May-26 Generation Trends

Battery storage transformed the NEM's evening peak in May-26, with prices dramatically lower across all regions year-on-year. QLD was the only region adding net renewable supply in the month, SA and VIC faced steep daytime price increases, and transmission flows increasingly shaped outcomes.

This article is entirely focussed on one chart - which is our Visual of the Month. It shows the intraday average generation in half-hour resolution for May-26 versus May-25 by Region by Technology. The chart can be found at the end of the story, and we think it is quite an enlightening ...

1. Executive Summary

May-26 saw a broad reduction in NEM spot prices driven by two concurrent forces: a structurally larger battery storage (BESS) fleet suppressing the evening peak, and a warmer month with lower solar irradiance across the southern states reducing heating demand.

The evening peak is historically the highest-priced period, has been transformed across every mainland region. NSW's evening peak average price fell from $349/MWh in May-25 to $103/MWh in May-26, with other collapses in QLD ($197 to $104), VIC ($132 to $87), and SA ($133 to $97). BESS average discharge now routinely exceeds 700--1,000 MW at the peak in NSW and QLD, displacing gas and hydro from the peaking role they played a year ago.

Net renewable growth is the increase in renewables during the day less the battery charging load, is real but uneven. This month, QLD was the only region delivering meaningful net new supply to the grid as wind capacity for May-26 dispatch was 80% above May-25. NSW, VIC, SA, and TAS were all broadly flat to declining in net renewable supply for the month, due to different reasons:

NSW because BESS charging absorbs most of the incremental solar
SA and VIC because May-26 solar irradiance was 17--19% lower than May-25
TAS because Basslink's capacity reduction forced a shift from Victorian imports to domestic hydro.

2. Analytical Context

This section looks at the specific weather conditions for the month, and the impact of generation outages.

2.1 Weather Conditions

Looking at Heating and Cooling Degree Days (HDD and CDD) along with Solar Irradiance

HDD and CDD are calculated as the average temperatiuure against an 18.5°C base. Higher HDD = colder, higher heating demand. Higher CDD = warmer, higher cooling demand. Capital city figures proxy each NEM region.

May-26 was notably warmer than May-25 across all mainland regions except Queensland:

Sydney — HDD fell from 79.6 to 46.8 (−41%)
Adelaide — HDD fell from 223.8 to 153.6 (−31%)
Melbourne — HDD fell from 290.1 to 233.0 (−20%)
Hobart — HDD fell from 185.8 to 138.6 (−25%)
Brisbane — essentially unchanged, consistent with its subtropical climate

A warmer May means less space heating load in morning and overnight periods, accounting for a meaningful share of the price declines across those periods — NSW morning peak −13%, VIC −31%, SA −27% — independently of any structural change.

2.2 Generation Outages: May-26

Much higher coal outages measured by outage MWhs occurred during May-26 in NSW and QLD compared to May-25. However, NSW compensated for the outages by other coal units having higher dispatching levels so the daily average coal decline of −61 MW was relatively minor. QLD coal outages contributing to that region's −371 MW (−7.9%) coal decline alongside the structural displacement from new renewables.

3. NEM-Wide Review

3.1 The BESS Transformation

Battery storage is the single most consequential structural change in the NEM over the past twelve months. BESS fleet growth has been rapid in every mainland region, and its effect on the dispatch stack is now unambiguous.

NSW — average BESS discharge grew from 27 MW to 149 MW (+458%), with average half-hour peak discharge of 738 MW at 18:00 versus 214 MW a year earlier. Average gas dispatch at 18:00 fell from 730 MW to 224 MW (−69%). Average evening peak price was $349/MWh in May-25 and $103/MWh in May-26 — a 70% collapse.
QLD — average BESS discharge grew from 41 MW to 168 MW (+312%), with average half-hour peak discharge of 988 MW at 18:00 — the highest in the NEM. Average gas dispatch at 18:00 fell from 1,307 MW to 815 MW (−38%). Average evening peak price fell 47% from $197 to $104/MWh.
VIC — average BESS discharge grew from 51 MW to 112 MW (+121%), with average half-hour peak discharge of 583 MW at 18:00. Average evening peak price fell 34% from $132 to $88/MWh.
SA — average BESS discharge grew from 36 MW to 50 MW (+37%), with average half-hour peak discharge of 197 MW at 18:30. Average evening peak price fell 27% from $133 to $97/MWh.

The BESS operating pattern is consistent across regions: charge during the midday shoulder (when solar surplus depresses prices) and discharge during the evening ramp. This has three cascading effects:

Average evening peak prices have collapsed — the most important single change in the NEM price signal this year.
Gas and hydro have been displaced from their traditional peaking role — average gas dispatch at 18:00 fell 69% in NSW and 38% in QLD year-on-year.
Average shoulder prices have risen as BESS charging competes for cheap midday solar surplus — up across every region (NSW +10.6%, QLD +7.2%, VIC +34.4%, SA +84.2%).

SA's BESS growth is the most modest and its shoulder price increase the most extreme — a direct consequence of less solar in May-26 reducing the midday surplus that BESS was competing to absorb.

The generation-weighted average price (WAP) received by wind generators has been directly damaged by the evening peak collapse. Wind generates roughly 14% of its output in the evening peak period and historically captured that premium; in May-26 that premium has largely evaporated.

3.2 Net Renewable Supply by Region

The net renewable supply picture — average renewables (MW) minus average BESS charging load — reveals that headline renewable growth overstates new supply:

NSW — gross renewables grew modestly from 2,271 MW to 2,329 MW (+2.5%), but BESS charging grew from 40 MW to 183 MW (+352%), resulting in a slight decline in net supply from 2,231 MW to 2,146 MW (−3.8%)
QLD — gross renewables grew from 1,847 MW to 2,423 MW (+31.2%), BESS charging from 49 MW to 202 MW (+314%), leaving net supply up from 1,798 MW to 2,221 MW (+23.5%) — the only region with meaningful net growth
VIC — essentially flat; gross renewables 1,950 MW to 2,038 MW (+4.5%), net supply 1,889 MW to 1,904 MW (+0.8%)
SA — outright lower; gross renewables from 1,107 MW to 1,051 MW (−5.1%, weather-driven solar decline), net supply 1,063 MW to 986 MW (−7.2%)
TAS — fell from 228 MW to 191 MW (−16.1%) due to lower wind and the shift away from mainland imports

Therefore for the month of May-26, QLD was the only region delivering meaningful net new renewable supply to the grid.

3.3 Generation Trends

Renewable generation shows clear seasonality across all regions — peaking in summer (Dec–Jan) when solar irradiance is highest, falling in autumn/winter. Within that seasonal pattern, QLD is the standout structural grower. QLD average May-26 renewables of 2,423 MW are 31% above May-25's average of 1,847 MW, with the step-change visible across all seasons since mid-2025. By December 2025, QLD renewable dispatch averaged 3,071 MW, up from 2,310 MW in December 2024.

NSW and VIC show modest underlying growth — NSW averaged 3,859 MW in Dec-25 compared to 3,554 MW in Dec-24. SA and TAS are flat to slightly lower on a year-on-year basis.

Coal shows a gradual downward trend across the last 2-years, with significant seasonal variation — lower in spring and summer when renewables peak, higher in autumn/winter:

4. Regional Analysis

Spot prices are reported across five standard periods using 5-minute ending:

Overnight (00:05--06:30)
Morning Peak (06:35--09:00)
Shoulder (09:05--16:30)
Evening Peak (16:35--20:00)
Late Evening (20:05--0:00)

Key findings. NSW has the most dramatic year-on-year price shift in the NEM. Average BESS discharge at 18:00 was 738 MW in May-26 versus 214 MW in May-25, while average gas dispatch at 18:00 fell from 730 MW to 224 MW (−69%). Hydro also stepped back as batteries assumed the peaking role. The NSW coal outages during May-26 suppressed coal output during affected intervals; the small daily average decline understates the per-interval impact. Solar PV (rooftop) continues its steady structural growth.

Solar curtailment fell from 8.2% to 6.3% in May-26, consistent with the growing BESS fleet absorbing more midday surplus. Sydney’s slightly higher irradiance (+4.3%) means the flat Utility Solar output reflects stable resource conditions, with new capacity partially absorbed by falling curtailment. Wind curtailment eased from 1.5% to 0.9%. VIC→NSW interconnector flows grew 67% (141 GWh to 235 GWh), with VIC increasingly filling a gap as Snowy hydro steps back and the maximum NSW→VIC transfer capability has declined from 1,785 MW to 989 MW.

Generation mix (average MW, May-25 → May-26):

Coal: 5,151 → 5,090 MW (−1.2%), a small decline consistent with no material retirements
Gas: 239 → 95 MW (−60.2%), displaced by BESS from the evening stack
Hydro: 461 → 330 MW (−28.5%), stepping back from its traditional peaking role as batteries took over
Wind: 858 → 833 MW (−2.9%), broadly flat
Utility Solar: 747 → 739 MW (−1.1%), consistent with Sydney’s slightly higher irradiance (+4.3%)
Solar PV (rooftop): 666 → 757 MW (+13.6%), continuing a steady accumulation trend since Jun-24
BESS Discharged: 27 → 149 MW (+458%)
BESS Charging: 40 → 183 MW (+352%)

Spot prices (average $/MWh, May-25 → May-26):

Overnight: $90.02 → $83.20/MWh (−7.6%), reflecting warmer conditions reducing heating load
Morning peak: $97.61 → $84.81 (−13.1%), similarly weather-driven
Shoulder: $59.04 → $65.30 (+10.6%), as BESS charging competed for midday surplus
Evening peak: $348.55 → $103.18 (−70.4%), driven by BESS discharge peaking at 738 MW at 18:00
Late evening: $115.12 → $91.13 (−20.8%)

Key findings. SA is a unique market — no coal, gas-dominant firming, and the highest renewable penetration in the NEM. The defining feature of May-26 is a substantial solar decline. The evidence that this is irradiance-driven rather than grid-constrained is conclusive: solar curtailment fell from 16.4% to 5.7% — the grid dispatched a higher share of available solar — yet output still dropped 33%. BoM irradiance data confirms Adelaide averaged 9.01 MJ m⁻² day⁻¹ in May-26 versus 11.13 in May-25 (−19.0%). Climate records show May-26 had active, cloudy, wetter conditions throughout, compared to May-25’s below-average rainfall (34–56% of average). SA wind curtailment also fell from 11.8% to 7.1%.

The consequence of lower solar is the average shoulder price rising 84.2% ($36 to $67/MWh). Perversely, SA solar generators received significantly higher prices in May-26 despite generating much less, because lower output removed the midday self-suppression that had previously held shoulder prices down. VIC→SA combined interconnector flows (Heywood + MurrayLink) nearly doubled from 75 GWh to 127 GWh as lower solar required more Victorian firming.

The structural SA story — separate from the May-26 weather event — is severe spring curtailment driven by the Heywood interconnector constraint. SA solar curtailment peaked at 45.3% in Dec-25, with spring 2025 consistently above 37–41% (Sep-25: 37.6%, Oct-25: 40.9%, Nov-25: 40.5%). Wind curtailment reached 14–21% during the same period. When SA generation exceeds local demand plus the ~700–800 MW Heywood export cap, surplus must be curtailed. SA is an increasingly net importer from VIC outside of surplus periods.

Generation mix (average MW, May-25 → May-26):

Gas: 439 → 409 MW (−6.7%)
Wind: 734 → 772 MW (+5.3%)
Utility Solar: 102 → 68 MW (−33.5%); average peak Solar PV fell from 1,088 MW at 13:30 in May-25 to 822 MW at 13:00 in May-26
Solar PV (rooftop): 272 → 211 MW (−22.5%)
BESS Discharged: 36 → 50 MW (+37%)
BESS Charging: 45 → 65 MW (+45%)

Spot prices (average $/MWh, May-25 → May-26):

Overnight: $83.72 → $73.92/MWh (−12.3%)
Morning peak: $117.98 → $86.20 (−26.9%)
Shoulder: $36.21 → $66.71 (+84.2%), the largest increase in the NEM
Evening peak: $133.20 → $96.86 (−27.3%)
Late evening: $105.63 → $81.11 (−23.2%)

5. Thematic Analysis

5.1 Solar and Wind Curtailment

The May comparison. In May conditions (lower solar angles, moderate wind), curtailment across all regions is considerably lower than in spring. Year-on-year changes are modest, meaning the May generation comparisons reflect genuine output changes, not curtailment artefacts:

NSW — solar 8.2% → 6.3% (down); wind 1.5% → 0.9% (down)
QLD — solar 4.1% → 5.0% (up marginally); wind 1.2% → 2.0% (up modestly)
VIC — solar 7.5% → 7.9% (broadly flat); wind 10.7% → 10.2% (flat)
SA — solar 16.4% → 5.7% (sharply down); wind 11.8% → 7.1% (down)

Structural divergence between regions. VIC and SA wind curtailment remains structurally elevated — VIC averaging 10–24% through spring and summer, SA 7–21% — reflecting persistent Heywood interconnector export constraints. By contrast, NSW and QLD wind curtailment is under 2% in May conditions and below 8% even at spring peaks, indicating considerably more headroom for new wind capacity in the northern states.

SA's solar output decline is confirmed as irradiance-driven, not curtailment-related. SA curtailment fell from 16.4% to 5.7% in May-26 yet output dropped 33%. The grid was dispatching a higher share of available solar, but that solar simply was not available due to the 19.0% irradiance reduction.

5.2 Interconnector Flows

The interconnectors also a role in impacting spot price outcomes.

Basslink (TAS↔︎VIC).. Historically the cable carried a large net flow from VIC to TAS — Tasmania was consistently a major importer, typically drawing 150–250 GWh/month net from Victoria.

From Jul-25, the TAS→VIC maximum transfer capability fell from approximately 590 MW to 330–394 MW, a 35–45% reduction. Simultaneously the VIC→TAS maximum dropped more modestly, from about 481 MW to 467–474 MW. The net flow effect was dramatic on the TAS→VIC transfers: Tasmania went from importing 211 GWh net from VIC in May-25 to just 31 GWh in May-26, a reduction of 180 GWh.

Across Sep–Nov 2025 the net flow reversed, with Tasmania exporting 50, 28, and 4 GWh net to Victoria in those three months — ending a 23-month consecutive run of net imports.

Historically Tasmania has been a frequent net exporter (most of 2021 and 2023 featured sustained TAS→VIC flows of 60–213 GWh/month), but the 2025 exports were modest, constrained by the reduced TAS→VIC capacity rating. This return to net exporting, combined with the collapse in VIC imports, is the direct explanation for the TAS hydro surge.

6. Conclusions

QLD is in the most active structural transition — wind capacity has more than doubled since Jun-24, coal is falling, and BESS is growing rapidly. During May, it was the only region delivering meaningful net new renewable supply to the grid (+23.5% net, +423 MW), and its growing exports to NSW are a structural feature most evident over the last 3-months.

NSW is experiencing the most dramatic price transformation from BESS — the evening peak spot price fell from $349 to $103/MWh year-on-year — but gross renewable growth is modest and BESS charging is consuming most of the incremental solar, leaving net supply down slightly (−3.8%). VIC→NSW interconnector flows grew 67%, with VIC increasingly supplying NSW as Snowy hydro steps back.

VIC presents an anomaly: coal is slightly up, solar is irradiance-driven lower (Melbourne −17.6%), but wind is growing and BESS is expanding. The shoulder price increase of 34.4% ($39 to $53/MWh) was significant, and VIC had a persistent wind curtailment of 10.2% in May.

SA is the most exposed to both structural and weather risk. The shoulder price rose 84% in a single year ($36 to $67/MWh) due to less solar, and SA is an increasingly net importer from VIC outside of surplus periods.

TAS has been transformed by the Basslink capacity reduction, shifting from a net importer of 211 GWh from VIC in May-25 to just 31 GWh in May-26. Average hydro dispatch rose to 957 MW in May-26 versus 699 MW in May-25 to compensate.

The common thread across all regions is the structural growth of BESS suppressing evening peak prices and thereby compressing the energy arbitrage value.

7. Visual of the Month

Here is our Visual of the Month and you can select the Region, then the technology and it shows you the May-25 versus May-26 average generation for each half-hour of the day.

You can Mouse over the chart to see the values, and swipe the x-axis to zoom - then hit the minus sign to reset.

Disclaimer and Notes

Energybyte is published by Empower Analytics Pty Ltd (ABN 38630239002), Authorised Representative no 1274453 of Capital Treasury Solutions (AFSL 429066). Any questions or feedback must be directed to Empower Analytics Pty Ltd as the sole publisher.

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