Unintended Consequences of Time-Of-Use Rates: EV Charging and Distribution Network Constraints
Abstract
We implement a field experiment to assess the effect of time-of-use (TOU) pricing and managed chargingto shift the timing of electric vehicle (EV) charging and reduce strain on the electric distribution grid. We randomly assign EVs into 10-vehicle “virtual transformer” groups that face randomized, daily
transformer constraints. We find that while TOU rates do deliver, as intended, a shift in electricity
consumption to off-peak periods—a useful outcome for the energy system—they also result in the
unintentional coordination of electricity consumption for EV charging in the cheaper evening TOU
off-peak hours. This unintended coordination aspect of TOU pricing increases the frequency of virtual
distribution transformer constraint violations compared to our control group. In contrast, centrally
managed charging of EVs reduces the frequency of virtual transformer constraint violations. Further, we
find that EV owners rarely opted out of managed charging, only overriding managed charging in
approximately 1% of charge sessions. These results highlight the potential for automation to facilitate
electrification of the transportation sector with lower distribution grid upgrade costs than expected.