Where does electricity come from? When you flip a light switch on, you’re getting electricity from somewhere—maybe a spinning gas turbine, or maybe a battery storing excess electricity generated by wind or solar power. When you flip the light switch off, the grid responds by shifting its sources around, ensuring everyone connected is receiving a steady flow of electrons.
The complexity of the grid complicates how we measure greenhouse gas (GHG) emissions from an electric vehicle (EV). Charging an EV at different times of the day or in different locations may change the electricity source that charges the EV, resulting in different GHG emissions. This challenge gets at the heart of an ongoing debate between average and marginal electricity.
Average electricity GHG emissions: This method averages GHG emissions from all electricity generation in a given region, treating all the electricity produced and consumed in the region equally. No matter how much electricity you use or when you use it, your electricity is assumed to be just as clean (or dirty) as anyone else’s in the same region. In essence, this approach assumes that any additional electricity needed to power an EV would come from the same mix of electricity sources (hydro, nuclear, natural gas, coal, wind, etc.) that provides electricity to meet current demand.
Marginal electricity GHG emissions: Marginal GHG emissions are estimated by examining what power plants, or types of power plants, are likely to be used to match any additional (or marginal) demand. In this type of analysis, the electricity consumed by additional demand—such as a newly purchased EV—is assigned a different GHG emissions intensity from electricity used by existing electric loads. This often results in additional demand having higher GHG emissions, as renewable sources of electricity are not often on the margin, even though we continue to add more and more solar and wind to the grid.
While the debate may rage on among academics, new technology is helping render it moot, giving consumers more control over what powers their EVs.
Recently, eMotorWerks and WattTime announced they are developing a product that analyzes the electricity grid in real time, allowing EVs to charge when more renewables are producing electricity. Not only would this reduce the GHG emissions from charging an EV, but it could also smooth out demand from renewable sources, increasing the reliability of the grid as a whole. You can read more about pairing renewable electricity and EV batteries in another recent blog post I wrote.
The information collected from this type of technology could also be useful for researchers, who could then more accurately estimate the GHG emissions from charging. Compared to what is already available in EVs today, it’s not far-off tech, either. “Delayed charging” is already a feature in many EVs, allowing them to charge at night when electricity is cheaper.
The bottom line? EVs are the cleanest vehicle in most regions of the US (as our updated State of Charge shows) and getting cleaner as we add more renewables to the grid—and that benefits everyone.