Company chief executive, David Baldwin said on Wednesday that the restart of the unit, one of four at the station, was one way Contact could contribute to meeting winter peak demand at a time when hydro storage levels were very low - currently the worst since the 1992 power crisis.

Hydro-electricity can supply up to about 60% of New Zealand's power needs, while gas-fired stations can contribute up to about 30%.

Baldwin said Contact was confident the unit would return to service in early June for peak winter electricity demands.