A Comprehensive Guide to Plug-in Hybrids

What Is A Plug-in Hybrid Car?

A plug-in hybrid car is similar to a conventional hybrid vehicle—both use a gasoline engine as well as an electric motor. However, a plug-in hybrid uses larger battery packs that can be recharged by connecting to common household electricity. Plug-in hybrids can be driven for long distances—from a few miles to as much as 40 miles—without using any gasoline.

Plug-in hybrids provide the benefits of an electric car, while maintaining the same driving range as conventional vehicles. Plug-in hybrid drivers travel in an all-electric mode for the vast majority of common local driving. When the battery’s electric charge is depleted, a downsized gas engine is used to either recharge the batteries (as the car moves), or as the primary source of propulsion until recharging the batteries via a plug.

Plug-in hybrid cars are also known as plug-in hybrid electric vehicles or PHEVs. Plug-in hybrid cars that use a gas engine exclusively for recharging batteries—rather than directly powering the wheels—are also called Extended-Range Electric Vehicles or E-REVs.

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ComparisonCompare a Plug-in Hybrid to Standard Hybrid

Point your mouse to the image to compare a plug-in hybrid to a standard hybrid.

Plug-in hybrid cars have considerable fuel efficiency benefits compared to other vehicles:

• A hybrid car, depending on the model, achieves about twice the fuel economy as a conventional car of the same size and capacity
• A plug-in hybrid car can obtain about twice the fuel economy of a conventional hybrid
• A plug-in hybrid, running on biofuel (e.g., 85-percent ethanol or biodiesel) could almost entirely eliminate its use of petroleum

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Availability of Plug-in Hybrids

Despite all the media attention about plug-in hybrids, it’s still not yet possible for an individual consumer to buy one. A few plug-in hybrids have been produced for testing in commercial fleets and government agencies. Many major automakers have produced concept prototype plug-in hybrids for display at international auto shows, but only a handful of carmakers have committed to a specific production date for these vehicles.

The following plug-in hybrids are scheduled for production:

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Common Plug-in Hybrid Criticisms, And Responses

• The extra batteries weigh too much.

  Response: The extra weight of the batteries will be offset somewhat by the reduced weight of the gas engine. At high speeds in particular, fuel efficiency is affected primarily by aerodynamics—the MPG is minimally affected by the added weight roughly equivalent of one or two additional passengers.

• The extra batteries cost too much.

  Response: If sold in high volumes by carmakers, more powerful and cheaper nickel metal hydride or lithium ion batteries could be sold at prices only a few thousand dollars above that of today’s hybrids. Recharging will take place mostly at night during cheaper off-peak hours. Counting purchases, fuel and service, total lifetime cost of ownership is lower than a gas car.

• Producing power from the grid (to charge the cars) will produce additional emissions.

  Response: What the industry calls "well-to-wheel" emissions (including greenhouse gases) for grid-powered vehicles is far lower than gasoline, even for the American power grid (which is 50 percent coal). Cars charging off-peak will use power from plants that can't turn off at night. Many parts of the country get most of their power from cleaner sources such as natural gas and hydropower. It's far easier to improve centralized power stations than millions of aging cars. Finally, plug-in hybrids recharged from rooftop photovoltaic systems would have virtually zero emission.

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Plug-in Hybrid Conversions

Since the time of the first plug-in conversion prototype, more than a dozen companies started offering PHEV conversions. Like any heavily modified car, the conversions are expensive, can have reliability issues, and have not been crash-tested in their modified form. But their owners enjoy exceptionally high gas mileage, greater all-electric range, and the privilege of being automotive pioneers.

Most of today’s plug-in conversions start with a stock, late-model (2004-2008) Toyota Prius. Larger battery packs are added, either supplementing the existing battery or replacing it entirely.

The list of companies offering plug-in conversions, kits, or related services is growing everyday. Many are focused on building vehicles for government agencies and other fleets, but some are now taking orders. We'll continue to add to this list as learn about new companies. Send us a note, if you hear of a new conversion company, and we'll add it to the list. You can also check with CalCars.org's page about "How to Get a PHEV." Because the sand is shifting so quickly, you'll need to do your own legwork in terms of getting an exact price, turnaround time, and technical specs.

List of Companies Offering Plug-in Conversion Services

• 3Prong Power, Inc. (Berkeley, Calif.)
• Amberjac Systems (UK)
• Edrive Systems (Calif.)
• Electric Auto Association-PHEV Project (San Jose, Calif.)
• EnergyCS (Calif.)
• HybridsPlus (Boulder, Colo.)
• Hymotion (Concord, Ontario, Canada)
• Manzanita Micro (Kingston, Wash.)
• OEM Tek (Milpitas, Calif.)
• Luscious Garage (San Francisco, Calif.)
• Pat's Garage/Green Gears (San Francisco, Calif.)
• Plug-in Conversions (Poway, Calif.)
• Plug-in Supply (Petaluma, Calif.)

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Plug-in Hybrid Battery Types

Today, there are a few hundred plug-ins on the road in North America, and a few more are built each month. It's instructive to take a look the wide range of performance in plug-in conversions. Why is there such a range among companies offering conversion services and kits? It's the batteries.

• Current Prius-based converted plug-in hybrids store between two and seven times the energy stored in a standard Prius battery. Overall, Prius-based plug-ins average between 65 and 95 miles per gallon.

The more energy in the battery pack, the further the vehicle can go in all electric-mode, and the longer it can “boost” MPG. Storing more energy isn’t just a matter of putting in a bigger battery—the type of battery that’s used also matters.

Modest Energy with Lead-Acid Batteries: On one end of the spectrum are Prius-based plug-in conversions that store modest amounts of energy on-board: roughly 2-3 kilowatt hours (kWh). The main advantage of lead-acid technology is that it’s affordable. It’s also reasonably safe and has proven performance. But lead-acid batteries don’t last as long as some other types of batteries. They also store less energy, so larger heavier packs must be used.

Lots of Energy with Lithium Ion Batteries: At the other end of the spectrum are Prius-based conversions, which have large amounts of on-board energy—as much as 9 kWh. These PHEVs use lithium ion batteries because they deliver lots of energy in a smaller, lighter package. This amount of extra energy allows a PHEV to drive in all-electric mode for 25-30 miles, and attain “boosted” mileage for longer distances of 40-50 miles. The downside is cost. In some of these conversions, the battery pack alone costs more than $10,000. Safety and battery life are also a concern.

Mid-range Energy with Nickel Metal Hydride Batters: In the middle are PHEVs with moderate amounts of on-board energy—around 4-5 kWh. Some of these vehicles combine additional nickel-metal hydride batteries (NiMH) with the existing NiMH battery pack in the Prius. Performance, lifetime, and safety characteristics of NiMH batteries are well understood. However, NiMH batteries generally store less energy than lithium ion batteries.

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