If you were to drive 100km in an electric car, it would at worst use half of the energy of a diesel car. Even when you consider the materials in the car and way the electricity was made, the electric car is still far better.
- Gasoline car engines are very heavy and produce lots of heat.
- They have many complicated moving parts that make the car less durable.
- Combustion of fossil fuels produces greenhouse gasses and mining for those fuels destroys the surrounding environment.
An average gasoline car is only 20% efficient and uses 80–120KWh of energy per 100km.
- Electric engines are smaller, lighter, quieter, more efficient, have fewer parts, are easier to repair and accelerate faster.
- The electricity used to power the engine can be generated with zero emissions from renewable sources.
An electric car is 75% efficient and uses 20KWh of energy per 100km.
How much energy would you use driving 100km?
Fuel economy — 7.4L/100km
Engine — 2.0L 122KW 4cyl diesel
Weight — 1500kg
Energy economy — 78KWh/100km
Fuel economy — 5.4L/100km
Engine — 2.5L 128KW 4 cyl diesel
Weight — 1600kg
Energy economy — 57KWh/100km
Fuel economy — 8.9L/100km
Engine —4.4L 200KW 8 cyl diesel
Weight — 2600kg
Energy economy — 93KWh/100km
Hyundai IONIQ electric
Weight — 1600kg
Energy economy — 16.9KWh/100km
Tesla Model S electric
Weight — 2200kg
Energy economy — 19.2KWh/100km
You will use around 30% of the energy when driving an electric car compared to an average gasoline car.
Energy economy math eg. Sonata
We need to get the numbers into the same units so we can make a comparison.
The Sonata is rated the most fuel-efficient, brand new mid-size diesel car.
On the highway, it will get 100km using just 7.4L of diesel.
That 7.4L of diesel contains 38MJ/L of energy.
J (Joules) is the unit we use for energy.
MJ (mega-joules) is 1 million joules.
7.4L x 38MJ/L = 281.2MJ
We added 281.2MJ of energy in the form of diesel into the engine to get us 100Km down the freeway.
Assuming we traveled at 100km/hour.
281.2MJ / 3600 seconds/hour= 78KJ/s
= 78KW (kilo-watts)
Over the 100km trip, we consume on average 78KW.
KW (kilo-watt = thousand-joule every second) is a unit that tells us the rate of energy being used.
Unit KW is used show the maximum amount of power (power = rate of energy) an engine can produce. This particular Hyundai vehicle engine is tested to produce a maximum of 122KW of power.
If we drive for 1 hour at 100km/h our total energy used is 78KWh.
KWh (Kilo-watt hours) is a measure of the total ‘amount’ of energy.
This is what we see on our electricity bill and makes it possible to compare with the electric vehicle.
We used 78KWh of energy to drive 100km
Why is electric more efficient?
Regular car with internal combustion engine
- An ‘internal combustion engine’ explodes a fuel source like diesel, at high heat and under pressure inside a piston chamber, which pushes the piston up, turning an axle connected to the wheels.
Imagine an explosion, everything pushes out right? Well if you confine that explosion you can use it to do work, like push an object.
- The combustion engine is built very heavy to contain the high heat and pressure of the explosion. Heavy means more weight to move, requiring more energy and more fuel. It’s harder to move 100kg vs 10kg.
- High temperatures give better ‘thermal efficiency’ in combustion — which means you turn more chemical energy inside the diesel fuel into mechanical energy in the form of a rotating axle. But with high temperatures, we also have greater energy losses as heat to the environment. You need high heat to make the reaction go, but you then lose that heat as waste forever, reducing the efficiency of the engine.
- Burning carbon (wood, diesel, petrol, kerosene etc) creates CO2.
CO2 is a greenhouse gas and increasing levels of greenhouse gas in the atmosphere is warming the planet driving climate change.
- The efficiency of an engine is a measure of the energy input/energy output. The volume of fuel put in, divided by the power output of the engine. Every bit of heat, friction, and exhaust is energy escaping the system — lowering the efficiency.
- The efficiency of a car engine is known to be 15–20%. Diesel engines are slightly more efficient than petrol, formula one cars are more efficient reaching 47% and rocket ships as much as 70%. Diesel burns hotter, F1 cars even hotter and rockets the hottest.
Electric car with electric engine
- Electric engines turn electricity into mechanical work using an electric motor. An electric motor is the opposite of an electric generator.
- In an electric motor, a coil of wire is placed between magnets. The coil of wire is connected to an electricity source eg battery. Imagine it in the same way a battery is connected to a light globe in a torch, the wound coil is like the globe, when both ends of the wound coil are connected to the battery a charge flows through the coil but instead of creating light, it creates an electric field. The wound coil with electric charge flowing through it, creates an electric field which interacts with the magnetic field of the magnets. The two fields push and pull on each other making the coil rotate.
- There’s very few parts, very little heat, and zero exhaust.This gives the electric motor a much higher efficiency of 90%.
- There are energy losses in the generation and transmission of the electricity before it reaches the car. The efficiency of fossil fuel generation is about 25%.
- There are energy losses in the inverter, battery, and charger of the vehicle. The total efficiency of the car including these energy losses comes to around 70% for the electric vehicle.
This analysis assumes we still use fossil fuels to produce electricity. So you might think ‘whats the point then?’.
An electric car still uses half the amount of energy compared to the MOST efficient gasoline car on the market.
That means if I was to take the 7.4L of diesel and place it into an electric generator instead of my car engine. I’ll get double the distance in my electric car.
And as we generate more electricity from renewable sources the emissions will plummet. The efficiency will not rise, but that becomes arbitrary once emissions are eliminated and electricity becomes sustainable.
Why do we even have gasoline cars then?
The main reason people will give for the lack of electric vehicle use is the battery technology, which is no longer a problem.
There are many other commercial reasons why the technology was help back, but I’ll leave that for you to find.
Batteries do use hazardous chemicals and rare earth metals — The key to this problem is figuring out how to recycle these chemicals effectively.
If your next car is an electric car and you drive 20 minutes each way to work every day. You will reduce your energy consumption by somewhere in the range of 100KWh each week.
The average family home uses between 20–35KWh each day.
Driving an electric car could be the equivalent of making your house completely energy neutral with zero lifestyle change impact to your life.
Riding a bike will reduce it even further… 🙂
Also published on Medium.