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Proportion of Fuel Energy Used to Move a Single Occupant
See also Truck Freight Movement
When considering the energy efficiency of a modern internal combustion engine (ICE) vehicle, very little of the fuel's energy actually goes toward moving the person inside. To find the proportion used to move a single occupant, we have to look at both the thermal efficiency of the engine and the weight of the passenger relative to the car.
1. Engine Efficiency Loss
Most of the energy in a liter of petrol is lost before it even reaches the wheels. For a typical petrol car:
- 70% to 80% of the energy is lost as heat through the exhaust and radiator, or to internal friction.
- Only about 20% to 25% of the energy from the fuel actually becomes mechanical energy used to turn the wheels.
2. The Weight Ratio
The mechanical energy that does reach the wheels must move the entire mass of the vehicle plus the occupant.
- Average Car Weight: ~1,500 kg
- Average Occupant Weight: ~75 kg
- Total Weight: 1,575 kg
In this scenario, the occupant represents only about 4.76% of the total mass being moved.
3. The Final Calculation
To find the total proportion of fuel energy used for the person, we multiply the energy reaching the wheels by the mass ratio: 0.20 \times 0.0476 = 0.0095
This means that roughly 1% of the energy in the fuel is used to move the occupant. The remaining 99% is used to heat the atmosphere, overcome internal friction, and move the heavy metal frame of the car itself.
| Factors That Change the Result | ||
|---|---|---|
| Idling: | If the car is stuck in traffic, 100% of the fuel is wasted as no distance is covered. | |
| Speed: | At higher speeds, aerodynamic drag becomes the dominant consumer of energy, though the ratio of car-mass to person-mass remains a primary factor during acceleration. | |
| Electric Vehicles (EVs): | Since EVs are much more efficient (converting about 80% to 90% of energy to the wheels), the proportion of energy used to move the occupant is higher, roughly 4% to 5%, though the car still weighs significantly more than the person. | |
| Vehicle | Energy to Wheels/Motors | Mass Ratio (People:Total) | Energy Used for People |
|---|---|---|---|
| Car (1 person) | ~20% | ~5% | ~1% |
| Car (5 people) | ~20% | ~20% | ~4% |
| Full Bus | ~30% | ~25% | ~7.5% |
| Full Electric Train | ~90% | ~19% | ~17.4% |
| Walking | ~25% (Human) | 100% | ~16% |
| Bicycle | ~25% (Human) | ~86% | ~21.5% |
Typical Time Distribution in City Driving
| Mode | Proportion of Time | Description |
|---|---|---|
| Idling / Stopped | 15% – 30% | Waiting at traffic lights, stop signs, or in heavy congestion. |
| Accelerating | 25% – 35% | Increasing speed from a stop or moving from a slower to a faster flow. |
| Decelerating / Braking | 25% – 35% | Slowing down for obstacles, intersections, or traffic ahead. |
| Cruising | 10% – 20% |
Well-to-Tank Energy Lifecycle
When you look at the entire lifecycle of fuel—from the moment it is pumped out of the ground to when it reaches your car's tank—the process is surprisingly energy-intensive. This is often called “Well-to-Tank” (WtT) efficiency.
For every litre of petrol or diesel you put in your tank, about 20% to 25% of the energy content has already been “spent” just to get it ther.
1. Breakdown of Energy Consumption
The energy is consumed across four main stages:
- Extraction (~2–5%): Drilling, pumping, and maintaining oil rigs (onshore or offshore) requires electricity and fuel for machinery.
- Transport to Refinery (~2–5%): Moving crude oil via pipelines or massive tankers. While tankers are efficient due to ther scale, the sheer distances involved add up.
- Refining (~10–15%): This is the most “expensive” stage. Refineries use massive amounts of heat and electricity to “crack” crude oil into petrol and diesel. It is estimated that refining one gallon of petrol consumes about 6 kWh of energy—ironically, enough electricity to drive a modern EV about 35–40 km.
- Distribution (~2%): Tanker trucks delivering the finished product to local service stations.
2. The "Hidden" Litre
To put this into perspective, if you wanted to deliver 100 units of energy to your car's tank:
- You must start with approximately 125 units of energy at the source.
- 25 units are burned or “lost” during the supply chain.
- Therefore, only 80% of the energy originally extracted actually makes it into your vehicle.
3. Comparison of Energy Loss
| Fuel Type | Well-to-Tank Efficiency | Energy “Spent” to Deliver 1 Litre |
|---|---|---|
| Diesel | ~85% | ~0.18 Litres equivalent |
| Petrol | ~80% | ~0.25 Litres equivalent |
Diesel is slightly more efficient to produce because it requires less intensive refining than high-octane petrol.
Why this matters for the "1%" figure
Earlier, we discussed that only ~1% of fuel energy moves a single person. When you include the 20% loss before the fuel even reaches you, the “system-wide” efficiency for moving a human in a car drops even further—to about 0.8%. You are effectively using 99.2% of the energy from the ground to move a machine and heat the air.
Well-to-Tank for Renewable Electricity
The “Well-to-Tank” lifecycle for renewable electricity is significantly more efficient than for fossil fuels. Because ther is no refining process and the “fuel” (sunlight or wind) is collected directly, the energy lost before it reaches an electric vehicle (EV) is much lower.
In Australia, the “Well-to-Tank” equivalent for renewables is essentially the efficiency of the electrical grid and the charging process.
1. Breakdown of Energy Consumption
- Generation (~0%): Unlike oil, which requires energy to extract from deep underground, solar and wind are captured at the surface. The “fuel” itself is free and doesn't need to be pumped.
- Transmission & Distribution (~5% – 10%): Energy is lost as heat as it travels through power lines. In Australia's National Electricity Market (NEM), these losses are usually around 5%, though they can reach 20% for very remote solar farms far from cities.
- Charging & Storage (~10%): Converting AC power from the grid into DC power for a car battery, and the chemical process of storing it, typically loses about 10% of the energy.
- Refining (0%): Ther is no chemical “cracking” or refining stage, which is the biggest energy drain for petrol.
—
2. The "Hidden" Watt
If you want to deliver 100 units of energy to an EV battery using renewable sources:
- You need to generate approximately 115 to 120 units at the source.
- Only 15 to 20 units are lost in the process.
- This means the “Well-to-Tank” efficiency is 80% to 85%.
3. Comparison Table: Well-to-Tank (Pre-Vehicle Loss)
| Transport Fuel | Supply Chain Efficiency | Energy Lost Before the Tank |
|---|---|---|
| Petrol | ~80% | 20% lost (Refining/Transport) |
| Diesel | ~85% | 15% lost (Refining/Transport) |
| Renewable Electricity | ~85% | 15% lost (Grid/Charging) |
4. The "System-Wide" Efficiency
When you combine these “Well-to-Tank” figures with the vehicle's “Tank-to-Wheel” efficiency, the difference becomes stark:
- Petrol Car: Only ~0.8% of the original energy from the ground moves the person.
- Renewable EV: About 12% to 15% of the original energy captured from the sun or wind moves the person.
This means that for every 100 units of energy nature provides, an EV powered by renewables is over 15 times more effective at moving a human being than a petrol car.
Average car Usage
The average car is only used 5% of all time. Meaning that 95% of the time cars are not used. And when they are used they are only one percent efficient at moving a person
See also Truck Freight Movement
See also Global Resource Management Strategy
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