How much Electricity does it use?
This page contains some notes and measurements on electricity consumption of various household items. I had to work out the cost of running a server for a year and was surprised at how many units of electricity were used, so I decided to start recording other household items. The items I've listed here are things which are typically left plugged in (on standby).
How much does it cost?
Electricity consumption (at least in the UK) is measured and paid for by units, one unit being the equivalent of 1 kilowatt hour. So a 100watt light bulb left on for ten hours uses 1unit of electricity (1kwh) as would a 2kw fan heater left on for half an hour.
The following table is provided as a guide and shows how many units (kwh) devices would use according to their rated power consumption:
| Rating | kw/hour | kwh/day | kwh/week | kwh/4 weeks | kwh/year |
|---|---|---|---|---|---|
| 1 watt | 0.001 | 0.024 | 0.168 | 0.672 | 8.76 |
| 5 watts | 0.005 | 0.12 | 0.84 | 3.36 | 43.8 |
| 10 watts | 0.01 | 0.24 | 1.68 | 6.72 | 87.6 |
| 20 watts | 0.02 | 0.48 | 3.36 | 13.44 | 175.2 |
| 50 watts | 0.05 | 1.2 | 8.4 | 33.6 | 438 |
| 100 watts | 0.1 | 2.4 | 16.8 | 67.2 | 876 |
| 200 watts | 0.2 | 4.8 | 33.6 | 134.4 | 1752 |
| 1 kw | 1 | 24 | 168 | 672 | 8760 |
So a 100 watt bulb left on 24hours a day for a year will use 876 units of electricity, which at (say) 10p per unit would work out at £87.60. By adding a time switch to switch that same bulb on for only 8 hours a day would reduce the annual electricity cost down to £29.20 (a saving of £58.40). So if the time switch cost £20 then it would pay for itself almost three times over within a year.
How much does it use?
The following table lists the power consumption figures that I have measured for a number of different devices:
| Device | Watts (approx) |
kwh per year (approx) | ||
|---|---|---|---|---|
| on 8 hours/day | on 24 hours/day | |||
| mechanical time switch | 2 watts (or less) | 6 | 17 | |
| laptop | on | 80 watts (average) | 234 | 700 |
| off, battery charging/charged | 45 watts | 131 | 394 | |
| video recorder | on standby | 4 watts | 12 | 35 |
| playing | 17 watts | 50 | 149 | |
| crt tv 21" | on standby | 3 watts | 9 | 27 |
| on | 44 watts | 128 | 385 | |
| cable set-top box | 13 watts | 38 | 113 | |
| 20watt energy saver bulb | 20 watts | 58 | 175 | |
| 100watt light bulb | 100 watts | 292 | 876 | |
| Dell 20" LCD monitor | on | 49 watts | 143 | 429 |
| standby (on but pc off) | 5 watts | 15 | 44 | |
| 14" LCD monitor (unbranded) | on | 18 watts | 53 | 158 |
| standby | 1 watt | 3 | 9 | |
| 2 kw fan heater | 2000 watts | 5840 | 17520 | |
| 3 kw fan heater | 3000 watts | 8760 | 26280 | |
| HP Laser Jet 4 (laser) printer. | printing | 800 watts | 2336 | 7008 |
| standby | 46 watts | 134 | 403 | |
Note:
- All measurements are approximate and may not be typical.
- Power consumption often fluctuates and for many devices it is not constant.
- Some devices (such as bulbs and fan-heaters) I have not measured but instead listed their rated value.