“Unintended Consequences of Time-of-Use Rates: EV Charging and Distribution Network Constraints”
Megan Bailey (University of Calgary), David Brown* (University of Alberta), Erica Myers (University of Calgary), Blake Shaffer (University of Calgary), and Frank Wolak (Stanford University)

We employ a field experiment to shift the timing of electric vehicle (EV) charging and reduce strain on the electric distribution grid. We assess the effect of time-of-use (TOU) rates and managed charging in which EV charging is automated using an algorithm, with the possible option for users to override. We use a novel approach to assess the impact of charging on the distribution grid by clustering EVs into 10-vehicle “virtual transformer” groups that face randomized, daily transformer network constraints. We find that while TOU rates are very effective at shifting EV charging demand to off-peak hours, TOU rates induce a “shadow peak”, too much simultaneous charging at the start of the cheaper TOU time block. This unintended coordination aspect of TOU leads to more constraint violations of the distribution network as compared to the status quo. In contrast, managed charging – automated, coordinated charging among EVs in a transformer group – reduces strain on the distribution system compared to the status quo. Further, we find that few EV owners subject to managed charging override the automation.



*Denotes presenter