how much additional electricity would we need to generate, If all cars be 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 info as you can, of course. Please state your answer in gigawatts per year and SHOW YOUR WORK. Thanks! (a)keirfamily: I did indeed mean gigawatt hours per year, i be just being lazy. I also spelled kilowatts wrong. you get the gyst of it though. Nice to see charging inefficiencies factored in to your thinking as well. I'd put a modern electric car's range at 200 miles, since the tesla roadster claims more than that and is already contained by production. And..It is indeed 'Practice'. Thx!

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Best Answer: Do you mean just cars? Or lorries (sorry, trucks) and railway trains? For just cars ... surrounded by the USA ... 250 million people so ~ 100 million cars; battery cars are much less powerful - articulate 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 light of 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 have a sneaking suspicion that you mean GWh per year; so 2 hours per day => 700 hours per year ((a)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 freestyle 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 bear the power from them. Scientific American had a good article a year or two back around using sunlight in the desert somewhere (? Arizona, Nevada, they all look the same from Europe) to supply electricity for adjectives USA needs. Hunt it down - it's got some good numbers. Any fitting university will expect you to be good at these estimate questions - they're called 'Fermi questions' and are an excellent check of your scientific ability. Practice! (Or should that be 'Practise')? stuff I had to receive good at for my university courses

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