Dear Pablo: I have read time and again that an all-electric vehicle can use as little as one dollar's worth of electricity to travel 100 miles. How can this be? Electric Power Plants are burning oill to create electricity, and oil is expensive. How do Power Plants convert oil to electricity at a rate that is five times more efficient than a 2010 Prius?
Over half of US electricity comes from coal (50.2% in 2004) while only 3% comes from oil. It is true that oil is expensive, which is why many oil-fired power plants have switched to natural gas, which produces 17.4% of our electricity. On the other hand most US automobiles are powered by gasoline which is a petroleum distillate, meaning that it is distilled from crude oil. The process of extracting and transporting foreign oil as well as processing and distributing the gasoline adds to its cost while coal is mostly extracted domestically and requires little processing.
Let's Look at the Cost of EnergyThe unfortunate result (for the climate and our air) is that coal is much cheaper than gasoline. A $3 gallon of gasoline contains 132 Megajoules (MJ). The equivalent amount of coal energy, 3.9 kg, costs only about $0.20. So, at 1/15th the price it's not hard to begin to understand why electric cars are cheaper to operate than gasoline powered ones.
Let's Examine Vehicle EfficiencyBy looking at the energy input into the vehicle, be it electricity or liquid fuel, versus the distance traveled with that energy, you can come up with a measure of efficiency. There are two components to consider: the efficiency of getting energy to the car (well to tank) and the efficiency of the car itself (tank to wheel). When combined, we get an understanding of the car's well-to-wheel efficiency, which is determined by both the design of the car and its energy source. According to Tesla, makers of the all-electric Roadster, the well-to-tank efficiency of gasoline is 81.7 percent, while the well-to-battery efficiency of natural-gas-generated electricity is 52.5 percent. At first glance, the gasoline looks more efficient, but keep in mind that efficiency is lost in the combustion engine.
Why Electric Vehicles Are Cheaper To OperateBecause electric vehicles have no internal combustion engine and no conventional transmission, their efficiency is almost 1.5 miles per MJ. For comparison, the hybrid Prius is 0.42 miles per MJ, and a conventional Honda Civic is 0.39 miles per MJ. When you combine the well-to-tank efficiency with the vehicle's efficiency, the electric vehicle has a well-to-wheel efficiency of 0.7 miles per MJ, compared with 0.35 miles per MJ for the Prius.If the well-to-wheel efficiency of an electric vehicle is about twice as good as an internal combustion vehicle, and the energy source is up to 15 times cheaper, it is easy to understand why an electric vehicle can travel 100 miles for a dollar, while the Prius does the same for about six dollars.Pablo Päster answers your questions in "Ask Pablo" every week. Got a question for Pablo? Write to Pablo(at)TreeHugger.com (replace "(at)" with "@").
Additional resources on Electric Vehicles:
Electric Vehicles: Good For Climate, Bad For Water?
17 Electric Cars You Must Know About
Converting Your Car To An Electric Vehicle