## Power ratings and energy consumption

For some bizarre reason electricity suppliers in the UK tend to bill their customers in kWh (that's kiloWatt hours). This can be useful if you know the power rating of your appliance is 1kW (say for an electric heater) and that if you leave it on for an hour, that's 1 kWh. Since you are billed x pence per kWh you know that this will cost you precisely x pence.

However, even more bizarrely this has resulted in the manufacturers of
certain goods powered by electricity describing the power ratings of
their goods in the horrendous kWh/y or kiloWatt hours per year. This
is a unit with 1 dimension of time on the numerator and 2 dimensions
of time on the denominator. Who honestly thought **that**
was a good idea? So, here are some useful conversions.

1 kW = 1 kJ/s, therefore 1 kWh = 3.6 MJ = 857 kc

1 kWh/y = 0.114 W

Therefore 1 kW = 8766 kWh/y

Pete Houston --- Comments welcomed