The cost of a cup of tea

This is the sort of thing that occupies my brain some days…

My jug broke just before I headed off on my winter migration, so I’ve been using a pot to boil water for my tea ever since. But ended up getting another electric kettle as an impulse buy, but it’s got me wondering, which one costs more.

On the face of it, I’d have thought gas was the cheapest. Per kWh (that’s 1 kiloWatt/hour of energy, which is sort of equivalent of turning on 10 x 100W lightbulbs for one hour of continuous use) I’m paying around 3.7p whereas electricity costs around 15.2p per kWh. The energy involved to heat a given volume of water should be roughly the same regardless of the energy source used to heat it.

Sure, there’ll be some differences. There’s probably a lot of waste heat being lost when heating water in a pot. And having to fill the kettle to a minimum line, means you’re boiling 750ml of water when you only need to use 250ml. The other bonus is the electric kettle will turn itself off automagically, whereas you’ve got to keep an eye on the gas one. (I’ve lost track of the number of times I’ve gotten ‘distracted’ only to find I’ve boiled away all the water. Yes! I can actually burn water…)

Without boring you with the methodology, here are the results:

So, boiling the water on the hob took a little more energy, but it’s a lot cheaper per kWh so ends up being the best option overall. And since I drink around 10 cups a day (well, a couple of coffees and a lot of Roibos), then it looks like I can buy a nice stove-top whistling kettle which will pay for itself in a year. Either that, or get cracking on my solar-powered samovar and get my hot water for free.

Update - 17 Sept 2013 - Oops! I had to edit my numbers as I’d transposed them. Took me this long to notice. But yeah, boiling a cuppa on a gas hob is a lot cheaper. Approx 40% of the cost of electricity. So go old-school!