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A plug-in hybrid electric vehicle (PHEV) is any vehicle powered by a combination of internal combustion engine and electric motor with storage batteries that can be recharged by connecting the vehicle by plug to an external electrical power source. Plug-in hybrids typically have characteristics of both conventional hybrid electric vehicles and of battery electric vehicles. While PHEVs are usually passenger vehicles, plug-in hybrid technology has been implemented or proposed in delivery vans, trucks, buses, military vehicles, and other medium- to heavy-duty vehicles.

The cost for electricity to power PHEVs in California is about one fourth the cost of gasoline. If their batteries are charged from renewable energy such as wind or hydropower, PHEVs use minimal amounts of fossil fuel for their all-electric range, and may thereby reduce dependence on petroleum and mitigate global warming by alleviating the greenhouse effect. Plug-in hybrids have been identified as having significant potential as alternative fuel vehicles.<ref>Simpson, A. (2006) "Cost-Benefit Analysis of Plug-in Hybrid Electric Vehicle Technology" National Renewable Energy Laboratory conference report CP-540-40485</ref>

Plug-in hybrid passenger vehicles are not in mass production as of early 2007, although some manufacturers have indicated that they intend to introduce PHEV production models. Prototypes have been built to demonstrate the technology and to encourage its widespread adaptation. Conversions of production model hybrid vehicles may be available from conversion kits and conversion services pending commercial production. Most existing PHEVs are conversions of Toyota Prius hybrid cars. These prototypes retain the Prius's "idle-off" capability and regenerative braking, among other characteristics, while adding extended electric-only drive capability, and electrical plug charging.

All-electric range is designated by the form PHEV-(number) representing the number of miles the vehicle can travel on electric power alone. For example, a PHEV-10 can travel ten miles without the use of petroleum gasoline.


In 1969, Popular Science did an article on the General Motors XP-883. This prototype was a commuter car with a plug-in hybrid electric drive system. It housed six 12-volt lead acid batteries in the trunk area and had a transverse mounted DC electric motor mounted to a front-wheel drive trans-axle. The gasoline powered engine was connected to the trans-axle via a worm gear.<ref>Popular Science (July, 1969) "Hybrid Car Ready in 1969" pp. 86-7</ref> The car could be plugged into a standard 110 Volt AC outlet for recharging. Although not very fast or a long-ranged, hybrids were off and rolling.

In about 1990, Prof. Andy Frank of the University of California at Davis used student teams to begin building operating prototype Plug-in hybrid electric vehicles. His work attracted industry support and funding from Nissan, Koyo Seiko, General Motors, Saturn, Ford, Visteon, JATCO, Ovonics, Defense Advanced Research Project Agency (DARPA), Sacramento Municipal Utility District, Southern California Edison, U.S. Department of Energy, and others. The UC Davis PHEVs won several DOE/USCAR "Future Car" and "Future Truck" national competitions. In 1994, the Esoro H301 was built in Switzerland. Four such prototypes are still on the road.

By 2000, the Electric Power Research Institute (EPRI) sponsored the broad-based Hybrid Electric Vehicle Alliance (HEVA) under the leadership of Bob Graham, to promote and develop Original Equipment Manufacturer commercialization of plug-in hybrid electric vehicles. Alliance members include major automakers, national labs, utilities, and the University of California at Davis. The Hybrid Electric Vehicle Working Group (HEVWG) published its landmark studies and reports on PHEV attractiveness. Dr. Frank received new support from Commission of the European Communities, Southern California Air Quality Management District, Yolo-Solano Air Quality Management District, CARB, and other governmental agencies. In 2001, the U.S. Department of Energy created the National Center of Hybrid Excellence at UC Davis, with Dr. Frank as Director, and Frank also obtained substantial GM funds to hybridize and plug-in GM's EV1, and EPRI funded Dr. Frank's work. In 2002, entrepreneurs, environmentalists and engineers created the California Cars Initiative, a non-profit PHEV advocacy and technology development group.

In 2003, Dr. Frank's vehicles are shown at the Paris International Auto Show and demonstrated to about 200 Renault engineers at a corporate event at their Paris headquarters. During the same year, Toyota shipped a University of California Davis Coulomb Plug-in Hybrid Electric Vehicles to Toyota City to demonstrate it to about 250 engineers and executives at two of Toyota's primary Tier 1 suppliers, Koyo Seiko, and Aisin AW (Aisin builds the Toyota Prius transmission system, which also is used in the Ford Escape and Nissan Hybrid). In 2003, Renault produced the "Elect'Road," a Plug-in Hybrid Electric Vehicle variant of its "Electri'cite" Kangoo battery electric van (50-80 km range) with a small gasoline "limp-home" engine able to drive 100 km before refueling. Renault discontinued the Elect'Road after selling about 500, mainly in France, Norway and a few in the UK, for about 25,000 euros. By 2004, Dr. Frank's student teams had built and operated seven proof-of-concept and proof-of-demonstration prototype Plug-in Hybrid Electric Vehicles, including 6-passenger sedans (Taurus and Sable), Sport Utility Vehicles (Suburban, Explorer), two-seater sports car (GM EV1), and two ground-up 80 mpg sports cars, and the CalCars PRIUS+ prototype and EDrive Systems conversions were demonstrated. In 2005, DaimlerChrysler Sprinter Van PHEV prototypes were completed.<ref>California Cars Initiative (2005-7) "Plug-In Hybrids: State Of Play, History & Players" (CalCars' PHEV History) accessed 18 April 2007</ref>

Production models, prototypes, and conversions

One production PHEV has gone on sale, the Renault Kangoo, in France in 2003. In addition, DaimlerChrysler is currently building PHEVs based on the Mercedes-Benz Sprinter van. Light Trucks are also offered by Micro-Vett SPA<ref>Template:Citation/core{{#if:2006|}}</ref> the so called Daily Bimodale. A number of prototypes have been created. At the UC Davis Hybrid Center, a team led by Prof. Andrew A. Frank Template:Citation/core{{#if:|}} have been designing and building working prototypes, the most recent of which is currently being installed into a GM Equinox for the Challenge X competition. Template:Citation/core{{#if:2006|}} Some independent researchers have demonstrated conversions of vehicles such as the Toyota Prius, while leaving the majority of the stock Hybrid Synergy Drive intact and unchanged by simply adding battery capacity and a grid charger.

The California Cars Initiative, a non-profit advocacy and technology development group in California, has converted the '04 and newer Toyota Prius to become a prototype of what it calls the PRIUS+. With the addition of 130 kg (300 lb) of lead-acid batteries, the PRIUS+ achieves roughly double the gasoline mileage of a standard Prius and can make trips of up to 15 km (10 miles) using only electric power.<ref>Template:Citation/core{{#if:2006|}}</ref> It is now working with EDrive Systems, a new Southern California company that plans to install aftermarket conversions for Priuses with a target fuel efficiency of 1.0 L/100 km (230 mpg).

The Electric Power Research Institute of Palo Alto, along with a number of utilities and government agencies, is working with DaimlerChrysler to deliver three plug-in hybrids built on the Mercedes Sprinter platform (a 15-passenger van). The Electric Auto Association is sponsoring the EAA-PHEV project, a "Do-It-Yourself" approach to enable those who are comfortable working with high wattage DC systems to do their own conversion. Hymotion, a Canadian company, introduced plug-in hybrid upgrade kits in February 2006. Designed for the Toyota Prius and the Ford Escape and Mariner Hybrids, these kits will be offered to fleet buyers at first and should be available to the general public in 2007.

Press reports on Nov 29, 2006, indicate GM's plans to introduce a production plug-in hybrid version of Saturn's Greenline Vue SUV in 2009<ref>General Motors (11/29/2006) "GM Announces Intention to Produce Plug-in Hybrid SUV" WebWire internet press release</ref> to be a PHEV-10.<ref>Magda, M. (November 29, 2006) "LA Auto Show: Saturn Vue Green Line will offer 2-mode and plug-in hybrid technology" AutoblogGreen accessed 18 April 2007</ref> Motorcycle and small car manufacturer Suzuki has produced several prototype light sports cars capable of operation in this mode. The first of these used a 400 cc motorcycle engine to give a primarily electric vehicle a "limp home" capability. A subsequent model was more capable of general operation over a wide range of conditions and ranges. PML built prototypes that it claims achieve 80 mpg; 0 to 60mph in 4.5 seconds; top speed of over 150mph; and a range of 1,000 miles.<ref>PML Flightlink Ltd. (August 2006) "MINI QED - A demonstration vehicle" accessed 18 April 2007</ref>


A plug-in hybrid may be capable of charge-depleting, charge-sustaining, and blended modes of operation. They may drive for an extended range in all-electric mode, either only at low speeds or at all speeds, with the internal combustion engine used secondarily for power-assist, and/or for longer range travel.

As with hybrid electric vehicles, the two major classifications are series and parallel. In a parallel hybrid the internal combustion engine (ICE) and the electric motor can both contribute to torque at the wheels. Coupling the ICE directly to the drive shaft bypasses inefficiencies associated with having the ICE generate electrical energy for motive power. However, parallel hybrids currently available automatically engage the ICE if the vehicle is driven beyond a particular electric only performance envelope, a matter of some concern with the Prius conversions mentioned below, since these will require conservative driving to avoid starting the ICE. Parallel implementations may use a common drivetrain for the two power sources or may be "road coupled", with different wheel sets operated by the motors.

In a series hybrid the ICE drives a generator to recharge the batteries and/or provide power to the electric motor, depending upon the load demand. This type is especially attractive to implementation as a plug-in hybrid, since such vehicles will ideally have an electric motor and battery capable of satisfying all performance needs of the vehicle and so will not require use of the ICE until the batteries have been discharged to a substantial level, and not at all if recharged between trips of electric-only range. In one recent (non-production) announcement of the series hybrid Chevrolet Volt,<ref>Abuelsamid, S. (January 7, 2007) "Detroit Auto Show: It's here. GM's plug-in hybrid is the Chevy Volt Concept" AutoBlogGreen</ref> a 40% remaining charge has been proposed for at least one vehicle as the start point for the ICE, the number of miles for electric-only operation will depend upon the battery capacity relative to the vehicle drag and weight, in this particular case projected at 40 miles (64km). In such a system the ICE and generator capacity, in concert with vehicle characteristics, will determine the maximum continuous performance without external recharge. Owing to the efficient fixed-speed operation of the relatively small (1 liter displacement) ICE and regenerative energy recovery, substantial economy of operation remains even without external power recharge of the batteries, in this example projected at 50 mpg (4.7 l/100 km).


Some early non-production plug-in hybrid electric vehicle conversions have been based on the version of Hybrid Synergy Drive (HSD) found in the 2004+ model year Toyota Prius. Early Pba conversions by CalCars demonstrated 10 miles (15 km) of EV-only and 20 miles (30 km) of double mileage mixed-mode range. A company offering conversions to consumers named Hybrids Plus is using A123 Li-ion batteries and has 15 or 30 miles of electric range. A company planning to offer conversions to consumers named EDrive systems will be using Valence Li-ion batteries and have 40-50 miles of electric range. Another company offering a plug-in module for the Toyota Prius is Hymotion.

All of the above systems replace the original battery and its ECU (Electronic Control Unit), while leaving the existing HSD system unchanged. This technology would be fairly simple to apply to other hybrid configurations. A conversion to plug-in mode involves increasing the capacity of the battery pack (in some cases the stock NiMH battery is retained), and adding an on-board AC powered charger to recharge the larger pack from mains power. Additionally, a method is required to encourage the vehicle to make full use the greater available electrical energy.


Cost savings

In California, as of 2006, the cost to plug in at night is equivalent to $0.75 per gallon of gasoline,<ref>HEV Center (2007) "What are Plug-In Hybrids?" Department of Mechanical and Aeronautical Engineering, UC Davis; retrieved 18 April 2007</ref> where gasoline sells for over $3 per gallon The cost of electricity for a Prius PHEV is about $0.03/mi ($0.019/km), based on 0.262 kilowatt hours per mile and a cost of electricity of $0.10 per kilowatt hour.<ref>California Cars Initiative (April 20, 2006) "Fact Sheet: PHEV Conversions" page 2, accessed 18 April 2006</ref><ref>Bluejay, M. (2006?) "How much does electricity cost?" accessed 18 April 2007</ref> Current PHEV conversions install a higher capacity battery than common hybrids like the Toyota Prius in order to extend the range. This additional cost is offset by fuel operating cost savings because just $1.00 worth of electricity from the wall (at $0.09/kW·h) is sufficient to drive the same distance as a gallon of gasoline. During the year 2007, many government and industry researchers will focus on determining what level of all-electric range is economically optimum for the design.

Fuel efficiency

A 70-mile range HEV-70 may annually require only about 25% as much gasoline as a similarly designed HEV-0, depending on how it will be driven and the trips for which will be used. A further advantage of PHEVs is that they have potential to be even more efficient than their HEV-0 cousins because more limited use of the PHEV's internal combustion engines may allow the engine to be used at closer to its maximum efficiency. While a Prius is likely to convert fuel to motive energy on average at about 30% efficiency (well below the engine's 38% peak efficiency) the engine of a PHEV-70 would likely operate far more often near its peak efficiency because it is not needed during transient operation conditions. These architectures would be highly likely to employ a parallel hybrid configuration whereby mechanical engine power is allowed to transfer most efficiently directly to the wheels (when the engine is activated).

Electricity infrastructure

PHEV and fully electric cars may allow for more efficient use of existing electric production capacity, much of which sits idle as operating reserve most of the time. This assumes that vehicles are charged primarily during off-peak periods (i.e., at night), or equipped with technology to shut off charging during periods of peak demand. Another advantage of a gridable vehicle is their potential ability to load balance or help the grid during peak loads. By using excess battery capacity to send power back into the grid and then recharge during off peak using cheaper power such vehicles are actually advantageous to utilities as well as their owners. This is accomplished with what is known as V2G or Vehicle to Grid technology.

Even if such vehicles just led to an increase in the use of night time electricity they would even out electricity demand (which is typically higher in the day time) and provide a greater return on capital for electricity infrastructure. Pacific Gas and Electric has shown PHEVs suggesting that they could be used as a source of emergency home power in the event of an electrical power failure. Regulations intended to protect electricians against power other than from grid sources would need to be changed, or regulations requiring consumers to disconnect from the grid when connected to non-grid sources will be required before such backup power solutions would be feasible.

Carbon emissions

Yet another advantage of PHEVs is a predicted reduction in carbon emissions should PHEV use become widespread. Increased drivetrain efficiency results in significant reduction of greenhouse gas emissions, even taking into account energy lost to inefficiency in the production and distribution of grid power and charging of batteries. A study by the American Council for an Energy Efficient Economy (ACEEE) predicts that, on average, a typical American driver is expected to achieve about a 15% reduction in net CO2 emissions compared to a regular hybrid, based on the 2005 distribution of power sources feeding the US electrical grid.

Additionally, for PHEV’s recharged in areas where the grid is fed by power sources with lower CO2 emissions than the current average, net CO2 emissions associated with PHEVs will decrease correspondingly. The same study predicts that in areas where more than 80% of grid-power comes from coal-burning power plants, local net CO2 emissions will increase.<ref>Kliesch, J. and Langer, T. (September 2006) "Plug-In Hybrids: an Environmental and Economic Performance Outlook" American Council for an Energy-Efficient Economy</ref> However, given the global nature of problems associated with CO2 emissions, specifically those related to global warming, localized increases in CO2 emissions are not considered a significant problem if global CO2 emissions are decreased.


Disadvantages include the additional weight and cost of a larger battery pack. The cost of a battery pack is especially relevant because with current technology battery packs may need to be replaced before the car itself is replaced. The fuel economy increase for a PHEV are highly dependent upon the way a vehicle is used (its duty cycle) and the opportunities to recharge by connecting to the electrical grid. In the most extreme of circumstances a PHEV might get worse mileage than an HEV. For example, in vehicles being used continuously without opportunities for recharging by connecting to the electrical grid the larger battery capacity (as compared to an HEV) might lack any advantage, while the greater battery weight (than in a corresponding HEV) would reduce fuel economy.

The study by the ACEEE also predicts that widespread PHEV use in heavily coal-dependent areas would result in an increase in local net sulfur dioxide and mercury emissions, given emissions levels from most coal plants currently supplying power to the grid.<ref>Clayton, M. (September 25, 2006) "A reality check on plug-in hybrids" The Christian Science Monitor</ref><ref>Kanellos, M. (April 28, 2006) "Plug in your hybrid, pollute less?" cNet</ref> Although "clean coal" technologies could create power plants which supply grid power from coal without emitting significant amounts of such pollutants, the higher cost of the application of these technologies may increase the price of coal-generated electricity dramatically. There is debate about whether or not PHEV or electric vehicle technology reduces pollution or simply "shifts" the pollution to another physical location. The net effect on pollution is dependent on the fuel source of the electrical grid (fossil or renewable, for example) and the pollution profile of the powerplants themselves. Identifying, regulating and upgrading "single point" pollution source such as a powerplant -- or replacing a plant altogether -- may also be more practical. From a human health perspective, "shifting" pollution away from large urban areas may be considered a significant advantage.


While PHEV concepts and research have been neglected for many years by industry and government, interest increased in 2006 to such a level that the architecture was included as an area of research in President George W. Bush's advanced energy initiative. The "addiction to oil" mentioned in his 2006 State of the Union Address could be largely eliminated by PHEVs and this fact is the most dramatic advantage of the architecture.


PHEVs involve frequent battery charging and discharging cycles. Because the number of such cycles influences battery lifetime, battery life may be less than in HEVs which don't fully discharge. However, some authors argue that PHEVs will soon become standard in the automobile industry.<ref>Roim, J. and Frank, A. (April 2006) "Hybrid Vehicles Gain Traction" Scientific American pp. 72-9</ref> Design issues and trade-offs concerning battery life, capacity, heat dissipation, weight, costs, and safety need to be solved.<ref>Bullis, K. (August 3, 2006) "Are Lithium-Ion Electric Cars Safe?" Technology Review (Cambridge, Mass.: MIT)</ref>

Advanced battery technology is under development.<ref>Fleissner, C. (8/14/06) "Johnson Controls partnership wins new contract" Wisconsin Technology Network</ref><ref>Lithium Technology Corp. (August 15, 2006) "Lithium Technology Corporation to Develop Highest Power and Highest-Energy Lithium-Ion Battery Solutions" PR Newswire press release</ref><ref>MIT News Service (August 10, 2006) "Researchers Fired Up over New Battery"</ref> Battery life expectancy is expected to increase.<ref>Altair Nanotechnologies Inc. (September 7, 2006) "Altair Nanotechnologies Details Long Life Features of Its Nano-Titanate Battery" MarketWire press release</ref> For lithium-ion (Li-ion) batteries, Toyota has reported a heat dissipation issue.<ref>Flint, J. (05.30.06) "The Frankenstein Hybrid"</ref> The next major update to the Toyota Prius, is said to use Li-ion batteries,<ref>Garcia, D. (May 10, 2006) "Japanese mag update"</ref> and have a 15 km (9 mile) electric only range,<ref>Gow, D. (March 31, 2006) "Ten years down the road: car giant foresees the non-polluting, accident-proof saloon" The Guardian</ref> which according to the 2000 U.S. Census is enough to power the entire daily commute of 29% of U.S. workers.<ref>US Bureau of the Census (March 2004) "Journey to Work: 2000" Census 2000 Brief</ref>

Patent protection on NiMH batteries

The oil company Chevron invests in key battery technologies and battery manufacturing facilities, through its subsidiary, Cobasys. According to the website, during the development of the battery-electric vehicle (BEV) EV1, General Motors made a controlling investment in Ovonics's battery development and manufacturing, with particular interest in the patents and trade secrets controlling the manufacturing of large nickel-metal hydride (NiMH) batteries. This interest was subsequently sold to the oil company Texaco, which was acquired in its entirety by another oil company, Chevron. The book "Plug-In Hybrids, The Cars That Will Recharge America" presents the argument that large-format NiMH batteries are commercially viable and ready for mass production, but that Chevron and other oil-related interests are suppressing this technology to forestall the introduction of plug-in hybrids. However, in December, 2006 General Motors announced that they will be using Cobasys NiMH batteries in the upcoming Saturn Aura hybrid model.<ref>Abuelsamid, S. (Dec 5th 2006) "Cobasys providing NiMH batteries for Saturn Aura hybrid" AutoblogGreen</ref>

See also

Future of the car, Petroleum electric hybrid vehicle, Blended mode, The Hype about Hydrogen, Hydrogen vehicle, Hypermiler, Automotive design terminology, Alternative fuel, Partial zero-emissions vehicle
Hybrid Synergy Drive, Ecodriving, Green tuning
Car types
List of hybrid vehicles, Ford Airstream, Mercedes-Benz Sprinter, Toyota Prius, Saturn VUE, Chevrolet Volt
Air car, Hydrogen vehicle, Flexible-fuel vehicle, Low-energy vehicle
Electric Vehicle
Battery electric vehicle (All-electric range), Production battery electric vehicle, Hybrid vehicle drivetrains, Vehicle propulsion, Who Killed the Electric Car?, Plug In America

External links


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