A double-decker bus on the streets of Auckland. Wellington will soon have its own fully-electric versions (file photo).

The country's first fully-electric double-decker buses will now hit Wellington's streets much sooner than expected, but some say the capital is taking a big risk on the new technology.

Bus company Tranzit, which will begin operating 60 per cent of the Wellington region's commuter bus routes from July next year, said 10 electric double-decker buses will feature among its 234-strong fleet.

Those buses, which will run between the suburbs of Island Bay and Churton Park, will be joined by another 12 in 2021 and a further 10 added to routes in Brooklyn in 2020.

PIERS FULLER/STUFF Tranzit managing director Paul Snelgrove says he is "absolutely adamant" Wellington's fully-electric battery buses won't fail.

The 82-seat double-deckers will be fully charged overnight, topping up their batteries during the day at various charging stations across the network.

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They will be two metres shorter than Wellington's trolley buses and 1.3 metres shorter than its existing diesel buses, and will be required to negotiate the capital's hilly terrain.

Tranzit managing director Paul Snelgrove was confident the fully-electric battery buses would be up to the task.

"In our business, you've got to be confident, and you've got to produce your promises," he said.

"It's a pretty big undertaking, because the technology is pretty advanced. Wellington has had its issues with electric buses, but we're absolutely adamant we'll have them and if we don't, I'll stand up and take the stick for it."

TRANZIT Tranzit recently won the contract to take over most of Wellington's commuter bus services.

The rest of Tranzit's new fleet will be Euro 6 diesels, which the company said met the highest global emissions standards for non-electric buses.

Since signing the death warrant for Wellington's trolley buses in 2014, Greater Wellington Regional Council has been promising a transition to hybrid diesel-electric buses in 2018 before making the jump to fully-electric battery buses once the emerging technology had been fully proven.

The council has, on several occasions, described jumping straight from diesel to fully-electric battery buses in the short-term as too risky.

MONIQUE FORD/STUFF Greater Wellington Regional Council chairman Chris Laidlaw says the time has come to embrace fully-electric battery bus technology.

Public transport advocate Tony Randle said double-decker buses were "doubly risky" because of the extra weight they would carry on relatively weak roads.

There were very few fully-electric buses overseas, and those that did exist operated mostly in flat cities with wide roads.

"A hilly city with windy roads is the worst place to start off testing electric technology."

ROGER BLAKELEY/SUPPLIED Wellington's promised Wrightspeed electric hybrid bus fleet have been hit by a series of delays.

Investing in fully-electric double-deckers neglected more worthwhile initiatives such as more bus lanes, better signalling systems, and integrated ticketing.

"The one advancement that will happen is the one thing that won't make any difference to getting a better service."

But regional council chairman Chris Laidlaw said fully-electric buses were no longer considered the risk they once were.

MAARTEN HOLL/STUFF Wellington's electric trolley bus fleet will be retired at the end of October.

"We're beyond the stage of 'maybe it will [work], maybe it won't'. We're now ready to do it ... I'm very pleased about this."

Reducing carbon emissions was a key factor in the council's tender negotiations, and Tranzit had shown it was "deadly serious" about that, Laidlaw said.

"We can expect, and do expect, electric buses on the road next year."

Go Wellington operator NZ Bus is currently fitting a "significant number" of its 1100 buses in Auckland and Wellington with Wrightspeed motors, which operate mostly on rechargeable electric batteries. But this project has been hit by a series of recent delays.

Snelgrove said he was "absolutely adamant" there would be no problems with Tranzit's new buses.

"We've just come back from Europe and Asia to finalise our sourcing of new buses, and the technology we'll be using in these fully-electric buses – rather than hybrids – is proven to be effective and efficient."

The buses will be built by Tauranga-based company Kiwi Bus Builders, with a Chinese railway company providing the motors and Dutch company Heliox supplying the rapid charging technology.

Global company Microvast will provide the batteries.