My usage has been pretty stable at an average of about 17kW/h per day for years, so around 510kW/h a month. It's horrendous, but down to working from home and having a LOT of equipment. At any one time during the working day I might have up to six or seven computers running, six 24 inch monitors, and assorted electronics gear.

The main CAD box, which is a 3GHz quad-core Core2 unit with three dual-head radeon cards, driving four Dell 24 inch monitors, a 17 inch Acer one, lots of USB devices, and three drives, pulls a peak of 720W on boot and an average of about 380W when running normally. This one is on for about 12 hours a day most days. The bulk of the others are used much less except for the mail server and file server, which only take about 25-30W.

On the upside, while I use a lot of electricity, my gas usage for anything other than cooking and hot water is minimal, I don't use the central heating more than about a week a year.

Since I got the house cavity-wall insulated, in fact, the big problem is getting rid of the heat. I haven't decided whether I have a computer system that doubles as a space heater, or a heating system with an awful lot of processing power

The lathe (3kW) and milling machine (2kW) don't help, but they're not used a lot. The fridge, freezer, and a couple of small low power servers are on all the time, but are fairly efficient. Low energy bulbs throughout, the first thing that I did when I moved in 13 years ago. I still have at least two of the original bulbs working

I replaced all the monitors with LCD ones, and have steadily upgraded all the computers with more efficient parts, so although the number of machines seems to have grown rather a lot the average power usage has stayed surprisingly consistent the whole time.

One big change I made was to make sure everything not used is turned off at the wall (something I really like about UK power sockets, integrated switches on each one), as it's quite amazing how much power some devices draw in the allegedly OFF state. One shuttle, for instance, took something like 180W when on and running flat out, and 70W (!) when it was turned off. What the hell is going on there?

When I found that, I went through the entire house with a wattmeter and measured everything I could get access to, and made sure that anything not being actively used was switched off at source. That made a large difference.

In the UK a useful metric is that a 1W load running 24/7 represents about £1 a year expenditure at common domestic energy rates. So you can easily add up how much that TV is costing if it's drawing 54W in standby, as mine was...

The plasma screen is MUCH better, around 1.5W.

I did have a surprise when setting up the fileserver that lives in the shed as a backup device. It's a mini-ITX board with about 8TB of drives plugged in, and the motherboard claims a power draw of about 22W. When I first set it up, with a spare 250W PSU I had lying around, the machine pulled about 78W. Replacing the PSU with a 1U shuttle one dropped this to 28W. The standby load of the PSU itself was the other 50W. Not very efficient.

pca