The electricity used to recharge a plug-in hybrid must first be generated and transmitted to the consumer’s home. From a quick internet search, I found that the efficiency of thermal generating plants can range from 35-55% and transmission losses can range from 5-7%. That means that 47-65% of the energy from the fuel going into the power plants is wasted before it reaches the plug-in hybrid.

I am skeptical that this loss has been properly incorporated into the fuel efficiency comparison of traditional and plug-in hybrids. Rather, I suspect that the “huge” gains offered by plug-in hybrids are greatly overstated because of the faulty assumption that electricity draw from the socket at home is produced at 100% efficiency. I have yet to see electricity producers – who stand to profit from huge increases in electricity demand – race to clarify this assumption.

I acknowledge that comparing the true efficiency of traditional and plug-in hybrids is very difficult – but it must be done in order to make the right choice of technology. Comparing the two technologies is a case of comparing apples to oranges. That does not mean they cannot be meaningfully compared. It just means that they should be compared only after one understands how they are alike and how they are different.

The differences are substantial. Traditional hybrids have one source of fuel: gas. Plug-in hybrids have two: gas and grid power (which in turn comes from a variety of sources). Furthermore, efficiency is measured in different ways for the two fuels. The efficiency of gasoline used in cars is most commonly expressed in MPG (or 100km/L). The efficiency of electricity generation and distribution is more commonly expressed as a percentage (the energy produced divided by the energy contained in inputs used by the power plant, i.e., oil, coal, gas, uranium, wind, water, etc.). The inputs used by power plants are generally not automotive gasoline and therefore contain different quantities of energy per gallon (or liter). Therefore our comparison problem cannot be resolved by simple arithmetic that translates the amount of grid power used into an equivalent quantity of gasoline. At this stage, it seems like apples really cannot be compared to oranges.

However that is not the case if one looks further upstream – all the way back to the well (or the mine or the corn field). By starting with primary resources, it is possible to calculate just how much energy is used (in extraction and processing) and wasted (in generating power) by the time the rubber hits the road. It is through this admittedly complex analysis that we can find a meaningful basis of similarity – the lifecycle use of energy – for comparing our apples and oranges. However complex, this is precisely the type of analysis that is required to answer the fundamental question: in which technology – traditional or plug-in hybrids – should we invest to make the best use of our resources?

I wrote about them in a post in my own energy policy blog (at http://www.interenergysolutions.com/blog/?cat=11), suggesting four basic tests that a new vehicle technology would have to pass in order to be accepted by the mass market.

1. they need to fit into the existing infrastructure of fuel distribution fairly seamlessly.

2. people need to be able to use the vehicle in much the same way they’ve used vehicles in the past.

3. their cost can’t be too much higher.

4. other advantages are nice. (faster acceleration is possible with hybrids, for example).

Plug-ins are doing well in three out of four of these categories. Other new vehicle technologies — hydrogen being a quite notable example — do not. This will be a very interested technology to watch.