Prime Minister John Key says the government has "put its best foot forward" and will offer Rio Tinto no more than the short-term subsidy offered last week.

Rio Tinto is doubtless more than happy that the Government has stepped in to try to broker a deal over the electricity supply contract for the Tiwai Pt aluminium smelter.

The Tiwai Pt power price stoush will probably have a small negative effect on the price of Mighty River - but it's not a showstopper say sharemarket analysts.

The Government has opened discussions with Tiwai Point aluminium smelter's ultimate owners Rio Tinto in a bid to broker a deal after talks between the smelter and Meridian Energy reportedly broke down.

Tiwai Pt aluminium smelter's owners have contradicted a report from Meridian, saying they think a power deal can be agreed on.

Potential investors in Mighty River Power, Genesis Energy and Meridian will be exposed to the financial impacts caused by any new charges linked to water or geothermal use and land resumption.

It is folly to press on with the partial privatisation of the state-owned power companies when the future of the Tiwai Pt aluminium smelter is unresolved, writes Brian Fallow.

Meridian Energy is considering the sale of its 50 per cent stake in the A$1 billion Macarthur wind farm in Australia.

Meridian Energy is not a private enterprise but in negotiation with Rio Tinto it must act like one. If it can get a better power price elsewhere, Tiwai smelter must go.

Rio Tinto's attempt to renegotiate New Zealand's largest electricity contract, for its aluminium smelter at Bluff, comes as the company's chief executive warns of "difficult decisions" ahead.