The non-domestic sector saw profits increase to £112 million in 2013, up from £91 million in 2012, while the domestic supply business saw profits fall by 5 per cent, from £141 million in 2012, to £134 million last year.
Domestic sales margins also fell from 3.9 per cent in 2012, to 3.4 per cent in 2013.
This resulted in Npower’s profit increasing by 6 per cent to £246 million in 2013, up from £231 million in the previous year.
Npower added that costs for meeting the energy company obligation increased by 48 per cent, from £122 million in 2012 to £181 million in 2013, while there were also “substantial” increases in distribution and transportation costs.
The supplier said “good progress” was being made on the customer service problems that led to it issuing an apology to all of its customers in December.
Parent company RWE’s generation business in the UK saw profits fall from £158 million in 2012 to a loss of £65 million in 2013, due to “very challenging market conditions”.
This comes despite an investment of more than £1,650 million on two combined cycle gas turbines in 2011 and 2012.
Paul Massara, Npower’s chief executive, said: “Our generation business lost money and our domestic electricity and gas business saw profits decline.
“There are those who claim there are excess profits in energy, but these figures show a very different story.”
He added that the £790 million RWE invested into the UK – more than four fifths of which went into renewable energy projects – demonstrated the company’s commitment to Britain.
Parent company RWE recorded a net loss of €2.8 billion, the first time in more than 60 years it has not posted a profit.
RWE said the loss was attributed to the €4.8 billion write down of its fleet of coal and gas fired power plants across Europe.