Contribution of electric cars to the environment: a mathematical analysis
Introduction
The current core strategy for reducing the amount of carbon expelled to the atmosphere is reducing the consumption of fossil fuels, mainly oil and coal.
Part of this core strategy is replacing vehicles powered by gas or diesel engines with electric motors; in this article we will analyze if such change does indeed contribute for a significant reduction in emissions.
The main assumption in this article is that the electricity used to power electric cars will all come from either coal or natural gas fired power plants.
CO2 Emissions per fuel per million BTUs
Coal: 210.6 lbs
Diesel: 161.3 lbs
Gasoline: 157.2 lbs
Natural gas: 117.0 lbs
Typical power generation efficiencies and losses (US)
Gas engine efficiency: 20% (percentage of heat converted into mechanical energy)
Diesel engine efficiency: 30% (percentage of heat converted into mechanical energy)
Coal fired power plant efficiency: 38% (percentage of heat converted into electricity)
Natural gas fired power plan (triple pressure HRSG and steam turbine): 60%
Electric motor efficiency: 90% (percentage of electricity converted into mechanical energy)
Power grid distribution efficiency: 95% (5% loss in transmission lines)
Total efficiency for electric vehicles (coal fired power plant to wheel): 0.38 x 0.90 x 0.95 = 33%
Total efficiency for electric vehicles (natural gas fired power plant to wheel): 0.60 x 0.90 x 0.95 = 50%
Total emissions calculations per fuel
In order to calculate the emissions from each type of fuel we will assume we want to generate the same power from each source.
For each fuel source we have:
and
therefore, the total emissions for the available energy for each fuel source is:
Since we want to compare the total emissions when generating the same amount of available energy, we can write:
The results are:
Electric (coal) x gas power: 80% emissions
Electric (coal) x diesel: 130% emissions
Electric (natural gas) x gas power: 30% emissions
Electric (natural gas) x diesel: 44% emissions
Therefore, by replacing all gas vehicles with electric cars and making sure the electricity for these new vehicles comes from natural gas power plants, the total emissions can be reduced by about 70%; this is very significant considering that transportation is responsible for almost 30% of all emissions.
Other considerations
About 390 million gallons of gasoline are consumed daily in the US; this represents on average about 34,000 tank truck trips daily. These trips would be eliminated by replacing gas powered with electric vehicles.
Refining oil into fuel produces around 180 million metric tons of emissions every year; those would be drastically reduced with introduction of electric cars.
Cost of electricity from natural gas is between 7 and 10 cents per kWh, on par with coal (between 7 and 14 cents per kWh).
The main blockers for widespread adoption of electric vehicles in the US are:
- Price of vehicles: the cheapest electric vehicle in the market costs about USD 31,000.00 with an autonomy of 150 miles
- Long charging time: the Tesla model 3, the fastest charging electric vehicle, with a software upgrade and using special ultrafast chargers will take about 25 minutes to fully charge for a 330 miles autonomy; compare that with 2–3 minutes to fill up a 10-gallon tank for a car with similar mileage.
- Lack of charging infrastructure: there are about 20,000 charging stations in the US; compare that with abou 110,000 gas stations across the country
Conclusion
In conclusion, switching the existing vehicle fleet from gas powered to electricity powered can represent significant reduction in greenhouse gas emissions; adoption will be greatly accelerated if the main blockers — both economical and technological — can be removed.
