Calculation of cost of electricity, and efficiency

1. Power Generation,
Efficiency and Cost of
Electricity

2. • Where does the electricity that we get from an
electrical outlet in our home come from?
• Electrical generating station (transfer of one
kind of energy to electrical energy):
– Hydroelectric
– Nuclear
– Coal
– Wind
– Solar
– Natural Gas
– Other (Geothermal, Biomass, etc.)ha

3. Energy Input
• No matter the type of energy input,
generators will take that energy and
transform mechanical energy to electrical
energy:

4. • Alternating Current (AC) produced by
generators at electric generating stations 
when flow of electrons alternates in direction
in an electric current
– Used in power generating stations because it is
more efficient method of distributing electrical
energy over long distances than DC
• Direct Current (DC) produced by an electric
cell  when flow of electrons in one direction
through an electric circuit

5. • Efficiency: comparison of energy output of a
device to energy input (energy supplied)
• % Efficiency = (Eout / Ein) x 100%
• Ex: an incandescent lightbulb uses 100 J of
electrical energy to produce 35 J of light
energy. Calculate the % efficiency of the light
bulb.
• % efficiency = (35 J / 100 J) x 100% = 35%

7. • What do you think is the best Type of Energy
to use in Power Generation?

8. • Typically rate charged by electrical generating
companies is per kilowatthour
• kilowatthour: the SI unit for measuring
electrical energy usage; the use of one
kilowatt of power for one hour
• Many electrical generating companies will bill
customers using time-of-use (TOU) rates
(based on supply and demand)

10. • Can use equation to determine how much it
costs to operate certain devices in your home:
• Cost to operate = power used x time x rate
charged
• Ex: Compare the cost to operate a 60 W
incandescent light bulb for 3 hours compared
to a 13 W CFL for 3 hours. Use Toronto Hydro
rates for off-peak hours. {These 2 bulbs are
comparable in the amount of light produced.}

11. • Incandescent Bulb:
– Power: 60 W = 0.060 kW
– Time: 3 hours
– Rate: 8.7 ¢/kWhr
– Cost 0.060 kW x 3 hr x 8.7¢/kWhr = 1.57¢
• CFL Bulb:
– Power: 13 W = 0.013 kW
– Time: 3 hours
– Rate: 8.7 ¢/kWhr
– Cost = 0.013 kW x 3 hr x 8.7 ¢/kWhr = 0.34¢

12. Homework Questions
From lesson on electrical quantities:
Questions on Elect. Power: w/b page 20 #1,3,4,5,6
Questions related to this lesson:
w/b page 20 Efficiency: 1-3
w/b page 20 Paying for Electricity: 1,2,4
From lesson on total resistance and complex circuits:
w/b page 22 attempt all questions.