Energy company SSE Power - which has around 1 million SWALEC customers in Wales - says fuel bills will be cut by around £50 a year on average.
Prices are due to drop from March 24th following a government decision to change green levies.
SSE says it will cost less to supply people with energy in 2014/15 and those on variable tariffs will see their rates cuts by 3.5%.
That means the annual bill for a typical dual fuel customer, averaged across all regions, will come down from £1,224 to £1,174 says SSE.
Unlike some other energy providers SWALEC customers with fixed and capped price tariffs will also have their rates cut by the same amount.