Exhibit 3.121

State of Delaware

Secretary of State

Division of Corporations

Delivered 01:48 PM 05/19/2014

FILED 01:43 PM 05/19/2014

SRV 140656482 - 5143039 FILE

STATE OF DELAWARE

CERTIFICATE OF AMENDMENT

1.Name of Limited Liability Company: Green Mountain Energy Company (NY COM) LLC

2.The Certificate of Formation of the limited liability company is hereby amended as follows:

1. Name: The name of the Limited Liability Company is NRG Business Solutions LLC

IN WITNESS WHEREOF, the undersigned have executed this Certificate on the 19th day of May, A.D. 2014.

By:	/s/ Elizabeth McCormack
	Authorized Person(s)
Name:	Elizabeth McCormack
	Print or Type

State of Delaware

Secretary of State

Division of Corporations

Delivered 01:58 PM 04/20/2012

FILED 01:40 PM 04/20/2012

SRV 120455807 - 5143039 FILE

CERTIFICATE OF FORMATION

OF

GREEN MOUNTAIN ENERGY COMPANY (NY COM) LLC

1.Name: The name of the limited liability company is Green Mountain Energy Company (NY COM) LLC.

2.Registered Office: The address of its registered office in the State of Delaware is Corporation Trust Center, 1209 Orange Street, in the City of Wilmington 19801, County of New Castle. The name of its registered agent at such address is The Corporation Trust Company.

3.Organizer: The name and address of the sole organizer of the limited liability company is Lynne Przychodzki, NRG Energy, Inc., 211 Carnegie Center, Princeton, NJ 08540.

IN WITNESS WHEREOF, the undersigned has executed this Certificate of Formation of Green Mountain Energy Company (NY COM) LLC this 19th day of April, 2012.

/s/ Lynne Przychodzki

Lynne Przychodzki

Authorized Person