Tuesday, August 18, 2009

It could also dim the Christmas lights...

As the marketing buildup for the Chevy Volt intensifies, something I had been wondering about is starting to occur to others:  Can you really just plug electric vehicles (EV) in like a shaver?

Consider the puff for a Mercedes EV:
All of the cars feature a liquid-cooled lithium-ion battery with a maximum capacity of 35 kWh; Mercedes says they charge in four hours when plugged into a typical wall outlet. The electric motor produces 70 kW (about 94 horsepower) and 236 foot-pounds of torque, propelling the little runabout to 62 mph in a little less than 11 seconds. [More]

Now do the math.

Imagine that. You could plug the BlueZero into your living room receptacle and in four hours transfer 35KWH of electricity from your incoming power line to your car's batteries. 35KWH in four hours. 8.75KWH in an hour. In the US, where we have 110V power, this means 79.5 amps of electricity are coursing through the walls of your house. I don't know about your house, but mine uses wiring that will safely pass 15A, less than a fifth of the 79.5A. That turns a four charging time in 20 hours. [More]

To put that in perspective, electric ovens are typically 30A (240V) circuits which would be equivalent to a 60A (110V) circuit.  That's big wire, dude.  Like #4 or #6.

Now add up the effect if all the houses on the  block suddenly went green.

Chief among those challenges is how thousands of power-hungry vehicles would tax distribution transformers at the local level. Such transformers have historically handled electricity load for about 10 average-size homes each.
Adding a plug-in car to the grid is equal to about a third of a house, Kjaer said. And because early adopters are likely to spring up in geographic concentrations, that could mean overloaded transformers at the distribution level or plug-in cars potentially causing power outages.
"The worst imaginable situation you could have is your neighbor yelling at you because you blacked out the neighborhood," Kjaer said.
Kjaer is less concerned about transmission or generation being overtaxed, as long as consumers are taught to charge their plug-in cars at night, during off-peak demand periods, to smooth the load. Kjaer said improving distribution is the key infrastructure challenge for utilities, aside from creating a network of charging stations.
"We're talking about the last 10 feet" between the house and the transformer, he said. "It's the last 10 or 20 feet that we've got to work on. We're got to work on it really hard, really quickly, because these cars are coming." [More]

Of course all these problems are simply opportunities for electricians and charger manufacturers, in a sense. But you probably ought to read the owner's manual before signing up to buy an EV and check your garage wiring.


Anonymous said...

In all fairness, you should seldom start with a totally dead battery. But What would happen if you got stuck along the side of the road with no power. Not as easy as getting a can of gas from the nearest station.

Anonymous said...

I heard the batteries are not too "green" if exposed in an accident