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RMI report finds substantial emissions reductions possible with smart EV charging

A new report from RMI has found that optimized charging of electric vehicles, which involves automatically and strategically shifting when an EV charges, could significantly reduce transportation sector emissions, and could potentially result in an average of 800 pounds of CO₂ saved per vehicle annually.

This is equivalent to avoiding the emissions resulting from 900 miles of driving by a typical gasoline-powered car, in addition to the emissions savings already captured by driving an EV.

The new report, More EVs, Fewer Emissions: How to Maximize Emissions Reductions by Smart Charging Electric Vehicles was published today by RMI in partnership with environmental tech nonprofit WattTime.

EV owners have an opportunity to reduce emissions associated with charging, reduce electricity costs, and support a faster transition to renewable energy. The report details how this can be achieved by using a real-time emissions signal—built-in software intelligence that leverages current grid emissions data—to control EV charging and shift electricity use to moments of cleaner power on the grid.

The potential implications of this approach to smart charging are substantial:

  • While EVs are already cleaner than internal combustion engine (ICE) vehicles, charging 1 million EVs at the right times on today’s grid is equivalent to taking between 20,000 and 80,000 additional ICE vehicles off the road.

  • In a future scenario with 70 million EVs on the road (one in four cars), emissions-optimized smart charging is the equivalent of taking an additional 5.73 million ICE vehicles off the road.

WattTime leveraged its real-time marginal emissions data to lead the analysis for the report. The organization’s 2019 report, How Emissions-Optimized EV Charging Enables Cleaner Electric Vehicles, first established how emissions-optimized charging can be leveraged to slash grid emissions, and found that emissions savings could be captured even on the dirtiest grids in the country. The new report uses updated WattTime data to dive deeper into the strategies that will maximize emissions reductions as EV adoption grows.

To create the report, RMI and WattTime explored daytime and nighttime charging scenarios for six US balancing authorities and compared uninterrupted or “baseline” charging with emissions-optimized charging. In their analysis, they found that a combination of faster charge time and longer dwell time (the amount of time the car is parked at a charger) allowed for the greatest emissions savings.

Two key factors leading to maximum emissions are also covered in the report: the impact of the local grid mix and EV owner charging behavior. Finally, the report includes clear and actionable recommendations for utilities, fleet operators, regulators, and other transportation sector stakeholders.

For utilities, the report recommends:

  1. When appropriate, prioritize Level 2 charging with longer dwell times, maximizing the flexibility of EVs as a grid asset.

  2. Incorporate transportation electrification into integrated resource planning, going beyond simply projecting EV adoption to considering how EVs can be used as a flexible asset.

  3. Align transportation electrification programs and offerings with the grid generation mix.

  4. Complement investment in new transmission lines that move renewable energy to load centers and can provide a structural solution for curtailment, with technology that optimizes charging around the marginal emissions rate to avoid curtailment in the near term in advance of new transmission coming online.

  5. 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.

Fleet operators who are transitioning to electric vehicles can also take advantage of emissions-optimized charging. Leading fleets, especially those electrifying to directly reduce their Scope 1 emissions, should consider emissions-optimized charging to maximize these direct emissions reductions, the report suggests.



Smart charging is a very good idea, in fact, it should be a no brainer.
The main thing should be to make sure as little solar or wind power is wasted as possible.
Unlike many tasks powered by electricity, charging batteries can be done at any time up to the time of departure, and this is the key to it.
On the other hand, if a driver is clever enough to charge when it is sunny, but they still have to bring up extra gas (if all the solar is spoken for), does anyone benefit?
This really only benefits the environment if you have excess wind or solar on the grid.


California should be mandating smart charging to permanently eliminate curtailment.


longer dwell times
Use buttery banks on fast chargers


The notion of eliminating curtailment using EVs is wishful thinking.  Anything with as low a capacity factor as PV (perhaps 20% at best, 11% in Germany IIUC) is going to have an extremely "peaky" generation profile.  To avoid curtailment using flexible charging, all of the following must be true:

1.  Enough vehicles must be plugged in at peak times.
2.  The chargers and vehicles must have sufficient power capacity.
3.  The vehicles must have sufficient un-charged battery capacity to absorb the generation peak.
4.  There must be sufficient energy to allow the EVs to accomplish their main purpose, transportation.

Doing this given the vagaries of "renewables" would be a feat not unlike juggling running chainsaws.  Know what would be far easier and cheaper?  Doing it with nuclear energy.


@EP, I was not suggesting we could eliminate curtailment, which as you have pointed out, is a huge task.
I was just suggesting that people should charge as much as possible when there is, or is likely to be, excess renewables on the grid.
The strategy will depend on the nature of the renewables.
If solar, you get a peak at noon, when a lot of people are at work.
Thus, they need to have chargers at work. If their batteries are already full, don't worry, at least they shouldn't need to charge later on from fossil electricity.
If wind, it is more complex as the windy times, while predictable out to say 3 days, are not regular. Thus, you would need to keep your car plugged into a "smart" charger when this was likely to happen, or at least overnight, or when the car is at home.
You would need to say: "I need X kWh by time Y" and let the system figure out when to do this.
You would probably want a minimum reserve of Z kWh, in case you need to make an unplanned trip.
Say you have a car with a 60 kWh battery, and drive 30 miles / day, using 10 kWh, you should be able to charge for 6 days at a time; so if you can see out 3 days for wind charging, you should be able to plan for wind charging, most of the time.
Whether most people are capable of, or care about this level of complexity is another matter.


One curtailment is working from home it took a pandemic to make that happen

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