Every winter the power bill climbs, and every winter it feels like a mystery dressed up as a utility. The short version is that two different things happen at once. You use a lot more electricity, and the market you buy it from gets tighter at exactly the same time. Understanding both is the difference between dreading the bill and knowing what is actually on it.
The good news this year is that the scary version, a repeat of the 2024 winter when low lakes and dwindling gas sent wholesale prices soaring, is not what is happening. The lakes are full. The bill still goes up anyway, and here is why.
Most of the jump is simply you using more
The largest reason a winter bill is bigger is the least exciting one. Heating is the single biggest load in a New Zealand home, and in June and July it runs for hours it never runs in January. Add lights on by 5pm, hot showers that start from colder water, and the clothes dryer earning its keep, and a household can comfortably use half as much power again as it does in summer.
None of that shows up as a higher price. It is volume. Before you blame the market or the retailer, the first culprit is the heat pump that has been on since you got home. That is also the part you have the most control over.
The wholesale market tightens in the cold
The second reason is hidden from most households, because you pay a retailer a fairly steady rate rather than the live wholesale price. But that wholesale price is the weather underneath your bill, and in winter it gets rougher.
The spot price moves with demand through the day. In a recent week the average wholesale price at Ōtāhuhu was about $69 a megawatt hour, but it spiked to $213 at 7:30 on a Friday morning, as the whole country switched on heaters and kettles at once. Those twice-daily peaks, morning and early evening, are when the grid strains hardest and the most expensive generation has to switch on to cover the gap.
Where your winter power comes from
What fills that gap is the fuel mix, and it shifts week to week. In a recent week hydro supplied about 59 percent of the country’s electricity, geothermal a steady 25 percent, wind around 6 percent and thermal, mostly gas and coal, about 6 percent. The trouble is that the small thermal slice does the heavy lifting at exactly the wrong moments, when the wind drops and demand peaks on a still, cold evening.
This is where the country’s gas problem matters. Domestic gas production has been falling for five years, which makes that firming fuel both scarcer and dearer. When hydro is plentiful it barely registers. When it is not, the shrinking gas supply is the reason a cold snap can send prices vertical. You can watch the mix and the price move in real time on our NZ Grid Live tool.
Why this winter is calmer than 2024
The saving grace this year is water. National hydro storage is sitting at about 113 percent of the historic average for this time of year, and the North Island lakes are extraordinarily full at around 208 percent of normal. The South Island, where the biggest lakes are, is close to average at about 106 percent.
Full lakes mean the system can lean on cheap hydro instead of expensive gas, which keeps a lid on the spot price even through the peaks. That is the opposite of the 2024 winter, when near-empty lakes and a gas squeeze combined into a genuine price crisis. The structural gas decline has not gone away, but a wet year buys the country breathing room.
What you can actually do about it
Because the bulk of the winter increase is volume, the bulk of the savings is too. Heating a smaller area, setting the heat pump a couple of degrees lower, and drying washing without the dryer all chip away at the biggest line on the bill.
If you are on a time-of-use or spot-linked plan, the second lever is timing. The grid is most expensive during the morning and evening peaks, so shifting the dishwasher, the laundry and any charging to the middle of the day or overnight moves your use to the cheapest hours. On a standard fixed plan that timing does not change your price, but it does ease the peaks that push wholesale costs up for everyone in the long run.
Quick answers
Why is my power bill higher in winter?
Mostly because you use more, with heating and lighting running far longer in cold, dark months. On top of that, winter demand peaks tighten the wholesale market, which feeds into retail prices over time.
Will power prices spike this winter like 2024?
It is far less likely this year. National hydro storage is about 113 percent of average, so the system can rely on cheap hydro rather than scarce gas. The 2024 crisis was driven by near-empty lakes.
Does the wholesale price affect my bill?
Not directly if you are on a fixed retail plan, but it flows through over time as retailers renew contracts. On a time-of-use or spot plan you feel the daily peaks much more directly.
As at June 2026. Sources, Transpower and Electricity Authority market data and em6 wholesale prices, summarised in Newswire’s NZ Grid Live tool. Wholesale and storage figures are recent weekly snapshots and move daily.
How much does your bill climb between summer and winter? Share your experience in the comments below.
This article was written by AI, briefed to report the facts, hopefully without some of the bias people bring to the job 🙂
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