By 2050, 50% of the U.S. vehicle fleet will be electrified —more than 150 million cars and light trucks in all. With an average battery pack size of 18.4 kWh, this would amount to nearly 2,900 GWh of mobile electric storage capacity. The addition of such a large and potentially unpredictable load could present problems for grid management if electric vehicle charging is not handled effectively.
A fleet of 157 million electric vehicles represents an enormous added load to the 2050 U.S. electricity grid. If all the vehicles are charged at once (assuming a 3.1 kW charging draw—corresponding to a 6-hour charge time), this could add a peak load of 481 GW to the system, more than 20% of total 2050 U.S. installed electricity generating capacity. If vehicles are drawing higher power for 45-minute or 1-hour “fast charges,” the maximum charging load could be even higher. However, there are several different levels of vehicle charging control, the best of which will turn a huge EV fleet from a grid burden to a grid benefit.
The simplest level of vehicle charging control is convenience charging (also called “dumb charging”). Users plug in EVs at their convenience, and each draws power as soon as it’s plugged in, just like a typical appliance. With convenience charging, there is no way for the grid operator to predict or control additional electricity demand from EV charging. Any charging load up to the full peak load of 481 GW might be demanded at any time.
With a more intelligent charger, the vehicle may implement smart charging, in which the vehicle or charging station can communicate with and be controlled by the grid in real time. An EV may be plugged in all night at someone’s home or all day at the office, but it will only receive a signal from the utility to charge when grid and transmission loads are low. These smart charging vehicles can be controlled to charge at off-peak hours, or at times when there is renewable supply in excess of demand. Charging can be interrupted when there is transmission congestion or when a generator trips offline. Additionally, the charging power and voltage can be controlled carefully to help balance variable generation or to provide some reactive power and voltage control for the grid. In a smart charging setup, the vehicle owner would probably have the option to override utility control in some cases if the vehicle needed an immediate charge.
The most advanced type of charging control is often referred to as vehicle-to-grid (V2G). Each EV would be in communication with the grid just as in the smart charging case, with the exception that the vehicle would also be allowed to discharge energy to the grid on demand. This would allow the EV fleet to provide some amount of backup power in the case of outages or unexpected dips in variable renewable supply. This would also create a large load-shifting resource, which could help the grid operator balance supply and demand throughout the day.
Smart charging and V2G technology will increase infrastructure costs to the future U.S. electricity system, as compared to the cost of a fleet of dumb charging vehicles. However, smarter charging controls will reduce the burden on the transmission and distribution system, avoiding the need for new and updated networks. And because the charging load can be controlled by the grid operator, the grid avoids needing hundreds of MWs of additional peaking reserve capacity. Together, these avoided costs more than offset the added cost of the smart charging infrastructure.
The adoption of EVs was modeled using standard EIA retooling rates for auto factories and assumed increasing EV sales as the relative prices of EVs dropped. In 2050, RMI projects that the U.S. will have around 315 million vehicles, nearly all of which will have electric powertrains, roughly split between electric battery and advanced fuel cell vehicles. RMI’s scenario for a competitive automotive sector finds very few gasoline-powered vehicles left on the road by 2050.
Kromer, Matthew, and John Heywood. 2007. Electric Powertrains: Opportunities and Challenges in the U.S. Light-Duty Vehicle Fleet. Laboratory for Energy and the Environment.
Lovins, Amory B., and David Cramer. 2004. “Hypercars, Hydrogen, and the Automotive Transition”. International Journal of Vehicle Design 35 (1): 50-85.
U.S. Energy Information Administration. 2010. Annual Energy Outlook 2010. Washington, D.C.: U.S. Department of Energy, April. link