Electric Vehicle Chargers

EV vs Gas – Part 2 Emissions

By on Jun 26, 2015 in Electric Vehicles, Environment |

Several articles and studies have been done recently regarding whether electric vehicles (EV’s) are really green. Are gas cars better for the environment? If we could switch to battery electric vehicles, should we?

In reviewing this question, there are three areas that I feel merit review:

  • Energy efficiency
  • Greenhouse gas (GHG) emissions
  • Cost comparison

Each is worth looking at independently. So I’ll look at each in a separate post, this being the second.


So with this second article, we’ll take a look at greenhouse gases.

The internal combustion engine generates a lot of toxic gases. There are definitive links between auto exhaust and asthma as well as cancer. There are also links between high levels of air pollution and heart attacks. Several studies have linked auto exhaust, especially diesel exhaust, to autism, Alzheimer’s and dementia, though I will point out that these studies do not necessarily show a cause and effect relationship. There are a lot of factors that have improved the quality of the exhaust from an internal combustion engine through the years. These include catalytic converters, filters, fuel injection, and other methods. Through the years, auto manufacturers have reduced the amount of poisonous emissions from gas burning engines dramatically. So much so that suicides by carbon monoxide poisoning from running a car in the garage have pretty much been eliminated and the number of accidental deaths from someone running the engine to make the heater work in a snowed-in vehicle is a rare occurrence. Even so, the nature of the internal combustion engine is that hazardous emissions, while they can be reduced, cannot be eliminated.

Electric Vehicles have no emissions at all at the point of operation. There are no gases generated at the point of use. Batteries are sealed and generally have a gel rather than a liquid core, so there are no harmful fumes. Recent breakthroughs in solid-state batteries may eliminate any liquid or out-gassing risk for battery electric vehicles. While there are no emissions generated at the point of use, the source of power used to generate the electricity may generate gasses. The generation of electricity is where an electric vehicle might not be green. On the other hand, the polluting power plant is probably not in your garage, backyard, or neighborhood, so the quality of the air one personally breathes will probably be improved by trading the gas burner for an electric vehicle. The gas burning car’s exhaust will always be a few yards away from your nose when you drive, though the electric power plant is probably miles away.

Each source of energy used to generate electricity has its own total GHG emission levels. To keep the analysis simple, I’ve chosen four sources for power and will compare GHG equivalents, which converts various pollutants into CO2 equivalent factors. First and last are Coal and Solar, which represent the worst and best GHG emissions for commonly used sources of energy. I’ve used grid mix emission numbers for comparison in the second and third positions. The US grid mix is used for the average. Those who live in high coal using states will have an emission level somewhere between the coal and US grid mix level. Since most EVs being driven today are in California, I’ve also included the CA grid mix, which is significantly cleaner than the US grid mix.


Unlike the prior article, where it made sense to show the Pump/Plug-to-Wheel (PTW) efficiency, because EVs have zero emissions, there’s no point in putting up a chart comparing PTW of gas to EV vehicles. The gas cars give off toxic gases at the point of use, the EVs don’t.


The chart below shows the well-to-wheels (WTW) emissions using the GREET application to generate our numbers. For the gas cars, I’ve compared a fuel-efficient 35mpg vehicle with a Nissan Leaf and BMW i3, the next comparison is between a luxury sedan/average car (both get the same MPG on average and generate similar emissions in the model) and the Tesla. The last comparison is the most apples to apples comparison, the RAV4 2 wheel drive gas burner vs. the RAV4 EV.

Total GHG emissions for Gas and Electric Vehicles of similar classes with multiple forms of generation

EV Generation

Note: The GHG emissions from solar (.027 g/mile) have been exaggerated in order to display on the chart.

Using grid power and especially solar power, the electric vehicles are significantly less polluting than gas burning vehicles. Only when comparing pure coal generated electricity against gas cars does the balance shift.  While it is true that when using coal, the WTW emissions of an EV can be as much as 20% more than a comparable gas burning vehicle, when powered by solar generated electricity the balance shifts in favor of the electric vehicle by more than 10,000 to 1 (3-400 g/mile vs. 0.027 g/mile = 11,000-14,000 to 1).

It can be argued that coal plants are favored when generating marginal electric power. For example, a grid running at night has a single EV plugged in and is forced to generate more electricity. The additional electricity will probably come from a coal plant. Under this marginal analysis, the EV uses coal, which is the dirtier alternative, thus EVs are dirtier. However, marginal analysis only works when there are small quantities of EVs. There were over 119,000 plug-in vehicles sold in the US last year and that is a number large enough that marginal analysis breaks down. With enough EVs on the road, the power companies will need to keep more efficient plants on line or build new plants. The power companies would build more efficient and less polluting power plants to generate the electricity needed to meet the new baseline power requirements caused by the EV usage. Which means it’s fair to compare the EVs using the average grid power mix rather than marginal power.


If one stopped the analysis at generation and Operation, EV’s are the clear winners. However, making batteries uses a lot of power and can generate a lot of GHG emissions. It’s pretty difficult to analyze the GHG emissions during production; firm numbers are not available. Even if they were, a change in the supply chain can dramatically impact emissions. The Leaf is built at an energy star compliant factory in an area with higher than average coal mix in the electric grid, is it a cleaner or dirtier factory because of it, or is it a wash? The BMW i3 is built at plants that are primarily powered by low emissions electricity such as solar and hydroelectric. These clean energy sources reduce the GHG emissions for the vehicle production, but how much does that reduce the emissions generated in building the battery? To generate an answer that is reasonable, but is really just an educated guess, I’ll go back to the Argonne National Lab and use an average number based on the weight of the batteries installed. A 2010 report on battery life-cycle costs gives an average of 12.5 kg CO2/kg of battery. Adding the other pollutants generated creating the battery gives a total average GHG CO2 equivalent of 13.0 kg/kg of battery. Multiplying by the weight of the battery gives ~2800 kg GHG for the battery of a Leaf, ~3000 kg for a BMW i3, ~7200 for a Tesla, and ~4900 for a RAV4. These numbers are probably high because EV battery producers have been working to reduce the emission profile of batteries. How much has been reduced is up for debate, so we’ll run with these numbers and just remember that the numbers are probably on the high side.

EV Production

From the chart, you can see that the GHG emissions from production of a gas car are somewhere between one half to one quarter the amount of GHG emissions from building an electric vehicle. The EV doesn’t look as good from an emissions point now, however, the one year operating GHG emissions of a gas car are almost twice that of the production emissions. What’s the best way to make sense of this information? Perhaps a good way is too look at the point in time where driving an EV equals the same emissions as driving a gas car. Here are several charts comparing emissions over time. The calculations below assume 12,000 miles per year of driving. Please note that the emissions from the operation of a solar vehicle have been exaggerated greatly in order to display something on the chart.


EV Yearly 1

The source of the generation power makes all the difference. EV’s powered by coal start out with an emissions disadvantage and never recover the emissions deficit. EVs that use US grid electricity or CA grid electricity will make up the deficit within 2 years and when solar energy is used to generate the electricity, the deficit is made up for in less than one year. Does the same ratio hold true with the larger EVs?


EV Yearly 2

These charts are similar to the more fuel-efficient vehicles above, but the larger battery packs mean a larger emission deficit to overcome and more time required to reach parity with the gas burning vehicle. As with the smaller vehicles, using straight coal to generate electricity means that the EV never recovers from the emissions deficit and actually creates more emissions than the gas car over time. The time to make up the emissions deficit is longer with these larger vehicles, with grid generated power being made up in the third year and even Solar generated power takes until early in the second year of operation to make up the emissions deficit caused by production.

I didn’t add in the replacement of the battery pack into this equation because the packs last 5+ years and I’m only looking at three years on the graph. However, battery packs degrade over time. If one assumes total replacement at 5 years, the EV will still create lower emissions than the gas burner, except in the case of coal generation. Why? Because the gas burner generates more emissions in two years than a battery lasting 5 years will generate. Replacing the battery still ends up giving the EV and edge over the gas burner. You might ask what happens to the old EV battery? Well, even an EV battery that can hold only a 50% charge has a smaller footprint than the lead acid batteries currently used in solar storage. There is a fledgling industry in taking those used batteries and using them for solar storage, which extends the life many more years. Because the batteries can be repurposed, they don’t need to be scrapped or recycled.

Given the average 10-year life of an automobile, the electric vehicle using US grid power for generation will be cleaner than any gas vehicle in its class. When using cleaner grid power such as that of California, the EV fairs even better. If the owner uses solar energy to power the EV, then the EV is dramatically cleaner. A gas car would have to stop driving somewhere before two years in order to generate the same amount of GHG as an electric vehicle powered by solar would in 10 years.


1) At the point of use, the electric vehicle will always have fewer emissions than a gas-burning vehicle. Due to modern zoning regulations, electric power plants are usually not located near residential areas. So, if you want to clean up the air around your home, school or just in the area you’re driving, an electric vehicle will do the trick.

2) When adding in the emissions caused by generation, under most circumstances, the EV is going to generate fewer emissions than a gas-burning vehicle of the same class. The exception is when coal is used to generate electricity. There are a few states, such as Kentucky, where coal is the source of almost all grid electricity generated. However, when solar is used to generate the electricity, the EV is practically a zero emissions vehicle, with less than three one-hundredths of a gram of emissions per mile. If one lives in a state with US grid level emissions or better, such as the Pacific Coast states of California, Oregon, and Washington, the EV is going to be the greener vehicle. If you can add solar to your house and use that to generate electricity for your EV, regardless of the grid power mix, you’ve pretty much eliminated GHG emissions from your driving.

3) Adding in the production emissions give EVs a slightly less rosy picture, but, still the EV looks better over time. The initial emissions deficit the EV has when it rolls off the production line is made up for in as little as one year of driving a gas burner and at most 3 years. Coal generated electricity is the exception to this rule.

Battery Electric Vehicles are generally cleaner than gas burning vehicles of the same class. When powered by renewable energy sources such as solar, they are significantly cleaner. So much so, that driving a gas burning vehicle for more than one year is worse than all the emissions of driving an electric vehicle until the battery needs to be replaced.

The tremendous (over 11,000 to 1 ratio) operational emissions reduction of driving on solar generated power is one of the reasons Sunspeed Enterprises is committed to using zero emissions power sources for our charging network.