Electricity generator and retailer Mighty River Power is changing its name to Mercury, in a move that underlines the increasing retail focus of the country's largest power companies.

Known as MRP since it was split out from Electricity Corp in 1999, the "mighty river" reference was to the eight Waikato River hydro power stations the company inherited in the split, but it kept the Mercury retail brand it inherited in Auckland from the old Auckland Electric Power Board, where it remains the dominant supplier.

The company was the first of three state-owned power companies to be partially privatised in the last term of the National-led government. It has invested heavily in geothermal electricity plants, is closing its one gas-fired power station, at Southdown in Auckland, and is seeking industry leadership on the potential for New Zealand to switch much of its private vehicle fleet to electric cars.

The rebranding will occur progressively from later this year, with a new iteration of the Mercury brand, and would "bring the company's near century-long heritage together with our customer-driven innovation," said chief executive Fraser Whineray.


One-off costs associated with the brand change would be offset by cost-savings by removing duplication and consolidating focus under the single Mercury brand.

Chair Joan Withers said there had been "remarkable loyalty" from Mighty River Power owners in the three years since the company listed on the stock exchange.

Withers said about 85 per cent of the original shareholders from listing were still with the company.

"Mighty River Power is the most widely-owned business in New Zealand with 95,000 shareholders. Their shareholding will continue under the Mercury name and we are looking forward to introducing them to the new brand," she said.