1. Electrical Power and Cost of Electricity.

2. What is Electrical Power?
Electrical power is the rate at which electrical energy is produced or consumed in a given time.
Unit of measurement = watt (W)
The higher the power rating value, or “wattage”, the more electrical energy a device produces (or uses to operate).

3. Power Power (watts) = energy (joules) ---------------------------
time (seconds)
One watt is the equivalent of one joule o f energy used in one second (J/s)

4. Question??
Consider a 60 W incandescent light bulb and a 15 W compact fluorescent bulb (CFL).
Which uses more electrical energy?
The incandescent light bulb
If both produce the same amount of light, where did the extra energy used by the incandescent light bulb go?
Converted to thermal energy, instead of light

5. Electrical Energy Usage
Electrical energy is usually measured in kilowatt-hours (kW.h). The use of one kilowatt of power for one hour.
A watt.hour is 3600 times greater than a joule.
A kilowatt hour is 1000 times greater than the watt hour
1 kilowatt hour runs a hot shower for three minutes.
10 kilowatt hours power 5 loads of laundry.

6. Type of Electricity Meters
Electricity meters keep track of how much electrical energy is used in homes, schools, and businesses in units of kW.h.
Older meters have a turning disc with a black band
Newer meters called smart meters record electricity usage hour by hour and send the information directly to the utility company

7. Energy Usage by Country
Energy Usage in Canada
Energy usage by province
Energy Usage by Country

8. Cost to operate = power used x time x cost of electricity
Current Rates of Electricity in Ontario
Equation:
Cost to operate = power used x time x cost of electricity
= kW∙h x cost of electricity

9. Sample Problem
A laptop computer uses a 75 W adapter when it is plugged in. Electricity costs 7.8 cents/kW.h . Calculate how much it would cost to operate the laptop for the month of December for 24 hours per day.

10. GRASSS Method
Given: Power = 75 W (converted to kW = 75 W x 1kW = kW 1000 W Time = 24 hours per day for the month of December 31 days x 24 hours = 744 hours Cost of Electricity = 7.8 cents/kW.h

11. GRASSS Method Required Cost to operate Appropriate Formula
Cost to operate = (Power Used) x (time) x (cost of electricity)
Cost to operate = (kW∙h) x (cost of electricity)

12. GRASSS Method
Substitute and Solve: kW∙h used = kW x 744 h = 55.8 kWh Cost to operate = kW∙h x cost of electricity = 55.8 kWh x 7.8cents/kW.h = cents = $4.35 Statement It would cost $4.35 to operate the laptop for 24 hours per day for the month of December.

13. Go to the following website to calculate energy usage and cost:
Energy Use and Cost
Device
Power
Rating
(W)
Daily Use
(h)
Energy Use
(kW•h)
Cost of Electricity
($/kW•h)
Cost per Day
($)
Cost per Month
Cost Per Year
Hair dryer
710
0.5
0.355
.12
.04
1.28
15.55