Charging into the electric vehicle future
By Judd Mahan, P.G. (Posted March 23, 2021)
Charging your electric vehicle battery at home is more effective than other charging strategies such as workplace charging or charging at stops along highways. That finding comes from researchers at the Massachusetts Institute of Technology (MIT) Data, Systems and Society Institute. A January 2021 Nature Energy article — Personal vehicle electrification and charging solutions for high-energy days — describes the research and results (Wei et al., 2021).
Businesses, governments, and individuals increasingly focus attention on reduction of greenhouse gas (GHG) emissions. In the U.S., approximately 30 percent of GHG emissions are attributed to transportation. Battery electric vehicles (BEVs) are expected to play a key role in reducing GHG emissions, but there will be substantial challenges. When most people are driving electric vehicles, where will the vehicle batteries be charged? What infrastructure changes will be necessary to accommodate the way Americans travel?
Those questions are especially pertinent as auto manufacturers are making aggressive marketing claims; Volvo plans to be fully electric by 2030 and GM has committed to 30 new global electric vehicles by 2025.
The aforementioned researchers used detailed longitudinal daily vehicle usage data gathered over the course of a year in the Seattle area. Longitudinal data reflect data gathering over an extended period. GPS tracking devices were used on vehicles to gather data for time spent parked at home, driving, and at work or other public locations. The TripEnergy model was developed and used to calculate the energy used by a vehicle for a given trip. The energy used to propel the vehicle as well as energy used to run auxiliary devices such as heating, cooling, and lights are incorporated into the model. Other factors include vehicle mass, drive efficiency [estimated from U.S. Environmental Protection Agency (USEPA) corporate average fuel economy (CAFE) results], and ambient temperatures. Heating and cooling are assumed to vary with ambient temperature by geographic region of the United States.
Charging options increase, but challenges and gas-reliance remain
Results of the Seattle study are discussed with respect to usage of different battery charging infrastructure. Vehicle electrification potential (VEP) is used to measure “the fraction of vehicles whose energy requirements can be met by a BEV with a given battery capacity on all vehicle days” (Wei et al., 2021). The study demonstrated that home charging alone resulted in a VEP of 12 percent. However, strategically adding to home charging with options for charging at work, and fast charging availability at highway stops for longer trips, increases VEP to 41 percent. The data distribution of vehicle-day energy requirements results in a “fat tail.” In other words, while most days’ vehicle energy demands are lesser and are within the range of a BEV’s battery capacity, study results indicate that there are a limited number of days with greater vehicle energy demands. This is due in large part to occasional use of vehicles for long trips. To mitigate this challenge, availability of long-range, presumably gasoline-powered, vehicles might be necessary until battery technology improves.
Analytical results of the Seattle data were applied to a short-term (cross-sectional rather than longitudinal) data set for the United States. A different metric, daily adoption potential (DAP), is used to characterize “the daily percentage of vehicle-days in a population whose energy requirements are met by a BEV” (Wei et al., 2021). DAP, which reflects the potential for an electric vehicle to meet a driving day’s energy requirements on a representative day, will generally be greater than VEP.
The study results indicate that DAP throughout the United States under a home-charging scenario is 98 percent. Adding options for at-work charging and fast charging for highway trips results in a DAP of 99 percent. The study looked at a lower-cost Nissan Leaf, which would be sufficient for most personal transportation. The authors also considered the higher-end Tesla Model S, which, due to greater battery capacity, more easily handles the energy demands of longer trips. Still, the data distribution for vehicle energy demand indicates that periodic use of alternative vehicles would be necessary to meet all personal transportation needs. Results of the study demonstrate that BEVs are viable as a key part of reducing GHG emissions and will help in planning new infrastructure as the United States transitions to electric transportation.
Emissions matter to Americans, but dependability and cost still reign
While GHG emissions are of increasing importance to Americans, dependability and cost still reign as the bottom-line determinants in the gas vs. electric decision.
Range anxiety is the fear we might have about being stranded by a car with no battery power or about being limited in our driving habits by a range that is considerably less than that offered by gasoline-powered vehicles.
As drivers of gasoline-powered automobiles, we are accustomed to thinking of fuel cost in terms of miles per gallon (mpg). The battery power used by a BEV is measured as kilowatt-hours (kWh) per 100 miles. The Nissan Leaf is rated at 30 kWh per 100 miles. To calculate the electricity cost of driving, you have to know the price that you pay for electricity. Check this table to see your state’s average electricity pricing.
As an example, the price of electricity in North Carolina, where I live, was 11.5 cents per kWh in December 2020. So, if I were driving a Nissan Leaf in December 2020 in North Carolina, my power cost for driving 100 miles would be $0.115 x 30 kWh = $3.45. That cost can be compared to about $10.76 to drive 100 miles in a gas-powered automobile, which gets 25 mpg assuming a gas price of $2.69 per gallon.
As individual drivers, we have a lot to consider and weigh in terms of cost, dependability, and the environment. However, the transition to electric vehicles is inevitable, so it’s a great time to learn more.
• Nature Energy article: Personal vehicle electrification and charging solutions for high-energy days
• MIT researchers compare costs and emissions of gas, diesel, hybrid, electric, and fuel cell vehicles.
• Utility company websites that offer electric vehicle and charging information: