Sylvie Willis
The shift towards electric vehicles (EVs) has been gaining momentum for over a decade, and with it comes a new way of measuring fuel efficiency. Unlike traditional combustion engines, which measure fuel efficiency in litres per 100 kilometres (L/100 km) or miles per gallon (MPG), electric vehicles use kilowatt-hours (kWh) as their standard unit of energy consumption. This is because electric motors operate differently from combustion engines, and their power outputs are more accurately quoted in kilowatts (kW). The most common way to express energy efficiency for EVs is kilowatt-hours per 100 kilometres (kWh/100km), representing the amount of electrical energy consumed per 100km. This measurement can be converted to kilometres per kilowatt-hour (km/kWh) or miles per kilowatt-hour (mi/kWh), indicating the distance travelled per unit of energy. While kWh/100km is the standard, some regions may use other measurements, such as kWh/mi or MPGe (miles per gallon of gasoline-equivalent). As the infrastructure for long-distance electric driving continues to develop, understanding these measurements will become increasingly important for consumers comparing the fuel efficiency of EVs with traditional gas-powered vehicles.
| Characteristics | Values |
|---|---|
| How is power output measured? | In kilowatts (kW) or brake horsepower (bhp) |
| How is fuel consumption measured? | Kilowatt-hours (kWh) |
| How is battery capacity measured? | Kilowatt-hours (kWh) |
| How is fuel efficiency measured? | Kilowatt-hours per 100 kilometres (kWh/100km) or kilowatt-hours per mile (kWh/mi) |
| How is energy unit per mile calculated? | In Europe, it is expressed in the metric system as litres per 100 kilometres (L/100km). In the US, it is measured in miles per gallon (MPG). |
| How is the energy unit per mile calculation different for electric vehicles? | Miles per gallon of gasoline-equivalent (MPGe) |
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What You'll Learn
Kilowatt-hours per 100 kilometres (kWh/100km)
For example, a family car with a fuel consumption of 6L/100km would equate to about 17kWh/100km. On the other hand, a muscle car with a fuel consumption of 17L/100km would translate to approximately 49kWh/100km.
It is important to note that the kWh/100km measurement does not mean that an EV will travel 100 kilometres on a full charge. Instead, it indicates the amount of power required to travel that distance. For instance, the Focus EV has an efficiency rating of 32 kWh/100km, but its estimated driving range is only about 83 kilometres on a full charge.
The kWh/100km unit is also used to compare the energy efficiency of EVs with that of traditional combustion engine vehicles. In Canada, the energy efficiency of combustion engine vehicles is typically measured in litres per 100 kilometres (Le/100km). The Environmental Protection Agency in the United States has calculated that 1 gallon of gasoline contains the electrical equivalent of 33 kWh. This allows for a reasonable estimate of how the energy efficiency of an EV compares to a combustion engine vehicle.
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Kilometers per kilowatt-hour (km/kWh)
Km/kWh is a useful metric for consumers to compare the fuel efficiency of electric vehicles with hybrid and gas-powered vehicles. The lower the number of km/kWh, the more efficient the vehicle. For instance, a family car with a fuel efficiency of 6L/100km would equate to about 17kWh/100km.
The electric range of a car depends on the battery size and capacity. The battery capacity of an electric vehicle is measured in kilowatt-hours (kWh) and reveals the amount of energy a battery can store. A larger battery capacity will usually result in more range, but bigger batteries add weight, which could reduce the efficiency of the vehicle.
It is important to note that the consumption figures quoted by manufacturers may not be the exact figures achieved in reality, as the energy efficiency of electric vehicles can vary based on factors such as external conditions and driving style.
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Miles per kilowatt-hour (mi/kWh)
The mi/kWh unit is an important metric for electric car owners focused on cost. The lower the mi/kWh number, the more efficient the electric vehicle is at converting electricity into miles travelled. For example, a mi/kWh of 1 means the vehicle can travel 1 mile using 1 kilowatt-hour of electricity.
Kilowatt-hours per 100 kilometres (kWh/100km) is the most common form of expressing energy efficiency for electric vehicles. This is because it is the equivalent of litres per 100 kilometres (L/100km) or miles per gallon (mpg) in fuel consumption for conventional cars. However, mi/kWh is also a useful metric for electric car owners to understand their vehicle's efficiency and compare it to conventional cars.
It is important to note that the consumption figures quoted by manufacturers may not be the exact figures achieved in reality. This is because the energy efficiency of electric cars can vary based on factors such as external conditions and driving style. Therefore, mi/kWh can be a useful metric for electric car owners to understand their vehicle's real-world efficiency and make informed decisions about their purchase.
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Kilowatt-hours per mile (kWh/mi)
KWh/mi is calculated by taking the kilowatt-hours consumed and dividing it by the number of miles travelled. For example, if an electric car consumes 24 kWh of energy to travel 100 miles, its kWh/mi is 0.24. This can also be expressed as 24 kWh/100 mi.
The lower the kWh/mi, the more efficient the vehicle is at converting electricity into miles travelled. For instance, the 2020 Tesla Model 3 has been recognised for its impressive kWh/mi of 0.24, resulting in an estimated annual fuel cost of $450. On the other hand, the 2001 Ford Explorer USPS Electric is considered the least efficient electric car in terms of kWh/mi, with a higher fuel cost of $1,700 per year.
It is important to note that the kWh/mi of an electric vehicle does not necessarily indicate the distance it can travel on a full charge. For example, while the Ford Focus EV has an efficiency rating of 32 kWh/100 mi, it can only travel about 83 miles on a full charge. This is because the range of an electric vehicle depends on various factors, including battery size and capacity, terrain, climate, and driving style.
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Miles per gallon of gasoline-equivalent (MPGe)
The unit of energy consumed is deemed to be 33.7 kilowatt-hours (kWh) without regard to the efficiency of the conversion of heat energy into electrical energy. This equivalence is true if the heat engine, generating equipment, and power delivery to the car battery are 100% efficient. However, actual heat engines differ vastly from this assumption.
MPGe was introduced in November 2010 by the EPA in the Monroney sticker of the Nissan Leaf electric car and the Chevrolet Volt plug-in hybrid. The ratings are based on the EPA's formula, in which 33.7 kWh of electricity is equivalent to one US gallon of gasoline. The EPA conducted focus groups that yielded research showing that participants did not understand the concept of a kilowatt-hour as a measure of electric energy use. Instead, participants favoured a miles per gallon equivalent, hence the use of MPGe today.
MPGe does not necessarily represent an equivalency in the operating costs between alternative fuel vehicles and the MPG rating of internal combustion engines. The kWh/100km metric is more commonly used and standardised for energy consumption in the electric vehicle industry.
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Frequently asked questions
The most common way to express energy efficiency for electric vehicles (EVs) is kilowatt-hours per 100 kilometres (kWh/100km). This represents the amount of electrical energy consumed per 100km.
Kilowatt-hours per mile (kWh/mi) is the Imperial conversion of kWh/100km. It indicates the kilowatt-hour energy used to travel one mile.
The Environmental Protection Agency (EPA) created the unit miles per gallon of gasoline-equivalent (MPGe) to compare the relative energy consumption of gasoline (or hybrid) cars with that of electric cars.
The electric range of a car depends on the battery size and capacity. Battery capacity is measured in kilowatt-hours (kWh) and reveals the amount of energy a battery can store. An estimated driving-range number is also a key part of the EPA sticker for EVs.
The cost of fuelling an EV can be calculated by multiplying the electricity rate by the kilowatt-hours consumed. For example, to consume 75 kWh of electricity to fully charge an empty 75 kWh battery at a rate of $0.082 per kWh, it would cost $6.15.
