Electric Cars Energy Savings

Transportation
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Contact	William Mook
Topics	Active Transit Autonomous Vehicles Connected Vehicles Electric Cars Energy Savings Electric Vehicle Charging Infrastructure Electric and Hybrid Vehicles Freight High Speed Rail Hyperloop Intelligent Transportation Measuring Transportation Performance Mobility Mobility Hubs Right-of-way Management Self Driving Policies and Procedures Shared Mobility Smart Building-related Mobility Transit-Oriented Development Urban Air Mobility

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Electric vehicles (EVs) can provide significant energy savings compared to traditional gasoline-powered vehicles. The exact amount of energy savings will depend on a variety of factors, including the specific EV model, the type of battery it uses, and the efficiency of the charging system.

One way to quantify the energy savings of EVs is to compare their "miles per gallon equivalent" (MPGe) to the fuel efficiency of traditional gasoline-powered vehicles. The MPGe of an EV refers to the distance it can travel on the same amount of energy as is contained in one gallon of gasoline.

For example, the average EV on the market in the United States in 2021 has an MPGe of about 110 miles per gallon of gasoline equivalent, while the average gasoline-powered vehicle has an efficiency of about 27 miles per gallon. This means that, on average, an EV is about 4 times more efficient than a traditional gasoline-powered vehicle.

In terms of actual energy consumption, this means that an EV will use about one-quarter as much energy as a traditional gasoline-powered vehicle to travel the same distance. This can translate into significant energy savings over the lifetime of the vehicle.

It is also worth noting that the energy savings of EVs can be further increased through the use of renewable energy sources to charge the battery, such as solar panels or wind turbines. This can help to reduce the overall carbon footprint of the vehicle and further contribute to energy savings.

Calculation

EVs have several advantages over conventional vehicles: Energy efficient. EVs convert over 77% of the electrical energy from the grid to power at the wheels. Conventional gasoline vehicles only convert about 12%–30% of the energy stored in gasoline to power at the wheels.

According to the EPA U.S. vehicle fuel economy has risen to record 24.7 mpg. A US gallon contains 130 MJ of energy. Dividing by 24.7 mpg obtains 5.26 MJ/mile. The EPA official range for the 2017 Model S 100D, which is equipped with a 100 kWh (360 MJ) battery pack, is 335 miles (539 km). Dividing 335 miles into 360 MJ obtains 1.08 MJ/mile.

Note: The 2020 Model S 100 long range has an improved permanent magnet motor giving the 100 kWh battery a 373 mile (600 km) range! This obtains 0.965 MJ/mile!

It takes 1.08/5.26 = 0.2053 ~ 20.5% as much energy to move a vehicle using a battery than using an internal combustion engine.

Note: The 2020 model 18.4% as much energy!

A gallon of petrol in the USA costs $2.83 and that takes a vehicle 24.7 miles or 11.457 cents per mile.

A kWh of electricity costs $0.12 in the USA. A kWh contains 3.6 MJ of energy. A Tesla battery is 93% efficient. So it takes 1.075 MJ of electricity to get 1.000 MJ to the wheels so $0.12 * 1.075/3.6 *1.08 = 3.87 cents per mile.

Note: For the 2020 model 3.46 cents…

A gallon of petrol releases 8.9 kg of CO2 for each gallon burned (2.8 kg). This is 360 grams of CO2 per mile traveled.

Using a wind turbine, solar panel, hydroelectric plant, or nuclear plant produces zero CO2 electricity. So this source of electricity has zero carbon footprint.

Crude oil is 86% carbon by weight and releases 46.4 MJ of energy per kg of fuel. Natural gas is 75% carbon by weight and releases 55.6 MJ of energy per kg of fuel and steam coal used in power plants is 78% carbon by weight and releases 29.2 MJ of energy per kg of fuel.

Thermal generators are typically 42% efficient making electricity from heat.

The carbon in the fuel just described is combined with oxygen to form carbon dioxide, which adds the mass of oxygen to each carbon atom. So on a molar basis;

C + O2 → CO2

12 grams of Carbon plus 32 grams of Oxygen yield 44 grams of Carbon Dioxide.

So now we can compute how much carbon dioxide is released for each MJ electrical of energy consumed.

Oil Fired Plant

0.86 * 44/12 / 46.4 = 68 grams/MJ thermal → 161.8 g/MJ electrical → 174.8 g/mile

Note: for 2020 model 156.2 g/mile

Natural Gas Fired Plant

0.75 * 44/12 / 55.6 = 50 grams/MJ thermal → 117.8 g/MJ elec → 127.2 g/mile

Note: for 2020 model 113.7 g/mile

Coal Fired Plant

0.78* 44/12 / 29.2 = 98 grams/MJ thermal→ 233.2 g/MJ elec → 251.9 g/mile

Note for 2020 model 225.1 g/mile

Direct Petrol Burning → 360 g/mile (above)

So, NO MATTER WHAT THE SOURCE - NO MATTER WHAT THE METRIC- electric autos use less energy, cost less and pollute less than petrol autos.

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