Making sure your home is not an energy sink - I

Science Alert | It makes no sense to turn off a light when you leave a room in which an electric heater has been left on. The power used by the light is 100 watts (W), while a heater typically draws 2000 W.

How big a yardstick is 100 W? Let’s assume that we leave a 100 W light globe on every night for six hours, which adds up to 2200 hours a year.

To calculate the energy used – measured in watthours – over the year, we simply multiply the hours by watts, which in this case is 220 000 watt-hours (Wh). As we know, ‘kilo’ means ‘thousand’, so a more manageable way of expressing this figure is 220 kilowatt-hours (kWh).

To most people, including me, a number like 220 kWh doesn’t mean much, so let’s convert it into something familiar – say litres of petrol – as an energy equivalent.

The best efficiency that can be achieved by burning brown coal to generate electricity is 25 per cent. This means four times the energy that comes through your electricity meter or power point is required to produce the energy you use in your home.

Taking the above example: 4 x 220 kWh, or 880 kWh, is required to produce that amount of electricity. If we go a step further, a litre of petrol contains about 10 kWh of energy. Thus, the 880 kWh equates to 88 litres – enough for the average car to drive 880 km, or from Melbourne to Sydney. That’s just to run one light globe each night for a year!