Saving Energy in the Workplace

Worked example of energy used by typical desktop PC

Electricity use is measured in units. 1 unit = 1 KWh (Kilo Watt hour)i.e. this is the amount of electricity used to power 1000 Watts for 1 hour, e.g. if you left 10 x 100 Watt light bulbs on for an hour, they would use 1 unit (1 KWh) of electricity.

1 unit costs just under 10p to buy from your supplier, and produces 0.44kg of CO2 to make. When on normal power, a desktop PC uses about 60 watts. A flat screen monitor (when not in power saving mode) about 20 watts. (A tube monitor consumes considerably more.) That comes to 80 Watts, or 0.08 kilowatts.

If left on for 24 hours a day for one year, the PC would use:

24 x 365 = 8760 hours;
8760 x 0.08 watts = 700.8 KWhs or units of electricity,
costing: 700.8 x 10p = £70.08

Compare this to the following:
If the PC is switched off every evening (between 6pm and 9am): 9 x 365 = 3285 hours;
3285 x 0.080 = 262.8 KWh
costing:
262.8 x 10p = £26.28

However:
Compared to a PC switched off every evening and over weekends: Approx.5/7 x £26.28 = £18.77

Compared to a PC switched off every evening between 6pm and 9am, and over weekends, and taking into account, say, 20 days leave:
345/365 x 18.77 = £17.74

Conclusion: In other words, 1 desktop PC with flat screen which is permanently left on costs approx. £70 p.a.; compared with just £17.74 if it is turned off over evenings, weekends and holidays.