Hawke's Bay lines company Unison is introducing an extra charge for solar panel users, in a move Greenpeace says is wrong.

People install the panels to reduce their power bills. But Unison fears this will reduce its income and make its assets hard to maintain, so it is bumping up its charges to make up the difference.

Photo: 123 RF

The electric lines industry has said many times that people using solar panels and batteries pay lower power bills, making less money available to pay for the electricity grid.

Yet most solar panel users still need that grid to be available as a fallback when solar power dries up overnight or on cloudy days.

Senior Unison manager Nathan Strong said his firm was acting now to protect its income and make sure the customer got a good idea of the real cost of providing an electricity network.

"Currently it costs us about $900 a year to serve a typical residential customer," he said.

"Under our old pricing approach, someone putting a solar panel on a roof would reduce their contribution by $300 and that $300 would have to be made up by someone who does not have solar panels on their roof."

Mr Strong said changing the rules brought fairness.

Unison said it was still calculating the exact figure, but network charges could rise by up to $150 each year.

From today, the scheme would affect the company's 110,000 consumers in Hawke's Bay, Taupo and Rotorua who put solar panels on their roof.

It would only happen if they used their panels to generate surplus power and feed it back into the national grid.

Greenpeace's Russel Norman said Unison was doing the wrong thing.

"The impact of Unison's solar tax is to change the economics around the installation of solar panels, when in the interests of climate change what we want to do is make it easier."

The move was incompatible with recent international pledges to reduce greenhouse gas emissions, Mr Norman said.

But the idea of charging solar power users extra money was an anathema to the Sustainable Electricity Association of New Zealand.

Chairman Brendan Winitana called the Unison action a solar tax.

"That solar tax is a 26 percent increase in a lines charge and we believe that is a very strong move to make, especially when the Electricity Authority called for submissions on distribution pricing," he said.

Unison said that was not correct and people would still save money on their power bills.

Solar panel installation company Solar City chief executive Andy Booth said Unison was being disingenuous and imposing an unfair tax.

"Customers who use low-energy light bulbs and energy efficient fridges to reduce their consumption aren't getting taxed, customers who put solar systems that generate power to reduce their energy consumption are. We believe fundamentally that's anti-competitive," he said.

Unison would be the first lines company to do something like this, but others were understood to have similar plans in train.

The company is a member of the the Electricity Networks Association and Its chief executive Graeme Peters said Unison was acting within its rights.

"Distributors are entitled to make their own decisions about pricing in their own areas," he said.

"But collectively, we are trying to bring about a menu of pricing options they can choose from."

There are 28 lines companies in New Zealand all facing falling revenue and static fixed costs.