Solar panels are being built across New Zealand, but are more batteries needed to store the excess energy? File photo. Photo: Supplied / Genesis Energy
Renewable energy advocates say New Zealand could learn from the experience of Australia, where solar panels are so popular they sometimes produce more electricity than people can use.
One third of Australian households have rooftop solar panels, and there are panels on half of the homes in some states.
But only a small proportion have batteries that can store excess power when it is sunny and release it in times of high demand.
With battery prices falling, clean energy experts in New Zealand say there is an opportunity to install both solar and batteries at once to take pressure off the electrical grid during peak times.
Unlike New Zealand's 85 percent renewable power grid, Australia still gets 60 percent of its electricity from gas and coal.
But when it comes to building solar power, Australia is ahead.
Matt Ward of NZ solar company solarZero said the drop in battery prices meant New Zealand could increase its penetration of solar and batteries together - without subsidies - if there were better incentives to sell surplus electricity from batteries to the grid.
Ward said that would take pressure off hydro, gas and coal-fired electricity generation during times of tight supply.
SolarZero installs batteries with its solar panels, typically on a subscription arrangement in which the company keeps ownership of the panels and batteries on the customer's home.
This gave it the ability to draw on its network of batteries in times of high demand, to make more electricity available to anyone connected to the main power grid. The company said it made sure its own customers had enough electricity first.
The company called on its 15,000-strong network of batteries to give the electricity grid a boost last month, after New Zealanders were warned that the nation's power was in danger of running low in a cold snap.
However, Ward said solarZero does not currently get paid for sharing its electricity.
Both here and in Australian, batteries have typically been seen as too expensive to make sense for many households.
A subscription service like solarZero's removed the upfront cost, but as a consequence customers did not own the panels and batteries on their homes.
But Mike Casey of clean energy charity Rewiring Aotearoa said battery prices were falling quickly, and combined solar and battery systems were now the cheapest source of energy available to households - even including the upfront cost of buying the equipment.
Although it was the cheapest way to get electricity when averaged over 15 years, the cost of buying a solar and battery system can be a barrier for many, he said.
Casey said if households had better access to low-cost loans, they could buy household batteries themselves and take pressure off electricity generators by using their own power in times of shortage. They could also sell their surplus to others, taking more pressure off the grid when supply is tight.
In Australia, some states have started installing big batteries - large enough to power entire neighbourhoods - to store excess solar from the electricity grid during sunny times and release it as needed, one of the ways the country plans to burns less gas and coal.
New Zealand's first grid-scale battery began operating near Waikato's Huntly power station this year and electricity retailer Meridian is building another one in Northland, near the site of a planned solar farm.