How much extra electricity would we need to generate, If all cars were electric?

Question

how much additional electricity would we need to generate, If all cars were electric?

Feel free to approximate the number of cars that exist in the United States, how many total miles are driven, and the mile/kilawatt ratio. Be as accurate with these figures as you can, of course.

Please state your answer in gigawatts per year and SHOW YOUR WORK.

Thanks!!!

Answer 1

Do you mean just cars? Or lorries (sorry, trucks) and railway trains? For just cars ... in the USA ...

250 million people so ~ 100 million cars; battery cars are much less powerful - say 20 hp (15 kW) cruising; most cars are used in cities going to work (electric cars don't have the range for long journeys) so estimate 2 hours per day commuting

100 million x 15 kW = 1.5 GW (a little over the output of the usual power station) BUT

battery charging, retention and motor inefficiencies would add to at least 25% (ie 75% efficiency) so that's 1.5/0.75 GW

= 2 GW; AND

GW is power, I think you mean GWh per year; so

2 hours per day => 700 hours per year (@2 GW)

so that's 1400 GWh per year

assuming we don't find a way to include lorries (oops again, trucks), long distance cars (current battery technology has a limit of 100 miles or so) and trains. Trains would be the easiest to electrify - 'just' fit cables over the tracks and take the power from them.

Scientific American had a good article a year or two back about using sunlight in the desert somewhere (? Arizona, Nevada, they all look the same from Europe) to supply electricity for all USA needs. Hunt it down - it's got some good numbers.

Any good university will expect you to be good at these estimate questions - they're called 'Fermi questions' and are an excellent test of your scientific ability. Practice! (Or should that be 'Practise')?