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Comment by Reason077 | Hacker News Reader

That's right. Grid frequency in the UK can be used as a signal indicating the real-time balance of supply and demand.

When the frequency drops below 50Hz, it suggests that demand is outpacing supply, and vice-versa when the frequency is above 50Hz.

Grid voltage can vary due to your location and all sorts of factors, but frequency is, of course, always synchronised wherever you are.

National Grid pays a lot of money for "frequency response" to ensure the grid remains balanced. Traditionally this was provided largely by coal spinning reserve. But as most coal-fired plants have now closed, it's now provided by diesel farms (yuck!) and increasingly, battery storage.

http://www2.nationalgrid.com/uk/services/balancing-services/...

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> National Grid pays a lot of money for "frequency response" to ensure the grid remains balanced

In the US frequency response is mostly Nat Gas powered. There are new projects that are battery based, but another way to achieve this is on the demand side, by requesting non critical loads to turn off or throttle themselves when the frequency drops too low. I think this is being done at an industrial scale (i.e aluminium smelters) but it is possible on the domestic scale also with EVs electric tank water heaters, etc.

Going forward, given the intermittency of renewable energy, these methods (primarily storage) will be more important as the energy supply becomes more variable.

> "...by requesting non critical loads to turn off or throttle themselves when the frequency drops too low."

I'm not sure about other utility companies, but when I was a TSO we never did this. For the most part, AGC worked fine to maintain frequency.

http://www.nerc.com/files/bal-005-0_2b.pdf

Autonomous Demand Response for frequency regulation is real, and being pursued as a way to deal with the intermittency of renewables and the resulting impact on grid supply. Here are some references:

General Topic: http://www.pnnl.gov/main/publications/external/technical_rep... http://www.sciencedirect.com/science/article/pii/S0196890416...

HVAC Demand/Response: http://ieeexplore.ieee.org/document/7407597/?reload=true

Aluminum Smelter Demand Response: http://repository.cmu.edu/cgi/viewcontent.cgi?article=1836&c...

Thanks for the excellent references, the PNNL report was a very interesting read.

> "Autonomous Demand Response for frequency regulation is real..."

I wasn't saying that ADR wasn't "real," just that it's not something we're currently doing for frequency control in actual practice...and of course that might change as engineers continue researching and pushing the field further. It definitely looks like ADR solutions are on the horizon though.

Ya, sorry about implying that. FWIW, I didn't read your comment as a dismissal of ADR.

No worries. Excellent resources BTW, they made for a great weekend morning read.

> "When the frequency drops below 50Hz, it suggests that demand is outpacing supply, and vice-versa when the frequency is above 50Hz."

As a former Transmission System Operator I can tell you the most likely scenario you see this is when generation trips offline (demand exceeds supply for a short time).

I've sat in an Arizona control room, 1700MW of NW hydro would trip offline and we'd see a massive drop in interconnect frequency.

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