Big Six utility ScottishPower has reported losing about 200,000 customers in the last year.
The energy firm said the number of accounts it held fell from 5.3 million to 5.1 million as it faced tougher competition and increased pressure from new entrants to the market.
The reduction contributed to its retail supply division’s earnings falling by around 51% to £98 million.
Earnings from power generation fell by 36% to £23 million, following the closure of a number of coal-burning plants associated with the business.
Despite this, earnings from the company’s renewables division rose to £316 million, an increase of 46%. This was largely driven by surging wind output and the installation of new facilities.
Keith Anderson, the UK subsidiary’s Chief Corporate Officer, said: “We now have more than 2GW of wind power capacity and the £2.5 billion East Anglia ONE offshore wind farm is well into construction.
“Over £600 million was also invested in to our networks business last year, as we continue to deliver smart and efficient grids capable of supporting the UK’s future energy needs.”
Parent company Iberdrola plans to invest €32 billion (£28.3bn) in the energy sector between 2018 and 2022 to build solid foundations for sustainable growth in the future.