We were compelled a few months back to view a documentary about “green energy” produced by a renowned liberal documentary-maker. Unaccountably, its writer/director undertook to essentially debunk the notion of green energy, by “revealing” various trade-offs and ironies and implying that believers in shifting to renewables and reducing carbon foot-prints were all being hood-winked — or hood-winking the naive liberals. A poorly researched piece of work, the narrative relied on ignorant testimony, almost zero data, and abundant inflammatory innuendo and imagery.
One of its supposedly profound revelations was that electric vehicles are virtually no better than internal combustion engine (ie. gas-burning) vehicles because they run on electricity generated largely by fossil fuels.
If you have been following our column you will guess that this is the kind of statement that drives us crazy enough to have to write a column. This claim has no inherent meaning whatsoever until you look at it quantitatively: HOW MUCH fossil fuel does an electric vehicle (EV) rely on compared to a gas-powered vehicle?
Let’s start with an understanding of the basics of domestic energy. The energy we use to do almost everything in our daily lives comes from various primary sources, depending on where and how your power is generated. Coal, gas, solar, nuclear, wind, and hydro are the most common sources.
Getting the energy from the primary source to the end use (lighting, heating, transportation. etc.) and converting it to the form needed for the end use typically involves a number of steps, each of which involves a loss of energy. So by the time the energy arrives at its end use only a fraction of it is left. This fraction is called its “overall efficiency.”
So, if your local power company runs primarily on coal (which is not the case in Maine, but is in many places), the steps in the energy chain to charge your EV are:
- Coal is mined and transported to the power plant, using 7% of its embodied energy in the process. So that step is 93% efficient.
- Coal is burned and the energy converted to high pressure steam to run turbines that run generators at the power plant. This step is 35% efficient (65% of the energy involved is lost to heat).
- The electricity is transported over power lines, losing 10% along the way, and thus is 90% efficient.
- The battery gets charged, losing 20% in the process, with a resultant 80% efficiency.
- The motor is powered with 90% efficiency.
- The transmission works at 90% efficiency.
To determine how much of the primary source is used to achieve the end use, in this case moving your EV, one simply multiplies all of those efficiencies together to get 0.93 x 0.35 x 0.90 x 0.8 x 0.9 x 0.9 = 19%. That means that 19% of the original energy actually becomes the motion of the vehicle. So the overall efficiency is 19%.
The primary source for the gas-powered vehicle is always crude oil, while the primary source for the electric car depends on where you live and the source of your electricity.
But anyway, to determine how much of the primary energy source is needed to move a gas-powered vehicle, the steps and efficiencies are:
- Oil extraction, refining and transport 83%
- Internal combustion engine 25%
- Mechanical losses 70%
- Transmission losses 70%
Overall efficiency 10%
In other words, 10% of the original energy actually becomes the motion of the vehicle. The electric car is almost twice as efficient at getting the energy source to its end use of moving the gasoline car, even if its primary source is the dirtiest fossil fuel available.
Now coal produces more CO2 than oil, so we have to do that carbon footprint comparison separately. One gallon of gasoline produces around 20 lbs of CO2 directly. The steps to get the gasoline to the car produce another 4 lbs or so, for a total of 24 lbs per gallon. Assuming the car has a reasonable gas mileage of 34 MPG, this results in a CO2 output of 0.7 lbs per mile.
The equivalent for an electric car will depend on the make and model. The Tesla 3 requires around 25 kWh to go 100 miles. In coal country electricity generation produces about 2 lbs of CO2 per kWh. This comes out to around 0.5 lbs per mile. Here in Maine the mix of electricity sources amounts to around 0.5 lbs of CO2 per kWh resulting in a net of 0.125 lbs of CO2 per mile.
Thus, the 34 mpg gas-powered car in Maine produces almost 6 times the CO2 of the electric car, and even in coal country the EV is 40% better in terms of CO2. With the energy source mix shifting rapidly to solar and wind, this advantage is steadily increasing.
Does this sound like a scam to you? To us it sounds like a fairly reasonable potential improvement in the greenhouse gas emissions of our transportation sector in the future – hopefully, the near future!
Paul Stancioff, PhD., is a professor of Physics at the University of Maine Farmington who studies energy economics on the side. He can be reached at [email protected] Cynthia Stancioff, MA, Public Administration, is an amateur naturalist/wordsmith. Previous columns can be found at https://paulandcynthiaenergymatters.blogspot.com/
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