Winter 2026: a record peak, a dry north and a full south

This review compares winter 2026, from 1 June to 31 August, with the five winters before it, back to 2021. Every figure comes from the Electricity Authority's market data, averaged over trading periods, the half-hours the wholesale market is settled in. A record here means the highest or lowest of those six winters.

Peak demand

7,421MW

Thu 6 Aug, 7:30 am

Renewable share

95.2%

of grid generation, up from 88.9% in 2025

Sent north on the HVDC

1.2TWh

net, 31% more than the next highest winter

Grid solar

366MW

trading period record, 18 Aug, beating every summer too

The coldest week

Demand climbed each morning and evening from Monday 3 August, and on Thursday 6 August the trading period from 7:30 am averaged 7,421 MW. Transpower's own measure put that morning at 7,415 MW.

The four days from 4 to 7 August set five of the six highest peaks of the six winters, and eight of the top ten are from this winter. Demand reached 7,000 MW in 31 trading periods this winter, against eight in the previous five winters combined. Each island set its own record too: 4,979 MW in the North Island and 2,445 MW in the South.

At the peak, hydro supplied 5,105 MW, its highest trading period of the six winters, with 3,381 MW from the South Island alone. Wind was almost absent, at 157 MW. Thermal plant ran at 1,020 MW, and batteries discharged 191 MW, also their most. The Haywards price reached $2,097/MWh at the peak, and $4,943/MWh at 7:30 pm on Tuesday 4 August, the highest of the week.

Total winter demand barely moved, at 11.1 TWh, the same as 2023. What changed was the shape of the day. Winter peaks used to come at about 6 pm; this year 30% of winter days peaked in the morning, against 13–16% in 2021–2023.

A wet south and a dry north

The South Island's hydro stations generated 5,212 GWh over the winter, the most of the six winters and 16% above the 2021–2025 average. North Island hydro gave 1,911 GWh, 8% below average and 21% less than last winter. Only 2021 was lower.

Total hydro output, 7,124 GWh, was close to an ordinary winter. Its location wasn't. Every main South Island scheme ran above its average, led by the Clutha, while every main North Island scheme ran below, led by Tongariro. Prices showed the same split: Haywards cleared at least $10 above Benmore in 18.5% of trading periods, more than in any of the six winters except 2021.

Power heading north

The HVDC link carried South Island power north almost without pause. Over the winter it sent a net 1,201 GWh north, 31% more than the next highest winter, 2023. It flowed north in 95% of trading periods, and on 62 of the 92 days it never flowed south at all. August, at 494 GWh, was the link's biggest month of any since 2021, winter or not.

The link also spent far longer running hard. It carried 1,000 MW or more for 184 trading periods this winter. In the previous five winters combined it did so for 44, all of them in 2023. Two years earlier the picture was reversed: in the dry South Island winter of 2024 the link sent a net 258 GWh south.

Solar records in mid-winter

Grid-connected solar farms generated 99 GWh this winter, more than double last winter's 47 GWh. New farms meant the records fell in the darkest months. The trading period record fell at 1 pm on 18 August, when grid solar reached 366 MW, the highest of the six winters and higher than any summer trading period too: the best before this winter was 219 MW in February. The same day set the daily record. Its 2,564 MWh beat the best summer day, 2,131 MWh on 7 February, by 20%, and the five best days for grid solar up to the end of August all came in August 2026. August's 47.7 GWh came within 1.3 GWh of the best summer month.

Five farms first generated between May and August:

Tauhei, which started on 30 June and reached 141 MW in August, supplied 139 MW of the record trading period on its own. The nine farms that first generated after last winter produced about half of this winter's grid solar. Kōwhai Park only appeared for two days of test output in August, so its effect is still to come.

The cleanest of the six winters

Renewables supplied 95.2% of grid generation this winter, up from 88.9% in 2025 and 77.3% in the dry winter of 2024. Gas generation fell to 377 GWh, a third of last winter's and less than a quarter of 2021's. Huntly's Rankine units added 184 GWh. On 34 days thermal output averaged under 200 MW; in the five earlier winters that happened once.

Wind had its best winter of the six, 1,119 GWh, up 30% on last year, with its highest trading period, 1,091 MW, on 31 August. New farms supplied 105 GWh of the increase. Kaiwera Downs stage 2 in Southland first generated in April and gave 96 GWh at up to 120 MW, more than doubling South Island wind output. Kaiwaikawe in Northland joined the market in mid-July and added 9 GWh. Existing farms supplied the other 150 GWh or so, led by Turitea, up 40 GWh.

Geothermal also had its best winter, 2,677 GWh, 8% more than in 2025. Eastland Generation's TOPP2 station at Kawerau, generating since December, added 107 GWh. Ngā Tamariki now runs at up to 134 MW, against 86 MW a year ago, and gave 94 GWh more. Tauhara, in its third winter, gave 48 GWh more. Several older stations gave a little less.

With water plentiful in the south and little fuel being burnt, prices were the lowest of the six winters: Haywards averaged $56/MWh and Benmore $47/MWh, against $133 and $131 last winter and more than $360 in 2024.