The operator of the national electricity grid says it lost millions of dollars dealing with last year's dry winter.
On Friday, Transpower announced an after-tax operating surplus of $67 million for the second half of last year.
There are concerns that some electricity companies may have profited from the shortage of power over winter, when people across the country were told to cut back their usage.
But Transpower chief executive Patrick Strange says that, in effect, the company's revenue is effectively fixed by the Commerce Commission, and that costs over the winter rose steeply.
Transpower says last winter cost it between $25 million and $30 million.
Meanwhile, state-owned power companies have all reported underlying profits for the six months to December.
Electricity generator and retailer Mighty River Power made underlying profits of $154 million. One-off accounting revisions cut the final profit to slightly more than $30 million.
Meridian reported an underlying profit of $85 million - although that became a $20 million loss after accounting revisions.
Genesis Energy, the third-biggest energy company, made a profit of $43 million.
Call for electricity rebate
The Progressive Party is calling on state-owned energy companies to give some of their profits back to lower-income households.
Party leader Jim Anderton says the companies are in a powerful position because they can simply raise prices to meet demand.
He says large companies spoke about doing their share during the economic downturn at last month's employment session.
Mr Anderton is calling on the power companies to give lower-income households a $200 winter rebate, either voluntarily or under Government order.