The use of plug-in hybrid vehicles has the potential to greatly reduce the amount of greenhouse gases in the environment, not only when compared to gasoline-powered cars, but also to standard hybrids. Because plug-in hybrids use batteries as their main source of power and standard hybrids use gasoline engines as their primary source, the amount of gasoline consumed by a standard hybrid is far greater than with PHEVs, which in turn reduces the amount of greenhouse gases outputted directly from emissions.
Some people have argued that recharging the PHEVs at night will put higher demands on power plants, and raise the amount of greenhouse gases because the plants will have to burn more coal in order to keep up with the demand. Although more power usage is likely with an increase in usage of PHEVs, the American power grid is consistently burning fuels cleaner than in the past and is constantly expanding into alternative energy sources. A study conducted in 2002 stated that the use of PHEVs using nighttime power to recharge would reduce greenhouse gases by 46 to 61 percent when compared with gasoline-powered cars [source: CalCars.org]. And a study conducted in 2001 by the Department of Energy found that a typical hybrid car reduces the amount of greenhouse gas emissions by 22 percent, while plug-in hybrids could reduce the amount by 36 percent [source: CalCars.org].
On top of a reduction of greenhouse gases, PHEVs potentially have the ability to emit near zero greenhouse gases by running on either biofuels or by recharging through rooftop photovoltaic systems, aka solar-powered systems [Source: CalCars.org]. Ethanol 85 (E85) biofuel would allow a PHEV to greatly reduce its petroleum usage, and recharging a PHEV with energy gathered from solar panels during the day would reduce the amount of power the car needs to take from the power grid.
Now that we've seen some of the environmental benefits of plug-in hybrids, we'll compare some of the convenience factors between the plug-ins and standard hybrids on the next page.