Energy Density

Energy Density and Power Density are two ways to measure the speed and range you can get with a given vehicle. Each vehicle has a maximum weight it can carry, and a maximum volume or size it can carry. Together those form a budget into which you fit the people, cargo, drive train, electronics, and battery pack.

volume = the size of the area for batteries (in liters)
weight = the carrying capacity of the vehicle (in kilograms)

Energy density is the kilowatt-hours stored by volume or by weight. Power density is the energy (in watts) that can be delivered by volume or by weight.

power-density = max-watts / liter or kilogram
energy-density = kilowatt-hours / liter or kilogram

These are usually measured as

volume energy density = kilowatt-hours / liter = kwh / l
weight energy density = kilowatt-hours / kilogram = kwh / kg

Remember that

1 kilowatt-hour = 1 kilowatt used over 1 hour = kwh
1 kilowatt = 1,000 watts

And remember that, as an electric vehicle moves down the road, it consumes electricity. Say the vehicle has a 120 volt electrical system, and uses 30 amps to cruise, therefore the vehicle cruises at 3.6 kilowatts. If the vehicle is run for an hour, it consumes 3.6 kilowatt hours of electricity.

The main measurement controlling the range capability of a given battery pack in a given vehicle is, how many kilowatt-hours can you carry in the vehicle. Each vehicle has a designed carrying capacity in both volume and weight. Based on the energy density of a given battery pack determines how many kilowatt-hours can be fit into the vehicle. Obviously the batteries have to fit within the physical dimensions and carrying capacity of the vehicle.

Adapted from: Power Density in Batteries and Electric Vehicles