How much power do you use when you're not using any power? Surprisingly, not zero. Take my house for example: it's a quiet Saturday afternoon, the family has gone out and everything is turned off, but our power monitor is reading 170 watts. How so? After 5 minutes poking around I found the culprits: microwave, radio, TV, DVD and a list of other things.
These devices draw a tiny amount of power, but they draw it all the time. That's the problem. So I spent another 5 minutes figuring out how much this 'background demand' is costing me. According to a really rather elegant coincidence, it turns out that 170 watts of background demand will cost about £170 a year. That's about 1 tonne of CO2 or 30% of the average UK electricity bill, just for stuff I'm not even using.
Let's call this the Carbon Census Rule Of Thumb: 1 watt of background power costs £1 a year.
(Interested in why this works? There are about 10,000 hours in a year, and a kilowatt hour of electricity costs about 10p. Well, just under 10,000 hours actually and just over 10p, but the rounding cancels out making the answer nice and easy.)
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