One Year of Electric Driving

I’ve driven my Chevy Volt for over a year now, and the numbers are in, with help from voltstats.net:

• 12,376 total miles driven
• 9,956 battery powered electric miles (80%)
• 2,420 gasoline generator powered miles (20%)
• 68 gallons of gasoline

Electricity bill doubled

Electric consumption increased 50%

So if my electric bill doubled, does that mean that my electricity consumption doubled with the car? Far from it. Home charging the car for a year added about 2,800 kWh, or about 233 kWh per month. That’s about a 50% increase over normal household consumption.

Household consumption is consistent and below average

Are my electric rates skewed because of high household electricity consumption (from air conditioning, or other variable demands)? No. The average annual electricity consumption in California was 6,296 kilowatt‐hours (kWh) per household in 2010, according to the 2009 California Residential Appliance Study conducted for the California Energy Commission. The chart below shows my household consumption, excluding EV charging, for 12 months before and after buying the Volt. This makes it clear that my normal household electricity usage is far from excessive, and in fact is less than average. Excluding EV charging consumption from this year, annual electric consumption is virtually identical to last year.

PG&E Rates are Crazy

PG&E’s “EA9 XB Residential Time-of-Use Service for Low Emission Vehicle Customers” provides baseline off-peak rates less than $0.05/kWh, and the Volt knows to only charge itself when the off-peak rates are in effect. So the 2,800 kWh of EV charging electricity should cost 2,800 x $0.05 = $140, right? Wrong! Instead, adding 50% to total electricity demand roughly doubles the total cost. This all happens through the combined magic of tiered rates and time-of-use rates. Tiers are typical in California electricity rate plans, including the conventional E1 residential rate plan that I used last year. With a tiered system, rates increase as usage increases, so this hits particularly hard for EV households. In the summer, I commonly reach the punitive >201% of baseline tier, with rates that can range up to 10 times the baseline. The E9A rate plan, an option specifically designed for EV households, adds another twist: rates change with the season and the time of day. So while off-peak rates can be under $0.05/kWh, they surge to $0.30/kWh or above $0.54/kWh in the summer during peak times. So the cheap electricity at night is more than offset by very expensive electricity for air conditioning on hot summer days. A typical summer electricity bill from PG&E looks like this:

My effective electric rate increased by 22%, and is 50% higher than the national average

So what are the true effective rates? Well, in the twelve months prior to owning an EV, my average rate under the standard E1 residential rate plan was $0.14/kWh. In the following twelve months, under the E9A time-of-use rate plan, my average rate increased to $0.18/kWh. From the chart below, its clear that in the winter months, the E9A plan offers effective rates that are equal to or lower than last year’s $0.14/kWh. In the summer months, though, rates are substantially higher. The EPA energy costs on the window sticker of a Volt assume the national average of $0.12/kWh, so the $0.18/kWh effective rate in PG&E’s California is 50% higher than the national average. It would be higher still if my household demand were higher than average, or if (gasp!) I owned a second EV.

Volt saves $1,180 in energy costs, compared with the car it replaced

So what’s the bottom line? How do the energy costs for a Volt compare with the gasoline costs of a conventional car? Well, that depends on the car used for comparison. My previous car required premium gas (as does the Volt) and averaged 24 mpg during the years that I drove it. Using California monthly average premium gasoline prices from the California Energy Commission, gas for my old car would have cost $2,167 for the 12,100 miles I drove in the past 12 months. That’s $18/100-miles. For the Volt, during this period, I used $293 in gas, and the incremental cost of electricity (compared with the previous year) was $767. So that’s a total of $1,059 in energy costs for the Volt, or a annual savings of $1,108. At $9/100-miles, that’s almost exactly half the energy costs for a 24 mpg conventional car.

EV energy costs vary by season

The chart above is strange. The slope of the Volt cost curve flattens out from 2,500 miles to 7,500 miles, which happens to correspond to the winter months. With E9A rate plan, the Volt energy advantage is much more impressive in winter, when a Volt operates for about 1/3 the cost of a conventional car. In the summer, the advantage is less impressive, with energy costs reaching 2/3 the costs of gasoline at times.

 What next?

With a year of data in the bag, I can get a better understanding of the costs and benefits of a solar system. This introduces yet another time-of-use rate plan option, as I described in Decoding Time of Use Rate Plans. And to make things even more interesting, PG&E plans to retire the crazy E9A rate plan, and replace it with a different crazy EV-A rate plan. The new plan was originally proposed in September 2011, and met with dozens of protests, including one from me. PG&E responded with a somewhat less objectionable proposal, which appears to have won support of the CPUC. Jack Lucero Fleck has followed these matters closely, and has a written a nice summary of the current PG&E proposal, and a letter to the CPUC with additional analysis.

We’re at the dawn of an electrified revolution that will have a profound impact on auto manufacturers, electric utilities, and the fossil fuel industry. Prospective EV buyers, and current EV owners face a shifting landscape, and considerable uncertainty about the true costs of energy. Governments and regulated utilities will stumble forward toward the inevitable future. It will be an interesting journey. I’ve been in the future for a year now, and complicated as it may be, I’m not going back!

The full year data and source charts from this post can be viewed in greater detail as a Google Spreadsheet. Comments, criticisms, and suggestions are welcome!