22 SEP 2026
Author: Jemesa Landers
New Zealand already gets most of its electricity from renewable sources, but there are still times when the system needs backup. Thermal generation can help when electricity demand is high, hydro lake levels are low, wind drops, or there is not enough renewable generation available at the exact time people need power.
That doesn’t mean thermal generation is the long-term goal. The challenge is to keep the lights on while New Zealand builds more renewable generation, storage, transmission and flexible ways of using electricity.
So while renewable electricity does most of the heavy lifting, thermal generation is still part of the backup system that helps keep power available when New Zealand needs it most.
Thermal electricity generation uses heat from fuel to make electricity. In New Zealand, this usually means gas, coal or diesel.
It’s different from geothermal generation. Geothermal also uses heat to make electricity, but that heat comes from the earth and is treated as renewable.
A simple way to think about it is: thermal generation burns fuel to create heat, while geothermal generation uses natural heat from underground.
Most of New Zealand’s electricity comes from renewable sources, especially hydro, geothermal and wind, with solar growing too.
But the renewable share isn’t fixed. It changes depending on rainfall, hydro storage, wind, sunshine, demand, plant availability and the time of year.
That means the mix of electricity generation can look different from season to season. In a wet, windy year, more electricity may come from renewable sources. In a dry or still period, thermal generation may play a bigger role.
Electricity has to be available at the same time people need it. That matters most on cold mornings, winter evenings, dry periods or still days when renewable generation may not be producing as much.
Hydro, wind, solar and geothermal all play important roles, but they don’t always respond in the same way. Hydro depends on rain and lake storage, wind depends on the weather, solar depends on daylight, and geothermal is steady but less flexible for sudden peaks.
That’s where thermal generation can still help. It can provide backup when the system needs extra electricity quickly, helping keep supply reliable while New Zealand builds more renewables, storage and smarter ways to manage demand.
For customers, the point is simple: electricity needs to be reliable, affordable and lower emissions over time. It’s not enough to focus on only one of those things.
If the system moves too slowly, emissions stay higher for longer. If it moves too quickly without enough renewable generation, storage and network capacity ready, customers could face reliability or cost issues.
That’s why the transition needs to keep moving, while still making sure homes, schools, hospitals and businesses have the electricity they need.
Over time, New Zealand should need less fossil-fuelled generation as more renewable electricity is built and the system becomes more flexible.
That will take a mix of practical changes: more geothermal, wind and solar generation, better storage, stronger electricity networks, more efficient homes and businesses, and plans that reward people for shifting some power use away from peak times.
There probably isn’t one single fix. The goal is to make thermal generation less necessary by giving the electricity system more clean, reliable options to call on.
No. Fossil-fuelled thermal generation uses fuels like gas, coal or diesel, so it is not renewable. Geothermal generation is different: it also uses heat to make electricity, but the heat comes from underground and is considered renewable.
Batteries are useful, especially for short bursts of extra supply or shifting electricity from one part of the day to another. But some gaps last much longer, such as dry periods when hydro inflows are low for weeks or months. Those gaps need more than short-term battery storage on its own.
New Zealand’s electricity system is already highly renewable, but it is not 100% renewable all the time. Thermal generation still plays a backup role when renewable output is lower or demand is higher.
Think of it as backup power for the electricity system. New Zealand uses lots of renewable electricity, but thermal generation can still help when the system needs extra supply at short notice.
Suggested next step: Want to see how Contact is helping build a more renewable electricity system? Explore the Energy Upgrade to learn about the projects supporting New Zealand’s energy future or visit the Electricity Authority to see New Zealand’s investment pipeline.
For independent complaint or pricing advice, UDL, Billy & Powerswitch can help.
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