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| Fig. 1: 2013 Tesla Model S (Source: Wikimedia Commons) |
Motor Trend named the Tesla Model S the 2013 car of the year. Virtually every major car manufacturer has promised some kind of electric concept (though few have yet to actually hit the market). The Chevy Volt and Nissan Leaf are competing for small, zero emission vehicles. Meanwhile Tesla offers a luxury sedan, the Model S, and just finished their Roadster line. SUVs are coming soon from Toyota, a tribute to their original electric RAV4, and Nissan. With electric vehicles of all shapes as sizes being promised in the next two years, so are hopes of finally lessening the United States' dependence on oil. However, less oil does not necessarily mean less energy. These cars all require electricity from the grid instead, and much of that energy simply comes from a different fossil fuel.
With oil representing almost a third of the energy use in the United States, vehicles need a lot of energy. Exactly how much? The following calculation is based off 2010 statistic from the Federal Highway Administration. [1] The vehicle miles traveled (VMT) used below is for Light Duty Vehicles, which includes "passenger cars, light trucks, vans and sport utility vehicles regardless of wheelbase." [1] The gasoline properties used are the latent energy, density, and average vehicle efficiency. [2]
| 2.648 × 1012
vehicle miles traveled 21.6 miles/gal |
= 1.226 × 1011 gal |
| 1.226 × 1011 gal × 44.0 MJ/kg × 2.84 kg/gal × 0.18 = 1.758 × 1012 MJ |
Let's say Tesla's dreams came true and everyone with a car traded their vehicle in for a Model S tomorrow. They would be sorely disappointed, because when they went home to plug in their shiny new car, there simply would not be enough electricity to power transportation needs and our existing electrical demands.
| 2.758 × 1012 MJ × | 1 kWh 3.6 MJ |
= 7.661 × 1011 kWh |
For some perspective, the US as a whole generated 4.125 trillion kWh in 2010. [3] Thus, electric vehicles would have increased the US energy demand by 18.6%! For these electric vehicles to truly approach Zero Emission Vehicles (ZEV), that electricity must come from a low emission source. Based on the concentrated solar plant Nevada Solar One, powering 230 million electric vehicles with solar would require 9147 km2. [4]
| 7.661 × 1011
kWh 134 GWh |
× 1.6 km2 = 9147 km2 |
This would mean covering about 90% of all of Delaware and Rhode Island with solar panels.
On the other hand, vehicle-to-grid storage is getting heavy attention from the utilities. Charging all of these vehicle batteries at night could help store extra generation that could be accessed later during peak hours. The large scale of energy has already been demonstrated, but batteries are popular for their ability to release energy in a slow, controlled manner. Nonetheless, over 230 million batteries at 85 kWh apiece can provide a surprising amount of power. [1] A standard charge time of 8 hours at 110V is used as the not- to-exceed discharge rate, though this rate could be increased 16x with specially designed supercharging electronics. [5]
| 85 kWh × 230.4
× 106 vehicles 8 hr |
= 2448 GW for 8 hours max |
That is nearly 2.5× the summer generating capacity of the entire US grid. [3]
There are many challenges for electric vehicles, particularly with production and sales. They are not selling as well as the manufacturers had hoped, and consumers consistently point to range, charging time, and cost. Basically, it is a battery problem. Predictions for adoption like Barack Obama's goal are expecting 1 million electric or hybrid vehicles by 2020. Out of 230 million, that is hardly a blip. But with virtually no serious energy storage options, we can see why utilities would support electric vehicles. A massive fleet of batteries on the road holds a lot of potential.
© William Greenbaum. The author grants permission to copy, distribute and display this work in unaltered form, with attribution to the author, for noncommercial purposes only. All other rights, including commercial rights, are reserved to the author.
[1] "Annual Vehicle Distance Traveled in Miles and Related Data - 2010," U.S. Federal Highway Administration, VM-1, February 2012.
[2] M. Z. Jacobson, "Review of Solutions to Global Warming, Air Pollution, and Energy Security," Energy Environ. Sci. 2, 148 (2009).
[3] "Electric Power Annual 2010," U.S. Energy Information Administration, November 2011.
[4] S. Herron, "Solar Irradiation and Energy from Deserts," Physics 240, Stanford University, Fall 2010.
[5] B. Berman, "Charging Ahead on an Electric Highway," New York Times, 28 Sep 12.
