Demand management is fantastic, batteries are just amazing and can sink power, provide power, manage reactive power and frequency and do it in milliseconds.
Being a giant nerd I of course asked if this was really happening via some network connection, but I was told they actually modulated the frequency of the entire grid in a very small, but predictable way. Some sort of device sat there and when it picked up the pattern in the frequency changes it would then trigger the shutdown.
I've spent a while doing some searches about such a system but couldn't find any information. Anyways, your comment about demand management made me think of this and how it's been possible in one way or another for a long time (albeit not milliseconds!).
https://en.wikipedia.org/wiki/Zellweger_off-peak
In use for 7 decades or so.
https://en.wikipedia.org/wiki/Utility_frequency#Frequency_an...
> Modern alternating-current grids use precise frequency control as an out-of-band signal to coordinate generators connected the network. The practice arose because the frequency of a mechanical generator varies with the input force and output load experienced. Excess load withdraws rotational energy from the generator shaft, reducing the frequency of the generated current; excess force deposits rotational energy, increasing frequency. Automatic generation control (AGC) maintains scheduled frequency and interchange power flows by adjusting the generator governor to counteract frequency changes, typically within several decaseconds.
If there's more demand on the grid, the generators have to work harder (slower) to generate the power and this shows up as a drop in the frequency of the grid. In New Zealand, that is 50 Hz. https://www.emi.ea.govt.nz/Wholesale/Datasets/FrequencyKeepi...
If the frequency drops a bit, it is then an indication for generators to kick on or load to be shed. If the frequency goes above the 50 Hz frequency, it becomes a sign that the price that power is being bought at is lower and so more expensive / dirty power generation should be throttled back or shut down (and batteries should recharge rather than discharge and pumped storage reservoirs should pump rather than generate https://www.energy-storage.news/new-zealand-considers-invest... )
On the other side of it, you can see the frequency changes back with the Texas blackout - https://www.houstonpublicmedia.org/articles/news/energy-envi...
Those changes are less than 1% of the frequency, but that's all that's needed to signal information between the generators and demand.