Study offers insight into EV charging habitsDavid Wagman | May 30, 2019
The Electric Power Research Institute (EPRI) released an analysis of charging and driving data collected from Tesla drivers. The findings may help electric grid operators prepare for widespread electric vehicle (EV) adoption.
EPRI collaborated with the Salt River Project (SRP) in Arizona to collect data from nine Tesla owners for one year. The study aimed to better understand the grid impact of Tesla owners’ charging behavior and driving practices.
An earlier 18-month study tracked 100 EVs in SRP’s service territory. EPRI later narrowed its focus to Tesla vehicles. The earlier study determined that the largest demand spikes took place when Tesla owners were charging at public SuperChargers.
EPRI said that because Tesla vehicles can charge at a higher power level than other EVs, its initial dataset represented the upper range of potential grid impacts related to EV charging.
Vehicle-mounted devices collected data as vehicles were charged and driven, regardless of where they were charged. EPRI said that this approach provided a better estimate relative to meter monitoring for projecting future load resulting from EV charging.
The devices collected data on voltage, current, GPS location and state of charge. Summary data included total yearly kilowatt-hours (kWh) and whether charging occurred at home, at work or in a public charging station. Other data included average kWh per charge, miles driven per kWh and grid-related data.
Researchers characterized the demand created by EV charging using “load curves” for weekends and weekdays as well as those associated with different rate structures.
The EPRI research found that participating Tesla owners used between 2,380 and 7,159 kWh of energy per year. The earlier report, which included more EV brands, found that participants used around 2,700 to 3,300 kWh per year.
The Tesla participants completed 63% of their charging at home. That rate was lower than EPRI’s previous analysis on vehicles other than Tesla. It found that 75% to 80% of EV charging took place at residential charging locations. Researchers said the difference could be due to Tesla’s free charging at its network of SuperChargers for vehicles purchased before 2018. What's more, nearly all home charging was at Level 2 (240 volts, 16 to 40 amps).
Public charging represented about 20% of the charging, the research showed, with nearly 80% of that taking place at DC fast charging stations.
More than half of the study’s vehicle owners were enrolled in a time-of-use rate, which EPRI said was effective in shifting charging to night and early morning hours.
EPRI said it is developing a larger study to track 40 Tesla vehicles (Models S, X or 3) over 60 days using the publicly available Tesla application programming interface (API).
EPRI said it also expects to launch during the fourth quarter a study to track thousands of vehicles. Its goals are to help EPRI refine its understanding of where EV customers charge, how much they charge, and how that varies over time and season. EPRI said it will focus also on how Tesla vehicles’ larger batteries and longer driving ranges combine with higher power charging to affect customer behavior and effects on the grid.