EV Efficiency: Why it’s Important

When coming from a gas car efficiency is often ignored. Cars have large gas tanks that can easily go 400 miles or more on a single tank of gas, even in a large fuel inefficient vehicle. The less efficient the vehicle the larger the gas tank to keep the same range.

Why is it different with EVs? It is all in the battery. To get more range from an EV a battery needs to have a larger capacity, or equivalent to a bigger fuel tank. Batteries measure their energy storage in kWh, that is how much power the battery can put out over a unit of time. Skip the background if you have a handle on units of efficiency.

Background

A car with a big battery like a Tesla Model 3 Long Range has a battery of about 80 kWh. A hair dryer you have in your bathroom uses roughly 1 kW (more on high, less on low) of power, so this battery could power your hair dryer for about 80 hours, or just over 3 days. A battery in the Honda Clarity is only 12 kWh usable (label is 17 kWh, it isn’t all used). This could power the same hair dryer for 12 hours.

Enough about split ends, what is EV efficiency? In the US people measure efficiency in how far the vehicle will go on a unit of power, other countries measure it in power to go a unit distance. In the US we often say bigger is better so we measure in miles/kWh (larger number, higher efficiency) where other countries want to minimize the number and use kWh/100 km or Wh/km. The choice doesn’t matter, but a typical vehicle might drive 3.3 miles / kWh, meaning every hour you use your hair dryer you could move a car 3.3 miles. In other parts of the world people might claim it gets 18.8 kWh / 100 km or 188 Wh/km.

What is an MPGe

I will discuss this more at a later date, but MPGe is a standard conversion to indicate how much energy an EV uses from the wall and converts that to the energy in a gallon of gasoline. This is intended to make it easier to compare EVs and gas cars in total energy used from the wall or from the pump.

Say what? For today’s purposes, take the MPGe and divide it by 33.7 kWh/gallon and you get the miles/kWh (from the wall) figure. Go find your favorite electric EV at fueleconomy.gov The most efficient is the Hyundai Ioniq at 150 MPGe, meaning it can go 150 miles on the energy contained in 1 gallon of gas, including charging losses, or 4.45 miles on a single kWh of electricity.

For the Ioniq this means it can use a smaller and cheaper battery than its competitors to go the same distance. The IPace at 80 MPGe is not really a competitor, but has about half the efficiency as the Ioniq, so to get the same range it would have to have almost twice as much battery.

Some of the PHEVs are the worse offenders, the Mercedes Benz GLE550e gets an appalling 38 MPGe. The competition of the Jaguar IPace, which is already not efficient, can drive twice as far on the same battery power.

Battery Costs

If a car has an 80 kWh battery and can drive an average of 3.5 miles per kWh, it can go about 280 miles on a charge. The bigger the battery in kWh the larger the range of the car for the same efficiency. So why don’t we just put a bigger battery in the cars?

We have to look at battery technology. For a given type of battery, the larger the capacity the heavier and more expensive the battery will be. How much do current battery costs? At the finished pack level the costs are about $200/kWh for the cheaper packs. An 80 kWh pack costs the manufacturer about $16,000. Add profit margin to that and it might be more like $20,000.

Why Efficiency Matters

Competition. Say we have 2 cars, one that gets 3.5 miles/kWh and one that gets 3 miles/kWh. If they both have the same 60 kWh battery size. The more efficient 3.5 mile/kWh car will go 210 miles on a charge and the less efficient car will only go 180 miles on a charge. Which would you buy, the 210 mile car or the 180 mile car for the same price?

Pretend we want to give the car an extra 30 mile range to match by making the battery 70 kWh, adding 10 kWh. How much will that cost? About $2,500 at $200/kWh plus some profit. Which car do you buy, the one that costs $2,500 more? Not only that, the vehicle starts adding weight.

Charging and Efficiency

Efficiency doesn’t matter only for range, it has the same effect on charging. If you charge both of these sample cars at the same charging rate, the more efficient car will charge quicker (meaning it will charge more miles per minute it is plugged in). This means that the more efficient car will be longer range and will charge more miles faster for the same battery size.

With gas cars this issue is not so apparent to the consumer as it is with EVs. A bigger gas tank only takes a small amount of time longer to fill, and the range is similar, the only time the consumer notices a gas vehicle efficiency is cost at the fuel up.

A less efficient EV has more impact to the purchase price than a gas car where you only pay for it at the pump. In 5 years it might not matter as batteries get cheap enough and chargers are fast enough, but in the meantime it does make a difference when shopping for a new EV. Is it a big enough difference it would change your buying habits? That is for you to decide, but there are definitely vehicles to avoid because of bad efficiency.