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Comment by cnj | Hacker News Reader

My uncle has implemented version 0.1 of this in his weekend house. Power is cheaper during the night, so he has installed a clock timer that only powers the water heater during the night. It holds enough hot water for two persons to take a shower, and to wash hands during the day. (There is a separate water heater in the kitchen).

Works great. If one should ever run out of hot water, it's simple to remove the clock timer... but we didn't need that when we spent a week there.

With a well-insulated water heater, the idea to use them as energy storage sounds like a great idea.

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I have version 0.2 in my London apartment - the bottom element of the water heater is connected to a different electric supply, with a separate meter, with energy that's almost 3 times cheaper than the rest of the wiring energy. The catch? The circuit is powered only when the power company feels like it (i.e. They need to dump excessive power somewhere), but they guarantee 2h power on by day and 6h by night.

Since this is the bottom element, and the top element is controlled by a thermostat (guaranteeing hot water on demand), this is a great setup for both the consumer and the power company!

What an unusual arrangement. Are you allowed to connect other things to that power source?

I am not sure, I also have a storage heater on the same circuit. Probably I need to speak to the power company if I want to connect a power bank of some sorts, like charging a car.

The tariff is called Economy9 for reference. It's not widespread outside London.

Is it not? I know at least a few people who use Economy9 in Newcastle. And yes, their storage heaters are hardwired to this secondary circuit.

We're on economy9 in Warwick. As I understand it, the landlord added it fairly recently (within the past decade).

I had Economy 7 when i was a student in Oxford twenty years ago. How things have come on - just imagine, by 2040 we may be up to Economy 11!

I had economy 9 heating in the flat I rented in London. It would come on at night and heat up large concrete blocks which would slowly release the heat while I was out at work during the day.

Had the drafty Victorian building been properly insulated it might have worked quite well.

Please make sure the water heater comes back up to temp (140F) before using water from it. This sort of scenario can cause bacteria to grow in the tank due to the hot-cold cycles, and unlike a gas water heater where convection takes place (which heat shocks the bacteria), it's unlikely all of the bacteria is killed before it flows out to hot water taps.

https://www.energy.gov/energysaver/services/do-it-yourself-e...

https://www.osha.gov/pls/oshaweb/owadisp.show_document?p_tab...

https://wwwnc.cdc.gov/eid/article/10/3/02-0707_article

Honestly I was a bit lost at what was the innovation in the article, but reading your comment I think it's just that the US (?) didn't know about that.

What you describe is how water heaters work in most households in France and Belgium, and - I assumed until now - mostly everywhere with a well developed electrical infrastructure.

Except instead on people manually setting up timers, the utility send a signal over the electrical wires when off-peak hours begin and end, and a device (owned and installed by the utility. It can be integrated into the counter like in France, or a separate Zellweger device like in Belgium) turns that into a third wire that power hungry appliances can use to turn on during off-peak hours.

Usually, the utility guarantees a minimum amount of off-peak hours per day, with min/max times that are convenient enough (you will never have two hours of off-peak at 9am, then one hour at 2pm and then five hours from 4pm to 9pm, is going to be between 10pm and 8am in any case).

Water heaters will rarely be turned on during the day in this configuration. It doesn't work that well will storage heaters though.

> the utility send a signal over the electrical wires when off-peak hours begin and end

Is that how they do it? In the UK, it was/is sometimes still done by piggybacking a signal on a BBC radio channel:

https://en.wikipedia.org/wiki/Economy_7#Timing_and_switchove...

Yeah. I'm not sure of the technology used in France, but in Belgium we get this: https://en.wikipedia.org/wiki/Zellweger_off-peak

It actually signals both the strict off-peak times (from 22:00 to 07:00 as well as Saturday and Sunday) and separately, a "night programme" that is variable and used to manage to grid more efficiently. Apparently, there are many different signals that go over the wire, and houses are more or less randomly tuned to one of them.

The strict times are used by the counter itself to know how to count usage, and the night programme is used for the appliances.

A lot of houses in Ireland and the UK do something similar.

But it doesn't work for "house heat" (storage heaters) as well as for water heaters

Presumably you can still make a dent in that 1 hour peak energy demand spike in the evening though? But yeah overall not as convenient

By the time I got home from work in the early evening heat from my storage heater had long since dissipated. If you were at home during the day or had better insulation maybe it would have been more useful.

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