4.2 KJ / kg / °C - that's the specific heat capacity of water. It doesn't matter how quickly your kettle boils it, it will take the same amount of energy to raise the temperature - assuming 1L of water at 10°C, at sea level (water boils at a lower temperature at altitude), that's 378 KJ, or pretty much spot on 0.1 KWh, which is, for some reason, the unit power companies use. It's actually a surprisingly large amount of energy, because water is funny stuff and has a higher heat capacity than most other substances, because $complicated_chemistry_reasons (hydrogen bonding, mostly).
The thing is, you probably want the most powerful kettle you can get, so it does it quickly, without losing too much heat to the environment, and if the kettle is insulated, and doesn't light up like a christmas tree, all the better. That's probably going to save you more money over a year than a "smart" meter with no obvious benefit other than to the energy company who can (allegedly) remotely turn off your supply if they think you've not paid your bill.
Biting the hand that feeds IT
