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A plug-in hybrid electric vehicle (PHEV) is a hybrid vehicle with batteries that can be recharged by connecting a plug to an electric power source. They share the characteristics of both conventional hybrid electric vehicles and battery electric vehicles, having an internal combustion engine and batteries for power. Most PHEVs on the road today are passenger cars, but there are also PHEV versions of commercial passenger vans, utility trucks, school buses, scooters, and military vehicles. PHEVs are sometimes called grid-connected hybrids, gas-optional hybrids, or GO-HEVs.

The cost for electricity to power plug-in hybrids for all-electric operation in California has been estimated as less than one fourth the cost of gasoline. Compared to conventional vehicles, PHEVs can reduce air pollution and dependence on petroleum, and lessen greenhouse gas emissions that contribute to global warming. Plug-in hybrids use no fossil fuel during their all-electric range if their batteries are charged from renewable energy sources. Other benefits include improved national energy security, fewer fill-ups at the filling station, the convenience of home recharging, opportunities to provide emergency backup power in the home, and vehicle to grid applications.

As of September 2007, plug-in hybrid passenger vehicles are not yet in production. However, Toyota, General Motors, Ford, and Chinese automaker BYD Auto have announced their intention to introduce production PHEV automobiles. Toyota obtained permission in July 2007 to sell their plug-in Prius in Japan, while BYD Auto expects to introduce their PHEV-60 sedan in the second half of 2008, and General Motors expects to introduce plug-ins in 2009 or 2010. Conversion kits and services are available to convert production model hybrid vehicles to PHEVs. Most PHEVs on the road in the U.S. are conversions of models from 2004 or later of the Toyota Prius hybrid car, which have had plug-in charging added and their electric-only range extended.

Terminology

A plug-in hybrid's all-electric range is designated by PHEV- or PHEVkm in which the number represents the distance the vehicle can travel on battery power alone. For example, a PHEV-20 can travel 20 miles without using its internal combustion engine, or about 32 kilometers, so it may also be designated as a PHEV32km.

The Institute of Electrical and Electronics Engineers (IEEE) defines a plug-in hybrid electric vehicle as any hybrid electric vehicle which contains at least:

• a battery storage system of 4 kW·h or more, used to power the motion of the vehicle;
• a means of recharging that battery system from an external source of electricity; and
• an ability to drive at least ten miles in all-electric mode, while consuming no gasoline.

This distinguishs PHEVs from hybrid cars mass-marketed today, which do not use any electricity from the grid.

History

Hybrid vehicles were produced beginning as early as 1899 by Lohner-Porsche. Early hybrids could be charged from an external source before operation. However, the term "plug-in hybrid" has come to mean a hybrid vehicle that can be charged from a standard electrical wall socket.

The July 1969 issue of Popular Science featured an article on the General Motors XP-883 plug-in hybrid. The concept commuter vehicle housed six 12 volt lead-acid batteries in the trunk area and a transverse-mounted DC electric motor turning a front-wheel drive. The car could be plugged into a standard North American 110 volt AC outlet for recharging.

In 2003, Renault began selling the Elect'road, a plug-in series hybrid version of their popular Kangoo, in Europe. It was sold alongside Renault's "Electri'cite" electric-drive Kangoo battery electric van. The Elect'road had a 150 km (93 mi) range using a nickel-cadmium battery pack and a Template:ConvertVolume, 16 kilowatt liquid-cooled gasoline "range-extender" engine. It powered two high voltage/high output/low volume alternators, each of which supplied up to 5.5 kW at 132 volts at 5000 rpm. The operating speed of the internal combustion engine—and therefore the output delivered by the generators—varied according to demand. The fuel tank had a capacity of Template:ConvertVolume and was housed within the right rear wheel arch. The range extender function was activated by a switch on the dashboard. The on-board 3.5 kilowatt charger could charge a depleted battery pack to 95% charge in about four hours from a 220 volts supply. Passenger compartment heating was powered by the battery pack as well as an auxiliary coolant circuit that was supplied by the range extender engine. After selling about 500 vehicles, primarily in France, Norway and the UK, at a price of about €25,000, the Elect'road was redesigned in 2007.

In September 2004, the California Cars Initiative (CalCars) converted a 2004 Toyota Prius into a prototype of what it called the PRIUS+. With the addition of 130 kg (300 lb) of lead-acid batteries, the PRIUS+ achieved roughly double the fuel economy of a standard Prius and could make trips of up to 15 km (9 mi) using only electric power. The vehicle, which is owned by CalCars technical lead Ron Gremban, is used in daily driving, as well as a test bed for various improvements to the system.

On July 18, 2006, Toyota announced that it "plans to develop a hybrid vehicle that will run locally on batteries charged by a household electrical outlet before switching over to a gasoline engine for longer hauls." Toyota has said it plans to migrate to lithium-ion batteries in future hybrid models, but not in the next-generation Prius, expected in fall 2008. Lithium-ion batteries are expected to significantly improve fuel economy, and have a lower weight-to-energy ratio, but cost more to produce, and raise safety concerns due to high operating temperatures.

On November 29, 2006, GM announced plans to introduce a production plug-in hybrid version of Saturn's Greenline Vue SUV with an all-electric range of 10 mi (16 km). The model's sale is anticipated by fall 2009, and GM announced in January 2007 that contracts had been awarded to two companies to design and test lithium-ion batteries for the vehicle. GM has said that they plan on introducing plug-in and other hybrids "for the next several years".

In January 2007, GM unveiled the Chevrolet Volt, which is expected to initially feature a plug-in capable, battery-dominant series hybrid architecture which they are calling E-Flex. Future E-Flex plug-in hybrid vehicles may use gasoline, diesel, or hydrogen fuel cell power to supplement the vehicle's battery. General Motors envisions an eventual progression of E-Flex vehicles from plug-in hybrids to pure electric vehicles, as battery technology improves. General Motors presented the Volt as a PHEV-40 that starts its engine when 40% of the battery charge remains, and which can achieve a fuel economy of Template:Mpg, even if the vehicle's batteries are not charged.

On July 9, 2007, Ford Motor Company CEO Alan Mulally said he expects Ford to sell plug-in hybrids in five to ten years, the launch date depending on advances in lithium-ion battery technology. Ford will provide Southern California Edison with 20 Ford Escape Hybrid sport utility vehicles reconfigured to work as plug-ins by 2009, with the first by the end of 2007.

On July 25, 2007, Japan's Ministry of Land, Infrastructure and Transport certified Toyota's plug-in hybrid for use on public roads, making it the first automobile to attain such approval. Toyota plans to conduct road tests to verify its all-electric range. The plug-in Prius has an all-electric range of 13 km (8 mi).

On August 9, 2007, General Motors vice-president Robert Lutz announced that GM is on track for Chevrolet Volt road testing in 2008 and production to begin by 2010. Announcing an agreement with A123Systems, Lutz said GM would like to have their planned Saturn VUE plug-in on the roads by 2009. The Volt has an all-electric range of 40 mi (64 km).

On October 11, 2007, Chinese manufacturer BYD Automobile Company (which is owned by China's largest mobile phone battery maker) announced that it would be introducing a production PHEV-60 sedan in China in the second half of 2008. BYD plans to exhibit it in January 2008 at the North American International Auto Show in Detroit. Based on BYD's midsize F6 sedan, it uses iron-based batteries instead of lithium-ion, and can be recharged to 70% of capacity in just 10 minutes.

Technology

Powertrains

PHEVs are based on the same three basic powertrain architectures as conventional hybrids:

Series hybrids use an internal combustion engine (ICE) to turn a generator, which in turn supplies current to an electric motor, which then rotates the vehicle’s drive wheels. A battery or capacitor pack, or a combination of the two, can be used to store excess charge. Examples of series hybrids include the Renault Kangoo Elect'Road, Toyota's Japan-only Coaster light-duty passenger bus, DaimlerChrysler's hybrid Orion bus, the Chevrolet Volt concept car, and many diesel-electric locomotives. With an appropriate balance of components this type can operate over a substantial distance with its full range of power without engaging the ICE. As is the case for other architectures, series hybrids can operate without recharging as long as there is liquid fuel in the tank.

Parallel hybrids, such as Honda's Insight, Civic, and Accord hybrids, can simultaneously transmit power to their drive wheels from two distinct sources—for example, an internal combustion engine and a battery-powered electric drive. Although most parallel hybrids incorporate an electric motor between the vehicle's engine and transmission, a parallel hybrid can also use its engine to drive one of the vehicle's axles, while its electric motor drives the other. The Audi Duo plug-in hybrid concept car is an example of this type of parallel hybrid architecture. Parallel hybrids can be programmed to use the electric motor to substitute for the ICE at lower power demands as well as to substantially increase the power available to a smaller ICE, both of which substantially increase fuel economy compared to a simple ICE vehicle.

Series-parallel hybrids have the flexibility to operate in either series or parallel mode. Hybrid powertrains currently used by Ford, Lexus, Nissan, and Toyota, which some refer to as “series-parallel with power-split,” can operate in both series and parallel mode at the same time. As of 2007, most plug-in hybrid conversions of conventional hybrids utilize this architecture.

Modes of operation

Regardless of its architecture, a plug-in hybrid may be capable of charge-depleting and charge-sustaining modes. Combinations of these two modes are termed blended mode or mixed-mode. These vehicles can be designed to drive for an extended range in all-electric mode, either at low speeds only or at all speeds. These modes manage the vehicle's battery discharge strategy, and their use has a direct effect on the size and type of battery required:

Charge-depleting mode allows a fully charged PHEV to operate exclusively (or depending on the vehicle, almost exclusively, except during hard acceleration) on electric power until its battery state of charge is depleted to a predetermined level, at which time the vehicle's internal combustion engine or fuel cell will be engaged. This period is the vehicle's all-electric range. This is the only mode that a battery electric vehicle can operate in, hence their limited range.

Charge-sustaining mode is used by production hybrid vehicles (HEVs) today, and combines the operation of the vehicle's two power sources in such a manner that the vehicle is operating as efficiently as possible without allowing the battery state of charge to move outside a predetermined narrow band. Over the course of a trip in a HEV the state of charge may fluctuate but will have no net change. The battery in a HEV can thus be thought of as an energy accumulator rather than a fuel storage device. Once a plug-in hybrid has exhausted its all-electric range in charge-depleting mode, it can switch into charge-sustaining mode automatically.

Blended mode is a type of charge-depleting mode normally employed by vehicles which do not have enough electric power to sustain high speeds without the help of the internal combustion portion of the powertrain. A blended control strategy typically takes more miles to use stored grid electricity than a charge-depleting strategy. The Renault Kangoo and some Toyota Prius conversions are examples of vehicles that use this mode of operation. The Electri'cité and Elect'road versions of the Kangoo were charge-depleting battery electric vehicles: the Elect'road had a modest internal combustion engine which extended its range somewhat. Conversions of 2004 and later model Toyota Prius can only run without using the ICE at speeds of less than about 42 mi:h due to the limits dictated by the vehicle's powertrain control software. However, at faster speeds electric power can still be used to displace gasoline, thus improving the fuel economy in blended mode and generally doubling the fuel efficiency.

Mixed mode describes a trip in which a combination of the above modes are utilized. For example, a PHEV-20 Prius conversion may begin a trip with 5 miles (8 km) of low speed charge-depleting, then get onto a freeway and operate in blended mode for 20 miles (32 km), using 10 miles (16 km) worth of all-electric range at twice the fuel economy. Finally the driver might exit the freeway and drive for another 5 miles (8 km) without the internal combustion engine until the full 20 miles (32 km) of all-electric range are exhausted. At this point the vehicle can revert back to a charge sustaining-mode for another 10 miles (16 km) until the final destination is reached. Such a trip would be considered a mixed mode, as multiple modes are employed in one trip. This contrasts with a charge-depleting trip which would be driven within the limits of a PHEV's all-electric range. Conversely, the portion of a trip which extends beyond the all-electric range of a PHEV would be driven primarily in charge-sustaining mode, as used by a conventional hybrid.

Batteries

PHEVs typically require deeper battery charging and discharging cycles than conventional hybrids. Because the number of full cycles influences battery life, this may be less than in traditional HEVs which do not deplete their batteries as fully. However, some authors argue that PHEVs will soon become standard in the automobile industry. Design issues and trade-offs against battery life, capacity, heat dissipation, weight, costs, and safety need to be solved. Advanced battery technology is under development, promising greater energy densities by both mass and volume, and battery life expectancy is expected to increase.

The cathodes of some early 2007 lithium-ion batteries are made from lithium-cobalt metal oxide. This material is expensive, and cells made with it can release oxygen if overcharged. If the cobalt is replaced with iron phosphates, the cells will not burn or release oxygen under any charge. The price premium for early 2007 conventional hybrids is about US$5000, some US$3000 of which is for their NiMH battery packs. At early 2007 gasoline and electricity prices, that would mean a break-even point after six to ten years of operation. The conventional hybrid premium could fall to US$2000 in five years, with US$1200 or more of that being cost of lithium-ion batteries, providing for a three-year payback. The payback period may be longer for plug-in hybrids, because of their larger, more expensive batteries.

Nickel-metal hydride and lithium-ion batteries can be recycled; Toyota, for example, has a recycling program in place under which dealers are paid a US$200 credit for each battery returned. However, plug-in hybrids typically use larger battery packs than comparable conventional hybrids, and thus require more resources. Recently Pacific Gas and Electric Company (PG&E) has suggested that utilities could purchase used batteries for backup and load levelling purposes. They state that while these used batteries may be no longer usable in vehicles, their residual capacity still has significant value.

In France, Électricité de France (EDF) and Toyota are installing recharging points for PHEVs on roads, streets and parking lots.. EDF is also partnering with Elektromotive, Ltd. to install 250 new charging points over six months from October 2007 in London and elsewhere in the UK. Recharging points also can be installed for specific uses, as in taxi stands.

Conversions of production hybrids

Conversion of an existing production hybrid to a plug-in hybrid typically involves increasing the capacity of the vehicle's battery pack and adding an on-board AC-to-DC charger. Ideally, the vehicle's powertrain software would be reprogrammed to make full use of the battery pack's additional energy storage capacity and power output.

Many early plug-in hybrid electric vehicle conversions have been based on the 2004 or later model Toyota Prius. Some of the systems have involved replacement of the vehicle's original NiMH battery pack and its electronic control unit. Others, such as Hymotion, the CalCars Prius+, and the PiPrius, piggyback an additional battery back onto the original battery pack, this is also referred to as Battery Range Extender Modules (BREMs). Within the electric vehicle conversion community this has been referred to as a "hybrid battery pack configuration". Early lead-acid battery conversions by CalCars demonstrated 10 miles (15 km) of EV-only and 20 miles (30 km) of double mileage blended mode range.

EDrive Systems use Valence Technology Li-ion batteries and have a claimed 40 to 50 miles (64 to 80 km) of electric range. Other companies offering plug-in conversions or kits for the Toyota Prius include Hymotion, Hybrids Plus, and Manzanita Micro.

The EAA-PHEV project was conceived in October of 2005 to accelerate efforts to document existing HEVs and their potential for conversion into PHEVs. It includes a Conversion Interest page. The Electric Auto Association-PHEV "Do-It-Yourself" Open Source community's primary focus is to provide conversion instructions to help guide experienced EV Converters through the process. Many members of organizations such as CalCars and the EAA as well as companies like Hybrids Plus, Hybrid Interfaces of Canada, and Manzanita Micro participate in the development of the project.

Advantages

Fuel efficiency

Claimed fuel economy for PHEVs depends on the amount of driving between recharges. If no gasoline is used the MPG equivalent depends only on the efficiency of the electric system. A 120 km (70 mile) range PHEV-70 may annually require only about 25% as much gasoline as a similarly designed PHEV-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 conventional hybrids because a more limited use of the PHEV's internal combustion engine 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 be likely to operate far more often near its peak efficiency because the batteries can serve the modest power needs at times when the combustion engine would be forced to run well below its peak efficiency. The actual efficiency achieved depends on losses from electricity generation, inversion, battery charging/discharging, the motor controller and motor itself, the way a vehicle is used (its duty cycle), and the opportunities to recharge by connecting to the electrical grid.

Greenhouse gas emissions

Another advantage of PHEV adoption is a predicted reduction in carbon emissions. 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 the driver of a regular hybrid, based on the 2005 distribution of power sources feeding the U.S. 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. PHEVs can be viewed as an element in the "Pacala and Socolow wedges" approach which shows a way to stabilize CO₂ emissions using a portfolio of existing techniques, including efficient vehicles.

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. However, given the global nature of problems associated with CO₂ emissions, specifically global warming, localized increases in CO₂ emissions are not considered a significant problem if global CO₂ emissions are decreased.

GM Vice Chairman Bob Lutz has said the Chevy Volt will emit 40 grams of carbon dioxide per kilometer. That is well below the proposed European Union emission standards of 120-130 g/km.

Operating costs

In a 2006 research estimate in California, the cost to plug in at night was equivalent to US$0.75 per U.S. gallon (3.8 L) of gasoline, whereas gasoline sells for over US$3 per gallon. The cost of electricity for a Prius PHEV is about US$0.03 per mile (US$0.019 per km), based on Template:KWh/mile and a cost of electricity of US$0.10 per kilowatt hour. During 2007, many government and industry researchers will focus on determining what level of all-electric range is economically optimum for the design.

Vehicle-to-grid electricity

PHEVs 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 plug-in vehicle is their potential ability to load balance or help the grid during peak loads. This is accomplished with vehicle to grid technology. By using excess battery capacity to send power back into the grid and then recharge during off peak times using cheaper power, such vehicles are actually advantageous to utilities as well as their owners. 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.

In October 2005, five Toyota engineers and one Asian AW engineer published an IEEE technical paper detailing a Toyota-approved project to add vehicle-to-grid capability to a Toyota Prius. Although the technical paper described "a method for generating voltage between respective lines of neutral points in the generator and motor of the THS-II (Toyota Hybrid System) to add a function for generating electricity", it did not state whether or not the experimental vehicle could be charged through the circuit, as well. However, the vehicle was featured in a Toyota Dream House, and a brochure for the exhibit stated that "the house can supply electricity to the battery packs of the vehicles via the stand in the middle of the garage", indicating that the vehicle may have been a plug-in hybrid.

In November 2005, more than 50 leaders from public power utility companies across the United States met at the Los Angeles Department of Water and Power headquarters to discuss plug-in hybrid and vehicle-to-grid technology. The event, which was sponsored by the American Public Power Association, also provided an opportunity for association members to plan strategies that public power utility companies could use to promote plug-in hybrid technology. Greg Hanssen and Peter Nortman of EnergyCS and EDrive attended the two-day session, and during a break in the proceedings, made an impromptu display in the LADWP parking lot of their converted Prius plug-in hybrid.

In September 2006, the California Air Resources Board held a Zero Emission Vehicle symposium that included several presentations on V2G technology. In April 2007, Pacific Gas and Electric showcased a PHEV at the Silicon Valley Leadership Alternative Energy Solutions Summit with vehicle-to-grid capability, and demonstrated that it 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.

Federal Energy Regulatory Commissioner Jon Wellinghoff coined the term "Cash-Back Hybrids" to describe payments to car owners for putting their batteries on the power grid. Batteries could also be offered in low-cost leasing or renting or by donation (including maintenance) to the car owners by the public utilities, in a vehicle-to-grid agreement.

Disadvantages

Disadvantages of plug-in hybrids include the additional cost and weight of a larger battery pack. General Motors may allow buyers of its Chevy Volt electric car to rent the vehicle's battery, offsetting some cost. Also used PHEV batteries can be sold to electric utilities to be employed at electrical substations.

Increased pollution is expected to occur in some areas with the adoption of PHEVs, but most areas will experience a decrease. A study by the ACEEE 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. 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. 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 power plants themselves. Identifying, regulating and upgrading single point pollution source such as a power plant—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. Martin Eberhard, who co-founded Tesla Motors, says "if you do the math, you´ll find that an electric car, even if you use coal to make electricity, produces less pollution per mile than burning gasoline in the best gasoline-powered car."

Commercialization

PHEVs have been sold as commercial passenger vans, utility trucks, general and school buses, scooters, motorcycles, and military vehicles. Hybrid Electric Vehicle Technologies, Inc converts diesel buses to plug-in hybrids, under contract for the Chicago Transit Authority.

Interest in plug-in hybrids 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 and mentioned in his 2007 State of the Union Address. After hearing an explanation of PHEVs, 49% of U.S. consumers surveyed in 2006 said they would consider purchasing one. That is about the same level of interest as standard hybrid technology.

Patent encumbrance of NiMH batteries

In 1994, General Motors acquired a controlling interest in Ovonics's battery development and manufacturing, including patents controlling the manufacturing of large nickel metal hydride (NiMH) batteries. In 2001, Texaco purchased GM's share in GM Ovonics. A few months later, Chevron acquired Texaco. In 2003, Texaco Ovonics Battery Systems was restructutred into Cobasys, a 50/50 joint venture between Chevron and Energy Conversion Devices (ECD) Ovonics.

In her book, Plug-in Hybrids: The Cars that Will Recharge America, published in February 2007, Sherry Boschert argues that large-format NiMH batteries are commercially viable but that Cobasys refuses to sell or license them to small companies or individuals. Boschert reveals that Cobasys accepts only very large orders for these batteries. When Boschert conducted her research, major auto makers showed little interest in NiMH batteries. Since no other companies were capable of producing large orders, Cobasys was not manufacturing any NiMH batteries for automotive purposes.

However, in December 2006, Cobasys and General Motors announced that they had signed a contract under which Cobasys provides NiMH batteries for the Saturn Aura hybrid sedan. In March 2007, GM announced that it would use Cobasys NiMH batteries in the 2008 Chevrolet Malibu hybrid as well. Cobasys remains unwilling to sell NiMH batteries in smaller quantities to individuals interested in building or retrofitting their own PHEVs.

See also

• Alternative propulsion
• Automotive design terminology
• Efficient energy use
• FreedomCAR
• Low-energy vehicle
• Mitigation of global warming
• Net metering
• Plug In America

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54. http://www.edrivesystems.com/
55. Green Car Congress (18 November 2005) "Plugging the Plug-In Hybrid" accessed 20 April 2007
56. Green Car Congress (September 27, 2006) The Plug-In and BEV Adoption Wild Card: Vehicle-to-Grid accessed April 28, 2007
57. Green Car Congress (April 9, 2007) "PG&E Demonstrates Vehicle-to-Grid Technology" accessed April 20, 2007
58. News.com (April 9, 2007) "PG&E sees plug-in hybrids as potential profit centers"
59. Liotsakis, P. (2007) "Cars, Power Plants and 'Cash Back Hybrids'" LiveNeutral (Presidio School of Management and Chicago Climate Exchange) accessed 12 July 2007.
60. Simon, B. (August 12, 2007) "GM eyes electric-car initiative" Financial Times accessed 19 September 2007
61. Knipping, E. and Duvall, M. (June 2007) "Environmental Assessment of Plug-In Hybrid Electric Vehicles Volume 2: United States Air Quality Analysis Based on AEO-2006 Assumptions for 2030" Electric Power Research Institute and Natural Resources Defense Council accessed July 21, 2007
62. Clayton, M. (September 25, 2006) "A reality check on plug-in hybrids" The Christian Science Monitor
63. Kanellos, M. (April 28, 2006) "Plug in your hybrid, pollute less?" cNet News.com
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65. "Hybrid Daily". Micro-Vett. {{cite web}}: Unknown parameter |accessmonthday= ignored (help); Unknown parameter |accessyear= ignored (|access-date= suggested) (help)
66. Green Car Congress: EPRI, Ford and Eaton Developing Plug-in Hybrid Utility Trouble Truck accessed April 23, 2007
67. Odyne Corporation press release: Odyne Corp. Announces Exclusive Agreement with Dueco, Inc.
68. "Florida Plug-In Hybrid School Buses to Go into Service" accessed 22 April 2007
69. UNEP news about plug-in school buses
70. Green Car Congress: Piaggio Launches Two Plug-In Hybrid Vespa Scooters accessed April 28 2007
71. http://www.enertiabike.com
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74. Roberson, J. (March 14, 2007) "Supplier Cobasys exploring more hybrid batteries" Detroit Free Press
75. Boschert, S. (2007) Plug-in Hybrids: The Cars that Will Recharge America (Gabriola Island, BC: New Society Publishers) ISBN 9780865715714
76. Abuelsamid, S. (December 6,2006) "Cobasys providing NiMH batteries for Saturn Aura hybrid" Autobloggreen.com

External links

• How Plug-In Hybrid Cars Work at HowStuffWorks
• Electric Automobile Association's Hybrid and Plug-In Hybrid Electric Vehicles Wiki - conversion and technical documentation
• Plug-in Hybrid Electric Vehicles - U.S. Office of Energy Efficiency and Renewable Energy
• 2008 Saturn VUE plug-in - Saturn plugs in 2008
• Senators plug in - video clip of U.S. senators talking about plug in hybrids
• Plug in for America - video clip about plug in hybrid vehicles
• IEEE PHEV info and reference documents.
• Green Car Advisor news, plug-in category.

Groups promoting plug-ins

• California Cars Initiative
• Plug-in Hybrid Development Consortium
• Plug-In Partners
• Set America Free Coalition

• Alternative propulsion
• Automotive technologies
• Plug-in hybrid vehicles
• Sustainable technologies