New Zealand has about 80 MW of solar, up 17 MW in the past year, according to Electricity Authority data. But only about 16 percent of that is at commercial and industrial sites.

EECA chief executive Andrew Caseley says residential uptake of solar will continue even though it is not a “one-way, sparkly street” in terms of affordability for all households.

Utility-scale projects are unlikely, given the high cost of land in New Zealand, but there is a lot of potential for solar arrays at commercial sites, he told delegates at the Sustainable Energy Association conference in Auckland on Friday.

“There is still a hell of a lot of rooftops, whether it be on shopping malls or warehouses on the outskirts of airfields - wherever they might be - where scale solar deployment I think is still a very practical and realistic option for us to tap into.”

He cited the example of the Corrections Department, which is looking at solar as an option for lowering the cost of summer air conditioning at some of its prisons.

“We just need to broaden our thinking about where that potential exists and where some of these opportunities are,” Caseley said.

One new solar array is installed in New Zealand every 25 minutes according to the association, which represents solar and battery suppliers and installers.

But that relatively slow uptake frustrates environmentalists who point to the extensive subsidies that have been offered in Australia, the UK and Europe – where electricity generation remains heavily reliant on fossil fuels. Greenpeace is currently campaigning for taxpayer subsidies and low-interest loans to put panels on 500,000 homes by 2030.

In Australia, the state government of Victoria has announced an A$1.2 billion programme to subsidise solar and battery systems for 650,000 homes during the next decade.

Victoria’s electricity generation remains heavily dependent on brown coal and is the most polluting of any state. The state is aiming to have 25 percent of its generation renewable by 2020 and 40 percent by 2025. New Zealand’s electricity was 85 percent renewable in the June quarter.

Simon Corbell, Victoria’s state renewable energy advocate, defended the use of subsidies, saying most of the benefit goes to average income earners. And he said developing programmes at scale, as with Victoria’s recent auction for capacity from large-scale wind and solar projects, drives down costs, creates jobs and accelerates the establishment of local capability.

While New Zealand appears to be on the right track to meet its renewable goals, Corbell urged delegates not to be complacent.

Greater electrification of the economy would need more generation capacity, which requires consistent policy. He observed that a generation investment “strike” in Australia in 2014 and the lack of affordable domestic gas supplies, had contributed to the jump in that country’s energy costs.

Vector chief executive Simon Mackenzie said there is still a bias within the electricity industry against solar. Even last month’s issues paper from the Electricity Price Review had been dismissive of the scope for utility-scale projects here.

Mackenzie said the industry has to be open to thinking about large-scale solar in new ways which don’t sacrifice productive land. A random aerial view of Manukau showed ample residential and commercial roof space, as well as potential for the floating solar structures now being deployed overseas, he said.

Solar and battery costs are falling rapidly and Mackenzie said Vector needs to use those technologies if it is to keep up with Auckland’s rapid population growth without building 40-year poles, cables and transformers, which could be uneconomic within 20 years, if not 10.

And if households are to really benefit from solar there needs to be a market that lets them buy and sell surplus power with neighbours, he said. That would sit “parallel” to the existing network.

EECA’s Caseley said solar has a growing role to play in New Zealand, but it is not the country’s only option. And he said the authority’s primary focus has to be on electrification of industry and transport which offer bigger potential climate benefits.

Care is also needed to ensure that the cheapest sources of renewable generation are deployed as the country moves toward 100 percent clean power generation, and that consumers pay a fair share of the fixed costs of distribution as electricity networks are reshaped to cater for more electric vehicles, solar and batteries.

Energy affordability is already an issue for too many households and he sees “greater risk” if the country gets its generation supply mix wrong in coming years, he said.

“It’s a complex balancing act.”