I like doing thought experiments. I often use them to help me envision the parameters of a complex problem. For example, a dozen years ago I attempted to calculate the area required to supply the entire U.S. with electricity from solar photovoltaic (PV) power.
Admittedly, these thought experiments require major simplifications. To completely run the U.S. on solar power would require a substantial amount of backup power or storage for when the sun isn’t shining.
I also knew that my solar PV calculation was subject to many assumptions, and the answer could therefore be 50% too large or 50% too small. But the number I calculated — an area less than 100 miles by 100 miles — at least provided me with a point of reference for the scale of such an undertaking.
I wanted to imagine about how much area it might take, and that calculation gave me a ballpark figure to visualize. The National Renewable Energy Laboratory (NREL) once calculated that there are about 2,000 square miles of suitable area for PV generation just on U.S. rooftops. So it didn’t seem like a preposterous notion.
In the dozen years since I did that calculation, U.S. solar power generation has increased by a factor of 66. U.S. wind power generation, which started from a larger base at that time, has increased by a factor of five. The number of electric vehicles (EVs) on the roads has also grown exponentially in the past decade.
That led me to wonder how much U.S. gasoline demand could be displaced if all of the wind and solar power generation went into powering EVs. In turn, that led me to wonder about the scale of displacing all U.S. gasoline consumption with wind and solar power.
Again, I will note that this is just a thought experiment. It isn’t constrained by issues like the number of available EVs, or the amount of storage required to ensure that the power is always available on demand. With those caveats, I will attempt the calculation — with no idea beforehand how it is going to turn out.
According to the Energy Information Administration (EIA), in 2019 the U.S. consumed 142 billion gallons of gasoline. The EIA value for the energy content of a gallon of gasoline is 120,286 British thermal units (Btu). Thus, in 2019 the U.S. consumed 17 quadrillion Btu (quads) of gasoline.
I could convert that number directly into an electricity equivalent, but internal combustion engines are less efficient than electric motors. So, even though 17 quads of gasoline is equivalent to 5 trillion kilowatt-hours (kWh), I have to make an adjustment because of the efficiency difference.
The average fuel economy of the U.S. fleet in 2019 was reportedly about 25 miles per gallon (MPG). Gasoline consumption of 142 billion gallons would translate into 3.55 trillion miles travel on U.S. highways, which is about 10% higher than the actual number of reported vehicle miles traveled in 2019. (This may be an indication that the fuel economy of the U.S. fleet is overstated, but also reflects gasoline sales that went into applications like boats and lawnmowers).
The Environmental Protection Agency (EPA) uses a conversion factor of 33.7 kWh per gallon of gasoline. This is consistent with the conversion factor I used above. To reflect the increased efficiency of EVs, the EPA rates them based on MPG equivalents (MPGe). The MPGe of an EV represents the distance the car can travel on 33.7 kWh of electricity (one gallon of gasoline equivalent).
The Department of Energy (DOE) reports that several 2020 model EVs get at least 120 MPGe in combined highway and city driving. That is nearly five times the fuel economy of the U.S. gasoline fleet.
However, there is a substantial difference noted when an EV isn’t using regenerative braking, which recaptures energy from the vehicle’s momentum. For example, the 2019 Nissan Leaf reports 110 MPGe when using regenerative braking, but that drops to 30 MPGe when not using it.
I would assume that EV drivers use regenerative braking most of the time. However, to be conservative, I took the average of the two modes across all 2019 EV models in the DOE’s database. That number was 70 MPGe for combined highway and city driving.
Thus, if we replaced the entire gasoline fleet at 25 MPG with EVs getting 70 MPGe, we could do so with 35.7% (representing the ratio of 25/70) of the energy. That means the 5 trillion kWh of gasoline could be replaced with 1.8 trillion kWh of electricity that is powering EVs.
Now I can do the final portion of the calculation. For perspective, according to the 2020 BP Statistical Review, the U.S. generated 4.4 trillion kWh of electricity in 2019. An additional 1.8 trillion kWh would represent a 41% increase in electricity generated from all sources.
The U.S. produced 0.108 trillion kWh of electricity from solar power in 2019 and 0.303 trillion kWh of electricity from wind power. Respectively, those sources represented 2.5% and 6.9% of all U.S. electricity generation.
Cumulatively, the 0.411 trillion kWh of electricity from wind and solar power represents 22.8% of the 1.8 trillion kWh required. If we added nuclear power and hydropower into the mix, 2019 generation from these non-fossil fuel sources would have equaled 85% of the amount required.
To put it another way it would require 4.4 times more electricity produced from wind and solar power in 2019 to equal the 1.8 trillion kWh required to replace gasoline. That may seem like a lot, but over the past decade wind and solar power generation have increased by a factor of 5.4. At the growth rate of the past decade, it is possible that in another decade we could produce enough wind and solar power to power all the nation’s automobiles with a 100% EV fleet.
My verdict? It’s not out of the realm of possibility that at least the energy requirement could be met by wind and solar power within a decade.