Last I heard electricity is worth the equivalent of about 75 cents per equivalent gallon of gas, based on 3 dollars a gallon for gas.
Using the average U.S. electricity rate of 9 cents per kilowatt-hour (kWh), 30 miles of electric driving will cost 81 cents. If we optimistically assume the average US fuel economy is 25 miles per gallon, at $3.00 gasoline this equates to 75 cents a gallon for equivalent electricity. Compared to a regular hybrid's real-world 45 miles per gallon, it's effectively $1.20/gallon. PHEVs are meant to plug-in at night. In many areas of the country, overnight power is available at a lower cost. As PHEVs start to enter the marketplace, we'll see increasing support from electric utilities, as they'll offer reduced nighttime rates to incentivize off-peak charging. In some areas where wind and hydropower is wasted at night, the rate can be as low as 2-3 cents per kWh. That's 20-25 cents a gallon.
http://www.calcars.org/vehicles.html
If demand for overnight power increases geometrically due to widespread adoption of electric vehicles, the price will go... down?
I would not count on it.
I've known several people with Hybrids, and none of them have gotten over the mid-thirties in gas mileage. Maybe some people do, but I haven't talked to any of them. Also, the Honda Civic Hybrid compared to the regular Civic, requires around 200,000 miles to recover the initial price disparity, that's assuming the batteries don't have to be replaced. The VW Beetle Diesel I had got a legitimate 45 mpg and could cruise at over 100 mph (didn't get 45 mpg at that speed, but got 45 at 70 on the highway.) I think the diesels are being overlooked because they're too practical. True Greenies want some pie in the sky thing that nobody's ever thought of. For the Greens to accept something, it has to require massive initial cash infusions, use solar or wind power, take at least 40 years to recover initial investment, and have a life span of around fifteen years.