Exhibit 99.1 NRG Energy, Inc. Reports Full Year 2023 Financial Results HOUSTON—February 28, 2024—NRG Energy, Inc. (NYSE: NRG) today reported Net Income for the three months ended December 31, 2023 of $482 million and a full year Net Loss of $202 million. The Net Loss was driven by unrealized non-cash mark- to-market losses on economic hedges due to large movements in natural gas and power prices. Adjusted EBITDA for full year 2023 was $3.3 billion, Net Cash Used by Operating Activities was $221 million, and ...