For an all electric car most people will get the power from a power generating plant. You have to add in the efficiency of the power plant along with the energy spent getting the fuel and other supplies for the power plant not to mention the losses in the power lines.
Bottom line they are not very efficient.
The other problem in the US is the lack of new power plants, that means if the electric car fleet grows very much it will be completing with other users for the capacity of the grid. Sure you can charge them at night when usage is down but even then it will be a problem in time.
Electric cars are several times more efficient than gas powered vehicles. It is not even close.
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The efficiency argument, however, is very complicated, and confuses a lot of people. Here are three facts which will make it very clear which is more efficient.
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It takes a huge amount of electricity and other energy just to refine oil into gasoline. About 6 kilowatt-hours per gallon refined, according to the Energy Information Administration. An EV could drive 20 to 30 miles just on that wasted refining energy. The gas car needs electricity AND gasoline. The EV only needs the electricity.
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The electricity "fuel" is distributed to electric cars by wire, over an electric grid which is 93% efficient. The same step for gasoline requires hundreds of tanker trucks visiting thousands of gas stations.
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Fuel prices are the best clue. Electricity for EVs costs 2 to 4 cents per mile (depending on your electric rate). Gasoline costs 15 to 30 cents per mile ( depending on the car's MPG). That huge difference in fueling cost is due to efficiency differences - indeed, it would be very hard to explain if EVs were not much, much more efficient.
"Efficiency" is a word that is sometimes used casually to imply something is "better." But a more careful definition admits the formula for efficiency is the amount of useful work obtained over the total energy supplied.
First we have to be concerned with how the efficiency is being measured. It can be calculated. This is the theoretical efficiency. The theoretical efficiency of an internal combustion engine (ICE) using standard gasoline is limited by the compressibility of the gasoline and is about 27%. Special blends of gasoline might raise this theoretical efficiency to slightly less than 35%.
A bench test is another way efficiency is measured. Actual efficiency in these lab tests are always less than theoretical efficiency. Both of these measures stop at the flywheel. When someone is looking to advocate the efficiency of the ICE these are the measures that are sometimes quoted.
But to make practical use of an ICE requires a transmission. At 0 RPM the engine has no torque and is only most efficient in the 3000 to 5000 RPM range. The required use of a transmission and a power train lowers the efficiency of the vehicle. We sometimes speak in terms of a tank to wheels efficiency of a vehicle (or battery to wheels for an EV.) The tank to wheels efficiency of an ICE vehicle can be less than 15% but this EPA cite suggests 17% to 21%: http://www.fueleconomy.gov/feg/atv.shtml
When we start to think in terms of a vehicle with an ICE engine usage must also be considered. Although the EPA chart takes into consideration idling this is an average. For a vehicle that is idling at a stop sign or in traffic efficiency has dropped to zero because no useful work is being done. In stop and go traffic overall vehicle efficiency will fall off dramatically with an ICE.
By comparison the EV can start with an electric motor that in some of the most efficient solar cars is 99% efficient. The engine and transmission of an ICE engine may have over 700 moving parts while the EV can have as few as 5. No transmission is required for the EV because it has full torque at 0 RPM. The Tesla Roadster claimed efficiency from battery to wheels of 92% When stopped the engine uses no energy, regenerative braking returns energy to the vehicle adding to overall efficiency.
When a vehicle is operating air resistance and to some extent rolling resistance work against overall fuel economy which is sometime called "fuel efficiency" This is the measure of efficiency most familiar to people and this is what is on EPA stickers. All of the most fuel efficient vehicles are electric: http://www.fueleconomy.gov/feg/topten.js...
When comparing two vehicles we sometimes add in the efficiency of the supply train of fuel for a "well to wheels" analysis of fuel efficiency. The two studies below compare a number of vehicles and show the Tesla roadster double the efficiency of a hybrid and almost three times the efficiency of an economy petrol vehicle. People can claim otherwise but this is what research offers to us.
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Some consider the Volt, a hybrid based upon a series hybrid platform, an electric car. The combined power train is not more efficient than the ICE alone (bench test efficiency) but in a vehicle, when considering real world usage the vehicle can be more efficient. This is due to advantages of the electric drive which allow stop start technology and regenerative braking which improve vehicle efficiency. At times the ICE can be turned off entirely and the vehicle operates more efficiently in electric only mode.
Sunlight to PV to an electric car is almost 100 times more efficient than sunlight to plants to biofuel to an internal combustion engine vehicle.
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Fossil fuel power plants are more efficient than car engines, because the car engine has to work at all sorts of speeds and be relatively lightweight, whereas a power plant's turbine can be designed to run at one speed always and can be heavy. Factor in distribution losses, battery charging inefficiencies, and the electric motors themselves though and the overall efficiency is probably about the same for petrol or for electric.
If you instead compare an electric car charged by renewable energy with a petrol or diesel car running on biofuel, I reckon the electric one will be significantly more efficient taking into account the whole energy "path" from sunlight to vehicle motion.
Pros and cons of both?
