Energy giant npower has been fined £125,000 for an error in reporting data related to two renewable energy subsidy schemes.

Ofgem said the fine was imposed after npower used incorrect information to calculate the amount of electricity it supplied to customers – under the Feed-in Tariff (FiT) and Renewables Obligation (RO).

As part of the RO, utilities are required to source a proportion of electricity supplied to customers from renewable sources while the FiT requires suppliers to provide an incentive to small-scale generators of renewable energy.

The Big Six supplier under-reported the amount by 0.08% in 2010-11 and by 0.28% in 2011-12 however it identified and reported the error to Ofgem and also took steps to prevent it from reoccurring, the watchdog said.

It added: “The size of today’s penalty takes into account that npower has already voluntarily forfeited Renewable Obligations Certificates valued at £896,900 and will make a late payment of £63,000 to account for the FIT reporting error.”

Paul Massara, CEO of npower said the energy firm discovered the error “during work to increase our controls around compliance reporting”.

He added: “Accurate reporting is extremely important to us – especially in areas of compliance – and we have assured Ofgem that the changes we have made to our controls and procedures will ensure this error does not happen again.”