Do electric cars really save energy?

According to the EPA, U.S. vehicle fuel efficiency has risen to record 24.7 mpg. Each US gallon now contains 130 MJ energy. Divided by 24.7 mpg, you get 5.26 MJ/mile.

The EPA’s official range for 2017 Model S 100D, which has a 100 kWh (360 MJ battery pack), is 335 miles (539km). Dividing 335 miles into 360 MJ obtains 1.08 MJ/mile.

Notice: The 2020 Model S 100 long-range has an upgraded permanent magnet motor that gives the 100 kWh battery a range of 373 miles (600 km). This gives you 0.965 MJ/mile

It takes 1.08/5.26 = 0.2053 = 20.5% more energy to drive a vehicle with a battery than an internal combustion engine.

Notice: 2020 model uses 18.4% more energy

The average cost of a gallon of gasoline in the USA is $2.83. This covers a distance of 24.7 miles. This is 11.457 Cents per mile.

In the USA, a kWh of electricity is $0.12. A kWh is 3.6 MJ in energy. A Tesla battery is 93% efficient. It takes 1.075MJ of electricity to deliver 1.000MJ to the wheels. This is $0.12 * 1.075/3.6*1.08 = 3.87c per mile.

Notice: The 2020 model will be 3.46 Cents…

8.9kg of CO2 is released per gallon for every gallon of petrol (2.8kg). This equals 360 grams CO2 per mile.

Zero CO2 electricity can be produced by a solar panel, wind turbine, or hydroelectric plant. This source of electricity leaves no carbon footprint.

Crude oil contains 86% carbon and emits 46.4 MJ per kg of fuel. Natural gas contains 75% carbon and emits 55.6 MJ per kg of fuel. Steam coal is 78% carbon and releases 29.2MJ per kg.

The efficiency of thermal generators is typically 42% when it comes to producing electricity from heat.

The carbon in the fuel is mixed with oxygen to create carbon dioxide. This adds mass oxygen to each carbon atom. On a molar basis.

C + O2 = CO2

Carbon Dioxide is made up of 12 grams of Carbon and 32 grams Oxygen.

Now we can calculate how much carbon dioxide is released per MJ of energy used.

Oil-fired Plant0.86 *44/12 / 46.4 = 68% MJ thermal – 161.8g/MJ electric – 174.8g/mile

Notice: 2020 model 156.2 g/mile

Natural Gas-Fired Plant
0.75 * 44/12/ 55.6 = 50g/MJ thermal – 117.2 g/MJ elect – 127.2g/mile

Not applicable to 2020 model.

Coal-fired Plant
0.78* 44/12/29.2 = 98g/MJ thermal- 233.2g/MJ elec- 251.9g/mile

Notice for 2020 model 225.1g/mile

Direct Petrol Burning – 360 g/mile (above).

It doesn’t matter what the source – it doesn’t matter what the METRIC-electric autos consume less energy, pollute less, and cost less than petrol cars.


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