I find that our hybrid vehicle gets about 25% more miles per gallon than the equivalent model with only a gasoline engine. Inasmuch as hybrid and all-electric vehicles have become more popular, it is worth asking if the energy used (and thus CO2 emitted) to make electric motors and lithium batteries is greater than that emitted during the production of gasoline engines for conventional vehicles, potentially discounting the advantages of electric vehicles in mitigating the potential for climate change. This is not a simple analysis, since there are many steps to the manufacture of either type of vehicle and calculations of CO2 emitted during its subsequent use.
Not surprisingly, there is a large range of CO2 emission during the manufacturing of lithium batteries, especially as improvements in batteries and their fabrication are occurring almost daily. Production- related emissions range from 38 to 356 kg CO2 per kW-hour of battery capacity. For an electric vehicle with a 30 kW-hr battery pack, this can be equivalent to 4.6 tons of CO2 just for the production of its batteries. Various studies indicate that the energy used to build the power-train of an electric vehicle is greater, perhaps as much as 30%, than that used to build the internal combustion engine for a gasoline or diesel vehicle.
Of course, for both types of vehicles, the energy is used in their operation dwarfs the energy used in their manufacture. An average gasoline-powered vehicle will release about 33 tons of CO2 during a 100,000-mile lifetime. Over a similar lifetime, electric vehicles emit about 10-24% less greenhouse warming potential than conventional vehicles, when both the manufacture and operation are considered. The contribution of electric vehicles (relative to conventional) to greenhouse gas emissions is greatest when they are powered by electricity derived from coal. See my earlier blog. Electric vehicles emit no tailpipe pollution; the pollution from power-plants can often be captured at the smoke stack.
Recycling of lithium batteries can also consume considerable quantities of energy, but this energy use is not the only reason to promote recycling. While lithium is not in particularly short supply, recycling reduces the release of toxic and valuable metals, such as cobalt, to the environment and SO2 to the atmosphere.
Overall, my analysis says that personal vehicles powered by electricity have advantages for the environment, which will improve with each new generation of battery design and the transition of the electric grid to renewable sources of power like solar and wind.
This post originally appeared on William H. Schlesinger’s blog Citizen Scientist, published by Duke’s Nicholas School of the Environment.