1. Calculating Energy Costs
Curriculum Links:
Mathematics 6
Numbers: Students will be expected to solve problems involving whole numbers and decimal numbers.
Mathematics 7-9
Students will solve problems involving the collection, display, and analysis of data
Science 9:
relate electrical energy to domestic power consumption costs
Mathematics 10
Students will be expected to solve problems that involve unit pricing and currency exchange, using proportional reasoning.
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2. How is energy measured?
Energy consumption is measured in watts over time (Watt-hours or kilowatt-hours)
We can waste less energy by reducing the watts used by an item, or by reducing the length of time the item is used
Example: Change to LED lightbulbs and turn off lights when not needed

3. Calculating the cost of electricity
1: Convert watts to watt-hours
2: Convert watt hours to kilowatt-hours
3: Multiply by the hours used per day
4: Multiply by the number of days used per year
5: Multiply by the electricity rate for Nova Scotia ($0.15/kWh)
6: Multiply by the number of items used in the house
Result: Cost of electricity ($)
Note: Do not clear your calculator when doing these calculations
After measuring energy with the energy meter, or using the approximation on the appliance specification sticker, you will have a number of Watts. Proceed with this method to find out how much money it takes to run a particular appliance.

4. Example Step 1: 60W x 1h= 60Wh Step 2: 60Wh ÷ 1000= 0.06kWh
Electricity used by 60W light bulbs in a home:
Step 1: 60W x 1h= 60Wh
Step 2: 60Wh ÷ 1000= 0.06kWh
If lights are left on an average of 5hrs/day:
Step 3: 0.06kWh x 5hrs/day= 0.3kWh
If lights are used 365 days/year:
Step 4: 0.3kWh x 365 days/yr= 109.5kWh
Step 5: 109.5kWh x $0.148= $16.206
If there are 30 bulbs in the house:
Step 6: $ x 30 bulbs= $486.18

5. Light Bulbs: LED vs incandescent Mini Lights: LED vs Incandescent
Air Hockey Table
Hair Dryer
These items will be tested using an energy meter to determine the number of Watts and then we will calculate electricity consumption for each item.

6. Incandescent Mini Lights
Step 1: 35W x 1h= 35Wh
Step 2: 35Wh ÷ 1000= 0.035kWh
If lights are left on from 5pm-10pm each night:
Step 3: 0.035kWh x 5hrs/day= 0.175kWh
If lights are left on for the month of December:
Step 4: 0.175kWh x 31 days/yr= 5.425kWh
Step 5: 5.425kWh x $0.15/kWh= $0.81…
If there are 4 strands on the tree:
Step 6: $ x 4 strands= $3.25
Suggestion: Calculate the cost of lighting your house with 10 strands of outdoor incandescent lights (185W/strand).
Answer: $42.44

7. LED Mini Lights Step 1: 1W x 1h= 1Wh Step 2: 1Wh ÷ 1000= 0.001kWh
If lights are left on from 5pm-10pm each night:
Step 3: 0.001kWh x 5hrs/day= 0.005kWh
If lights are left on for the month of December:
Step 4: 0.005kWh x 31 days/yr= 0.155kWh
Step 5: 0.155kWh x $0.15/kWh= $0.02…
If there are 4 strands on the tree:
Step 6: $ x 4 strands= $0.09

8. Compare Mini Lights If there are 4 strands used,
If lights are left on 5 hours/day,
If lights are left on for a month…
COMPARE THE ENERGY COST:
LED Mini Lights = $0.09
Incandescent Mini Lights = $3.25

9. Incandescent Light Bulb
Step 1: 60W x 1h= 60Wh Step 2: 60Wh ÷ 1000= 0.06kWh If lights are left on for an average of 5hr/day: Step 3: 0.060kWh x 5hrs/day= 0.3kWh Lights are used approximately every day for a year: Step 4: 0.3kWh x 365days/yr= 109.5kWh/yr Step 5: 109.5kWh x $0.15/kWh= $16.43/yr If there are 30 bulbs in the house: Step 6: $16.43 x 30 bulbs= $429.90/yr/house

10. LED Light Bulb Step 1: 7W x 1h= 7Wh Step 2: 7Wh ÷ 1000= 0.007kWh
If lights are left on from 5pm-10pm each night:
Step 3: 0.007kWh x 5hrs/day= 0.035kWh/day
Lights are used approximately every day for a year:
Step 4: 0.035kWh x 365 days/yr= 12.78kWh/yr
Step 5: kWh x $0.15/kWh= $1.92/yr
If there are 30 bulbs in the house:
Step 6: $1.92 x 30 bulbs= $57.49/yr/house

11. Compare Light Bulbs
If lights are left on for an average of 5hr/day, used every day for a year, and if there are 30 bulbs in the house…
COMPARE THE ENERGY COST:
LED light bulb: $57.49/yr/house
Incandescent light bulb: $429.90/yr/house

12. Air Hockey Table
Step 1: 180W x 1h= 180Wh Step 2: 180Wh ÷ 1000= 0.18kWh If table is used for an average of 1.5hrs per day: Step 3: 0.18kWh x 1.5hrs/day= 0.27kWh Table is only used during school days: Step 4: 0.27kWh x 195 days/yr= 52.65kWh/yr Step 5: 52.65kWh x $0.15/kWh= $7.90/yr There are 2 air hockey tables: Step 6: $ x 2 tables= $15.80/yr

13. Hair Dryer Step 1: 1500W x 1h= 1500Wh Step 2: 1500Wh ÷ 1000= 1.5kWh
Hair dryer is used for an average of 15min:
Step 3: 1.5kWh x 0.25hrs/day= 0.375kWh/day
Hair is washed and dried every other day:
Step 4: 0.375kWh x 183 days/yr= 68.63kWh/yr
Step 5: 68.63kWh/yr x $0.15/kWh= $10.29/yr
If there are 2 people who dry their hair in the house:
Step 6: $ x 2 people= $20.58/yr/house

14. Average Cost Per Year Incandescent mini lights (tree only): $3.25
LED mini lights (tree only):
$0.09
Incandescent light bulbs:
$429.90
LED light bulbs:
$57.49
Air hockey table:
$15.80
Hair dryer
$20.58

15. Discussion Which lights in the school are on the longest?
Are those light bulbs LED?
Provide an example where LED light bulbs can save a lot of energy.
What time of year do we use lights more frequently?
How can we waste less energy?

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