Energy Efficiency, Grid Scale, Storage

Mileage Costs of Plug-in Hybrids

I continue to read with optimism the PHEV (plug-in hybrid vehicle) concept, especially the Chevy Volt. TESLA also put out a paper a while back (July, 2006) regarding its entry. My question is this: At US $0.10-0.12 a kWh from my local utility, how much will it cost me to drive the Volt’s fully charged 40 miles? Since I don’t have any idea how many “miles per kWh” it takes, I can’t make the calculation…and I’ve looked at BTU and megajoule equivalents and I now have a headache. — Art F., Dallas, TX

Art, I am glad you asked this question because I have heard from many people the need to address this issue.

To figure this out, I first calculated the average cost per mile of a car powered by gasoline. The gasoline car at US $3.50/gal driving for the equivalent of one gallon of gas, say 20 miles, comes to $3.50/20 = $0.18 per mile. If we assume that the nationwide average fuel economy for autos is approximately 25 mpg, then we’re looking at US $0.14/mile for gasoline @ US $3.50/gal. You also have to factor in the cost of motor oil, say US $50/oil change for 5,000 miles, which adds $.01/mile to the gasoline cost, or a total of US $0.15 per mile.

I then asked then Dave Goldstein, President of the Electric Vehicle Association of Washington, DC, and a nationally-known electric-vehicle expert, to provide the calculation on electric vehicles. He states that, “on electric power only, [the] Volt should get approximately 40 miles all electric range (AER) on about 10 kWh or $1.20 (@$0.12/kWh) /40 = $0.03/mi AER. I don’t have a solid figure yet on what the anticipated Volt mpg will be on gasoline (which powers a generator that recharges the battery.) I will have to check the claimed fuel economy on *gasoline only* from the Volt Website. Rough guesstimate: 45-50 mpg, about equivalent to a Prius, which @ 3.50/gal /47.5 av. mpg = $0.07/mi. So I would expect averaging more gasoline than electric would hover around $0.06 per mile.”

I would like to put a little rain on this parade regarding environmental benefits of electric-grid charged vehicles. For pure electric vehicles, while they may have zero tail pipe emissions, the electricity that charges their batteries can come from coal, possibly oil, etc. and emissions from power plants make this a less optimum approach.

Plug-in hybrids help alleviate this because they may be able to provide peaking electric power back into the grid when not in use. This would then offset electricity from the older, more polluting electric power plants. Renewable-based electricity tied to pure electric vehicles has the best emissions profile, and use of plug-in hybrids on a large scale would aide greater use of intermittent renewables such as solar and wind by providing storage.

So it is critical to look at the entire fuel cycle when looking at emissions. But I must say, I truly enjoy driving my Prius and I am achieving high 40’s/low 50’s in miles per gallon, especially these days.