NREL review explores potential value of EV managed charging for realizing effective vehicle-grid integration
19 January 2022
A team at the National Renewable Energy Laboratory (NREL) has completed a literature review on the potential value of EV managed charging. Their findings, published in Energy & Environmental Science, provide a comprehensive look at how EVs and the grid could work together as the electric and transportation sectors become intertwined.
Although many studies have considered the benefits of EV managed charging, 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.
Anwar et al.
The simplest form of EV managed charging is time-of-use pricing that offers lower electricity rates to charge 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, in which EVs can act as temporary electricity suppliers by sharing power back to the grid or local needs, such as 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. 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 come with a cost.—Matteo Muratori, NREL analyst and principal investigator of the study
Across the hundreds of studies reviewed, NREL researchers found significant benefits of EV managed charging, such as 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, 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 to produce 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.
Muhammad Bashar Anwar, Matteo Muratori, Paige Jadun, Elaine Hale, Brian Bush, Paul Denholm, Ookie Ma and Kara Podkaminer (2022) “Assessing the value of electric vehicle managed charging: a review of methodologies and results”Energy Environ. Sci.
This is absolutely key - and it will be different country by country.
Those with a lot of solar will have a curve as shown here, so that is a plan for SPain and Arizona.
Other countries like Ireland and Scotland have a lot fo wind power, but not much solar.
Thus, they might be better off charging from 11pm - 6am (when demand is lowest), or when the wind blows.
The problem is that the wind is intermittent but reasonably predictable up to say 72 hours out. Thus, you could be told that the best time to charge is tomorrow afternoon or this evening or two days hence at night.
This is reasonable as most vehicles now have 50+ kWh of storage, enough for 150-200 miles or 5-7 days "normal" driving (at 30 miles/day).
Thus, you should be able to time your charging to times of highest renewable penetration (or lowest cost power).
Obviously, you'll probably keep 20-40% as a minimum level of charge, but it should work out OK with 50 kWh of storage.
So you will need some software and weather forecast input, or you could have a system where you let the utility decide when to charge your car, given constraints which you can decide, like, I need 40 miles / day usually. If you expect a long run, you obviously would be able to charge up for that.
You might need a charger in work as well, which is networked to your main charging account.
The ultimate outcome of this could be that you allow the utility to use X percent (say 20-30%) of your capacity for load balancing N times / year (say 20), and that in an emergency, you could run your house for a while from the car battery, assuming it was charged.
Posted by: mahonj | 20 January 2022 at 03:08 AM