Power company Vector is unable to say how a so-called "world first" to light up the Auckland Harbour Bridge by solar power will work.
Two months ago, Vector and Auckland Council said the bridge would be the first in the world to be illuminated entirely by solar-stored energy.
The project partners said the bold plan to transform the city skyline at night and create a global attraction would be powered by 630 solar panels on top of North Wharf at Wynyard Quarter and a mega-storage battery.
I think it is very likely that the solar panels and battery simply feed into the grid at Wynyard Quarter and they take the power from grid just as they always have
"Powered by solar energy, it will reflect our commitment as a city to energy efficiency, sustainability and low carbon emissions," Auckland Mayor Phil Goff said two months ago.
At the same time, Vector chief executive Simon Mackenzie said the company's innovation in the energy sector had allowed it to develop the expertise to deliver a solar energy "world first".
A source in the electricity industry, who did not want to be named, said a lot of expensive cabling from the solar panels and battery would be needed from Wynyard Quarter to the bridge.
"I think it is very likely that the solar panels and battery simply feed into the grid at Wynyard Quarter and they take the power from grid just as they always have," the source said.
A spokesman for Vector said the solar and battery solution will easily power the requirements of the lights, but there will always be a connection to the power network for security of supply reasons.
Asked if there will be a direct power connection from the solar panels and battery to the bridge, the spokesman said the engineering works were still being finalised.
"There are a number of connection point options being considered, both direct and virtual," the spokesman said.
Vector has not provided more details about how the connection will work.
The project, estimated to cost $10 million, will transform the harbour bridge into spectacular displays for events like New Year's Eve and Auckland Pride Festival.
The bridge will join landmark buildings such the as the Sydney Opera House, Eiffel Tower and Empire State Building, which all light up in customised displays.
The planning, consenting and installation of nearly 90,000 LED lights and 200 floodlights on the bridge is expected to take several months. It is hoped the lights will be turned on at a special event before the end of the year.