Document:

EX-4.3

THIRTIETH SUPPLEMENTAL INDENTURE FOR

ADDITIONAL SUBSIDIARY GUARANTEES

Thirtieth Supplemental Indenture (this “Supplemental Indenture for Additional
Guarantees”), dated as of April 16, 2010, among Carbon Management Solutions LLC, Clean Edge Energy
LLC and NRG Artesian Energy LLC (each a “Guaranteeing Subsidiary” and together the “Guaranteeing
Subsidiaries”), each an indirect subsidiary of NRG Energy, Inc., a Delaware corporation (the
“Company”), the Company, the Existing Guarantors set forth on the signature page hereto (the
“Existing Guarantors") and Law Debenture Trust Company of New York, as trustee under the indentures
referred to below (the “Trustee”).

W I T N E S S E T H

WHEREAS, the Company has heretofore executed and delivered to the Trustee an indenture (the
“Base Indenture”), dated as of February 2, 2006, between the Company and the Trustee, as amended by
a ninth supplemental indenture (the “Ninth Supplemental Indenture”), dated as of November 21, 2006,
among the Company, the Guarantors named therein and the Trustee, providing for the original
issuance of an aggregate principal amount of $1,100 million of 7.375% Senior Notes due 2017 (the
“Initial Notes”), and, subject to the terms of the Ninth Supplemental Indenture, future unlimited
issuances of 7.375% Senior Notes due 2017 (the “Additional Notes,” and together with the Initial
Notes, the “Notes”), as amended by a twelfth supplemental indenture, dated as of July 19, 2007,
among the Company, the Existing Guarantors party thereto and the Trustee (the “Twelfth Supplemental
Indenture”), a fifteenth supplemental indenture, dated as of August 28, 2007, among the Company,
the Existing Guarantors and the Trustee (the “Fifteenth Supplemental Indenture”), an eighteenth
supplemental indenture dated as of April 28, 2009, among the Company, the Existing Guarantors party
thereto and the Trustee (the “Eighteenth Supplemental Indenture”), a twenty-first supplemental
indenture dated as of May 8, 2009, among the Company, the Existing Guarantors party thereto and the
Trustee (the “Twenty-First Supplemental Indenture”) and a twenty-sixth supplemental indenture dated
as of October 5, 2009, among the Company, the Existing Guarantors party thereto and the Trustee
(the “Twenty-Sixth Supplemental Indenture” and together with the Base Indenture, the Ninth
Supplemental Indenture, the Twelfth Supplemental Indenture, the Fifteenth Supplemental Indenture,
the Eighteenth Supplemental Indenture and the Twenty-First Supplemental Indenture, the
“Indenture”);

WHEREAS, the Indenture provides that under certain circumstances the Guaranteeing Subsidiaries
shall execute and deliver to the Trustee a supplemental indenture pursuant to which the
Guaranteeing Subsidiaries shall unconditionally guarantee all of the Company’s Obligations under
the Notes and the Indenture (the “Additional Guarantees”); and

WHEREAS, pursuant to Section 4.17 of the Ninth Supplemental Indenture, the Trustee, the
Company and the Existing Guarantors are authorized and required to execute and deliver this
Supplemental Indenture for Additional Guarantees.

NOW THEREFORE, in consideration of the foregoing and for good and valuable consideration, the
receipt of which is hereby acknowledged, the Guaranteeing Subsidiaries, the Trustee, the Company
and the Existing Guarantors mutually covenant and agree for the equal and ratable benefit of the
Holders of the Notes as follows:

1. Capitalized Terms. Unless otherwise defined in this Supplemental Indenture for Additional
Guarantees, capitalized terms used herein without definition shall have the meanings assigned to
them in the Indenture.

2. Agreement to be Bound; Guarantee. The Guaranteeing Subsidiaries hereby become parties to
the Ninth Supplemental Indenture as Guarantors and as such will have all of the rights and be
subject to all of the Obligations and agreements of Guarantors under the Indenture. The
Guaranteeing Subsidiaries hereby agree to be bound by all of the provisions of the Ninth
Supplemental Indenture applicable to a Guarantor and to perform all of the Obligations and
agreements of a Guarantor under the Ninth Supplemental Indenture. In furtherance of the foregoing,
the Guaranteeing Subsidiaries shall be deemed Guarantors for purposes of Article 10 of the Ninth
Supplemental Indenture, including, without limitation, Section 10.02 thereof.

3. NEW YORK LAW TO GOVERN. THE INTERNAL LAW OF THE STATE OF NEW YORK SHALL GOVERN AND BE USED
TO CONSTRUE THIS SUPPLEMENTAL INDENTURE FOR ADDITIONAL GUARANTEES BUT WITHOUT GIVING EFFECT TO
APPLICABLE PRINCIPLES OF CONFLICTS OF LAW TO THE EXTENT THAT THE APPLICATION OF THE LAWS OF ANOTHER
JURISDICTION WOULD BE REQUIRED THEREBY.

4. Counterparts. The parties may sign any number of copies of this Supplemental Indenture for
Additional Guarantees. Each signed copy shall be an original, but all of them together represent
the same agreement.

5. Effect of Headings. The Section headings herein are for convenience only and shall not
affect the construction hereof.

6. The Trustee. The Trustee shall not be responsible in any manner whatsoever for or in
respect of the validity or sufficiency of this Supplemental Indenture for Additional Guarantees or
for or in respect of the recitals contained herein, all of which recitals are made solely by the
Guaranteeing Subsidiaries and the Company.

7. Ratification of Indenture; Supplemental Indenture for Additional Guarantees 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 for Additional Guarantees shall form a part of the Indenture
for all purposes, and every Holder of Notes heretofore or hereafter authenticated and delivered
shall by bound hereby.

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

Guaranteeing Subsidiaries:

CARBON MANAGEMENT SOLUTIONS LLC

By: /s/ Christopher Sotos

Name: Christopher Sotos

Title: Vice President & Treasurer

CLEAN EDGE ENERGY LLC

By: /s/ Christopher Sotos

Name: Christopher Sotos

Title: Vice President & Treasurer

NRG ARTESIAN ENERGY LLC

By: /s/ Christopher Sotos

Name: Christopher Sotos

Title: Vice President & Treasurer

Issuer:

NRG ENERGY, INC.

By: /s/ Christopher Sotos

Name: Christopher Sotos

Title: Vice President & Treasurer

Existing Guarantors:

ARTHUR KILL POWER LLC

ASTORIA GAS TURBINE POWER LLC

BERRIANS I GAS TURBINE POWER LLC

BIG CAJUN II UNIT 4 LLC

CABRILLO POWER I LLC

CABRILLO POWER II LLC

CHICKAHOMINY RIVER ENERGY CORP.

COMMONWEALTH ATLANTIC POWER LLC

CONEMAUGH POWER LLC

CONNECTICUT JET POWER LLC

DEVON POWER LLC

DUNKIRK POWER LLC

EASTERN SIERRA ENERGY COMPANY

EL SEGUNDO POWER LLC

EL SEGUNDO POWER II LLC

HANOVER ENERGY COMPANY

HOFFMAN SUMMIT WIND PROJECT, LLC

HUNTLEY IGCC LLC

HUNTLEY POWER LLC

INDIAN RIVER IGCC LLC

INDIAN RIVER OPERATIONS INC.

INDIAN RIVER POWER LLC

JAMES RIVER POWER LLC

KAUFMAN COGEN LP

KEYSTONE POWER LLC

LAKE ERIE PROPERTIES INC.

LANGFORD WIND POWER, LLC

LOUISIANA GENERATING LLC

MIDDLETOWN POWER LLC

MONTVILLE IGCC LLC

MONTVILLE POWER LLC

NEO CHESTER-GEN LLC

NEO CORPORATION

NEO FREEHOLD-GEN LLC

NEO POWER SERVICES INC.

NEW GENCO GP, LLC

NORWALK POWER LLC

NRG AFFILIATE SERVICES INC.

NRG ARTHUR KILL OPERATIONS INC.

NRG ASIA-PACIFIC, LTD.

NRG ASTORIA GAS TURBINE OPERATIONS, INC.

NRG BAYOU COVE LLC

NRG CABRILLO POWER OPERATIONS INC.

NRG CADILLAC OPERATIONS INC.

NRG CALIFORNIA PEAKER OPERATIONS LLC

NRG CEDAR BAYOU DEVELOPMENT COMPANY, LLC

NRG CONNECTICUT AFFILIATE SERVICES INC.

NRG DEVON OPERATIONS INC.

NRG DUNKIRK OPERATIONS INC.

NRG EL SEGUNDO OPERATIONS INC.

NRG GENERATION HOLDINGS, INC.

NRG HUNTLEY OPERATIONS INC.

NRG INTERNATIONAL LLC

NRG KAUFMAN LLC

NRG MESQUITE LLC

NRG MIDATLANTIC AFFILIATE SERVICES INC.

NRG MIDDLETOWN OPERATIONS INC.

NRG MONTVILLE OPERATIONS INC.

NRG NEW JERSEY ENERGY SALES LLC

NRG NEW ROADS HOLDINGS LLC

NRG NORTH CENTRAL OPERATIONS INC.

NRG NORTHEAST AFFILIATE SERVICES INC.

NRG NORWALK HARBOR OPERATIONS INC.

NRG OPERATING SERVICES, INC.

NRG OSWEGO HARBOR POWER OPERATIONS INC.

NRG POWER MARKETING LLC

NRG RETAIL LLC

NRG ROCKY ROAD LLC

NRG SAGUARO OPERATIONS INC.

NRG SOUTH CENTRAL AFFILIATE SERVICES INC.

NRG SOUTH CENTRAL GENERATING LLC

NRG SOUTH CENTRAL OPERATIONS INC.

NRG TEXAS C&I SUPPLY LLC

NRG TEXAS LLC

NRG TEXAS HOLDING INC.

NRG TEXAS POWER LLC

NRG WEST COAST LLC

NRG WESTERN AFFILIATE SERVICES INC.

OSWEGO HARBOR POWER LLC

PADOMA WIND POWER, LLC

RELIANT ENERGY POWER SUPPLY, LLC

RELIANT ENERGY RETAIL HOLDINGS, LLC

RELIANT ENERGY RETAIL SERVICES, LLC

RELIANT ENERGY SERVICES TEXAS, LLC

RELIANT ENERGY TEXAS RETAIL, LLC

RE RETAIL RECEIVABLES, LLC

RERH HOLDINGS, LLC

SAGUARO POWER LLC

SAN JUAN MESA WIND PROJECT II, LLC

SOMERSET OPERATIONS INC.

SOMERSET POWER LLC

TEXAS GENCO FINANCING CORP.

TEXAS GENCO GP, LLC

TEXAS GENCO HOLDINGS, INC.

TEXAS GENCO OPERATING SERVICES, LLC

VIENNA OPERATIONS INC.

VIENNA POWER LLC

WCP (GENERATION) HOLDINGS LLC

WEST COAST POWER LLC

By: /s/ Christopher Sotos

Name:  Christopher Sotos

Title:  Treasurer

GCP FUNDING COMPANY, LLC

TEXAS GENCO LP, LLC

By: /s/ Christopher Sotos

Name:  Christopher Sotos

Title:  Management Board Member

NRG SOUTH TEXAS LP

By: Texas Genco GP, LLC, its General Partner

By: /s/ Christopher Sotos

Name:  Christopher Sotos

Title:  Treasurer

TEXAS GENCO SERVICES, LP

By: New Genco GP, LLC, its General Partner

By: /s/ Christopher Sotos

Name:  Christopher Sotos

Title:  Treasurer

NRG CONSTRUCTION LLC

By: /s/ Rachel Smith

Name:  Rachel Smith

Title:  Treasurer

Attest:

By: /s/ Tanuja M. Dehne

Name:  Tanuja M. Dehne

Title:  Corporate Secretary

LAW DEBENTURE TRUST COMPANY OF NEW YORK,

as Trustee

By: /s/ James D. Heaney

Name: James D. Heaney

Title: Managing DirectorEX-4.4

THIRTY-FIRST SUPPLEMENTAL INDENTURE FOR

ADDITIONAL SUBSIDIARY GUARANTEES

Thirty-First Supplemental Indenture (this “Supplemental Indenture for Additional
Guarantees”), dated as of April 16, 2010, among Carbon Management Solutions LLC, Clean Edge Energy
LLC and NRG Artesian Energy LLC (each a “Guaranteeing Subsidiary” and together the “Guaranteeing
Subsidiaries”), each an indirect subsidiary of NRG Energy, Inc., a Delaware corporation (the
“Company”), the Company, the Existing Guarantors set forth on the signature page hereto (the
“Existing Guarantors”) and Law Debenture Trust Company of New York, as trustee under the indentures
referred to below (the “Trustee”).

W I T N E S S E T H

WHEREAS, the Company has heretofore executed and delivered to the Trustee an indenture (the
“Base Indenture”), dated as of February 2, 2006, between the Company and the Trustee, as amended by
a Twenty-Second Supplemental Indenture (the “Twenty-Second Supplemental Indenture”), dated as of
June 5, 2009, among the Company, the Guarantors named therein and the Trustee, providing for the
original issuance of an aggregate principal amount of $700 million of 8.50% Senior Notes due 2019
(the “Initial Notes”), and, subject to the terms of the Twenty-Second Supplemental Indenture,
future unlimited issuances of 8.50% Senior Notes due 2019 (the “Additional Notes,” and together
with the Initial Notes, the “Notes”), a twenty-third supplemental indenture, dated as of July 14,
2009, among the Company, the Existing Guarantors and the Trustee (the “Twenty-Third Supplemental
Indenture”) and a twenty-seventh supplemental indenture, dated as of October 5, 2009, among the
Company, the Existing Guarantors and the Trustee (the “Twenty-Seventh Supplemental Indenture” and
together with the Base Indenture, the Twenty-Second Supplemental Indenture and the Twenty-Third
Supplemental Indenture, the “Indenture”);

WHEREAS, the Indenture provides that under certain circumstances the Guaranteeing Subsidiaries
shall execute and deliver to the Trustee a supplemental indenture pursuant to which the
Guaranteeing Subsidiaries shall unconditionally guarantee all of the Company’s Obligations under
the Notes and the Indenture (the “Additional Guarantees”); and

WHEREAS, pursuant to Section 4.17 of the Twenty-Second Supplemental Indenture, the Trustee,
the Company and the Existing Guarantors are authorized and required to execute and deliver this
Supplemental Indenture for Additional Guarantees.

NOW THEREFORE, in consideration of the foregoing and for good and valuable consideration, the
receipt of which is hereby acknowledged, the Guaranteeing Subsidiaries, the Trustee, the Company
and the Existing Guarantors mutually covenant and agree for the equal and ratable benefit of the
Holders of the Notes as follows:

1. Capitalized Terms. Unless otherwise defined in this Supplemental Indenture for Additional
Guarantees, capitalized terms used herein without definition shall have the meanings assigned to
them in the Indenture.

2. Agreement to be Bound; Guarantee. The Guaranteeing Subsidiaries hereby become parties to
the Supplemental Indenture as Guarantors and as such will have all of the rights and be subject to
all of the Obligations and agreements of a Guarantor under the Indenture. The Guaranteeing
Subsidiaries hereby agree to be bound by all of the provisions of the Supplemental Indenture
applicable to a Guarantor and to perform all of the Obligations and agreements of a Guarantor under
the Supplemental Indenture. In furtherance of the foregoing, the Guaranteeing Subsidiaries shall
be deemed Guarantors for purposes of Article 10 of the Supplemental Indenture, including, without
limitation, Section 10.02 thereof.

3. NEW YORK LAW TO GOVERN. THE INTERNAL LAW OF THE STATE OF NEW YORK SHALL GOVERN AND BE USED
TO CONSTRUE THIS SUPPLEMENTAL INDENTURE FOR ADDITIONAL GUARANTEES BUT WITHOUT GIVING EFFECT TO
APPLICABLE PRINCIPLES OF CONFLICTS OF LAW TO THE EXTENT THAT THE APPLICATION OF THE LAWS OF ANOTHER
JURISDICTION WOULD BE REQUIRED THEREBY.

4. Counterparts. The parties may sign any number of copies of this Supplemental Indenture for
Additional Guarantees. Each signed copy shall be an original, but all of them together represent
the same agreement.

5. Effect of Headings. The Section headings herein are for convenience only and shall not
affect the construction hereof.

6. The Trustee. The Trustee shall not be responsible in any manner whatsoever for or in
respect of the validity or sufficiency of this Supplemental Indenture for Additional Guarantees or
for or in respect of the recitals contained herein, all of which recitals are made solely by the
Guaranteeing Subsidiaries and the Company.

7. Ratification of Indenture; Supplemental Indenture for Additional Guarantees 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 for Additional Guarantees shall form a part of the Indenture
for all purposes, and every Holder of Notes heretofore or hereafter authenticated and delivered
shall by bound hereby.

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

Guaranteeing Subsidiaries:

CARBON MANAGEMENT SOLUTIONS LLC

By: /s/ Christopher Sotos

Name: Christopher Sotos

Title: Vice President & Treasurer

CLEAN EDGE ENERGY LLC

By: /s/ Christopher Sotos

Name: Christopher Sotos

Title: Vice President & Treasurer

NRG ARTESIAN ENERGY LLC

By: /s/ Christopher Sotos

Name: Christopher Sotos

Title: Vice President & Treasurer

Issuer:

NRG ENERGY, INC.

By: /s/ Christopher Sotos

Name: Christopher Sotos

Title: Vice President & Treasurer

Existing Guarantors:

ARTHUR KILL POWER LLC

ASTORIA GAS TURBINE POWER LLC

BERRIANS I GAS TURBINE POWER LLC

BIG CAJUN II UNIT 4 LLC

CABRILLO POWER I LLC

CABRILLO POWER II LLC

CHICKAHOMINY RIVER ENERGY CORP.

COMMONWEALTH ATLANTIC POWER LLC

CONEMAUGH POWER LLC

CONNECTICUT JET POWER LLC

DEVON POWER LLC

DUNKIRK POWER LLC

EASTERN SIERRA ENERGY COMPANY

EL SEGUNDO POWER LLC

EL SEGUNDO POWER II LLC

HANOVER ENERGY COMPANY

HOFFMAN SUMMIT WIND PROJECT, LLC

HUNTLEY IGCC LLC

HUNTLEY POWER LLC

INDIAN RIVER IGCC LLC

INDIAN RIVER OPERATIONS INC.

INDIAN RIVER POWER LLC

JAMES RIVER POWER LLC

KAUFMAN COGEN LP

KEYSTONE POWER LLC

LAKE ERIE PROPERTIES INC.

LANGFORD WIND POWER, LLC

LOUISIANA GENERATING LLC

MIDDLETOWN POWER LLC

MONTVILLE IGCC LLC

MONTVILLE POWER LLC

NEO CHESTER-GEN LLC

NEO CORPORATION

NEO FREEHOLD-GEN LLC

NEO POWER SERVICES INC.

NEW GENCO GP, LLC

NORWALK POWER LLC

NRG AFFILIATE SERVICES INC.

NRG ARTHUR KILL OPERATIONS INC.

NRG ASIA-PACIFIC, LTD.

NRG ASTORIA GAS TURBINE OPERATIONS, INC.

NRG BAYOU COVE LLC

NRG CABRILLO POWER OPERATIONS INC.

NRG CADILLAC OPERATIONS INC.

NRG CALIFORNIA PEAKER OPERATIONS LLC

NRG CEDAR BAYOU DEVELOPMENT COMPANY, LLC

NRG CONNECTICUT AFFILIATE SERVICES INC.

NRG DEVON OPERATIONS INC.

NRG DUNKIRK OPERATIONS INC.

NRG EL SEGUNDO OPERATIONS INC.

NRG GENERATION HOLDINGS, INC.

NRG HUNTLEY OPERATIONS INC.

NRG INTERNATIONAL LLC

NRG KAUFMAN LLC

NRG MESQUITE LLC

NRG MIDATLANTIC AFFILIATE SERVICES INC.

NRG MIDDLETOWN OPERATIONS INC.

NRG MONTVILLE OPERATIONS INC.

NRG NEW JERSEY ENERGY SALES LLC

NRG NEW ROADS HOLDINGS LLC

NRG NORTH CENTRAL OPERATIONS INC.

NRG NORTHEAST AFFILIATE SERVICES INC.

NRG NORWALK HARBOR OPERATIONS INC.

NRG OPERATING SERVICES, INC.

NRG OSWEGO HARBOR POWER OPERATIONS INC.

NRG POWER MARKETING LLC

NRG RETAIL LLC

NRG ROCKY ROAD LLC

NRG SAGUARO OPERATIONS INC.

NRG SOUTH CENTRAL AFFILIATE SERVICES INC.

NRG SOUTH CENTRAL GENERATING LLC

NRG SOUTH CENTRAL OPERATIONS INC.

NRG TEXAS C&I SUPPLY LLC

NRG TEXAS LLC

NRG TEXAS HOLDING INC.

NRG TEXAS POWER LLC

NRG WEST COAST LLC

NRG WESTERN AFFILIATE SERVICES INC.

OSWEGO HARBOR POWER LLC

PADOMA WIND POWER, LLC

RELIANT ENERGY POWER SUPPLY, LLC

RELIANT ENERGY RETAIL HOLDINGS, LLC

RELIANT ENERGY RETAIL SERVICES, LLC

RELIANT ENERGY SERVICES TEXAS, LLC

RELIANT ENERGY TEXAS RETAIL, LLC

RE RETAIL RECEIVABLES, LLC

RERH HOLDINGS, LLC

SAGUARO POWER LLC

SAN JUAN MESA WIND PROJECT II, LLC

SOMERSET OPERATIONS INC.

SOMERSET POWER LLC

TEXAS GENCO FINANCING CORP.

TEXAS GENCO GP, LLC

TEXAS GENCO HOLDINGS, INC.

TEXAS GENCO OPERATING SERVICES, LLC

VIENNA OPERATIONS INC.

VIENNA POWER LLC

WCP (GENERATION) HOLDINGS LLC

WEST COAST POWER LLC

By: /s/ Christopher Sotos

Name:  Christopher Sotos

Title:  Treasurer

GCP FUNDING COMPANY, LLC

TEXAS GENCO LP, LLC

By: /s/ Christopher Sotos

Name:  Christopher Sotos

Title:  Management Board Member

NRG SOUTH TEXAS LP

By: Texas Genco GP, LLC, its General Partner

By: /s/ Christopher Sotos

Name:  Christopher Sotos

Title:  Treasurer

TEXAS GENCO SERVICES, LP

By: New Genco GP, LLC, its General Partner

By: /s/ Christopher Sotos

Name:  Christopher Sotos

Title:  Treasurer

NRG CONSTRUCTION LLC

By: /s/ Rachel Smith

Name:  Rachel Smith

Title:  Treasurer

Attest:

By: /s/ Tanuja M. Dehne

Name:  Tanuja M. Dehne

Title:  Corporate Secretary

LAW DEBENTURE TRUST COMPANY OF NEW YORK,

as Trustee

By: /s/ James D. Heaney

Name:  James D. Heaney

Title:  Managing Director

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