Shifting Electric Vehicle Owners to Off-Peak Charging

Featured in print Digest

This figure is a two-panel line graph titled, Effect of Incentives of EV Charging Behavior. The following pertains to the left-side panel. The y-axis is labeled, normalized share of kWhs charged off-peak. It ranges from 0.9 to 1.4, increasing by 0.1. The x-axis represents month and ranges from February to August. There is a vertical dotted line at April labeled, Phase 1.  There are three lines labeled on the graph: Nudge, Rewards, and Control. The Nudge line starts at above 1 in February but slowly decrease to about 0.95 by August. The Rewards line starts at near 1 in February before dipping below 1 in between March and April. To the right of the vertical dotted line labeled Phase 1, the Rewards line experiences a steep increase to over 1.3 by May before experiencing fluctuations and then dropping down to about 1.2 by the end of the period. The Control line starts at near 1 in February and experiences a slight increase to about 1.05 by July.  The following pertains to the right-side panel. The y-axis is labeled, normalized share of kWhs charged off-peak. It ranges from 0.9 to 1.4, increasing by 0.1.  The x-axis represents month and ranges from April to December. There are two vertical dotted lines. One at April labeled, Phase 1, and another at September labeled, Phase 2.  There are three lines labeled on the graph: Rewards (continue), Rewards (stop), and Control. The Rewards continue line starts at near 1.3 in April. It initially increases before dropping to 1.2 in September. After September, it increases to about 1.25 and levels off. The Rewards stop line starts at 1.2 in April and fluctuates between 1.2 and 1.3 until Phase 2 in September. After September, the line steeply declines to about 1 in December. The control line fluctuates between 1 and 1.1 for whole period. The follow pertains to both panels. Shaded areas represent 95% confidence intervals. Off-peak hours are 10 PM–6 AM. Nudge group received information on the benefits of shifting EV charging to off-peak hours. Rewards group received same information

Electric vehicle (EV) sales have been rising as a share of new car purchases, and they are expected to continue to do so because a range of public policies support the decarbonization of the transportation sector. The electricity used to charge an EV can be substantial. An average household consumes approximately 1 kilowatt-hours of electricity per hour. An EV charging on a common (level 2) fast charger typically uses 7 to 8 kWh per hour. The impact of greater EV penetration on the cost of electricity and reliability of electricity distribution systems will depend critically on when EVs are charged, as charging during high-demand times could strain the system and necessitate substantial investments in grid infrastructure. Encouraging EV drivers who might charge at high-demand times to shift to other times when there is surplus grid capacity can significantly reduce the cost of EV integration.

In Show Me the Money! Incentives and Nudges to Shift Electric Vehicle Charge Timing (NBER Working Paper 31630), Megan R. Bailey, David P. Brown, Blake C. Shaffer, and Frank A. Wolak use a field experiment to measure the relative effectiveness of financial rewards and behavioral nudges in shifting EV charging to off-peak times.

Households in Calgary, Alberta were recruited from a municipally owned electricity distribution utility. They were randomized into one of three groups: a rewards group that received a financial incentive of 3.5 cents Canadian per kilowatt-hour, roughly a 23 percent discount from their hourly electricity rate, for charging during the off-peak hours from 10 pm to 6 am; a nudge group that received information from the company on the societal benefits of charging in off-peak hours; and a control group that received no intervention. The hourly electricity consumption of all three groups was monitored during the experiment.

Financial incentives were effective at shifting EV charging behavior, with the households receiving the off-peak discount collectively shifting their average share of kWh charged during off-peak hours from 59 to 77 percent. The nudge group showed no change in charging behavior and was statistically indistinguishable from the control group.

To test for habit formation, a randomly selected half of the rewards group was told they would no longer receive financial incentives for off-peak charging while the other half continued to receive the off-peak discounts. The charging behavior of the group that no longer received the subsidy reverted to its pre-intervention pattern. Continued financial incentives were needed to maintain the shifts in charging-time behavior.

The researchers conclude that EV charging behavior is more price-responsive than many other forms of residential electricity use, perhaps because shifting charging times does not sacrifice driving capability. This contrasts with the effect of timing shifts in the use of many residential appliances, such as air conditioners, the use of which must coincide with the electricity draw.

— Susan Stewart


The researchers are grateful to their partner utility, ENMAX Power, for sponsoring and managing this field experiment.