May 6 (Reuters) - Power producer NRG Energy NRG.N on Wednesday missed Wall Street estimates for first-quarter adjusted profit, hurt by milder weather in Texas and increased costs.

The company's interest expenses in the quarter rose to $285 million from $163 million a year ago, impacted by costs related to the completed acquisition of power generation assets from investment firm LS Power in a deal valued at $12 billion.

Houston, Texas-based NRG's operating costs were up 33.4% to $9.93 billion.

The company expects commercial operations at the 415-megawatt T.H. Wharton facility in Texas, its first project, to begin by the end of May.

It plans to return $1 billion to shareholders through share repurchases and nearly $407 million through common stock dividends in 2026.

Separately, insider Robert Gaudette succeeded Larry Coben as the company's CEO on April 30.

NRG posted quarterly revenue of $10.26 billion, up from $8.59 billion a year ago.

Its Texas unit posted first-quarter adjusted core profit of $216 million, down from $299 million a year ago, amid mild winter weather that saw a nearly 30% decrease in heating degree days leading to lower retail load.

The company reaffirmed its 2026 adjusted earnings forecast of $7.90 to $9.90 per share.

Adjusted profit of $1.49 per share for the three months ended March 31 fell short of analysts' average estimate of $1.78, according to data compiled by LSEG.