Mighty River Power experienced 12 per cent growth in sales in the three months to December 31.

Most of the gain came from a 22 per cent increase in volume to business customers, compared to the December 2011 quarter, potentially indicating an uptick in economic activity in Auckland, where MRP is strongest and where Mercury Energy is based. MRP also showed customer growth in both the North and South Islands, with 391,000 customers in the north, compared with 383,000 a year earlier, and 43,000 southern customers, up from 37,000.

The company's combination of hydro-electric dams on the Waikato River and an increased portfolio of geothermal generation plant saw MRP increase its total electricity production by 6 per cent in the quarter, compared with the same period a year earlier.