With growing public concern over greenhouse gas emissions and the environment, the use of plug-in hybrid electric vehicles (PHEVs) is one way to curb our appetite for oil and reduce traffic emissions. These vehicles can be available to consumers without challenging our transportation engineers, governments and policymakers to build expensive infrastructure to support their operation. Consumers who purchase these PHEVs do not have to worry about being stranded when on the road because once exhausted, the system will switch to fuel.  These cars start off by using battery power and then switch to fuel when battery life is depleted.

In the U.S., PHEVs can drive on the battery powered feature (all electric) for 30-38 miles (driving range), but this is dependent on whether a driver is on an urban or highway setting. Minimum driving range thresholds have been set by The Energy Policy Act of 1992 and the National Highway Traffic Safety Administration for these vehicles in order to comply with environmental requirements. However, in an effort to find out the best all-electric driving range of a PHEV, one that minimizes the daily cost absorbed by society when using this technology, a group of researchers at UF, led by Dr. Yafeng Yin and his graduate student, Eleftheria Kontou, worked to create an optimization framework, using available U.S. market data. The driving range is essentially how far the vehicle can operate utilizing its electric battery. The researchers believe that if this optimal driving range is not investigated, it could be an issue for the success of PHEVs in the form of bad-policy making and cost to society.

The researchers divided the “social cost” they set forth to minimize into three components: 1) the internal cost that incorporates purchasing the electric vehicle’s battery and operating the vehicle; 2) the external cost that is composed by summing up the emissions cost of manufacturing the vehicle’s battery and the emissions cost for operating the vehicle; and 3) the amount of money the government will have to invest for installing public chargers.

Results of the study showed that the optimal range is 22 miles with an average cost to society of $3.02/day when charging at home only, but the optimal range was sensitive to the cost of battery packs and the retail price of gasoline. So, to put things into perspective, if the U.S. automobile market was about to deploy only one PHEV so as to minimize the average total social cost up to $3.02 per day, it would be a PHEV with an all-electric driving range of 22 miles. Also, when public charging options were introduced in this study, the optimal all-electric driving range increased from 22 to 24 miles, so if you owned a PHEV you would benefit more from recharging this way because you would be more inclined to travel a longer “electrified” distance.

The researchers also demonstrated that offering consumers varying sizes of battery packs for PHEVs could further benefit the cost to society.

This study was funded in part by the National Science Foundation and support from Lloyd’s Register Foundation.

Investigators:  Dr. Yafeng Yin, UF; Eleftheria Kontou, graduate student, UF; and Dr. Zhenhong Lin, Oak Ridge National Laboratory

For more information, contact: Dr. Yafeng Yin at yafeng@ce.ufl.edu or Eleftheria Kontou at ekontou@ufl.edu