I remember when I was discussing a story about fast-charging batteries with someone that there was the conjecture that this was the hurdle to getting electric cars on the road. And I realized it wasn’t — heat dissipation issues aside (charging a cell-phone battery is one thing, but trying to scale that up is quite another) — the real issue is how much energy you need and how quickly you can deliver it. Grid capacity.

Electric cars will travel a few km per kWh of energy, so a 350 km range takes about 100 kWh, or 3.6 x 10^8 Joules. The good news is that this is more efficient than gasoline, which lets you go about 1 km per kWh. A gallon of gasoline has a little over 10^8 Joules stored in it, so 31 mpg is about 50 km/gal, and that makes an electric car with the above specs about twice as efficient. But if I can pump a gallon of gas in ten seconds, that means my energy transfer rate is 10 MW. That’s about 3 orders of magnitude higher than standard electricity delivery.

It’s pretty clear that any electric solution in the near future is going to involve shorter-range vehicles, be they pure electric or plug-in hybrid, which you could recharge overnight.

Challenges to grow with electric cars’ sales: Aging grid needs to handle more power

When a Chevrolet Volt is plugged into a 240-volt outlet, it will use about 3.3 kilowatts of power, or about the same amount of power as a dishwasher or air conditioner.

Most people are already familiar with what can happen when thousands of air conditioners are plugged in and running at the same time during the summer: brownouts.

“The last thing we would want is for everyone to come home … and plug them in at 5 or 6 o’clock on a hot, muggy summer afternoon … when we are at our peak,” DTE Energy Chairman Anthony Earley Jr. told the Free Press in an interview recently.

US residential consumption is about 30 kWh of electricity every day; houses probably more and apartments less. Regardless, 3.3 kW for 8 hours = 26.4 kWh, which is a significant bump.