corporation (An Electric Membership Generation & Transmission Corporation), an electric membership corporation organized and existing under the laws of the State of Georgia, as grantor (the “Company”), and U.S. BANK NATIONAL ASSOCIATION, a national banking association, as successor to SunTrust Bank, formerly SunTrust Bank, Atlanta, as trustee (in such capacity, the “Trustee”).

WHEREAS, the Company has heretofore executed and delivered to the Trustee an Indenture, dated as of March 1, 1997 (the “Original Indenture”), for the purpose of securing its Existing Obligations and providing for the authentication and delivery of Additional Obligations by the Trustee from time to time under the Original Indenture (capitalized terms used herein and not otherwise defined shall have the meanings assigned to them in the Original Indenture as provided in Section 1 hereof);

WHEREAS, the Original Indenture has heretofore been amended and supplemented by seventy-two Supplemental Indentures (the Original Indenture, as heretofore, hereby and hereafter supplemented and modified, the “Indenture”), and the Original Indenture and the seventy-two Supplemental Indentures have been recorded as set forth on Schedule 1 attached hereto;

WHEREAS, the Company desires to execute and deliver this Seventy-Third Supplemental Indenture, in accordance with the provisions of the Original Indenture, for the purpose of subjecting, conveying and confirming to the Trustee the lien of the Indenture with respect to the agreements and licenses more particularly described on Exhibit A attached hereto; and

WHEREAS, Section 12.1 of the Original Indenture provides that, without the consent of the Holders of any of the Obligations at the time Outstanding, the Company, when authorized by a Board Resolution, and the Trustee may enter into Supplemental Indentures for the purposes set forth in said Section 12.1, including to better assure, convey and confirm unto the Trustee any property subjected to the lien of the Indenture;

NOW, THEREFORE, THIS SEVENTY-THIRD SUPPLEMENTAL INDENTURE WITNESSES, that, to secure the payment of the principal of (and premium, if any) and interest on the Outstanding Secured Obligations, to confirm the lien of the Indenture upon the Trust Estate, including property purchased, constructed or otherwise acquired by the Company since the date of execution of the Original Indenture, to secure performance of the covenants therein and herein contained, and in consideration of the premises thereof and hereof, the Company by these presents does grant, bargain, sell, alienate, remise, release, convey, assign, transfer, mortgage, hypothecate, pledge, set over and confirm to the Trustee, and its successors and assigns in the trust created thereby and hereby, in trust, all property, rights, privileges and franchises (other than Excepted Property or Excludable Property) of the Company, whether now owned or hereafter acquired, of the character described in the Granting Clauses of the Original Indenture, wherever located, including all such property, rights, privileges and franchises acquired since the date of execution of the Original Indenture, including, without limitation, the agreements and licenses more particularly described on Exhibit A attached hereto, subject to all

exceptions, reservations and matters of the character referred to in the Indenture, and does grant a security interest therein for the purposes expressed herein and in the Indenture subject in all cases to Sections 5.2 and 11.2 B of the Original Indenture and to the rights of the Company under the Indenture, including the rights set forth in Article V of the Original Indenture; but expressly excepting and excluding from the lien and operation of the Indenture all properties of the character specifically excepted as “Excepted Property” or “Excludable Property” in the Indenture to the extent contemplated thereby.

PROVIDED, HOWEVER, that if, upon the occurrence of an Event of Default, the Trustee, or any separate trustee or co-trustee appointed under Section 9.14 of the Original Indenture or any receiver appointed pursuant to statutory provision or order of court, shall have entered into possession of all or substantially all of the Trust Estate, all the Excepted Property described or referred to in Paragraphs A through H, inclusive, of “Excepted Property” in the Original Indenture then owned or thereafter acquired by the Company, shall immediately, and, in the case of any Excepted Property described or referred to in Paragraphs I, J, L, N and P of “Excepted Property” in the Original Indenture (excluding the property described in Section 2 of Exhibit B in the Original Indenture), upon demand of the Trustee or such other trustee or receiver, become subject to the lien of the Indenture to the extent permitted by law, and the Trustee or such other trustee or receiver may, to the extent permitted by law, at the same time likewise take possession thereof, and whenever all Events of Default shall have been cured and the possession of all or substantially all of the Trust Estate shall have been restored to the Company, such Excepted Property shall again be excepted and excluded from the lien of the Indenture to the extent and otherwise as hereinabove set forth and as set forth in the Indenture.

The Company may, however, pursuant to the Granting Clause Third of the Original Indenture, subject to the lien of the Indenture any Excepted Property or Excludable Property, whereupon the same shall cease to be Excepted Property or Excludable Property.

TO HAVE AND TO HOLD all such property, rights, privileges and franchises hereby and hereafter (by a Supplemental Indenture or otherwise) granted, bargained, sold, alienated, remised, released, conveyed, assigned, transferred, mortgaged, hypothecated, pledged, set over or confirmed as aforesaid, or intended, agreed or covenanted so to be, together with all the tenements, hereditaments and appurtenances thereto appertaining (said properties, rights, privileges and franchises, including any cash and securities hereafter deposited or required to be deposited with the Trustee (other than any such cash which is specifically stated in the Indenture not to be deemed part of the Trust Estate) being part of the Trust Estate), unto the Trustee, and its successors and assigns in the trust created by the Indenture, forever.

SUBJECT, HOWEVER, to (i) Permitted Exceptions and (ii) to the extent permitted by Section 13.6 of the Original Indenture as to property hereafter acquired (a) any duly recorded or perfected prior mortgage or other lien that may exist thereon at the date of the acquisition thereof by the Company and (b) purchase money mortgages, other purchase money liens, chattel mortgages, conditional sales agreements or other title retention agreements created by the Company at the time of acquisition thereof.

BUT IN TRUST, NEVERTHELESS, with power of sale, for the equal and proportionate benefit and security of the Holders from time to time of all the Outstanding

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Secured Obligations without any priority of any such Obligation over any other such Obligation and for the enforcement of the payment of such Obligations in accordance with their terms.

UPON CONDITION that, until the happening of an Event of Default and subject to the provisions of Article V of the Original Indenture, and not in limitation of the rights elsewhere provided in the Indenture, including the rights set forth in Article V of the Original Indenture, the Company shall be permitted to (i) possess and use the Trust Estate, except cash, securities, Designated Qualifying Securities and other personal property deposited, or required to be deposited, with the Trustee, (ii) explore for, mine, extract, separate and dispose of coal, ore, gas, oil and other minerals, and harvest standing timber, and (iii) receive and use the rents, issues, profits, revenues and other income, products and proceeds of the Trust Estate.

THE INDENTURE, INCLUDING THIS SEVENTY-THIRD SUPPLEMENTAL INDENTURE, is intended to operate and is to be construed as a deed passing title to the Trust Estate and is made under the provisions of the laws of the State of Georgia relating to deeds to secure debt, and not as a mortgage or deed of trust, and is given to secure the Outstanding Secured Obligations.  Should the indebtedness secured by the Indenture be paid according to the tenor and effect thereof when the same shall become due and payable and should the Company perform all covenants contained in the Indenture in a timely manner, then the Indenture shall be canceled and surrendered.

GENERAL PROVISIONS

Section 1.              Supplemental Indenture.

This Seventy-Third Supplemental Indenture is executed and shall be construed as an indenture supplemental to the Original Indenture, and shall form a part thereof, and the Original Indenture, as heretofore supplemented and modified and as hereby supplemented and modified, is hereby confirmed.  All capitalized terms used in this Seventy-Third Supplemental Indenture but not defined herein shall have the same meanings ascribed to them in the Original Indenture, as such terms may have been or may be amended or modified from time to time pursuant to the Indenture, except in cases where the context clearly indicates otherwise.  All references herein to Sections, Articles, definitions or other provisions of the Original Indenture shall be to such Sections, Articles, definitions or other provisions as they may be amended or modified from time to time pursuant to the Indenture.

Section 2.              Recitals.

All recitals in this Seventy-Third Supplemental Indenture are made by the Company only and not by the Trustee; and all of the provisions contained in the Indenture, in respect of the rights, privileges, immunities, powers and duties of the Trustee shall be applicable in respect hereof as fully and with like effect as if set forth herein in full.

Section 3.              Successors and Assigns.

Whenever in this Seventy-Third Supplemental Indenture any of the parties hereto is named or referred to, this shall, subject to the provisions of Articles IX and XI of the Original Indenture, be deemed to include the successors and assigns of such party, and all the covenants

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and agreements in this Seventy-Third Supplemental Indenture contained by or on behalf of the Company or by or on behalf of the Trustee shall, subject as aforesaid, bind and inure to the respective benefits of the respective successors and assigns of such parties, whether so expressed or not.

Section 4.              No Rights, Remedies, Etc.

Nothing in this Seventy-Third Supplemental Indenture, expressed or implied, is intended, or shall be construed, to confer upon, or to give to, any person, firm or corporation, other than the parties hereto and the Holders of the Outstanding Secured Obligations, any right, remedy or claim under or by reason of this Seventy-Third Supplemental Indenture or any covenant, condition, stipulation, promise or agreement hereof.

Section 5.              Counterparts.

This Seventy-Third Supplemental Indenture may be executed in several counterparts, each of such counterparts shall for all purposes be deemed to be an original, and all such counterparts, or as many of them as the Company and the Trustee shall preserve undestroyed, shall together constitute but one and the same instrument.

Section 6.              Security Agreement; Mailing Address.

To the extent permitted by applicable law, this Seventy-Third Supplemental Indenture shall be deemed to be a Security Agreement and Financing Statement whereby the Company grants to the Trustee a security interest in all of the Trust Estate that is personal property or fixtures under the Uniform Commercial Code, as adopted or hereafter adopted in one or more of the states in which any part of the properties of the Company are situated.

The mailing address of the Company, as debtor, is:

Oglethorpe Power Corporation

(An Electric Membership Corporation)

2100 East Exchange Place

Tucker, Georgia 30084-5336

and the mailing address of the Trustee, as secured party, is:

U.S. Bank National Association

Attention:  Corporate Trust Services

1349 West Peachtree Street, NW

Suite 1050, Two Midtown Plaza

Atlanta, Georgia  30309

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IN WITNESS WHEREOF, the parties hereto have caused this Seventy-Third Supplemental Indenture to be duly executed as of the day and year first written above.

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Exhibit A

All of the Company’s right, title and interest in, to and under each of the following agreements and licenses (in each case, as the same may have been and may be amended, supplemented or otherwise modified from time to time):

Amended and Restated Services Agreement, dated as of July 20, 2017, between Georgia Power Company, for itself and as agent for Oglethorpe Power Corporation (An Electric Membership Corporation), Municipal Electric Authority of Georgia, MEAG Power SPVJ, LLC, MEAG Power SPVM, LLC, MEAG Power SPVP, LLC and the City of Dalton, Georgia, acting by and through its Board of Water, Light and Sinking Fund Commissioners, and Westinghouse Electric Company LLC and WECTEC Global Project Services Inc.

Facility IP License in the Event of a Triggering Event, dated as of July 20, 2017, between Georgia Power Company, for itself and as agent for Oglethorpe Power Corporation (An Electric Membership Corporation), Municipal Electric Authority of Georgia, MEAG Power SPVJ, LLC, MEAG Power SPVM, LLC, MEAG Power SPVP, LLC and the City of Dalton, Georgia, acting by and through its Board of Water, Light and Sinking Fund Commissioners, and Westinghouse Electric Company LLC and WECTEC Global Project Services Inc.

IP License, dated as of July 20, 2017, between Georgia Power Company, for itself and as agent for Oglethorpe Power Corporation (An Electric Membership Corporation), Municipal Electric Authority of Georgia, MEAG Power SPVJ, LLC, MEAG Power SPVM, LLC, MEAG Power SPVP, LLC and the City of Dalton, Georgia, acting by and through its Board of Water, Light and Sinking Fund Commissioners, and Westinghouse Electric Company LLC and WECTEC Global Project Services Inc.

Settlement Agreement, dated as of June 9, 2017, by and among Toshiba Corporation and Georgia Power Company, Oglethorpe Power Corporation (An Electric Membership Corporation), Municipal Electric Authority of Georgia, and the City of Dalton, Georgia, acting by and through its Board of Water, Light and Sinking Fund Commissioners

A-1

Schedule 1

RECORDING INFORMATION

FOR

                                         COUNTY, GEORGIA