April 18, 2022

By Melanie Thompson

The idea for this week’s science note came as I was browsing the comments of an article about Colorado’s Clean Truck Strategy in the Denver Post. It was exciting to read that a draft of the clean truck strategy had been released, accompanied by the news that Eco-cycle unveiled the nation’s first 100% electric compost collection truck in Boulder this February. But I was curious to see people’s opinions in the comments.

There were many thoughtful questions about cost of these vehicles, their driving range, accessibility of charging stations, and whether we should wait for emerging technologies such as hydrogen fuel cells, but one question in particular was whether these electric vehicles actually produce fewer green-house gases than a standard gasoline or diesel-powered model. After all, as commenter MarcSpiro pointed out: the electricity has to come from somewhere.

Having often wondered this myself, I decided it was time for an answer.

The Electricity Has to Come From Somewhere

Just because Electric vehicles have zero tailpipe emissions, doesn’t mean they have zero greenhouse gas (GHG) emissions overall. The electricity comes from our power grid and our power grid is fueled in part by fossil fuels. So, it’s worth asking: is an electric vehicle actually reducing greenhouse gas emissions, or just moving them upstream?

With the single exception of an electric grid almost entirely powered by coal (not applicable in the US) yes, an electric car does produce fewer GHG emissions over its lifetime than a vehicle powered by gasoline or diesel — 33% on average.

For an overhead view, here are some tools that can show you how much less emissions per your state, per your specific vehicle, and even give you a price comparison:

This tool, From the Department of Energy, lets you see the electric grid make-up in your state and the average GHG emissions for an electric vehicle there compared with the national average, and average for a gasoline powered car.

If you want something even more specific, this site, also from the Department of Energy will let you enter specific car make and models as well as your zip code.

This interactive graph, developed by the MIT Trancik Lab, will even let you compare the cost and lifespan GHGs for individual gasoline, diesel, hybrid, plug-in hybrid, electric, and fuel cell vehicles.

But maybe you don’t just want to know if an electric vehicle produces less GHGs, you also want to know how.

When you look at any of the graphs above, there are 3-4 components that go into that GHG emissions number: the battery lifecycle, vehicle lifecycle, fuel from tank to wheels, and fuel from well to tank. The graph below shows these breakdowns for average internal combustion engine vehicles (ICEVs (gasoline and diesel)), plug in hybrid electric vehicles (PHEVs), and battery electric vehicles (BEVs):

As you can see, electric vehicles lose some ground on emissions because of the battery manufacture process, but they make up for it with a much cleaner fuel cycle.

The graph above, as well as the tools I mentioned are calculated using a comprehensive model developed by the Argonne National Laboratory, called Greenhouse Gasses, Regulated Emissions, and Energy use in Transportation, or GREET. GREET is a full life cycle model that evaluates “energy and emission impacts of advanced vehicle technologies and new transportation fuels, the fuel cycle from wells to wheels and the vehicle cycle through material recovery and vehicle disposal.” If you have the time and interest I recommend using this application.

But for a brief explanation of how an electric vehicle’s fuel cycle produces fewer greenhouse gasses, I’ve outlined the important factors below.

(The longer explanation, i.e. take me to the math)

The difference in emissions between gasoline vehicles and Electric Vehicles (EVs) come down to 2 main factors:

• Fuel Sources
• Energy Efficiency

First, let’s examine the sources of energy that are going into gasoline vehicles and EVs

Most fuel sources that contribute to the electric grid emit less CO2 per unit of energy produced than gasoline or diesel, with the exception of coal. Zero emissions fuel sources like nuclear and renewables account for around 32% in Colorado. The combination of cleaner fossil fuels and zero emission fuel sources means the Colorado grid produces 24.5% less CO2 per kWh than gasoline.

Next, let’s examine efficiency

Electric vehicles overall use fossil fuels more efficiently than gasoline vehicles, even with energy losses before the electricity enters the car.

For electric vehicles well to tank is about 36% (in Colorado) while the tank to wheels ranges from 77-100% for a total efficiency of 28-36%

Gasoline vehicles well to tank is around 84% while the tank to wheels ranges from 12-30% for a total efficiency of 10-25%One reason for this difference is that fossil fuel power plants are more efficient than internal combustion engines in gasoline powered cars. Natural gas plants (which produce 26% of the electricity in Colorado) are around 60% efficient, while coal plants (which produce 42% of our total electricity) are around 33% efficient. Another factor in efficiency is that electric vehicles recapture around 22% of their energy from regenerative braking.

In conclusion

Combined with the diversification of fuel sources provided by the electric grid, an electric vehicle’s efficiency means that it not only uses fuel sources that produce less CO2 than gasoline or diesel, they also use less of them. Over the same distance, an EV in Colorado would produce 48-74% less CO2 emissions than a gasoline powered vehicle. This difference is what allows electric vehicles to make up for the higher GHG emissions during battery manufacture, resulting in GREET’s 33% less emissions figure cited at the beginning of this note.

When considering the transfer to electric, whether it’s our state’s Clean Truck Strategy or your personal car, there are many questions to consider: the price of the vehicle, its driving range, charging accessibility, and emerging technologies. However, when it comes to greenhouse gas emissions I hope you have your answer. Yes, electric vehicles produce less of them.

---

Additional Notes (i.e. The Math)

The Electricity Has to Come from Somewhere

So you want to check my math?

Disclaimer: The calculations below are intended to be illustrative, not comprehensive. For the top tier, bullet-proof version, please use GREET 🙂

The difference between and EV and ICEVs greenhouse gas emissions actually come down to 3 factors:

1. Fuel sources
2. Energy efficiency
3. Vehicle and battery lifespan

Fuel Sources: Most fuel sources that contribute to the electric grid emit less CO2 per unit of energy produced than gasoline or diesel, with the exception of coal. The chart below gives the CO2 in pounds per kilowatt hour of energy produced for gasoline, diesel, and the primary fossil fuels powering the American electric grid.

electricity source	Pounds CO2 per kWh
coal	0.72
natural gas	0.40
Diesel	0.56
gasoline	0.53

Next is the percentage of these fuels that go into our electric grid. Here are graphs for the US and for Colorado.

To find out how much CO2 per kWh our power grids produce, we need to multiply the percentage of a given fossil fuel source by its pounds CO2 per kWh.

Nationally:

0.72 (lbs CO2/kWh) x  0.22(% coal) + 0.40 (lbs CO2/kWh) x 0.38(% nat. gas) = 0.31

Or 42% less than gasoline and 45% less than diesel

And in Colorado:

0.72(lbs CO2/kWh) x 0.42(% coal) + 0.40(lbs CO2/kWh) x 0.26(% coal) = 0.40

Or 24.5% less than gasoline, and 28.5% less than diesel.

Energy Efficiency

Energy efficiency is calculated by multiplying well to tank efficiency by well to wheels efficiency. Well to tank accounts for all the energy lost in production of fuel or electricity. Tank to Wheels is the efficiency of the vehicle, usually advertised as miles per gallon or miles per gallon equivalent.

Electric Vehicles Well to Tank (WtT)

Part of the reason electric vehicles produce fewer GHGs is because fossil fuel power plants are more efficient than internal combustion engines in gasoline cars. In the US, most power generated by fossil fuels is natural gas or coal. In Colorado, 41.61% of our power comes from coal, 25.51% from natural gas, and less that 1% other fossil fuels. For simplicity, let’s say 42% coal and 26% natural gas out of 68% total fossil fuels. Natural gas plants with combined cycle generators (meaning they recapture heat energy to drive steam turbines) have an average efficiency of 60%. Coal plants on average have a 33% efficiency. 

To get the combined efficiency, we divide the percent fuel source by total percentage fossil fuels and multiply by multiply the efficiency of the plant:

An additional 7% will be lost through the electric grid. Extraction of the resources on average requires 9% of the energy, and shipping it another 1.5%. We multiply these efficiencies by that of the generator to get the total:

0.91 (extraction) x 0.985 (shipping) x 0.93 (line losses) x 0.43 (plant) = 0.36

Total fossil fuel efficiency from well to tank in Colorado: 36%A similar calculation for the national grid results in 42%

Electric Vehicles Tank to Wheels (TtW)

According to the Department of Energy, Electric vehicles on average range from 77%-100% efficient when accounting for regenerative braking. (For example: a Nissan Leaf loses approximately 10% when charging the battery, 3% to accessories, 18% to the Electric Drive system and 0-4% to Auxiliary electrical. Leaving 65-69% energy to wheels plus around 22% recaptured from regenerative braking for an overall efficiency of 87-91%.)

Total Electric Vehicle Well to Wheels fossil fuel efficiency:

To get the total, we multiply our Well to Tank efficiency by Tank to Wheels:

0.36 (WtT) x 0.77 (TtW) = 0.28

or

0.36 (WtT) x 1.0 (TtW) = 0.36

Giving Electric vehicles in Colorado a total fossil fuel efficiency of 28-36%

Or 32-42% nationally.

Internal Combustion Engine Vehicle (ICEV) Well to Tank (WtT):

For ICE vehicles, the well to pump efficiency includes the energy used in crude oil extraction, the energy lost in refining crude oil into gasoline, and the transportation from refinery to pump. The energy used in oil extraction is about 6%. The efficiency of oil refinery plants on average is around 92%. And the energy lost to transportation is on average 3%.

0.94 (extraction) x 0.92 (refinery) x 0.97 (transportation) = 0.84

ICEV gasoline Well to Tank efficiency is 84%For crude oil to diesel similar numbers result in efficiency of 81%

ICEV Tank to Wheels (TtW):

According to the department of energy, the efficiency from pump to wheels of ICE vehicles ranges from 12% to 30%.

Losses come from the engine (60-72%), drivetrain (3-5%), auxiliary electrical (0-2%), idling (3%), and parasitic losses (4-6%)

ICEV Well to Wheels:

Again, we multiply the Well to Tank by Tank to Wheels:

0.84 (WtT) x 0.12 (TtW) = 0.10

or

0.84 (WtT) x 0.3 (TtW)= 0.25

Giving Gasoline ICEVs a total efficiency of 10-25%

So not only do the fuel sources powering an electric vehicle produce less CO2 per kWh, and electric vehicle can also use fewer of those original kWhs to drive the same distance. The CO2 from the car’s fuel source and its overall efficiency can help us calculate how much less CO2 it emits than an ICEV when driving the same distance. 

Percentage Fewer Emissions per kWh Driving

First, to calculate the pounds CO2 released per energy (kWh) that goes into actually moving the vehicle we need the following table and equation

Vehicle	Lbs CO2 per kWh	Well to Wheel efficiency
EV	0.40 (Colorado power grid)	26-36%
ICEV	0.53 (gasoline)	10-25%

Now to plug in the values for EVs and ICEVs

So for one kWh to go towards moving the car, an EV emits between 1.11 and 1.43 pounds of CO2.

An ICEV using gasoline emits between 2.12 and 5.3 pounds of CO2.

To get the percentage less CO2 per kWh moving the vehicle, we divide the lowest value of CO2 for the EV by the lowest for the ICEV and subtract from 1. Then do the same with the highest. 

Meaning if an EV and ICEV drive the same given distance in Colorado, the EVs emissions will be 48-74% lower than the ICEV using gasoline.

The final factor effecting lifetime GHG emissions is vehicle and battery life

What offsets the significant reduction in GHGs produced by an EVs fuel cycle is its battery. Because of the battery, manufacturing an EV produces significantly more GHGs than manufacturing a traditional vehicle. Many people wonder about the lifespan of electric cars and their batteries – will they need to replace them more frequently that ICEVs? If so, this would have a negative impact on overall GHG emissions of EVs.

In the graph produced by GREET below, the emissions are calculated for the total lifecycle of each vehicle. This comparison assumes that the lifecycle of each of these vehicles is the same, 173,151miles. Is the GREET model right to suppose the same lifespan for each car?

Again, I will not presume to do better calculations than the scientists at AGL — please take their numbers as gospel, not mine. However, I hope to offer a simplified explanation of why the car lifespan can be assumed to be the same.

All other things being the same, the lifespan of an electric car (i.e. its battery) comes down to a question of range. Over time, electric batteries lose some of their original capacity meaning that the car can drive fewer miles on a single charge. So, how long before limited capacity makes the car non-functional?A new electric car these days has a range of 250-300 miles, roughly equivalent with the range of a ICEV on one tank of gas. New electric cars also have more durable batteries, and the US Department of Transportation reports only an average of 10% loss of driving range after 120,000 miles. If degradation rates stay consistent, that equates to 14.5% losses over the 173,151 miles lifespan estimated by GREET.

An Electric Vehicle with a range of 214–257 miles can easily handle the 26 miles per day driven by the average American. Meaning that the car will likely be retired due to the same factors that affect ICEVs before the battery needs to be replaced.

Additionally, Battery technology will likely continue to improve, yielding longer driving ranges and better durability. The ability to manufacture batteries from recycled materials as well as reuse old car batteries in other capacities may also reduce the overall GHG emissions of electric cars.

Additional Notes:

The One Exception

In the original science note I stated that there was one scenario in which an EV could emit more GHGs than an ICEV, which is if the electric grid is powered almost completely by coal. How completely, you ask? Well even in West Virginia, the state with the highest percentage of coal power with of 90.9%, an EV still emits less GHGs on average than a gasoline vehicle and according to the EPA.

Power Grid Fuel Sources Vary by Time of Day and Time of Year

When calculating the carbon per kWh emitted by an EV charged on the grid, it’s important to consider what time of day or year the vehicle is being charged. For instance, cars are usually charged at night, which means they won’t be getting power from solar, but night time is also off peak hours, meaning fewer fossil fuels are being burned to meet the demand and things like nuclear and wind power make up a larger percentage of the grid.You can use this tool to check out seasonal and hourly energy contributions by region in the US.