Kettle or Microwave - to warm a mug of squash

[nannynick]

If you are making a mug of warm squash/ribena, is it cheaper to boil the kettle, or heat in the microwave? My 800watt microwave seems to use 1.3kWh according to the smartmeter display... seems a bit odd but I guess it does use more than the microwave wattage itself.
Kettle is rated at 2900watts.

So if it takes 90 seconds to warm a mug of squash in the microwave, or about the same time to boil a mug of water in the kettle, is microwave cheaper?

You are talking about boiling water, and 'warming' a mug. What is the final temperature of each drink?

800 W is the power rating of the microwave. kWh is a measure of energy use.

Energy = power x time.

Microwave = 800 W x 90 s = 72 kJ

How long is the kettle on for one mug? Multiply its power rating by the number of seconds.

Drinkable temperature. Hard to know when to turn the kettle off to achieve that, unless having a kettle with variable temperature sensor.

I guess a kettle is more efficient, as the heating element is nearer the water. But if boiling water and then letting cool down to drinking temperature, you are putting energy in which is being wasted.

If you can put 4/5 of a cup of water in the kettle then top up with cold then it's not wasted. That's how I make black coffee except I fill it to 500ml for two cups.

Also depends if the mug is sitting on a table or in your hands warming you as it cools down, heat not wasted there.

Boil the kettle once in the morning, use it to fill aThermos flask and you have hot water all day.