*4.4. Limitations*

One of the limitations of this study is that it focuses on the break-even costs and environmental effects. Consumer vehicle type selection (e.g., gasoline versus hybrid versus fully electric) is often based on other criteria such as driving range, charging time, and performance [66]. A BEV may not be pragmatic for exceedingly long trips.

Another limitation of this simulation is that it assumes zero gray-power costs for solar charging of BEVs. This simplification belies the fact that many solar power systems do not have battery back-up. This is an important limitation when considering environmental effects.

A third limitation is that the simulation is based on data and distributions generated from the United States. There are valid reasons to assume that future costs of gasoline, electricity, and natural gas are unlikely to be the same among countries. Further, other factors are likely to be different, including driving range, availability of recharging stations, and energy policy.
