System frequency at 11 am in 2026, September update

In this article we update our look a how the supply-demand balance has been faring around these “free-power window” boundaries, through the lens of system frequency.

I don’t have anwers to Paul’s “Did ‘Three Hours Free Power’ produce a ~500MW unforecast jump in ‘Market Demand’ in Victoria on Fri 28th August 2026?”. This might, however, add context to any future investigations.

Free power offers underway

Retail tariff offers in some states have begun to include a ‘three hours free power’ offer.

For the most part, these offers are mandated for states falling under the default market offer framework; NSW, SA, Qld. Starting from July 1^st.

For these “DMO jurisdictions” the “Solar Sharer Offer” (SSO) represents this requirement.

When we looked last time (before 1 July) there were some interesting features of ‘System frequency at 11 am in 2026’ . These features were indicating an emerging trend for frequency to dip at 11am.

In ready or not here we come we hypothesised that this frequency dip was due to sudden and coincident charging of batteries (not grid-scale ones) incentivised by cost of electricity and bolstered by the number of batteries out there.  The SSO program hadn’t gone live at that point in time yet it was interesting to observe such a prominent 11am dip.

The timing of these new free power windows aligns, somewhat

In SA the SSO window is 12pm to 3pm local Adelaide time.

In NSW the window is 11am to 2pm local time.

In Qld the window is 11am to 2pm local time.

Victoria isn’t part of the DMO framework. There is a Victorian equivalent however – the Victorian Default Offer (VDO).  Under that framework the Victorian Midday Power Saver program will implement the three-hour free electricity offer for Victoria. Later. It will commence from 1 October 2026.

In Vic the window will be 11am to 2pm local time.

There is also the Victorian “Solar Soak”, a specific time-of-use network pricing structure introduced for the VDO from 1 July 2026, featuring a discounted midday usage window from 11:00 am to 4:00 pm.

Prior to 1 July, some retailers were offering time-of-use plans that included free or discounted electricity during a midday period.  This was not particularly widespread though, compared to the mandated SSO and the Victorian version.

The initiative is not offered or mandated in Tasmania. The default market offer (DMO) framework is not used there.

System frequency – March to August

We captured frequency series each day, grouped by month.

The dip at 11am appears to have become more consistent:

In August an average delta of nearly -50 mHz, from 50Hz, is seen at the lowest part of the dip. That represents a third of the distance to the low side of the NOFB.

In the afternoon, at 2pm when the SSO ends in Qld and NSW there is an emerging tendency for frequency to be on the high side:

It seems plausible that not all storage systems taking advantage of the window will still be charging (and suddenly stop) at the end of the window.

The alignment of windows will shift

As mentioned above, window times are in local time. Alignment between jurisdictions will therefore differ depending on the time zone and whether daylight savings applies.

In the final chart, if I’ve done the math right, we present how the different time zones overlap in a given year.

We can see that the strongest overlap is when all four states have an active window. This timing changes when daylight savings is in effect.

Yet, from the frequency charts we note it is the very start of the window where frequency is most strongly impacted. The sudden change in consumption occurs at the start of the window as systems all start charging at once.

The strongest alignment for a window-start is when Qld, Vic and NSW all start at 11am, between April and October. Once daylight savings kicks in it is just Vic and NSW starting first because their local 11am is 10am NEM time.