Title: Interactive Example: Efficiencies

Let's look at an example analyzing the energy flow for 2 types of vehicles:

(i) an internal combustion engine (ICE) vehicle running on gasoline

(ii) an electric vehicle (EV) that is charged with electricity from a coal powerplant

Which vehicle do you think will have a lower environmental impact?

First let's look at the ICE vehicle running on gasoline and its energy flow.

ICE Vehicle - Energy Flow

- Crude Oil
- Gasoline
- Heat Engine (SI Engine)
- Kinetic Energy
- Drag the text at the bottom of the bubbles into their corresponding energy stage.
Q: Primary Energy
A: Crude Oil
Q: Secondary/Final Energy
A: Gasoline
Q: Conversion Step
A: Heat Engine (SI Engine)
Q: Useful Energy
A: Kinetic Energy

This is an example of an energy flow from the primary source to the end use, as seen in the previous chapter, for a gas vehicle.

NOTE: A heat engine is a device that converts energy (heat) from one form to another. In this case, our heat engine is a spark ignition engine for gasoline vehicles. We will see more on heat engines in the next chapter.

[Image: Energy Efficiencies added]

Q: Given the above diagram, calculate the overall system efficiency and choose the correct answer.
- 14.6% (correct)
- 19.8%
- 69.0%
- 13.5%
Feedback (0 to 100%): Total efficiency = 86% * 17% = 14.6%

Electric Vehicle

Q: What do you think is different for the EV in terms of Primary Energy, Secondary Energy, Final Energy, Useful Energy, and its conversion? What do you think is the same?
A: As stated in the name, electric vehicles run on electricity.

So, instead of an internal combustion engine we would have (i) a battery (charged from the electricity in the grid), (ii) an inverter (converts the electricity from DC to AC) and a (iii) motor (converts electricity to kinetic energy).

Proceed to the next slide to see other differences/similarities in the energy flow!

Now, let's look at the energy flow for the EV.

Drag the text boxes into the correct energy stages.

EV - Energy Flow

- Coal
- Electricity
- Battery & E-Motor
- Kinetic Energy
Q: Primary
A: Coal
Q: Secondary/Final Energy
A: Electricity
Q: Conversion
A: Battery & E-Motor
Q: Useful Energy
A: Kinetic Energy

EV Efficiency

Q: Given the above figure, calculate the efficiency for an EV.
- 45.8%
- 23.8% (correct)
- 39.0%
- 72.0%
Feedback (0 to 100%): Total efficiency = 33% * 72% = 23.8%

Now let's compare the 2 vehicles. Solely comparing efficiencies, we have calculated the following:

System efficiency for ICE vehicle: 14.6%

System efficiency for EV: 23.8%

Immediately, we see the EV is more efficient at converting primary energy to useful energy.

Let's see what happens when we drive both vehicles for 100km at 33km/h.

Flat Distance to drive: 100km @ 33km/h

Fill in the missing words

Q: Given (i) efficiencies for both vehicles and (ii) the energy required to drive both vehicles for 100 km, calculate the actual amount of primary energy required to drive the 100km. (Round to 1 decimal point)

For the ICE vehicle, [...] MJ are required.

For the EV, [...] MJ are required.
A: 228.6; 163.5
Feedback (0 to 100%): Total energy = energy per 100km / efficiency.

HINT: A kettle requiring 2W with a 60% efficiency would need 3.33W to be fed to it.

NOTE: Energy demand is the (force required to overcome resistive forces) x (distance = 100 km). It is a function of multiple vehicle parameters such as vehicle mass, velocity, frontal area, etc.

Let's look at CO2 Emissions!

Fill in the missing words

Q: Given the CO2 intensities for each primary energy source, calculate the kg of CO2 emitted by driving each vehicle 100km (round to 1 decimal point).

The ICE vehicle emitted [...] kg CO2.

The EV emitted [...] kg CO2.

Is this result surprising to you?
A: 16.2; 24.0
Feedback (0 to 100%): Total emissions = emissions per MJ * total amount of MJ

HINT: Use the required energy found in the previous question.

CO2 emissions are calculated based on which fossil fuel is being burned.

Q: What are you main conclusions from this simple analysis?
A: Some good takeaways could be the following:

- Solely looking at system efficiencies can be misleading

- Primary energy resources are important to consider; if the EV is charged with coal-electricity, it can actually emit MORE CO2 than a gasoline car even though they are more efficient!

Q: Since EVs have a higher driving efficiency, this means that they have a lower environmental impact when driving.
A: false