With the 500 car Cooper Mini E field trial, we're finally started to get some real-world data on the performance of electric vehicles.
The WSJ recently ran an article which surveyed participants in the field test and found they were generally getting in the 100-110 miles per charge range, less than the advertised 150. The battery in the Mini E is 35 kWH (not 35 kW as stated in the article). Combining this with data from a standard Mini Cooper, we can start to get a look at the actual emissions and cost of driving of the Mini E.
On the emissions front, if we assume 35 kWH for 100 miles, we can calculate the emissions if we use grid electricity. Using the EPA's eGRID data, we can calculate the emissions per 100 miles. On the gas-powered Mini, the average fuel economy is 32 MPG, and with 19.9 pounds of CO2 per gallon of gas, 100 miles produces a little over 62 pounds of CO2. I've attached a chart (pdf, xlsx) which shows the comparison on a state-by-state basis (the pdf is set to 100 miles of range for the Mini E, and the spreadsheet shows the same data, but lets you change the Mini E range and see the effect).
As we can see from the chart, with 100 mile range the Mini E has less emissions in 40 states, and has more in 10 states and the District of Columbia. Based on 12,000 miles of driving (a year's worth for many people), the Mini E would save 0.85 tons of CO2 per car, assuming they were spread across the US. To see the effect of state electricity sources, we see that in Wyoming the Mini E would generate almost a ton more CO2 than the gas-powered version, and in California it would generate almost 2.5 tons less. (Note to electric car marketeers - please stop telling me your car is zero-emissions.)
By playing with the range of the Mini E in the spreadsheet you can start to see that it is right on the cusp of being either a carbon winner or carbon loser. At 70 miles range (as some claim they were getting on the highway), the Mini E is worse than the gas-powered vehicle in 26 states plus the District of Columbia, and the national average goes negative. But at 150 mile range it is better everywhere in the US, saving 1.7 tons/12K miles.
In addition to GHG emissions we can trivially use this data to calculate the relative operating cost of the two Minis. In general we see the Mini E being $2 to $6 per 100 miles cheaper than its gas-powered sibling, or $250-$700 per year assuming 12,000 miles. While we don't know what the final price of the Mini E will be, we do know that the lease rate is about $500 more per month than the standard Mini, so its pretty safe to say that people won't be jumping on the Mini E as a cost-saving measure unless we (the taxpayers) all pitch in with an amazing rebate program (which wouldn't surprise me).
Finally, we don't have to settle for standard grid power. If I were to generate 10kW of solar a day, I could cover the 12,000 miles with no driving emissions (for real, this time). The DOE says I'd need 1,000 square feet or more of solar area to do this, but that's not out impossible (though it does dwarf the 30 sq ft area of the car itself!). The problem is that this would also raise the price of electricity over grid power, so would make the financials look even worse (unless, again, I can hit the rebate jackpot).
The other thing to keep in mind is that we assumed that we could power the car from the existing grid capacity. If we add lots of electric cars we'll have to turn on some more electrical generation capacity (aka 'non-baseload'), which is usually coal. We can see from the eGrid numbers that the CO2/kWh goes up from 1.29 lbs to 1.58 lbs when we use non baseload electricity, and the result (bottom row of the chart) is that we drop the Mini E emissions advantage from 0.85 to 0.37 tons per year.
In summary, its great to see the first electric cars finally hitting the road, and that we can start to get our first real data. For an initial pilot I consider these results to be quite good, assuming that you weren't really expecting zero emissions. But as we've seen, government subsidies and overall energy policy will be critical in determining whether electric cars will be a financial and environmental success.