Comments on my Telewest cable box entry below seem to bear out my rough calculations, so I thought I’d share this with anyone that doesn’t know how to calculate rough costs.

The standard electricity unit is the Kilowatt hour, or kWh. It’s enough power to run an appliance using 1kW for 1 hour, so if you have a 3kW electric heater (the heaviest consumer you can plug into a standard 13A socket, since 3000W at 240V gives you around 13A), then you can run it for 20minutes on one unit. You can get the cost of one unit from your bill, or from one of the bill comparison websites. I did the latter and came up with 15p.

So if we take the consumption of a device, say the teleest box at 24 watts:

24 watts divided by 1000 is 0.024kW, so in an hour it will use 0.024 units of power.

0.024 units multiplied by 24 hours in a day, is 0.576 units per day.

0.576 units per day multiplied by 365 days in a year is 210.24 units per year.

At 15p per unit, 210.24 multiplied by 0.15 is £31.54, rounded to the nearest penny.

You need the *actual* power consumption though. Thats fine for light bulbs, and most appliances ahve their figures in the instruction leaflet. PCs are an odd one though. Most have 350 or 400W PSUs, but won’t be using anything like that- it’s a maximum capacity- hence the dangerous experiment LeeW did to find the actual power consumption of his home network. You could do the same thing with the power meter described below, but we are techies, and have multimeters. Exposed live wiring is fun.

Interestingly, since he did the calculation, either power had gone up a great deal, or I got my price wrong.
[*note to self: find electricity bill*]

I dread to think what the servers at work cost, wiith 3 phases at (roughly) 15A per phase, 24×7.