Electric Vehicles: Zero Emission?

Since an electric vehicle has no tailpipe emissions it does not require any emission checks. At the first sight, they appear to be completely green and even have been labelled as 'zero emitting vehicles'. Are they really so? The answer is both 'yes' and 'no'.
  It is true that the electric car is pollution-free in the locality where it is driven, but may not be so at global level. For recharging the battery of an electric car about 20 to 30 kWh of electrical energy is needed and it has to be drived from the electricity grid in the area. The amount of global warming emissions producing in generating this electricity has to be considered in evaluating the overall impact of the electric car on the environment.
  The Union of Concerned Scientists  (UCS) - an organisation in the USA has evolved methods of evaluating the environmental impact of electric vehicles vis-à-vis conventional vehicles, by developing a standard know as Co2e - "Carbon dioxide equivalent".
  Electricity is generally produced using various technologies  - burning fossil fuels like coal and natural gas, nuclear reactors and renewable energy sources such as water, wind and Sun. Though the renewable energy sources are known to be clean because of technical reasons their contributions in the total electricity generation in any country is still small  (except for a few countries like the Netherlands).
  Hence, most of the electricity is still generated by burning fossil fuels, which emit significant quantities of greenhouse gases that have different potentials for global warming. Carbon dioxide, however is the most common among them. For purposes of comparison, the UCS "converts the global warming potential of all emissions to units of carbon dioxide equivalent or CO2e - the amount of carbon dioxide required to produce an equivalent amount of global warming".
  This can be used to compare the global warming potential of gasoline car emissions with emissions from the electricity grid. To estimate the CO2e of an electricity grid, emission from all stages from mining the fuel, its transport to the power station, burning the fuel to generate electricity and transmission loss from the power station to where the vehicle is recharged all will be taken into account. Similarly, to calculate the CO2e of a gasoline vehicle, emission from various stages of fuel production to delivery to the petrol pump and also the CO2e of the various greenhouse gasses emitted per mile by the vehicle during driving are considered. In addition, the CO2e of pollution caused during vehicle manufacturing, battery manufacturing and final disposal of the vehicle also will be taken into account.
  Production of lithium-ion batteries is energy and resource intensive. Based on these parameters the UCS has evaluated the life-cycle global warming emissions from manufacturing, use and disposal of gasoline and electric cars. While a mid size petrol-driven vehicle emits nearly 400 grams of CO2e per mile during its lifespan, it is about 200 grams of CO2e for a similar electric car.
  Similar comparison holds for full-sized cars. (Calculations are based on the average American grid electricity mix in which fossil fuels constitute about 64 percent. In India about 80 percent of electricity comes from fossil fuels).
  For both types of cars, the major portion of CO2 equivalence arises from the operational stage. While in the case of conventional cars it is due to burning the petrol directly, for an electric car it comes from the use of grid electricity for recharging the battery pack. This means that while an electric car is not entirely a zero emission vehicle, it is still far cleaner than a petrol vehicle.
  With the global tendency to move away from fossil fuels to renewable energy resources to generate electricity, this comparison becomes even more favourable to electric vehicles in due course.