Plug-in Hybrid Electric Vehicles
The Next Step Toward Energy Independence

By now most people that are interested in energy independence have at least heard the term "Plug-in Hybrid". If you haven’t heard it yet you most likely will in the near future. So what is a Plug-in Hybrid Electric Vehicle (PHEV)? A PHEV is a "traditional" Hybrid Electric Vehicle (HEV) that can be recharged from an external electrical source and is capable of running in electric only or electric assist mode for a longer distance. For light duty vehicles, that currently means it will still have an internal combustion engine that utilizes gasoline. The goals behind PHEVs are to lower emissions and increase fuel economy which helps to reduce dependency on foreign oil.

A traditional HEV is only capable of running in an electric only mode (no internal combustion engine operation) for approximately one to two miles. Obviously this doesn’t get you very far without using gasoline. The PHEVs currently available can provide an electric only range from 20-60 miles under certain driving conditions and fuel economy as high as 100 miles per gallon by utilizing extended electric assist. The increased range of PHEVs gives them the advantages of an Electric Vehicle (EV) for short distances yet still provides the flexibility of being able to take them on long distance trips.

In order to gain the increased range PHEVs must have a battery with a much higher storage capacity than current HEVs and a charging system for that battery. The charging system will allow the high capacity battery to be recharged from virtually any electrical outlet. This has led to many arguments about trading one emission source (the vehicle) for another (the electric plant). While this is true, the electricity can be produced from a clean and renewable source such as wind or solar which significantly reduces or eliminates the emissions.

By now you may be thinking "this sounds too good to be true, if PHEVs could do that, all of the manufacturers would be making them." However, there is still a large obstacle that has to be overcome for PHEVs to be viable. This obstacle is the battery. Current HEVs utilize a Nickel Metal Hydride (NiMH) battery in their design. NiMH batteries don’t have the energy density needed in order to be used in PHEVs. This means in order to have enough electrical storage capacity to operate the PHEVs the batteries would be much too large and heavy to be practical if NiMH is used.

The best current battery option for PHEVs is Lithium Ion (Li-ion). In general Li-ion batteries can be one half to one third the size and weight of a NiMH battery with the same amount of energy storage. Li-ion batteries have their own concerns though. These include cost, safety, durability, etc. Safety and durability can be addressed but Li-ion batteries are still very expensive. For a PHEV to be marketable the return on investment must be acceptable to the consumer. If adding a PHEV option costs the consumer $10,000 + how many will buy it? The cost of Li-ion batteries is expected to come down as production levels go up but that has yet to be seen.

Toyota Prius Plug-in Hybrid Electric Vehicle shown on display at the EDTA Conference. Photos Courtesy of NAFTC.

So, are we actually going to be able to purchase PHEVs any time soon? Currently the only way you can get a PHEV is by converting an HEV into one. There are several companies out there such as A123 Systems, Plug-In Conversions Corp, Plug-In Supply, and Hybrids-Plus, to name a few, that offer PHEV conversions. Most of these conversions are designed for the 2004 and up Toyota Prius. These generally cost in the neighborhood of $10,000 and will most likely void any warranty on the vehicle (check with your dealer first if this is a concern). The other option to get a PHEV is to wait until the automobile manufacturers offer them. This option may not be as far off as you might think. Toyota has promised a PHEV model by the year 2010. They haven’t specified a model yet but speculation points towards the next generation of the Prius which is due out in 2009. General Motors has also promised the Chevy Volt and Saturn Vue Green Line PHEV for 2010 (although that was before their current financial troubles). Many other manufacturers including Audi, Chrysler, Saab, Volvo, and Ford also have PHEV prototypes on the road.

The outlook is promising for PHEVs and I feel it’s a necessary step away from traditional fossil fuels. While this doesn’t completely remove us from dependence on nonrenewable energy like other options such as hydrogen would, it is a step in the right direction. The key advantage to this technology is the fact that it can be implemented using the existing infrastructure of fuel stations and electrical transmission. Most of the other emerging technologies will require infrastructure changes to be implemented on a large scale. This technology is just one of the many pieces of the puzzle that needs to be assembled to reduce our energy dependence and reduce emission production.