Mighty River Power says sales rose 12% in the three months to December boosted by a jump in residential and commercial volumes.
The wholesale market price fell as a result of high inflows into South Island hydro lakes.
Mighty River Power said this affected the average price it received for its total generation sales which fell by 19% to $66 dollars a megawatt hour.
In response, Mighty River generated more from its lower cost hydro and geothermal plants, and less from its Auckland gas-fired power station.
The energy company gained market share, with customer numbers increasing 2% to 391,000.
The state-owned energy firm is expected to be partly privatised in the first half of this year.