4 ms·

Once upon a time (~15 years ago!), I worked at a ski resort in New Zealand that had a fancy new "automated" snowmaking system. When all 200 (give or take) snow

Once upon a time (~15 years ago!), I worked at a ski resort in New Zealand that had a fancy new "automated" snowmaking system. When all 200 (give or take) snow guns were running, along with the required water pumps/air compressors, the system could draw megawatts of power. Generally it didn't get below zero very often in the closest city to the resort (Queenstown), but when it did, people would turn on their electric heaters, and demand would go through the roof. The way it was explained to me is that the power company actually sent a signal through the power supply which would trigger our snowmaking system to shut itself off. It was pretty cool to see and also infuriating, because of course you can make much more snow when it's cold. 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!).

flakeoil 2y ago
Are you sure they modulated the frequency of the actual AC power (typically 50 or 60 Hz) and didn't overlay it with a high frequency signal? It's very common with power line communication or power line modems. You modulate a data signal on top.
- immibis 2y ago
  It's a data signal on top. The system is called "ripple control".
- ZeroGravitas 2y ago
  Possibly some version of this: https://en.wikipedia.org/wiki/Zellweger_off-peak https://en.wikipedia.org/wiki/Zellweger_off-peak In use for 7 decades or so.
  - gorbypark 2y ago
    This sounds like what I remember it being described as. Thanks!
shagie 2y ago
> The way it was explained to me is that the power company actually sent a signal through the power supply which would trigger our snowmaking system to shut itself off. https://en.wikipedia.org/wiki/Utility_frequency#Frequency_and_load 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/FrequencyKeeping 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-investing-us9-8-billion-in-5twh-of-pumped-hydro-to-bridge-energy-deficit/ 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-environment/2021/02/24/392290/texas-power-grid-was-4-minutes-and-37-seconds-away-from-collapsing-heres-how-it-happened/ 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.

flakeoil 2y ago

Are you sure they modulated the frequency of the actual AC power (typically 50 or 60 Hz) and didn't overlay it with a high frequency signal? It's very common with power line communication or power line modems. You modulate a data signal on top.

immibis 2y ago
It's a data signal on top. The system is called "ripple control".
ZeroGravitas 2y ago
Possibly some version of this: https://en.wikipedia.org/wiki/Zellweger_off-peak https://en.wikipedia.org/wiki/Zellweger_off-peak In use for 7 decades or so.
- gorbypark 2y ago
  This sounds like what I remember it being described as. Thanks!

shagie 2y ago

> The way it was explained to me is that the power company actually sent a signal through the power supply which would trigger our snowmaking system to shut itself off. https://en.wikipedia.org/wiki/Utility_frequency#Frequency_and_load 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/FrequencyKeeping 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-investing-us9-8-billion-in-5twh-of-pumped-hydro-to-bridge-energy-deficit/ 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-environment/2021/02/24/392290/texas-power-grid-was-4-minutes-and-37-seconds-away-from-collapsing-heres-how-it-happened/ 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.