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Power prices have risen by up to 10 per cent in the past year, and analysts warn more increases are likely at the end of winter.
Consumer New Zealand's Bill Whitley said retail electricity rates went up between 7 and 10 per cent in the year to March.
He said companies would be looking to make further increases as the wholesale price of electricity rose.
Retailers spoken to by the Weekend Herald said rising prices for coal and gas, low rainfall and the need to invest in new generating capacity would push power bills up again this year.
Another factor is lines company charges, which make up about 40 per cent of a typical power bill, though the figure varies from region to region. Electricity accounts for about 50 per cent, while national grid operator Transpower charges between 8 and 9 per cent.
This is how some of the main power companies see the year ahead:
Contact Energy: A company official said residential bills had gone up an average of 6 to 7 per cent in the past six months. Further rises of up to 8 per cent for some parts of the country would be needed this year to cover costs including higher gas prices and the company's commitment to spending $2.5 billion over the next five years on geothermal and wind generation.
Meridian Energy: Alan Seay said Meridian would probably put up prices again in September. He could not yet put a figure on the rise, but said price hikes in the past three years had been between 3 and 4 per cent.
TrustPower: Community relations officer Graeme Purches said residential prices went up between 4 and 9 per cent around the country in the past year, depending on the cost of local lines charges. Bay of Plenty customers received a 6.5 per cent price rise this month, while Nelson power bills recently went up 9 per cent. Mr Purches said price rises this year would be slightly above the rate of inflation, which is 3.4 per cent. Higher increases had been needed since 2002 to invest in new generating capacity.
Mercury Energy: A representative would not share any details about residential price increases, saying such details were commercially sensitive.
If higher prices lead consumers to cut power use, that may help the industry deal with worryingly low levels at vital South Island storage lakes. Hydro lakes were at 63 per cent of their average level this week, and a smattering of rain had added only a few days' worth of power to the country's electricity coffers.
Transpower boss Patrick Strange said the national grid operator was on guard in case of a dry winter. "From now on, demand goes up very strongly. All we're asking for is that people turn off the lights as they leave the room and switch off unused equipment."
Mr Seay said lake levels were still "some comfortable distance" above where they were in 1992, when the country had its last major power shortage. He likened this year's lake levels to 2003, when a lack of coal also reduced power generation at the Huntly power plant.
This year there is plenty of coal, but the power grid faces two new setbacks - the closure of Contact Energy's New Plymouth oil-fired power station and the de-commissioning of one of two systems running the Cook Strait power cable.
