Long Island Power Authority has overcharged its customers by $231 million due to a faulty formula it used to calculate charges for power that seeps from its electric grid.
LIPA has begun returning $129 million of the money through incremental rate cuts spread over three years, according to Newsday.
Beginning in April, customers will see an average $2.85 reduction in their monthly bill for the rest of the year, and $1.50 a month for 2012 and 2013.
LIPA approved a measure to change the way it calculates the charges at a meeting in January.
LIPA's interim chief executive, Michael Hervey, says the company became aware of the "lost'' power last summer.