Saturday, January 22, 2011

The Right Time to Charge a Car

Some engineers studying the problem of supplying electricity to electric cars are assuming that the right time to recharge a car is at night. That might make sense if you are looking only at making the most efficient use of the electric grid, and it works for commercial fleets that are used only during the day, but it is not the right answer in many other cases.

If an electric car is your personal car, this also means it is your primary means of emergency transportation. If a disaster forces you to evacuate, or if someone needs to go to the hospital, you will be glad to have your car running. That means the right time to charge the car, if it is mostly discharged, is the first chance you get. For commuters, this may mean recharging the car the minute you get home, and perhaps also when you park the car at work.

Another scenario involves charging cars from solar panels that are right there in the parking lot. Surely the price of solar panels will fall again by a factor of 2, and then this will become one of the more popular ways of charging a car, bypassing the grid entirely — but obviously, only during daylight.

Some of the engineers looking at the electric grid appear to have an exaggerated idea of the energy electric cars will consume. Realistically, the world won’t switch to electric cars until they become more efficient than they are now. But look at it this way: if we stopped making new fuel-burning cars today, it would take until 2036 to wear out and use up the fuel-burning cars we already have. The transition to electric transportation will be so slow electric planners won’t even see the changes from one year to the next, amid all the other changes that will be happening at the same time. Just to keep things in perspective, technological changes in refrigerators and air conditioners, as old equipment is retired and replaced, will make a bigger difference on the grid than electric cars will.