Energy at Home
Applied Science: BTEC Level 3 National Extended Diploma, topic 3.6.5
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 Energy at Home
What units are used in an energy bill?