It is 5 p.m., and you arrive home from work when it is peak demand for the grid. Your electric vehicle (EV) is 50% charged — you could either plug it in and charge right away or, if it works for your plans, schedule the vehicle to charge at a better time for the grid.
With more and more EVs on the road, the grid of the future can greatly benefit from EV managed charging — "smart" charging. EV managed charging coordinates charging based on people’s travel needs, electricity supply, and grid conditions. This flexibility could be especially valuable for the grid as it transitions to high shares of variable renewable generation, like solar and wind.
A team at the National Renewable Energy Laboratory (NREL) completed a literature review on the potential value of EV managed charging. Findings, published in an Energy & Environmental Science article provide a complete look at how EVs and the grid could work together as the electric and transportation sectors become intertwined. Many studies have considered the benefits of EV managed charging, but this review summarizes findings from hundreds of studies considering multiple value streams for the power system, enablement costs, and perspectives of different stakeholders, including utilities, EV owners, charging station operators, and rate payers.
The simplest form of EV managed charging is time-of-use pricing, which offers lower electricity rates for charging during off-peak periods. More advanced managed charging could dynamically control charging based on a user’s travel needs and grid conditions to provide additional values to the power system. The most sophisticated form of managed charging goes two ways — EVs could act as temporary electricity suppliers by sharing power back to the grid or local needs, like meeting critical loads for resiliency (V2X).
Any form of EV managed charging requires communication between the utility and the vehicles. In some approaches, the communication is one-directional and less frequent. More complex implementations require two-way dynamic communication.
"Managed charging can be a tremendous resource for the grid but there are trade-offs to solutions at different levels of commercial readiness," said Matteo Muratori, NREL analyst and principal investigator of the study. "Some solutions offer a wider range of grid services and value streams but require increasingly complex communication and control technology and demands on users, which comes with a cost."
Across the hundreds of studies reviewed, NREL researchers found significant benefits of EV managed charging, like decreased emissions, improved reliability, supporting large-scale deployment of variable generation, and lower power system costs. Some studies show that EV managed charging could provide thousands of dollars of value per EV every year.
Although EVs will likely require upgrades to parts of the power system, the studies show that managed charging improves system efficiency and can lower average retail electricity rates for all consumers — benefiting more people than just EV owners. Managed charging is particularly valuable in systems with high levels of variable renewables to provide flexibility to match supply and demand.
A few important factors do change the value of EV managed charging, according to the study. Power system cost savings from managed charging is lower in systems with other sources of flexibility. In addition, the type of charging strategy can significantly change the value. For example, if EV managed charging is based solely on minimizing owner cost with no consideration of the grid, it could negatively impact system cost and operation. Moreover, the study highlights that enablement and implementation costs remain highly uncertain due to limited market implementations and a lack of scale.
Benefits of managed charging for distribution systems are more difficult to nail down, NREL researchers found. "Distribution system issues are location- and system-specific, so it's very hard to generalize insights," Muratori said. Overall, it’s understood that managed charging can noticeably reduce distribution system peak loads and congestion across the board, but more modeling and analysis is needed in collaboration with utilities.
Many questions remain about the potential value of EV managed charging and also questions about producing reliable benefit-cost assessments. Among other things, the researchers recommend additional data modeling and analysis to better estimate charging needs, customer participation, and constraints for various types of EVs and applications as the EV market expands. This research will help determine charging loads and the ability for EVs to provide demand-side flexibility. Demonstration projects are also needed to fully understand implementation costs and customer participation. Comprehensive analysis across the entire power system at bulk system- and distribution-levels is also needed to better understand the total benefit EV managed charging can provide.
Finally, a complete benefit-cost assessment that considers the entire extent of value streams for the power system, enablement costs, and the perspectives of all stakeholders, even at a regional level, is still missing. The analysis should consider the entire extent of all stakeholders' values, costs, and perspectives, including utilities, EV owners, charging station operators, and rate payers.