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A KW/h is only a measure of how much electricity something uses to run and how long it runs for. You will be billed for your electricity in ‘units’ but these equate exactly to 1Kw for 1 hour. This is written as a Kilowatt Hour or sometimes as KW/h.

Examples:

A kettle boiling uses approximately 3.5KW/h but only for 3 minutes at a time.

You therefore need to boil the kettle 20 times for one hour of usage.
In that hour the kettle will use 3.5KW/h or 3.5 units
At today’s electricity prices this would cost you 53p on high rate or 22p on low rate

Ye olde style 100w bulb uses 0.1KW/h
The bulb must run for 10 hours to use 1KW/h
This will cost you 1 unit or 15p on high rate or 9p on high rate for 10 hours of light.

A low energy light (20w) equivalent to a 100w ye olde bulb uses 0.02KW/h
The low energy bulb must run for 50 hours to use 1KW/h
This will cost you 1 unit or 15p on high rate or 9p on high rate for 50 hours of light

A 42” plasma TV uses 0.18KW/h
The TV must run for 6 hours to use 1KW/h


Where it gets interesting is when you look at Halogen Down lights.

A single halogen down light is usually 50w or .05KW, if you do the math this works out as 20 hours for one unit. This sounds like half the power of a 100w incandescent bulb, however, you will typically have 4, 6 or even 10 halogen down lights in a room. 10 down lights on for an hour is 0.5KW/h, so on for two hours for one unit. On for say 5 hours a night over a year that’s £120 or about £10 a month to light one room.