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Comment by advisedwang | Hacker News Reader

Water has a specific heat capacity of 4184J/kg/C. Lets say to get to the boil you need to go from 20C to 100C and that a kettle holds 1.75L.

59MJ / (80C * 4184J/kg/C) = 176kg ~= 176L ~= 100 kettles.

Water has a latent heat of vaporization of 2260 kJ/kg. So to boil it dry:

59MJ / (80C * 4184J/kg/C + 2260 kJ/kg) = 22kg ~= 22L ~= 12 kettles.

I have no idea what the journalist calculated.

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I suppose it's possible that the "standard" kettle size is ~3L. They don't seem too uncommon on Amazon.

I think the journalist is calculating load capacity. A 1500A @120V kettle requires 0.18 MW. Rounding up, 60 kettles requires 12 MW. It's not how much water you can boil, it's how many kettles you can run at the same time.

But they’re UK, so it wouldn’t be 110V. Nice try, though!

A 180kW kettle ?! Great Scott !

59MJ over 5 seconds would be 11GW, so if it was load, that would be 6000 2kw kettles!

Although obviously those kettles wouldn't achieve much in those 5 seconds!

I'm way off. I meant 15A. Now I've no clue what the journalist is calculating.

They should start selling 1500A kettles though. Bring a pot of water to the boil instantly.

Did you factor in the inefficiencies of the power distribution grid and the heating element of the kettle? I'd say the journalists are just repeating what they've been told by the scientists, and the scientists factored inefficiency in on a calculation similar to your first.

Nope, I didn't factor in anything like that. Also kettle's don't actually heat every ml to 100C so there's some fudge in the other direction. I mostly was just getting nerdsniped.

Thermodynamics is very good at sniping nerds. The first law is basically a universe builder. The second law is maybe a universe destroyer? :)

There may exist inefficiencies in the transfer of heat from the element to the water, but there is no such thing as an inefficient heating element. All of the power it uses will be converted to heat. Take a light bulb for example. When used to light a space, the inefficient part would be the energy that is lost to heat. The rest is converted to light, but as soon as that light hits an object, it's converted to heat. So even a light bulb is a perfectly efficient heating element.

With this in mind, you aren't saving any money on your electric bill by turning off lights when your furnace is on.

The kettle is also losing a lot of heat to the air in the room.

Presumably heat dispersing into the air rather than into the water would be an example of an inefficient heating element.

The internal heating element isn’t strictly speaking 100% efficient on AC as it’s producing a changing electric field etc. It’s just generally ignorable in practical terms.

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