A study based on a spatial and longitudinal travel dataset by a team from Lamar University, Iowa State University and Oak Ridge National Laboratory found that whether plug-in hybrids (PHEVs) have lower energy costs that conventional gasoline vehicles (CGVs) or hybrid-electric vehicles (HEVs) depends on charger coverage.

Their paper is published in the journal Energy Policy.The researchers used the spatial, longitudinal travel data of 415 vehicles over 3–18 months in the Seattle metropolitan area to estimate the operating costs of plug-in hybrid electric vehicles (PHEVs) of various electric ranges (10, 20, 30, and 40 miles) for 3, 5, and 10 years of payback period, considering different charging infrastructure deployment levels and gasoline prices.

Among their findings:

• PHEVs could help save around 60% or 40% in energy costs, compared with conventional gasoline vehicles (CGVs) or hybrid electric vehicles (HEVs), respectively. However, for motorists whose daily vehicle miles traveled (DVMT) is significant, HEVs may be even a better choice than PHEV40s, particularly in areas that lack a public charging infrastructure. In other words, with low charging coverage, a PHEV40 is more costly than an HEV if one’s DVMT is large.
• The incremental battery cost of large-battery PHEVs is difficult to justify based on the incremental savings of PHEVs’ operating costs unless a subsidy is offered for large-battery PHEVs.
• When the price of gasoline increases from $4/gallon to $5/gallon, the number of drivers who benefit from a larger battery increases significantly. If the gas price is $3, PHEV10 is the least costly even if the battery cost is $200/kW.
• Although quick chargers can reduce charging time, they contribute little to energy cost savings for PHEVs, as opposed to Level-II chargers.