1. 2.2 Energy performance of transportation
Greener transportation
Electric vehicles
Hybrid vehicles
Check-point 4
Efficient use of transportation
Check-point 5 1 2 3
Book E3 Section 2.2 Energy performance of transportation

2. Greener transportation
Exhaust from vehicles is one of the major sources of air pollution.
However, transportation is essential in daily life.
What can we do to reduce pollution caused by transportation?
Use electric or hybrid vehicles.
Book E3 Section 2.2 Energy performance of transportation

3. 2.2 Energy performance of transportation
One of the greatest consumer of energy in HK is in the transport sector.
(~35% of annual energy usage)
Book E3 Section 2.2 Energy performance of transportation

4. 2.2 Energy performance of transportation
Most of the energy usage is made up of goods vehicles, buses, cars and taxis.
 These vehicles powered mainly by fossil fuels (cause air pollution when burning)
Cut down energy consumption for transportation
 Air pollution will be greatly reduced.
Book E3 Section 2.2 Energy performance of transportation

5. Book E3 Section 2.2 Energy performance of transportation
1 Electric vehicles
 Conventional petrol powered vehicles propelled by internal combustion engines
 Electric vehicles propelled by electric motors
Trams, trains and some cars are electric vehicles.
Expt 2d
A model of regenerative braking system
Book E3 Section 2.2 Energy performance of transportation

6. Book E3 Section 2.2 Energy performance of transportation
Experiment 2d
A model of regenerative braking system
d.c. power supply
two-way switch
motor
flywheel
light bulb
Set up the apparatus.
Connect the motor to the d.c. output through the two-way switch.
Switch on the power supply. When the flywheel rotates at a steady high speed, turn the switch to connect the motor to the light bulb. Observe the light bulb.
Video
2.4 Expt 2d - A model of regenerative braking system
Book E3 Section 2.2 Energy performance of transportation

7. Book E3 Section 2.2 Energy performance of transportation
1 Electric vehicles
Electrochemical energy conversion device
 Either a battery or fuel cell
 Operate an electric motor to move the vehicle
 Can be run on d.c. or a.c. power
Regenerative braking system
 Accomplish braking, but not using friction
 KE will not be converted as heat and wasted.
Book E3 Section 2.2 Energy performance of transportation

8. Book E3 Section 2.2 Energy performance of transportation
1 Electric vehicles
During braking, the motor’s connections are changed.
 Motor  generator of electricity
 Recharges the battery of the vehicle
i.e. KE of the car  chemical energy
In practice, as regenerative braking is not effective at low speeds, friction braking is still used.
Book E3 Section 2.2 Energy performance of transportation

9. Book E3 Section 2.2 Energy performance of transportation
1 Electric vehicles
Advantages of electric vehicles:
Fewer or even no air pollutants
More efficient in terms of energy conversion.
 End-use energy efficiency
 Electric car = 85%
 Conventional vehicle = 40%
Much quieter
Smaller moving parts  maintenance cost 
Book E3 Section 2.2 Energy performance of transportation

10. Book E3 Section 2.2 Energy performance of transportation
1 Electric vehicles
Disadvantages of electric vehicles:
Some electric vehicles are powered by batteries.
 Limited capacity
 Have only a short range (the travel distance without being recharged or refuelled)
 Heavy and bulky
 A few hours to be recharged
The cost and running cost of the electrochemical energy conversion device are quite high.
Book E3 Section 2.2 Energy performance of transportation

11. Book E3 Section 2.2 Energy performance of transportation
1 Electric vehicles
Different types of electric vehicles:
Battery electric vehicles (BEV)
 Power generated by batteries
 Can be recharged
 Still causes air pollution, but in a less direct way:
air pollutants produced by power station supplying the electricity to the vehicle, instead of by the vehicle itself
Book E3 Section 2.2 Energy performance of transportation

12. Book E3 Section 2.2 Energy performance of transportation
1 Electric vehicles
Different types of electric vehicles:
Fuel-cell vehicles (FCV)
Power generated by fuel cells, which use hydrogen to generate electricity
Much lighter and have lower greenhouse gases emissions than BEV
Refuelling takes only ~10 min
 More convenient than the BEV
Book E3 Section 2.2 Energy performance of transportation

13. Book E3 Section 2.2 Energy performance of transportation
1 Electric vehicles
Different types of electric vehicles:
Fuel-cell vehicles (FCV)
However…
 Fuel cells are expensive and fragile.
Production of hydrogen fuel from fossil energy emits greenhouse gases.
The scale of renewable energy today is not sufficient to meet the demand for widespread use in transportation.
Example 6
Charging an electric car
Book E3 Section 2.2 Energy performance of transportation

14. Book E3 Section 2.2 Energy performance of transportation
Example 6
Charging an electric car
An electric car uses a battery pack (store 20 kW h of energy when fully charged). The battery pack should be charged at 220 V.
(a) The battery pack is charged from 0% to 85% of its full energy storage.
If the average charging current is 30 A, find the time required to charge it.
Book E3 Section 2.2 Energy performance of transportation

15. Book E3 Section 2.2 Energy performance of transportation
Example 6
Charging an electric car
Energy stored in the battery pack
= 20  85%
= 17 kW h
By E = VIt, E VI
t =
17  103
220  30 =
= 2.58 hours
∴ It takes 2.58 hours to charge the battery pack to 85%.
Book E3 Section 2.2 Energy performance of transportation

16. Book E3 Section 2.2 Energy performance of transportation
Example 6
Charging an electric car
(b) The battery is further charged to 100% for another 2 hours at the same charging voltage.
Find the new average charging current during these 2 hours.
Additional energy required
= 20 – 17
= 3 kW h E Vt
I =
3  103
220  2 =
By E = VIt,
= 6.82 A
Book E3 Section 2.2 Energy performance of transportation

17. Book E3 Section 2.2 Energy performance of transportation
Example 6
Charging an electric car
(c) If the efficiency of the charging process is 73%, find the total energy consumed from the input source for a full charge.
Total energy required
= 20  73%
= 27.4 kW h
Book E3 Section 2.2 Energy performance of transportation

18. Book E3 Section 2.2 Energy performance of transportation
Example 6
Charging an electric car
(d) Estimate the amount of heat released in the entire charging process.
Heat released
 27.4 – 20
= 7.4 kW h (or 2.66  107 J)
Book E3 Section 2.2 Energy performance of transportation

19. Book E3 Section 2.2 Energy performance of transportation
1 Electric vehicles
Example 7
Range of an electric vehicle
Book E3 Section 2.2 Energy performance of transportation

20. Book E3 Section 2.2 Energy performance of transportation
Example 7
Range of an electric vehicle
An electric vehicle uses a pack of 26 batteries, each storing 1.15 kW h when fully charged.
When the vehicle moves steadily at 50 km h–1, the output power is 15 kW.
(a) End-use efficiency of the vehicle = 85%
Determine the range of the vehicle under this mode of driving.
Book E3 Section 2.2 Energy performance of transportation

21. Book E3 Section 2.2 Energy performance of transportation
Example 7
Range of an electric vehicle
(a) Total amount of chemical energy stored by the batteries
= 26  1.15
Energy output for driving the vehicle
= 29.9  85%
= 29.9 kW h
= kW h
Time for consuming all the energy E P =
25.415 15 =
= hours
Range of the vehicle = 50  1.694
= 84.7 km
Book E3 Section 2.2 Energy performance of transportation

22. Book E3 Section 2.2 Energy performance of transportation
Example 7
Range of an electric vehicle
(b) What will most of the mechanical power eventually be used for?
Most of the mechanical energy will be used to overcome air resistance and the friction between the tyres and the road.
Book E3 Section 2.2 Energy performance of transportation

23. Book E3 Section 2.2 Energy performance of transportation
2 Hybrid vehicles
Vehicles powered by fossil fuels use an internal combustion engine for propulsion:
Energy is dissipated mainly as heat in the combustion reaction and the rubbing between movable parts.
Book E3 Section 2.2 Energy performance of transportation

24. Book E3 Section 2.2 Energy performance of transportation
2 Hybrid vehicles
Hybrid vehicle
Containing an internal combustion engine and an electric motor
Propelled by the electric motor and/or the engine
A computer in it decides when to use the engine or the motor.
  consumption of fossil fuel
Book E3 Section 2.2 Energy performance of transportation

25. Book E3 Section 2.2 Energy performance of transportation
2 Hybrid vehicles
Hybrid vehicle
 Has a regenerative braking system
 Converting KE into chemical energy in the battery
 Storing energy for future use
Does not need external source to charge the batteries
 High end-use energy efficiency
Simulation
2.3 The working principles of hybrid vehicles
Book E3 Section 2.2 Energy performance of transportation

26. Book E3 Section 2.2 Energy performance of transportation
2 Hybrid vehicles
Advantages of hybrid vehicles:
High end-use energy efficiency
The regenerative braking system allows the vehicle to reuse its KE.
 Lower fuel costs
Less fuel consumption
 Emits less greenhouse gases and other pollutants to the environment
3. Lower energy usage
 Turns off the combustion engine when stationary
Book E3 Section 2.2 Energy performance of transportation

27. Book E3 Section 2.2 Energy performance of transportation
2 Hybrid vehicles
Advantages of hybrid vehicles:
4. Smaller combustion engines (more efficient) are used since the electric motors can share the load.
  efficiency of hybrid vehicles
Efficiency of vehicles: fuel efficiency
Measured by looking at the distance travelled per unit fuel used
Unit: km L–1
 Higher value  more efficient
Example 8
Hybrid vehicles
Book E3 Section 2.2 Energy performance of transportation

28. Book E3 Section 2.2 Energy performance of transportation
Example 8
Hybrid vehicles
The fuel efficiency of a petrol car and a hybrid car are 21.4 km L–1 and 30 km L–1 respectively.
(a) By how many percent is the hybrid car more efficient than the petrol car?
Percentage difference
30 – 21.4
21.4
=  100%
= 40.2%
The hybrid car is 40.2% more efficient than the petrol car.
Book E3 Section 2.2 Energy performance of transportation

29. Book E3 Section 2.2 Energy performance of transportation
Example 8
Hybrid vehicles
(b) Besides efficiency, state another advantage of a hybrid car over a petrol car.
A hybrid car emits less pollutant and greenhouse gases than a petrol car.
Book E3 Section 2.2 Energy performance of transportation

30. Book E3 Section 2.2 Energy performance of transportation
Check-point 4 – Q1
Consider an electric vehicle and a combustion engine vehicle.
An electric vehicle is propelled by
A a combustion engine.
B an electric motor.
C both a combustion engine and an electric motor.
Book E3 Section 2.2 Energy performance of transportation

31. Book E3 Section 2.2 Energy performance of transportation
Check-point 4 – Q2
Consider an electric vehicle and a combustion engine vehicle.
A combustion engine vehicle
A has a regenerative braking system.
B is propelled by an electric motor.
C has a longer range than an electric car.
Book E3 Section 2.2 Energy performance of transportation

32. Book E3 Section 2.2 Energy performance of transportation
Check-point 4 – Q3
Consider an electric vehicle and a combustion engine vehicle.
Which vehicle does each of the following sentences describe?
(a) It produces less noise.
(b) It has a longer range.
(c) It produces fewer air pollutants.
(d) It is more efficient.
Electric vehicle
Combustion engine vehicle
Electric vehicle
Electric vehicle
Book E3 Section 2.2 Energy performance of transportation

33. 3 Efficient use of transportation
Different modes of transportation need different amounts of energy:
The amount of energy needed per passenger per kilometre is the smallest for the electric train.
 Most efficient mode of transportation
Book E3 Section 2.2 Energy performance of transportation

34. 3 Efficient use of transportation
Advantages of public transportation:
 usage of oil-based fuels by around half
  emission of smog-causing particles
 no. of vehicles on the road
 Avoiding traffic jams
 cost of transportation
 Passengers can pay less
Book E3 Section 2.2 Energy performance of transportation

35. 3 Efficient use of transportation
Advantages of public transportation:
Large-scaled transportation networks are usually built when high-speed transportation systems (e.g. electric trains) are developed.
  time spent, especially for long-distance travel
Example 9
Buses and cars
Book E3 Section 2.2 Energy performance of transportation

36. Book E3 Section 2.2 Energy performance of transportation
Example 9
Buses and cars
In 2006, there were 4 million people using buses each day. Suppose that all of them travelled by car instead of bus.
(a) How much more energy per km would have been used each day? The amount of energy needed per passenger per km for buses and cars are 1.5 MJ and 2.9 MJ respectively.
Additional amount of energy used each day
= (2.9 – 1.5)  106  4  106
= 5.6  1012 J km–1
Book E3 Section 2.2 Energy performance of transportation

37. Book E3 Section 2.2 Energy performance of transportation
Example 9
Buses and cars
(b) How much more CO2 per km would be emitted each day? The amounts of CO2 emitted per passenger per km by buses and cars are 28 g and 130 g respectively.
Additional amount of CO2 emitted each day
= (130 – 28)  4  106
= 4.08  108 g km–1
= 4.08  105 kg km–1
Book E3 Section 2.2 Energy performance of transportation

38. 3 Efficient use of transportation
Example 10
Travelling expenses
Book E3 Section 2.2 Energy performance of transportation

39. Book E3 Section 2.2 Energy performance of transportation
Example 10
Travelling expenses
It costs $23.2 for a round trip between Tsing Yi and Tung Chung by MTR. When travelling by car, the cost of fuel is $7.3 and a toll of $30 is charged. Also, a parking fee of $1900 is needed each month.
(a) Sam lives in Tung Chung and works in Tsing Yi. If he works 22 days each month, find the difference in the monthly expense between travelling by MTR and car.
Book E3 Section 2.2 Energy performance of transportation

40. Book E3 Section 2.2 Energy performance of transportation
Example 10
Travelling expenses
(a) Difference in travelling expenses
= ( – 23.2) 
= $2210.2
(b) Apart from the cost, state two advantages of public transport over private car.
 usage of fuel and emission of air pollutants
 no. of vehicles using a road
 Avoids traffic jams
Book E3 Section 2.2 Energy performance of transportation

41. Book E3 Section 2.2 Energy performance of transportation
Check-point 5 – Q1
Which of the following transportations in HK is the most energy-efficient?
A Bus
B Car
C Electric train
D Tram
Book E3 Section 2.2 Energy performance of transportation

42. Book E3 Section 2.2 Energy performance of transportation
Check-point 5 – Q2
The inside of railways X and Y on a weekday:
Which railway is more energy-efficient?
A Railway X
B Railway Y
C Both are the same
Book E3 Section 2.2 Energy performance of transportation

43. Book E3 Section 2.2 Energy performance of transportation
The End
Book E3 Section 2.2 Energy performance of transportation