If It's Too Good To Be True ...

Chevrolet leads off the content at its website for the Volt electric car with a cryptic explanation of the test conditions that allow them to claim 230 mpg fuel economy for an electric car. That's good, because nobody in their right mind would accept such an outlandish figure without at least a stab at knowing the test conditions. It's bad because fuel economy figures for an electric vehicle are meaningless, since an electric vehicle does not run on fuel.

Hybrid automotive propulsion systems run primarily on fuel (gasoline, diesel, liquified natural gas, etc.) with a means of capturing energy generated when the car's propulsion demand is lower than the engine's available output, then delivering it back when propulsion demand is high. That allows the vehicle to have an undersized engine and still deliver bursts of performance equivalent to a car with a much more powerful engine.

As an example of how this works in practice, some Formula One race cars use a similar technology called the kinetic energy recovery system (KERS). While braking for a corner, the KERS system captures some of the energy that would be burned off as heat in the brakes and stores it in a battery. The driver has a push button that pours that energy back through the drive train, delivering some 80 HP in excess of the engine's maximum output.

Two anecdotes are available from this experiment. First, it is said that KERS equipped cars are nearly impossible for non-KERS cars to pass under acceleration. Does that surprise anyone? The second bit of information is that the leader in this year's F1 constructors championship does not use KERS. What that really means, and what the standings will be at the end of the season are valid topics for beer hall debates.

Electric vehicles - the Volt included - are primarily driven by electric motors. From an engineering standpoint, there's a lot to be said for this architecture. It's well understood. It vastly simplifies the mechanical drive train. Leaving out the battery pack, it reduces the powerplant weight by a lot. Consequently, it will likely reduce the energy cost of getting the payload from A to B. It probably will reduce maintenance requirements as well, since the components are few, quite robust, and don't suffer much wear.

I said that the technology is well understood. It is and has been for a very long time. Some of the earliest experiments in automotive technology were electric vehicles. I drove an electric forklift during the 1960s. My grandson has owned and operated a series of electric go karts for most of his life. Electric golf carts dot the fairways of America. Electric vehicle technology has been under development for at least as long as the internal combustion engine. What we know about it is a lot!

The problem, which I sidestepped above, is that battery technology is such that storing the energy needed to get that payload from A to B is enormously bulky and heavy. If A and B are significantly far apart, the size and weight of the battery becomes impractical.

The problem is storing enough energy in electric form to run the thing a reasonable distance. The Volt gets around this problem by installing an auxiliary power unit (APU) to provide power when the driver has been foolish enough to drive past the vehicle's point of no return on battery power, and wants to get back by, say, 3:45 PM for a meeting. The APU kicks in, providing enough juice to get you home.

Altogether, I have no problem with the Volt itself. It looks great - or at least as good as allowed by the inaesthetic drech that passes for automobile styling today. Not having driven one myself, yet, I can't answer for its performance, but electric vehicles generally can be made to go as fast as you want (for a while). From my comments above, you can tell that I like the concept from an engineering standpoint - especially for short trips with long recharge spells in between.

My problem is with the idea of assigning a miles per gallon performance figure. It makes sense for hybrid vehicles because the whole driving experience is energized by fuel from a tank. For an electric vehicle, with the bulk of the energy theoretically supplied by an electric outlet, it is rediculous.

So what if the current test protocol returns a result of 230 mpg? I can double that just by jiggering the test protocol for shorter trips so the horse gets back to the barn for more oats before having to limp the last few furlongs. If the car is good for 40 mi on battery power, I can jack the fuel economy rating to infinity just by allowing test trips of 39.5 mi.

It's just soooo bogus!