The result comes at a time when MRP is broadening its generation base to include more renewables – hydro, wind and geothermal - more natural gas, and perhaps coal.

MRP generated its profit on the back of operating revenue of NZ$684.4 million, which was up from $599.2 million last year.

Company chief executive Doug Heffernan yesterday said the result was driven by healthy inflows into the Waikato-Taupo hydro catchment area in the first half of the year, as well as continued retail growth. Customer numbers for Mighty River's Mercury Energy retail business climbed from 300,000 to 317,000 over the year.

MRP said it had reinvested most of the profit as it was exploring options for growing its generation capacity and establishing a diverse supply portfolio.

"We are looking at all the energy options available," Heffernan said.

"In looking at these options there is a need to get the balance right and recognise the trade-offs between economic, social and environmental considerations."

Expanding wind, coal and gas generation could all be on the cards, with additional wells already drilled at MRP’s Rotokawa geothermal station.

The company is looking at restarting the mothballed Marsden B power station using coal. It has also filed consent applications for a 70MW geothermal plant at Kawerau, and has formed a partnership with Palmerston North City Council for a potential wind farm development at Turitea in the Manawatu.

As well, Swift Energy New Zealand and MRP are believed to be near the Eocene-aged target depth at Tawa-A1 – the first of three joint venture onshore Taranaki gas exploration wells aimed at securing more gas for MRP, primarily for its gas-fired Southdown power station.