1. Energy Efficiency

2. Energy Efficiency
An incandescent light bulb uses about 5% of its input energy to create light and converts 95% of its input energy into heat.

3. Energy Efficiency
Compact fluorescent lights transform about 20% of their energy input into light, so they are more efficient than incandescent light bulbs.

5. Which one will you use?

6. Efficiency
The efficiency of a device is the ratio of the useful energy that comes out of the device to the total energy that went in
The more input energy that a device converts into usable output energy, the more efficient the device is.

7. Calculating Percent Efficiency
Efficiency is usually calculated as a percentage:
E out
percent efficiency = × 100%
E In

8. Example
Suppose a light bulb uses 780 J of input energy to produce 31 J of light energy. What is its percent efficiency?

9. Data: Input energy = 780 J Output energy = 31 J Percent efficiency =
Data: Input energy = 780 J Output energy = 31 J Percent efficiency = ? Equation: E out percent efficiency = × 100% E In

10. Substitute: 31 J Percent efficiency = x 100 % 780 J Calculate: 4.0 % Answer: The efficiency of the light bulb is 4 percent.

11. Practice Question
A car produces 27.5 kJ of useful output energy from 125 kJ of fuel. What is the car’s percent efficiency?

12. Calculation Write the equation E out
percent efficiency = × 100%
E In
Replace the known values
27.5kJ
125kJ
Solve
Percent efficiency = 22
Label
Percent efficiency = 22%

13. A fluorescent light produces 3
A fluorescent light produces 3.6 kJ of useful light energy from 21 kJ of input energy. What is its percent efficiency?

14. Calculation Write the equation E out
percent efficiency = × 100%
E In
Replace the known values
3.6kJ
21kJ
Solve
Percent efficiency = 17
Label
Percent efficiency = 17%

15. A new high-efficiency brushless motor designed for electric-powered
vehicles has an input energy of 75 kJ and an output energy of 72 kJ.
What is its percent efficiency?

16. Calculation Write the equation E out
percent efficiency = × 100%
E In
Replace the known values
72kJ
75kJ
Solve
Percent efficiency = 96
Label
Percent efficiency = 96%

17. Comparing Efficiency - EnerGuide
= yearly consumption in kWh
Compares this model to other like appliances
Indicates whether it is a high efficiency appliance

18. ENERGY STAR
A program started in 1972
A rating given to the most efficient electrical devices

19. Energy Consumption at Home
Are lights being left on in rooms that are not being used?
Is the clothes dryer being used for small loads like one shirt?
Is the hot water running continuously while the dishes are being done?

20. Is a lot of hot water being used for long showers?
Are incandescent light bulbs being used instead of compact fluorescent bulbs?