Time-of-use (TOU) pricing might seem like the ultimate solution to ensure electric vehicle charging loads won’t overburden the grid. But will TOU rates guide drivers’ behavior when it’s time to...
Connecting vehicles to smart systems.
EVs will have different driver behavioral patterns, which will have different impacts on power demand.
For starters, all EVs aren’t alike. There will be two types of passenger vehicles that dominate electricity demand, and they have different consumption characteristics. The all-battery electric vehicle (BEV) has no other means of locomotion; it requires a charge to move anywhere. The other vehicle type is plug-in hybrid electric vehicle (PHEV), and it can be found in two forms. The first is the hybrid drive system, where there is both an electric and an internal combustion drivetrain. As the battery drains on this type of PHEV, it’s charged by operation of the ICE drivetrain, if the vehicle is moving, or through a plug, if it’s stationary. The second type of PHEV has an onboard ICE that only acts a generator, powering the battery for extended range.
The two dominant EVs in the market represent these two broad groups. The Nissan LEAF is a BEV with a range of 70 to 100 miles from its 25-kWh battery pack. Another example is the Tesla Roadster, whose long range is powered by a 56-kWh battery pack. GM’s Chevy Volt is an extended-range PHEV, and uses the onboard engine primarily as a generator to extend the 40-mile range of its 16-kWh battery pack.
How the buyers of these vehicles behave, especially in these early stages, will be interesting to note. For the BEV, early data indicate that drivers are relying primarily on a home charge, with a supplement from charging at the workplace. Although BEV drivers will no doubt use third-party charging locations, in the early stages the drivers appear to have sufficient charge for their daily activities. It’s anticipated, however, that these are the vehicles that will occupy the level-3 chargers—a 420-volt fast charger that reaches an 80-percent charge in less than 30 minutes.
By contrast, the PHEV has different use characteristics, even though it also will require electricity to power its drivetrain. Since the vehicle range from the electric motor is much shorter than it is for a BEV, it’s unlikely to power the vehicle for an entire day. This is the reason for the onboard generator, which requires gasoline. Whether the PHEV owner purchased for sustainability, environmental concerns, cost of ownership, or just the high price of gasoline, most owners aim to use as little gas as possible. It has developed into a social game, as drivers compare how little gas they use to go greater and greater distances. While these are terrific owner characteristics that demonstrate the demand for the vehicle, they also create a challenge.
Where the BEV is likely to have a relatively consistent routine, charging at home or work primarily, the PHEV is much less likely to have a consistent routine. Without a routine and being able to go essentially anywhere, and with a mindset to maintain battery charge as much as possible, the PHEV represents a roaming demand that looks quite different from its BEV compatriots. This matters because each vehicle’s demand for power might be the equivalent of multiple houses per