We know that EVs produce much less pollution over their lifetimes than fossil-powered vehicles (regardless of the thousands of daily Facebook posts claiming the opposite). However, generating the electricity to charge them is not emission-free, and as millions more EVs get hooked up to the grid, smart charging to maximize efficiency will be an important part of the picture.
A recent report from two environmental nonprofits, the Rocky Mountain Institute and WattTime, examined how scheduling charging for times of low emissions on the electrical grid can minimize EV emissions.
According to the report, in the US today, EVs deliver about 60-68% lower emissions than ICE vehicles, on average. When those EVs are optimized with smart charging to align with the lowest emissions rates on the electricity grid, they can reduce emissions by an additional 2-8%, and even become a grid resource.
Increasingly accurate real-time models of activity on the grid are facilitating interaction between electric utilities and EV owners, including commercial fleets. The researchers point out that, as more accurate models provide dynamic signals about the costs and emissions of power generation in real time, there is a significant opportunity for utilities and drivers to control EV charging according to emissions signals. This can not only reduce costs and emissions, but facilitate the transition to renewable energy.
The report found two key factors that are critical to maximizing CO2 reduction:
The local grid mix: The more zero-emissions generation available on a given grid, the greater the opportunity to reduce CO2 emissions. The highest possible savings found in the study were on grids with high levels of renewable generation. However, even relatively brown grids can benefit from emissions-optimized charging.Charging behavior: The report finds that EV drivers should charge using faster charging rates but over longer dwell times.
The researchers listed several recommendations for utilities:
When appropriate, prioritize Level 2 charging with longer dwell times.Incorporate transportation electrification into integrated resource planning, considering how EVs can be used as a flexible asset.Align electrification programs with the grid generation mix.Complement investment in new transmission lines with technology that optimizes charging around the marginal emissions rate to avoid curtailment of renewable energy generation.Continually re-evaluate time-of-use tariffs as real-time grid data becomes readily available. For example, rather than just considering rates that reflect peak and off-peak loads, adjust rates to incentivize EV charging when there is likely to be curtailment.