7 Nov 2022 – Driven To Write

Two decades before BMW launched its first production EV, there was the E1 Concept.

Energy Density and Specific Energy are the twin holy grails for any automaker wishing to bring a viable electric vehicle to market. These two units of measurement are often confused, even by people who really should know better⁽¹⁾. In simple terms, energy density is the amount of energy that can be stored in a given volume, whereas specific energy is the amount of energy that can be stored in a given mass. The S.I. unit for the former is joules per cubic metre and for the latter is joules per kilogramme. In the context of electric vehicles, the energy component is more usefully measured in kilowatt-hours, since the joule is a very small unit of energy⁽²⁾.

Petrol has a specific energy⁽³⁾ of around 12.5kWh/kg. Diesel is slightly lower at around 11.5kWh/kg. These numbers might appear meaningless in isolation, but compare them with the specific energy of a traditional lead-acid battery, which is a tiny 0.04kWh/kg and you can Continue reading “E1 before i3”