Mighty River Power has delivered a nine-fold increase in first-half net profit.
The company made a $74 million net profit in the six months ended in December compared with $8m the year earlier.
But revenue fell 7 percent to $813m and full year profit expectations are down amid intense competition.
The revenue drop reflected subdued wholesale electricity prices and competitive pressure on pricing for residential and business customers.
Mighty River is forecasting a full year operating profit in the range of $480m-$500m.