Calculating Fuel Bills
Science: KS3, topic 3.1.18
Calculating Fuel Bills
Electrical appliances are often on for long periods of time. So fuel bills are calculated over hours and use the unit kilowatt hour [kWh] for the amount of energy the appliances have used. These units are then used to work out the cost of your electricity bill.
Converting seconds to minutes
- There are 60 seconds in one minute. So in two minutes, there will be 120 seconds.
- In one hour there are 60 minutes.
- To work out the number of seconds in one hour:
- 60 minutes × 60 seconds = 3,600 seconds.
Fuel bill calculation
- The power rating on fuel bills is calculated in kilowatts (kW)
- The fuel bill is calculated over hours.
- Energy transferred is measured in kilowatt hours [kWh].
- This is called units on the fuel bill.
Calculating a fuel bill
- To work out the number of units used:
- Units = power × time.
- You can then work out the cost of the bill by units × cost per unit.
- If a bill payer used 100kWh over three months, and the cost was 5p per unit, the bill would total £5.
- 100 × £0.05 = £5.
Payback time
- You may wish to install features to your house to reduce the cost of your fuel bill.
- These features will reduce the amount of energy you use.
- Once installed, you can work out the payback time of the feature.
- This is calculated by adding the total cost of the feature ÷ how much money it saves per year.
- Triple glazing could cost £10,000 and you know it saves £200 per year.
- The payback time for triple glazing is 10000 ÷ 200 = 50 yrs.
Test yourself on Calculating Fuel Bills
What units are used in an energy bill?
A toaster has a power rating of 1 kW and a heater has a power rating of 2 kW. Both are switched on for the same amount of time. Which uses more units of energy?
Select the true statement in each pair.