Environmental impact of electric cars

Tesla Motors announced this week its new electric car, the Model S. A description of the car can be found here, with a video here. The car is to be around $50,000, after a tax break from the government, can seat up to 7, has storage space in the trunk and under the hood and can go for 300 miles before recharging. Oh, and it goes 0-60mph in 5.6 seconds and looks gorgeous. Tesla claims that, taking into account gas, etc., the car will actually compete cost wise with $35,000 gasoline powered cars.

My roommate and I were speculating on whether electric cars are actually more environmentally friendly than hybrids, or even normal cars. I crunched the numbers for Tesla's previous car, the Roadster ($100,000), and it looks like it depends on where your city gets its electricity. For coal only production, the Roadster actually produces 9% more CO2 than the Toyota Prius ($22,000). Using the U.S. average electricity production methods, it produces about 30% less CO2 than the Prius. It beats the average U.S. car, which gets about 27 mpg, significantly in both categories.

Keep in mind, this is only for the burning of coal for electricity and does not include extraction costs. It also does not necessarily reflect what the Model S can do.

Here's the calculations:

According to Tesla, the Roadster requires 110 Watt hours (Wh) per km, which is 183 Wh/mile. Coal produces 2.095 pounds CO2/kWh. Converting this into Watt hours means that to go 1 mile in the Tesla Roadster produces 0.384 pounds of CO2 if only coal power is used.

Of course, the U.S. does not only produce electricity from coal. On average, coal accounts for between 51%-54% of electricity, though this percent can vary widely depending on your location. Taking into account natural gas, wind, nuclear, etc., the average U.S. rate for all electicity sources is 1.341 pounds CO2/kWh. Using this number, the Roadster produces 0.246 pounds of CO2 to go 1 mile.

The Toyota Prius can get up to 55 mpg. Burning gasoline for fuel produces 19.4 pounds of CO2 per gallon. To go 1 mile in a Prius thus produces 0.353 pounds of CO2.

The average American car gets 27 mpg, though most are much lower as this number includes the very high hybrid cars. So, to go 1 mile, the average American produces 0.719 pounds of CO2.

But the Tesla Roadster is also a sports car that can go 0 to 60 mph in 3.9 seconds. The Ferrari 599 goes from 0 to 60 mph in 3.7 seconds and gets 15 mpg. Thats a similar mpg to a truck. In this case, going 1 mile produces 1.293 pounds of CO2. (The Roadster though is definitely no truck, and at less than one-third the cost, it is no Ferrari 599)