New Zealand's two biggest cities have been singled out in a new report highlighting the world's best users of renewable energy.

But Auckland Council's sustainability tsar says our cities run the risk of being overtaken by those in other countries if "we keep coasting".

Auckland, Wellington - and Kapiti - were named among more than 100 towns and cities whose electricity was at least 70 per cent sourced from renewable energy.

The three New Zealand centres were powered by around 80 per cent renewable electricity, with 57 per cent coming from hydro and between 16 and 17 per cent coming from geothermal energy.

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While they ranked ahead of some cities on the list - such as Aspen in the US, Nakuru in Kenya and Zurich in Switzerland - the centres fell behind world leaders for renewables that now sourced 100 per cent of their electricity from clean energy.

Those included Brasilia (Brazil), Basel (Switzerland), Reykjavik (Iceland), Winnipeg (Canada), Burlington (US), Medellin (Colombia), Bolzano (Italy) and Fafe (Portugal).

The report, by global environmental impact non-profit CDP, covered 570 of the world's towns and cities and found the number that reported over 70 per cent renewable electricity had doubled since 2015.

Auckland Council's chief sustainability officer, John Mauro, said the report wasn't surprising, given New Zealand's electricity grid was usually between 80 and 85 per cent sourced from renewables.

"What's encouraging is that we're continuing to bring new renewable sources on-line and driving innovation in R&D globally."

Replacing New Zealand's former 90 per cent by 2025 target with an aspirational drive for 100 per cent, along with the new Zero Carbon Bill, showed the Government wanted to step up its ambition, he said.

Mauro believed that goal could be reached – and new breakthroughs in enabling increasingly localised renewable energy, through storage, district systems and smart grids, was making the future look brighter.

"Or at least possible," he added, "if we want it badly enough and are willing to put in the policy drivers, framework and signals to get there.

"What's discouraging is that we're generally and perhaps lazily riding our geographic luck – hydropower is about half of our total electricity supply, depending on the year.

"We've been coasting for a while, unlike other countries - Denmark comes to mind - where a really hard and deliberate push on energy supply is happening to push up to 30 per cent renewable by 2020: it was 17 per cent in 2005.

"We had a head start with our historical energy luck compared to Denmark and they'll catch us if we keep coasting."

A new Stats NZ report out earlier today found how, nationwide, electricity generated from renewables accounted for 82 per cent of total.

Mauro believed that, while a renewable electricity target was important in the short-term, a renewable energy target was important as it took in "the whole picture".

Wellington has been previously ranked among the world's greenest cities. Photo / File
Wellington has been previously ranked among the world's greenest cities. Photo / File

"An ambitious renewable energy target - or Zero Carbon Bill - simply must take into account more than just how we use electricity but how we design and plan our cities and towns, how we get around, and how we create a far more circular economy.

"This could be done at the national level, but there's no reason it couldn't be local – such as in Auckland - as well.

READ MORE: The French Connection: Making Auckland Green Again

"The future of energy is local. It's not likely that solar PV on all roofs will be viable, desirable or even efficient – or even that district heating or cooling will make sense everywhere.

"But it is undeniable that the future of energy generation and supply is and will be dramatically disrupted."

According to the World Economic Forum, unsubsidised renewables were the cheapest source of electricity in 30 countries in 2017, with renewables predicted to be consistently more cost effective than fossil fuels globally by 2020.

'Immense potential' for cities

Burlington - Vermont's largest city - now obtained all of its electricity from wind, solar, hydro, and biomass, while Iceland's capital Reykjavik sourced all electricity from hydropower and geothermal, and was now working to make all cars and public transit fossil-free by 2040.

Iceland had almost entirely transitioned to clean energy for power and household heating.

Most electricity in Basel, powered by its own energy supply company, came from hydropower and 10 per cent from wind.

CDP's analysis comes on the same day the UK100 network of local government leaders announced that over 80 UK towns and cities have committed to 100 per cent clean energy by 2050, including Manchester, Birmingham, Newcastle, Glasgow and 16 London boroughs.

In the United States, 58 cities and towns have now committed to transition to 100 per cent clean, renewable energy, including big cities like Atlanta (Georgia) and San Diego (California).

Earlier this month, US municipalities Denton (Texas) and St Louis Park (Minnesota), became the latest communities to establish 100 per cent renewable energy targets.

In addition to these recent pledges, CDP data shows a further 23 global cities targeting 100 per cent renewable energy.

Showing a diverse mix of energy sources, 275 cities are now reporting the use of hydropower, with 189 generating electricity from wind and 184 using solar photovoltaics.

A further 164 use biomass and 65 geothermal.

Much of the drive behind city climate action and reporting comes from the more than 7000 mayors who signed up to The Global Covenant of Mayors for Climate and Energy who have pledged to act on climate change.

"Cities are responsible for 70 per cent of energy-related CO2 emissions and there is immense potential for them to lead on building a sustainable economy," said CDP's director of cities, Kyra Appleby.

"Reassuringly, our data shows much commitment and ambition.

"Cities not only want to shift to renewable energy but, most importantly - they can."

Auckland has a current goal of achieving 40 per cent less greenhouse gas emissions, below 1990 levels, by 2040.

It also wasn't the first time Wellington had been named in a global index.

Arcadis' recent Sustainable Cities Index, which ranked 100 of the world's cities, put the capital sixth overall, reflecting strong results across the board, and particularly good results when it came to environmental risks, air pollution and greenhouse gas emissions.