Understanding the Emissions of Your Electric Vehicle

In the last four years, there has been a four-fold increase in the number of Fortune 500 companies that have made commitments to achieve carbon neutrality, use 100% clean energy, or reduce their emissions by amounts recommended by scientists in order to avoid catastrophic climate change. As companies like Amazon continue to set ambitious targets such as carbon neutrality by 2040 and take steps towards these goals like ordering 100,000 electric delivery trucks, the demand for products that can accurately measure the indirect emissions of a company’s electricity generation will continue to grow.

Currently, there is no standard methodology for reporting the carbon dioxide emissions associated with charging an electric vehicle. This makes it hard to reliably measure and compare electrification-driven emissions reduction across fleets since each fleet can use a different methodology. To make matters worse, emissions from electricity generation can vary dramatically in time and by region — rendering the use of a single national average inaccurate and imprecise.

Sources: EIA (for national average) and WattTime (for balancing authorities). The New England Balancing Authority covers the six New England states; the Midcontinent Balancing Authority covers a swath of the central part of the United States from Minnesota to Louisiana.

Fortunately, we have identified a method to provide accurate, real-time emissions data for electric vehicle fleets. eIQ Mobility is excited to partner with WattTime, an environmental tech nonprofit which utilizes real-time emissions data to optimize the electricity use of smart devices, to provide a standardized sustainability reporting metric for electric vehicle fleets.

Using more granular emissions data is important because it can:

  • Accelerate decarbonization, by shifting energy consumption to low-carbon periods
  • Provide transparency into a company’s Environmental, Social, and Governance (ESG) metrics
  • Enable services such as emissions-optimized electric vehicle charging

Not all power grids are created equally

Before we can calculate how much carbon dioxide is emitted from EV charging, we must first understand how our electricity system works. The contiguous United States does not consist of a single, massive power grid. Instead, it can be thought of as three main grids, or interconnections, which can be further broken down into 66 balancing authorities.

Image source: EIA

As their name suggests, each balancing authority is responsible for ensuring that electricity demand always equals electricity supply. If demand begins to increase, the balancing authority must increase supply, either by generating more electricity or by importing electricity from a neighboring balancing authority.

What does this have to do with electric vehicles?

While electric vehicles (EVs) are cleaner than internal combustion engine (ICE) vehicles on practically every power grid, the amount by which they are cleaner depends heavily on the power plant that must be dispatched to supply the EV’s power, which in turn depends on when and where the vehicle is charged.

The power plant that increases electricity generation when a new load appears is referred to as the marginal power plant. It could be a hydroelectric turbine, a natural gas turbine, or even a solar farm! The following figure shows an example power plant dispatch, with low marginal cost renewables being dispatched to generate electricity before expensive gas and oil peaker plants, power plants that are only called upon in times of high demand.

Example power plant dispatch order. Source: WattTime

Each unique power plant has its own emissions factor, which refers to the amount of carbon dioxide emitted for each unit of energy produced. We will refer to the plant’s emissions factor as the marginal emissions factor. The marginal emissions factor can be quite different from the average emissions factor of all electricity generated on the grid.

For example, in the power dispatch graphic above, the power grid will have a low average emissions factor (since baseload power is renewables, nuclear, and hydro), but will have a high marginal emissions factor whenever coal-, gas-, or oil-fired power plants are utilized.

How much do marginal emissions vary?

Just like average emissions, marginal emissions vary by both time and location.

In the CAISO (California) balancing authority, which has a large amount of solar and hydroelectric power, the highest marginal emissions factor was over 24 times higher than the lowest marginal emissions factor in 2019.

The ERCOT (Texas) balancing authority, which generates approximately 20% of its electricity from coal, has much less volatile marginal emissions, but higher emissions on average.

Data source: WattTime

Let’s dig deeper and observe how the marginal emissions varied in each balancing authority on an hourly basis. The following heat maps show the date on the x-axis and the hour on the y-axis.

CAISO: Typically, marginal emissions in California are lowest around midday in spring, when solar generation is high and air conditioning loads are still low. Marginal emissions are highest on hot summer evenings, when peak loads, driven by air conditioning, are being met by gas-fired peaker plants.

Heatmap of CAISO marginal emissions for 2019. Data from WattTime. Plot by eIQ Mobility.

ERCOT: In ERCOT, the lowest marginal emissions tend to occur in the afternoon and evenings during summer. This is likely caused by the existence of gas peaker plants that actually have a lower marginal emissions factor than the coal-heavy baseload power.

Heatmap of ERCOT marginal emissions for 2018. Data from WattTime. Plot by eIQ Mobility. Note that the heatmap color scale is different from the CAISO heatmap color scale.

In summary, variations and trends in marginal emissions vary widely between regions. These trends will be a function of the region’s electricity generation portfolio, as well as its climate.

Who cares?

We all should! Electric vehicles are required to achieve deep decarbonization of the transportation sector. However, without properly measuring and verifying their impact on the grid, companies will not be able to accurately report their sustainability achievements to their investors and customers, and grid operators will have to rely on dirtier electricity sources more often.

Optimized Charging

By combining WattTime’s real-time marginal emissions data with eIQ Mobility’s EV management platform, we can help our fleet customers maximize their emissions reductions. We also expect that our technology can enable partnerships with utilities that are attempting to do any of the following.

Reduce the curtailment of wind and solar power

  • In some regions, such as Southern California, so much solar is generated during the day that wholesale power prices go negative and marginal emissions are almost 0.
  • This is a great time to charge an EV, as they can use clean electricity that would otherwise not be generated!

Reduce fleets’ average energy costs

  • The power plants that are ‘on-the-margin’ are almost always more expensive to run than the plants that are already operating (otherwise they would have been selected!)
  • By avoiding times of peak demand, electricity prices can be lowered for all energy consumers on the grid

Reduce their carbon footprint

  • In many regions, the most expensive power plants are also the dirtiest
  • WattTime has found that optimized charging of EVs can make them almost 20% cleaner

Standardizing sustainability reporting is important both for accelerating our transition away from fossil fuels and for creating a level playing field when it comes to accounting for emissions reductions. To demonstrate the importance of standards, imagine if each Fortune 500 company was mandated by the federal government to pay a carbon tax. However, suppose each state was tasked with developing its own metric for measuring electric vehicle emissions. Some states might use average emissions, others would use marginal emissions, and some would probably include lifecycle emissions! Each corporation would be burdened with figuring out the intricacies of each state’s regulation, and would likely find loopholes to avoid paying the carbon tax. Furthermore, investors and sustainability advocates would have no idea how to compare the progress of any two companies.

Providing our customers with accurate EV sustainability reporting enables them to make informed decisions about where to electrify and when to charge. Fleet managers will be able to visualize the emissions (and emissions savings), vehicle behavior, and total cost of ownership of their EVs all from one dashboard.

We look forward to deploying our new reporting tool to customers this quarter!




We are a data science startup building a trusted platform that drives vehicle fleets into a smart, electric, and cost-effective future. www.eiqmobility.com

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eIQ Mobility

eIQ Mobility

We are a data science startup building a trusted platform that drives vehicle fleets into a smart, electric, and cost-effective future. www.eiqmobility.com

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