Energy in the Battery

The Ford Focus Electric has a 23 kilowatt-hour battery but this doesn’t mean a whole lot at first. It sounds like a lot of energy, but is it? Even if you consider the car can drive about 75 miles it still doesn’t tell you anything about what 23 kWh actually is. A gas car would use maybe 2.5 to 4 gallons of gas to pull off driving 75 miles but how does that compare with 23 kWh?

What we can look as is the energy content of gasoline and compare that to 23 kWh. The energy content is simply how much energy a certain amount of fuel contains. This is usually defined by volume of fuel as energy density refers to how much energy is in a unit of mass. That is important when it comes to batteries as they have low energy densities but for now let’s stick with energy content. There will be a post on that topic later.

Gasoline has an energy content of about 33 kWh per gallon. As stated my car has a 23 kWh battery. Based on total energy my car has the same energy content as 0.7 gallons of gasoline! That’s a tiny amount of energy for a vehicle and imagining driving around with a half-gallon of gasoline is shocking! If you imagine a gas car with a ten gallon fuel tank the car has a total of 330 kWh of energy. Once again compare this to an electric cars’ total energy of less than 30 kWh. This is partially why electric cars have such small ranges; they simply don’t have as much energy to work with.

But if you look what you can do with that energy a clearer picture appears. On that 23 kWh my car drive 70 miles: this is an average of 330 Watts per miles. If you consider the very good gasoline car from above using 2 gallons to drive 70 miles (35 mpg) you get an average of 940 Watts per mile; the gas car uses three times the energy of the gas car. This makes intuitive sense as the miles per gallon of a gas car is about a third of an electric when you account for energy used equivalently. According to energy use alone, my car gets about 100 miles per gallon: about three times as good as anything else.

Even though electric cars have a tiny amount of energy compared to a gasoline car they still use that energy much more efficiently than a gas car could. Numbers alone show at least a 200% gain of efficiency and that seems to be a minimum. Heavier gas vehicles have much lower mpg values so a 500 or 600% gain on efficiency isn’t surprising. Electric cars get more “bang for your energy buck” or something like that!

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