ARACAJU, Brazil, July 24 (Reuters) - Brazilian energy firm Eneva expects to invest some 4 billion reais ($711.33 million) to expand the capacity of its Celse thermoelectric power pant if it wins an upcoming government auction, Chief Marketing Officer Marcelo Lopes said.

The company will participate in the so-called power reserve auction, which provides extra capacity for peak-demand hours, and would work to expand Celse's capacity to 2.8 gigawatts (GW) from the current 1.6 GW if it wins it, according to Lopes.

"We tend to be quite competitive in this auction," the executive told Reuters in an interview on Tuesday, citing unspecified internal budget estimates. (Reporting by Marta Nogueira; Editing by Sarah Morland)