Light duty vehicles such as automobiles and light trucks account for 40% of all petroleum use. But they can be powered by battery-electric power using current technology. Their energy requirements are well within the capabilities of current battery storage capacity. And their shift would be a large first step on the path to curtailing global carbon emissions.
This goes hand in hand with shifting towards electricity production from renewable sources such as wind, geothermal, and solar. At the present, coal power plants represent one of the common yet “dirtiest” means of generating electricity. But it is worth mentioning that, even if all the light duty vehicles were to switch to electric power overnight, the resulting “extra” carbon emissions from the coal plants would be less than half of what is currently emitted from light duty gas powered vehicles. This is due to the higher efficiency of electric motors. For more information on this see Coal Generating Plants And Electric Vehicles.
Hydrogen is another potential clean alternative for light duty vehicles, but only if produced by electricity (electrolysis) from renewable sources. However, the efficiency of doing this would be much less than using battery-electric power. To illustrate this consider the following.
Let’s assume a power plant is generating electricity to produce hydrogen, using electrolysis. An approximate production efficiency is 70%; meaning that the energy released from the hydrogen when it is “burned” in the vehicle is 70% of the electrical energy that went into producing it.
Now, internal combustion engines (ICE) convert at most 20% of the fuel energy into mechanical power that moves the vehicle (the rest of the energy is lost as heat).
Therefore, the total efficiency of hydrogen as a fuel is 0.70×0.20 = 14%.
Now, let’s take this same electricity produced by the power plant and use it to charge an electric vehicle. What is the efficiency then?
Let’s say transmission efficiency from the power plant to your home is around 90%.
Electric motor efficiency is around 80%, and battery storage efficiency is around 85%.
Therefore, the total efficiency for a battery-electric vehicle is 0.90×0.85×0.80 = 61%.
So clearly, charging an electric vehicle is much more efficient than using the same electricity to produce hydrogen and use it as fuel. It is about four times more efficient!
As an example, let’s calculate how much electricity would be needed to charge all the light-duty vehicles in the United States.
In 2007, the energy from petroleum used to power all light duty vehicles in the United States was about 16.5 x 1015 Btu. Given that electric vehicles are generally about four times more efficient than ICEs, it would take about 4.1 x 1015 Btu worth of electricity from the grid in a year.
Now, 4.1 x 1015 Btu = 4.32 x 1018 J.
Assuming a steady grid load, the average power output is 4.32 x 1018/(8,800×3,600) = 136 GW. Note that 8,800 is the number of hours in a year, and 3,600 is the number of seconds in an hour.
136 GW is well within the generating capacity of the United States, which is close to 1000 GW (ref: http://www.eia.doe.gov/cneaf/electricity/epa/epaxlfilees1.pdf). However, it can still represent a burden on the grid, especially at peak times during the summer months. One way to help mitigate this burden is by charging vehicles only at night, when power demand is normally low.
From an economic perspective it is also much less expensive to “fill up” an electric vehicle than your average gas tank. Have a look at Cost Of Electric Vs. Gas Powered Vehicles.