I was reading the latest issue of “Automotive Engineering” magazine and i read an article about the factors in “Fuel Economy” ratings for electric vehicles. this is a very interesting subject because electric vehicles need to have a universal measuring unit for efficiency that needs to be understood by the general public.
our current system of MPG (miles per gallon) is a ratio of distance/1 gallon of gasoline. these are 2 very common units that are easily understood by anyone who had graduated from high school. therefore electric vehicle efficiency needs to be broken down to a simple to understand measuring system, similar to MPG. The EPA and US Department of Energy have collaborated to mandate a unit system for electric vehicles.
For all electric vehicles the calculation begins with the gasoline equivalent energy factor, we are going to do this by breaking down both one gallon of gasoline and 1 watt/hour of electricity to their simplest common units of energy units, or BTU’s.
(One BTU equates to the amount of energy needed to heat one pound of water one degree Fahrenheit)
therefore we can deduct that one gallon of gasoline equals 115,006 BTU, or 12,307 watt/hour per gallon. now any electric vehicle’s energy can be measured in output of watts, therefore we now have a common unit that can be measured very easily and converted to a “Equivalent MPG” notice the quotes because we have only converted it to a unit that can be easily understood by the basic public, because most people you ask will not understand what 36Kw/100 miles means.
So why are the numbers so high? well the Mini-e (the window sticker picture) has an estimated 102 MPG/94 MPG these numbers are calculated properly, electric vehicles are FAR more efficient with the energy usage then ANY other gasoline engine in existence. This has to do with many factors with gasoline engines that consume energy, the heat from the exhaust, coolant heat, block heat, parasitic drag of the hundreds of moving parts in the engine and transmission, shifting of multiple gears. These items use almost 85%-95% of the available BTU output of a properly operating gasoline engine, leaving only approximately 10% or less to actually move the vehicle down the road, this number decreases with cold weather, wear and age. Contrast this to electric vehicles which use about 75%-85% of there available BTU to move the vehicle down the road, this is so much higher because there is little to no heat waste, no transmission, no wasted between shift time, no “cold engine” problems, and usually only about a dozon or less total moving parts. This efficiency also does not count the oil changes, timing belts, spark plugs, head gaskets, coolant, of maintenance parts that dont even exist on an electric vehicle.
In a simple conclusion, these numbers do not lie. Electric vehicles are far more efficient and far simpler in design and will be the next generation of transportation. The next debate is going to be if the companies will be allowed to use these high “equivalent MPG” numbers towards their CAFE numbers (corporate average fuel economy) the US dept. of energy is still debating this subject.
Experimental Electric Vehicles 