A plug-in hybrid electric vehicle (PHEV) is a hybrid electric vehicle that uses rechargeable batteries, or another energy storage device, that can be recharged by plugging it in to an external source of electric power as well as an on-board internal combustion engine and generator. Most PHEVs are passenger cars but there are also PHEV versions of commercial vehicles and vans, utility trucks, buses, trains, motorcycles, scooters, and military vehicles.
The cost of electricity to power plug-in hybrids for all-electric operation has been estimated at less than one quarter of the cost of gasoline in California.  Compared to conventional vehicles, PHEVs produce less air pollution locally and require less petroleum. PHEVs may produce less in the way of greenhouse gases, which contribute to global warming,  than conventional vehicles do. PHEVs also eliminate the problem of range anxiety associated with all-electric vehicles, because the combustion engine works as a backup when the batteries are depleted, giving PHEVs driving-range comparable to that of other vehicles that have gasoline and diesel tanks.   Plug-in hybrids use no fossil fuel at the point of use during their all-electric range.
Plug-in hybrids' greenhouse-gas emissions, during operation in their all-electric range mode, depend on the type of power plant used to feed the electrical grid when the battery is charged.  (See "", below.) If the batteries are charged directly from renewable sources off the electrical grid, then the tailpipe greenhouse gas emissions are zero when running only on battery power. Other benefits include improved national energy security, less frequent fill-ups at the filling station, the convenience of home recharging, opportunities to provide emergency backup power in the home, and vehicle-to-grid (V2G) applications.   Several countries, including the United States, China, and several European countries, have enacted laws to ease the introduction of PHEVs through grants and tax credits, emissions mandates, and financing research and development in advanced batteries and related technology.
Chinese battery manufacturer and automaker BYD Auto released the F3DM to the Chinese fleet market in December 2008   and began sales to the public in Shenzhen in March 2010.   GM began delivering the Chevrolet Volt in the United States in December 2010; it was the first electric car with a range extender for retail sale in the American market.  As of December 2016, there are over 30 models of series-production highway legal plug-in hybrids for retail sales, including some limited-production luxury sport cars. Plug-in hybrid cars are available mainly in the United States, Canada, Western Europe, Japan, and China. As of December 2016, the Chevrolet Volt family, including its siblings Opel/Vauxhall Ampera, is the world's best-selling plug-in hybrid in history with combined sales of about 134,500 units.  The Mitsubishi Outlander P-HEV is the world's second top-selling plug-in hybrid, with global sales of about 119,500 units, followed by the Toyota Prius PHV, with almost 78,000 units delivered globally, both, through December 2016. 
As of December 2016, the global stock of plug-in hybrid cars totaled almost 800,000 units, out of over 2 million light-duty plug-in electric cars on the world roads at the end of 2016.   As of December 2015, the United States ranked as the world's largest plug-in hybrid car market with a stock of 193,770 units, followed by China with 86,580 vehicles, the Netherlands with 78,160, Japan with 55,470 units, and the UK with 28,250. 
Flexibility in power demand, diverse usage patterns and storage capability of PHEVs grow the elasticity of residential electricity demand remarkably. This elasticity can be used to form the daily aggregated demand profile and/or alter instantaneous demand of a system wherein a large number of residential PHEVs share one electricity retailer.
A plug-in hybrid's all-electric range is designated by PHEV- [miles] or PHEV [kilometers] km in which the number represents the distance the vehicle can travel on battery power alone. For example, a PHEV-20 can travel twenty miles (32 km) without using its combustion engine, so it may also be designated as a PHEV32km. 
The Energy Independence and Security Act of 2007 defines a plug-in electric drive vehicle as a vehicle that:
- draws motive power from a battery with a capacity of at least 4 kilowatt hours;
- can be recharged from an external source of electricity for motive power; and
- is a light-, medium-, or heavy-duty motor vehicle or nonroad vehicle.
The Institute of Electrical and Electronics Engineers (IEEE) defines PHEVs similarly, but also requires that the hybrid electric vehicle be able to drive at least ten miles (16 km) in all-electric mode (PHEV-10; PHEV16km), while consuming no gasoline or diesel fuel. 
The California Air Resources Board uses the term "off-vehicle charge capable" (OVCC) to mean having the capability to charge a battery from an off-vehicle electric energy source that cannot be connected or coupled to the vehicle in any manner while the vehicle is being driven. 
Other popular terms sometimes used for plug-in hybrids are "grid-connected hybrids", "Gas-Optional Hybrid Electric Vehicle" (GO-HEV) or simply "gas-optional hybrids".    GM calls its Chevrolet Volt series plug-in hybrid an "Extended-Range Electric Vehicle".  
Invention and early interest
The Lohner-Porsche Mixte Hybrid, produced as early as 1899, was the first hybrid electric car.   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 term "plug-in hybrid electric vehicle" was coined by UC Davis Professor Andrew Frank,  who has been called the "father of the modern plug-in hybrid."   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 120 volt AC outlet for recharging.
Revival of interest
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'cité" electric-drive Kangoo battery electric van. The Elect'road had a 150 km (93 mi) range using a nickel-cadmium battery pack and a 500 cc (31 cu in), 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 10 liters (2.6 U.S. gal; 2.2 imp gal) 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 240 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 2004, 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.
In 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."  In April 2007 Toyota said it planned to migrate to lithium-ion batteries in future hybrid models,  but not in the 2009 model year Prius.  Lithium-ion batteries are expected to significantly improve fuel economy, and have a higher energy-to-weight ratio, but cost more to produce, and raise safety concerns due to high operating temperatures. 
In 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).  GM announced in January 2007 that contracts had been awarded to two companies to design and test lithium-ion batteries for the vehicle but the Saturn line was discontinued before the hybrid Vue could be released. GM has said that they plan on introducing plug-in and other hybrids "for the next several years". 
In 2007, GM unveiled the prototype of the Chevrolet Volt, which was expected to feature a plug-in capable, battery-dominant series hybrid architecture called 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. 
Also in 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 Prius Plug-in Hybrid was said to have an all-electric range of 13 km (8 mi). 
In, 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.  The Volt was designed with all-electric range of 40 mi (64 km). On September 5, Quantum Technologies and Fisker Coachbuild, LLC announced the launch of a joint venture in Fisker Automotive.  Fisker intended to build a US$80,000 luxury PHEV-50, the Fisker Karma, initially scheduled for late 2009. 
In 2007, Aptera Motors announced their Typ-1 two-seater. They planned to produce both an electric 2e and a plug-in series hybrid 2h with a common three-wheeled, composite body design. As of 2009, over two thousand hybrid pre-orders had been accepted and production of the hybrid configuration was expected to begin in 2010.  However, the company folded in December 2011. 
In 2007, Chinese BYD Auto, owned by China's largest mobile phone battery maker, announced it would be introducing a production PHEV-60 sedan in China in the second half of 2008. BYD exhibited it January 2008 at the North American International Auto Show in Detroit. Based on BYD's midsize F6 sedan, it uses lithium iron phosphate (LiFeP0 4 )-based batteries instead of lithium-ion, and can be recharged to 70% of capacity in just 10 minutes. 
In 2007 Ford delivered the first Ford Escape Plug-in Hybrid of a fleet of 20 demonstration PHEVs to Southern California Edison.  As part of this demonstration program Ford also developed the first flexible-fuel plug-in hybrid SUV, which was delivered in June 2008.  This demonstration fleet of plug-ins has been in field testing with utility company fleets in the U.S. and Canada,  and during the first two years since the program began, the fleet has logged more than 75,000 miles.  In August 2009 Ford delivered the first Escape Plug-in equipped with intelligent vehicle-to-grid (V2G) communications and control system technology, and Ford plans to equip all 21 plug-in hybrid Escapes with the vehicle-to-grid communications technology.  Sales of the Escape PHEV are scheduled for 2012. 
On January 14, 2008, Toyota announced they would start sales of lithium-ion battery PHEVs by 2010,   but later in the year Toyota indicated they would be offered to commercial fleets in 2009.
On March 27, the California Air Resources Board (CARB) modified their regulations, requiring automobile manufacturers to produce 58,000 plug-in hybrids during 2012 through 2014.  This requirement is an asked-for alternative to an earlier mandate to produce 25,000 pure zero-emissions vehicles, reducing that requirement to 5,000.  On June 26, Volkswagen announced that they would be introducing production plug-ins based on the Golf compact. Volkswagen uses the term 'TwinDrive' to denote a PHEV. In September, Mazda was reported to be planning PHEVs.  On September 23, Chrysler announced that they had prototyped a plug-in Jeep Wrangler and a Chrysler Town and Country mini-van, both PHEV-40s with series powertrains, and an all-electric Dodge sports car, and said that one of the three vehicles would go into production.  
On October 3, the U.S. enacted the Energy Improvement and Extension Act of 2008. The legislation provided tax credits for the purchase of plug-in electric vehicles of battery capacity over 4 kilowatt-hours.   The federal tax credits were extended and modified by the American Clean Energy and Security Act of 2009, but now the battery capacity must be over 5 kWh and the credit phases out after the automaker has sold at least 200,000 vehicles in the U.S.
On December 15, 2008 BYD Auto began selling its F3DM in China, becoming the first production plug-in hybrid sold in the world, though initially was available only for corporate and government customers.   Sales to the general public began in Shenzhen in March 2010,   but because the F3DM nearly doubles the price of cars that run on conventional fuel, BYD expects subsidies from the local government to make the plug-in affordable to personal buyers.  Toyota tested 600 pre-production Prius Plug-ins in Europe and North America in 2009 and 2010.  
Volvo Cars, in a joint venture with Vattenfall, a Swedish energy company, began a demonstration project with two Volvo V70 Plug-in Hybrids in Göteborg, Sweden since December 2009. As reported by the test drivers, the V70 Plug-in Hybrid demonstrators have an all-electric range between 20 kilometres (12 mi) to 30 kilometres (19 mi). The test plug-in hybrids were built with a button to allow test drivers to manually choose between electricity or diesel engine power at any time.   Volvo announced series production of plug-in diesel-electric hybrids as early as 2012. Volvo claimed that its plug-in hybrid could achieve 125 miles per US gallon (1.88 L/100 km; 150 mpg ‑imp ), based on the European test cycle.  
In October 2010 Lotus Engineering unveiled the Lotus CityCar at the 2010 Paris Motor Show, a plug-in series hybrid concept car designed for flex-fuel operation on ethanol, or methanol as well as regular gasoline.   The lithium battery pack provides an all-electric range of 60 kilometres (37 mi), and the 1.2-liter flex-fuel engine kicks in to allow to extend the range to more than 500 kilometres (310 mi).  
GM officially launched the Chevrolet Volt in the U.S. on November 30, 2010, and retail deliveries began in December 2010.  Its sibling the Opel/Vauxhall Ampera was launched in Europe between late 2011 and early 2012. The first deliveries of the Fisker Karma took place in July 2011,  and deliveries to retail customers began in November 2011. The Toyota Prius Plug-in Hybrid was released in Japan in January 2012,  followed by the United States in February 2012.  Deliveries of the Prius PHV in Europe began in late June 2012.  The Ford C-Max Energi was released in the U.S. in October 2012,  the Volvo V60 Plug-in Hybrid in Sweden by late 2012. 
The Honda Accord Plug-in Hybrid was released in selected U.S. markets in January 2013,  and the Mitsubishi Outlander P-HEV in Japan in January 2013, becoming the first SUV plug-in hybrid in the market.  Deliveries of the Ford Fusion Energi began in February 2013.   BYD Auto stopped production of its BYD F3DM due to low sales,  and its successor, the BYD Qin, began sales in Costa Rica in November 2013, with sales in other countries in Latin America scheduled to begin in 2014.    Qin deliveries began in China in mid December 2013.  [
Deliveries to retail customers of the limited edition McLaren P1 supercar began in the UK in October 2013,  and the Porsche Panamera S E-Hybrid began deliveries in the U.S. in November 2013. The first retail deliveries of the Cadillac ELR took place in the U.S. in December 2013.  The BMW i8 and the limited edition Volkswagen XL1 were released to retail customers in Germany in June 2014.   The Porsche 918 Spyder was also released in Europe and the U.S. in 2014. The first units of the Audi A3 Sportback e-tron and Volkswagen Golf GTE were registered in Germany in August 2014. 
In December 2014 BMW announced the group is planning to offer plug-in hybrid versions of all its core-brand models using eDrive technology developed for its BMW i brand plug-in vehicles (BMW i3 and BMW i8). The goal of the company is to use plug-in technology to continue offering high performance vehicles while reducing CO 2 emissions below 100g/km. At the time of the announcement the carmaker was already testing a BMW 3 Series plug-in hybrid prototype.  The first model available for retail sales will be the 2016 BMW X5 eDrive, with the production version unveiled at the 2015 Shanghai Motor Show.  The second generation Chevrolet Volt was unveiled at the January 2015 North American International Auto Show,  and retail deliveries began in the U.S. and Canada in October 2015.  
In March 2015 Audi said they planned on making a plug-in hybrid version of every model series, and that they expect plug-in hybrids, together with natural gas vehicles and battery-electric drive systems, to have a key contribution in achieving the company's CO 2 targets. The Audi Q7 e-tron will follow the A3 e-tron already in the market.  Also in March 2015, Mercedes-Benz announced that the company's main emphasis regarding alternative drives in the next years will be on plug-in hybrids. The carmaker plans to introduce 10 new plug-in hybrid models by 2017, and its next release was the Mercedes-Benz C 350 e, Mercedes’ second plug-in hybrid after the S 500 Plug-In Hybrid.  Other plug-in hybrid released in 2015 are the BYD Tang, Volkswagen Passat GTE, Volvo XC90 T8, and the Hyundai Sonata PHEV.
Global combined Volt/Ampera family sales passed the 100,000 unit milestone in October 2015.  By the end of 2015, over 517,000 highway legal plug-in hybrid electric cars have been sold worldwide since December 2008 out of total global sales of more than 1.25 million light-duty plug-in electric cars.  
In February 2016, BMW announced the introduction of the "iPerformance" model designation, which will be given to all BMW plug-in hybrid vehicles from July 2016. The aim is to provide a visible indicator of the transfer of technology from BMW i to the BMW core brand. The new designation will be used first on the plug-in hybrid variants of the new BMW 7 Series, the BMW 740e iPerformance,  and the 3 Series, the BMW 330e iPerformance. 
Hyundai Motor Company made the official debut of its three model Hyundai Ioniq line-up at the 2016 Geneva Motor Show.  The Ioniq family of electric drive vehicles includes the Ioniq Plug-in, which is expected to achieve a fuel economy of 125 mpg‑e (28 kW·h/100 mi; 17.1 kW·h/100 km) in all-electric mode.  The Ioniq Plug-in is scheduled to be released in the U.S. in the fourth quarter of 2017. 
The second generation Prius plug-in hybrid, called Prius Prime in the U.S. and Prius PHV in Japan,  was unveiled at the 2016 New York International Auto Show. Retail deliveries of the Prius Prime began in the U.S. in November 2016,  and is scheduled to be released Japan by the end of 2016.   The Prime has an EPA-rated all-electric range of 25 mi (40 km), over twice the range of the first generation model, and an EPA rated fuel economy of 133 mpg‑e (25.9 kW·h/100 mi) in all-electric mode (EV mode), the highest MPGe rating in EV mode of any vehicle rated by EPA.   Unlike its predecessor, the Prime runs entirely on electricity in EV mode.  Global sales of the Mitsubishi Outlander P-HEV passed the 100,000 unit milestone in March 2016.   BYD Qin sales in China reached the 50,000 unit milestone in April 2016, becoming the fourth plug-in hybrid to pass that mark. 
In June 2016, Nissan announced it will introduce a compact range extender car in Japan before March 2017. The series plug-in hybrid will use a new hybrid system, dubbed e-Power, which debuted with the Nissan Gripz concept crossover showcased at the 2015 Frankfurt Auto Show. 
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 supercapacitor pack, or a combination of the two, can be used to store excess charge. Examples of series hybrids vehicles include the Chevrolet Volt (first generation), Fisker Karma, Renault Kangoo, Elect'Road, Toyota's Japan-only Coaster light-duty passenger bus, Daimler AG's hybrid Orion bus, Opel Flextreme concept car, Swissauto REX VW Polo  prototype 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 axle and/or a generator used for recharging the batteries. This type is called a road-coupled hybrid. 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, Chevrolet, 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 use this architecture.  The Toyota Prius Plug-in Hybrid operates as a series-parallel hybrid. 
Batteries are DC devices while grid power is AC. In order to charge the batteries, a DC charger must be used. The charger can be located in several locations:
On-board chargers are mounted inside the vehicle. Since the charger takes up space and adds weight, its power capacity is generally limited by practical considerations, avoiding carrying a more powerful charger that can only be fully utilized at certain locations. However, carrying the charger along with the vehicle ensures that power will be available anywhere a power connection can be found.
Off-board chargers can be as large as needed and mounted at fixed locations, like the garage or dedicated charging stations. Built with dedicated wiring, these chargers can handle much more power and charge the batteries more quickly. However, as the output of these chargers is DC, each battery system requires the output to be changed for that car. Modern charging stations have a system for identifying the voltage of the battery pack and adjusting accordingly.
Using electric motor's inverter allows the motor windings to act as the transformer coils, and the existing high-power inverter as the AC-to-DC charger. As these components are already required on the car, and are designed to handle any practical power capability, they can be used to create a very powerful form of on-board charger with zero additional weight or size. AC Propulsion uses this charging method, referred to as "reductive charging". 
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. 
- Blended mode is a kind of charge-depleting mode. It is 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 increases the distance from stored grid electricity compared to 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 mph (68 km/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.
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.
Mixed mode describes a trip in which a combination of the above modes are used. 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 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.
Electric power storage
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. Pacific Gas and Electric Company (PG&E) has suggested that utilities could purchase used batteries for backup and load leveling purposes. They state that while these used batteries may be no longer usable in vehicles, their residual capacity still has significant value. More recently, General Motors (GM) has said it has been "approached by utilities interested in using recycled Volt batteries as a power storage system, a secondary market that could bring down the cost of the Volt and other plug-in vehicles for consumers." 
Lithium iron phosphate (LiFePO 4 ) is a class of cathode materials used in lithium iron phosphate batteries that is getting attention from the auto industry. Valence Technologies produce a lithium iron manganese phosphate (LiFeMnPO 4 ) battery with LG Chem selling lithium iron phosphate (LiFePO 4 ) batteries for the Chevy Volt and A123 produces a lithium nano-phosphate battery. The most important merit of this battery type is safety and high-power. Lithium iron phosphate batteries are one of three major types in LFP family, the other two being nano -phosphate and nano-cocrystalline- olivine.
In France, Électricité de France (EDF) and Toyota are installing charging stations 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 taxicab stands. Project Better Place began in October 2007 and is working with Renault on development of exchangeable batteries (battery swapping).
Ultracapacitors (or "supercapacitors") are used in some plug-in hybrids, such as AFS Trinity's concept prototype, to store rapidly available energy with their high power density, in order to keep batteries within safe resistive heating limits and extend battery life.  The CSIRO's UltraBattery combines a supercapacitor and a lead acid battery in a single unit, creating a hybrid car battery that lasts longer, costs less and is more powerful than current technologies used in plug-in hybrid electric vehicles (PHEVs). 
The optimum battery size varies depending on whether the aim is to reduce oil consumption, running costs, or emissions, but a recent study  concluded that "The best choice of PHEV battery capacity depends critically on the distance that the vehicle will be driven between charges. Our results suggest that for urban driving conditions and frequent charges every 10 miles or less, a low-capacity PHEV sized with an AER (all electric range) of about 7 miles would be a robust choice for minimizing gasoline consumption, cost, and greenhouse gas emissions. For less frequent charging, every 20–100 miles, PHEVs release fewer GHGs, but HEVs are more cost effective. "
Conversions of production vehicles
Conversion of fossil-fuel vehicles
Retrofit electrification requires only one-fifth the energy required to build a new vehicle. This is called ACEV-to-PHEV conversion.  There are several companies that are converting fossil fuel non-hybrid vehicles (also called all- combustion engine vehicles) to plug-in hybrids:  
Colorado is going to offer $6,000 credit for PHEV conversions (in addition to a federal 10% credit up to $4,000 for qualifying vehicles). 
Conversions of production hybrids
Aftermarket conversion of an existing production hybrid (a charge-maintaining hybrid) to a plug-in hybrid (called CHEV-to-PHEV conversion ) 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 A123 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 (some of them also for Ford Escape Hybrid) include Hymotion, Hybrids Plus Manzanita Micro and OEMtek BREEZ (PHEV-30).  AFS Trinity's XH-150 claims that it has created a functioning plug-in hybrid with a 40 miles (64 km) all-electric range and that it has solved the overheating problem that rapid acceleration can cause in PHEVs and extend battery life. 
The EAA-PHEV project was conceived by CalCars and the Electric Auto Association in October 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 converters through the process, and to provide a common design that could demonstrate multiple battery technologies. 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.
Plug-In Supply, Inc. of Petaluma, California offers components and assemblies to build the Prius+, the plug-in conversion invented by CalCars.  Their lead–acid battery box assembly forms a complete install package, providing access to the spare tire and containing twenty 12 volt lead–acid batteries and all high voltage components and control electronics. The "PbA Battery Box Assembly" is also available without batteries. It provides about 10 miles (16 km) of EV mode range.  Conversion time was reduced by plug-in supply to one day.
Oemtek offers a Valence powered lithium iron phosphate conversion that should provide 50 miles (80 km) of all-electric range. The Motor Industry Research Association has announced a retrofit hybrid conversion kit that provides removable battery packs that plug into a wall outlet for charging.  Poulsen Hybrid is developing a conversion kit that will add through-the-road plug-in hybrid capability to conventional vehicles by externally mounting electric motors onto two of the wheels. 
MD-Tech offers a PHEV Kit for hybrid vehicles that acts as a hybrid battery re-charger. The kit supplies power to the hybrid battery without modifying the powertrain of the hybrid vehicle. It fits into the back of a hybrid vehicle, originally designed to fit under the rear floor of a Toyota Prius. The kit uses lithium iron phosphate cells in a battery supplying 4 kWh of energy. This gives it a range of 30 km in charge-depleting, EV mode and provides a boost of power in blended mode. The battery charger uses mains electricity and takes 4–5 hours to charge. The battery supplies power to the DC to DC boost converter which regulates power to the hybrid battery. The converter output can be adjusted to set voltage and current output. A proprietary battery management system uses active battery balancing to monitor the battery state of health.
Enginer Inc. of Troy, Michigan offers universal plugin conversion kits with components and assemblies to build two stage hybrid battery system. Their lithium-ion battery box assembly forms a complete install package, providing access to the spare tire and containing 16/32 lithium phosphate battery cells, a DC/DC converter, a BMS and a charger. It provides about 10 miles (16 km) of EV mode range for under $2000 (2 kWh model). Longer range 4 kWh model is also available for $1000 more. Conversion time was reduced to two/three hours.
With the exception of Tesla Motors, demand for all-electric vehicles, especially in the U.S. market, has been driven by government incentives. In particular, American sales of the Nissan Leaf have depended on generous incentives and special treatment in the state of Georgia, the top selling Leaf market.  According to international market research, 60% of respondents believe a battery driving range of less than 160 km (99 mi) is unacceptable even though only 2% drive more than that distance per day.  Among popular current all-electric vehicles, only the Tesla (with the most expensive version of the Model S offering a 265 miles (426 km) range in the U.S. Environmental Protection Agency 5-cycle test) significantly exceeds this threshold. The Nissan Leaf has an EPA rated range of 75 miles (121 km) for the 2013 model year.
Plug-in hybrids provide the extended range and potential for refueling of conventional hybrids while enabling drivers to use battery electric power for at least a significant part of their typical daily driving. The average trip to or from work in the United States in 2009 was 11.8 miles (19.0 km),  while the average distance commuted to work in England and Wales in 2011 was slightly lower at 9.3 miles (15 km).  Since building a PHEV with a longer all-electric range adds weight and cost, and reduces cargo and/or passenger space, there is not a specific all-electric range that is optimal. The accompanying graph shows the observed all-electric range, in miles, for four popular U.S. market plug-in hybrids, as tested by Popular Mechanics magazine. 
A key design parameter of the Chevrolet Volt was a target of 40 miles (64 km) for the all-electric range, selected to keep the battery size small and lower costs, and mainly because research showed that 78% of daily commuters in the U.S. travel 40 mi (64 km) or less. This target range would allow most travel to be accomplished electrically driven and the assumption was made that charging will take place at home overnight. This requirement translated using a lithium-ion battery pack with an energy storage capacity of 16 kWh considering that the battery would be used until the state of charge (SOC) of the battery reached 30%. 
In October 2014 General Motors reported, based on data collected through its OnStar telematics system since Volt deliveries began, and with over 1 billion miles (1.6 billion km) traveled, that Volt owners drive about 62.5% of their trips in all-electric mode.  In May 2016, Ford reported, based on data collected from more than 610 million miles (976 million km) logged by its electrified vehicles through its telematics system, that drivers of these vehicles run an average of 13,500 mi (21,700 km) annually on their vehicles, with about half of those miles operating in all-electric mode. A break down of these figures show an average daily commute of 42 mi (68 km) for Ford Energi plug-in hybrid drivers. Ford notes that with the enhanced electric range of the 2017 model year model, the average Fusion Energi commuter could go the entire day using no gasoline, if the car is fully charged both, before leaving for work and before leaving for home. According to Ford data, currently most customers are likely charging their vehicles only at home. 
The 2015 edition of the EPA's annual report " Light-Duty Automotive Technology, Carbon Dioxide Emissions, and Fuel Economy Trends " estimates the following utility factors for 2015 model year plug-in hybrids to represent the percentage of miles that will be driven using electricity by an average driver, whether in electric only or blended modes: 83% for the BMW i3 REx, 66% for the Chevrolet Volt, 45% for the Ford Energi models, 43% for the McLaren P1, 37% for the BMW i8, and 29% for the Toyota Prius PHV.  A 2014 analysis conducted by the Idaho National Laboratory using a sample of 21,600 all-electric cars and plug-in hybrids, found that Volt owners traveled on average 9,112 miles in all-electric mode (e-miles) per year, while Leaf owners traveled 9,697 e-miles per year, despite the Volt's shorter all-electric range, about half of the Leaf's. 
Between January and August 2014, a period during which US sales of conventional hybrids slowed, US sales of plug-in hybrids grew from 28,241 to 40,748 compared to the same period in 2013. US sales of all-electric vehicles also grew during the same period: from 29,917 vehicles in the January to August 2013 period to 40,349 in January to August 2014. 
Fuel efficiency and petroleum displacement
Each kilowatt hour of battery capacity in use will displace up to 50 U.S. gallons (190 l; 42 imp gal) of petroleum fuels per year (gasoline or diesel fuels).  Also, electricity is multi-sourced and, as a result, it gives the greatest degree of energy resilience. 
The actual fuel economy for PHEVs depends on their powertrain operating modes, their all-electric range, and the amount of driving between charges. If no gasoline is used the miles per gallon gasoline equivalent (MPG-e) depends only on the efficiency of the electric system. The first mass production PHEV available in the U.S. market, the 2011 Chevrolet Volt, with an EPA rated all-electric range of 35 miles (56 km), and an additional gasoline-only extended range of 344 miles (554 km) has an EPA combined city/highway fuel economy of 93 MPG-e in all-electric mode, and 37 mpg ‑US (6.4 L/100 km; 44 mpg ‑imp ) in gasoline-only mode, for an overall combined gas-electric fuel economy rating of 60 mpg ‑US (3.9 L/100 km; 72 mpg ‑imp ) equivalent (MPG-e).   The EPA also included in the Volt's fuel economy label a table showing fuel economy and electricity consumed for five different scenarios: 30, 45, 60 and 75 miles (121 km) driven between a full charge, and a never charge scenario.  According to this table the fuel economy goes up to 168 mpg ‑US (1.40 L/100 km; 202 mpg ‑imp ) equivalent (MPG-e) with 45 miles (72 km) driven between full charges. 
For the more comprehensive fuel economy and environment label that will be mandatory in the U.S. beginning in model year 2013, the National Highway Traffic Safety Administration (NHTSA) and Environmental Protection Agency (EPA) issued two separate fuel economy labels for plug-in hybrids because of their design complexity, as PHEVS can operate in two or three operating modes: all-electric, blended, and gasoline-only.   One label is for series hybrid or extended range electric vehicle (like the Chevy Volt), with all-electric and gasoline-only modes; and a second label for blended mode or series-parallel hybrid, that includes a combination of both gasoline and plug-in electric operation; and gasoline only, like a conventional hybrid vehicle.  
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.
The Society of Automotive Engineers (SAE) developed their recommended practice in 1999 for testing and reporting the fuel economy of hybrid vehicles and included language to address PHEVs. An SAE committee is currently working to review procedures for testing and reporting the fuel economy of PHEVs.  The Toronto Atmospheric Fund tested ten retrofitted plug-in hybrid vehicles that achieved an average of 5.8 litres per 100 kilometre or 40.6 miles per gallon over six months in 2008, which was considered below the technology's potential.
PHEV batteries also allow for an additional efficiency when converting solar power directly into a DC storage system, as opposed to converting the energy into AC home or building. DC to DC direct conversion is more efficient, therefore, potentially allowing the more efficient capture of solar energy. 
In real world testing using normal drivers, some Prius PHEV conversions may not achieve much better fuel economy than HEVs. For example, a plug-in Prius fleet, each with a 30 miles (48 km) all-electric range, averaged only 51 mpg ‑US (4.6 L/100 km; 61 mpg ‑imp ) in a 17,000-mile (27,000 km) test in Seattle,  and similar results with the same kind of conversion battery models at Google's RechargeIT initiative. Moreover, the additional battery pack costs US$10,000 – US$11,000.  
The following table compares EPA's estimated out-of-pocket fuel costs and fuel economy ratings of serial production plug-in hybrid electric vehicles rated by EPA as of January 2017 expressed in miles per gallon gasoline equivalent (mpg-e),   versus the most fuel efficient gasoline-electric hybrid car, the 2016 Toyota Prius Eco (fourth generation), rated 56 mpg ‑US (4.2 L/100 km; 67 mpg ‑imp ), and EPA's average new 2016 vehicle, which has a fuel economy of 25 mpg ‑US (9.4 L/100 km; 30 mpg ‑imp ).    The table also shows the fuel efficiency for plug-in hybrids in all-electric mode expressed as KWh/100 mile, the metric used by EPA to rate electric cars before November 2010. 
|Comparison of out-of-pocket fuel costs and fuel economy for plug-in hybrid electric cars rated by EPA as of January 2017 with MPGe and conventional MPG (1) (as displayed in the Monroney label and the US DoE fueleconomy.gov website)|
|Vehicle||Year model||Operating mode (EV range)||EPA rated Combined fuel economy||EPA rated city/highway fuel economy||Fuel cost to drive 25 miles||Annual fuel cost (1) (15,000 mi)||Notes|
|Toyota Prius Prime  ||2017||Electricity (25 mi)||133 mpg-e (25 kWh/100 mi)||-||$0.82||$550||The Prius Prime is the most energy-efficient vehicle with a gasoline engine in EV mode.  During the first 25 mi might use some gasoline.  The 2017 Prime has a combined gasoline/electricity rating of 78 mpg-e (city 83 mpg-e/hwy 73 mpg-e). |
|Gasoline only||54 mpg||55 mpg/ 53 mpg||$1.08|
|BMW i3 REx (60 A·h)  ||2014 2015 2016||Electricity only (72 mi)||117 mpg-e (29 kWh/100 mi)||97 mpg‑e (35 kW·h/100 mi)/ 79 mpg‑e (44 kW·h/100 mi)||$0.94||$650||The EPA classifies the i3 REx as a series plug-in hybrid while CARB as a range-extended battery-electric vehicle (BEVx). The 2014/16 i3 REx is the most fuel efficient EPA-certified current year vehicle with a gasoline engine with a combined gasoline/electricity rating of 88 mpg-e (city 97 mpg-e/hwy 79 mpg-e).  |
|Gasoline only (78 mi)||39 mpg||41 mpg/ 37 mpg||$1.79|
|Honda Accord Plug-in Hybrid||2014||Electricity and gasoline (13 mi)||115mpg-e (29 kWh/100 mi)||-||$1.03||$650||The 2014 Accord is the most fuel efficient plug-in hybrid in blended EV mode with a rating of 115 mpg-e. The Accord has a rating for combined EV/hybrid operation of 57 mpg-e. |
|Gasoline only||46 mpg||47 mpg/ 46 mpg||$1.11|
|BMW i3 REx (94 A·h)  ||2017||Electricity only (97 mi)||111 mpg-e (30 kWh/100 mi)||-||$0.98||$650||The EPA classifies the i3 REx as a series plug-in hybrid while CARB as a range-extended battery-electric vehicle (BEVx). The 2017 i3 REx (94 A·h) has a combined gasoline/electricity rating of 88 mpg-e (city 95 mpg-e/hwy 81 mpg-e), the highest rating among 2017 MY plug-in hybrids. |
|Gasoline only (83 mi)||35 mpg||36 mpg/ 33 mpg||$1.99|
|Chevrolet Volt (2nd gen)  ||2016 2017||Electricity only (53 mi)||106 mpg-e (31 kWh/100 mi)||113 mpg-e (29 kWh/100 mi)/ 99 mpg-e (34 kWh/100 mi)||$1.01||$650||The 2016/17 Volt has a combined gasoline/electricity rating of 77 mpg-e (city 82 mpg-e/hwy 72 mpg-e).  Regular gasoline.|
|Gasoline only||42 mpg||43 mpg/ 42 mpg||$1.39|
|Hyundai Sonata PHEV ||2016||Electricity and gasoline (27 mi)||99mpg-e (34 kWh/100 mi)||-||$1.19||$700||During the first 27 mi uses some gasoline. The actual all-electric range is between 0 to 27 mi. |
|Gasoline only||40 mpg||-||$1.28|
|Chevrolet Volt (1st gen)  ||2013 2014 2015||Electricity only (38 mi)||98 mpg-e (35 kWh/100 mi)||-||$1.01||$650||The 2013/15 Volt has a combined gasoline/electricity rating of 62 mpg-e (city 63 mpg-e/hwy 61 mpg-e).  Premium gasoline.|
|Gasoline only||37 mpg||35 mpg/ 40 mpg||$1.21|
|Ford Fusion Energi ||2017||Electricity and gasoline (22 mi)||97 mpg-e (35 kW-h/100 mi)||-||$1.14||$700||The actual all-electric range is between 0 to 21 mi. |
|Gasoline only||42 mpg||-||$1.21|
|Toyota Prius PHV ||2012 2013 2014 2015||Electricity and gasoline (11 mi)||95 mpg-e (29 kWh/100 mi plus 0.2 gallons/100 mi)||-||$1.03||$600||After the first 11 miles the car functions like a regular Prius hybrid The 2012/15 Prius has a combined gasoline/electricity rating of 58 mpg-e (city 59 mpg-e/hwy 56 mpg-e). |
|Gasoline only||50 mpg||51 mpg/ 49 mpg||$1.02|
|Chevrolet Volt ||2011 2012||Electricity only||94 mpg-e (36 kWh/100 mi)||95 mpg-e (36 kWh/100 mi)/ 93 mpg-e (37 kWh/100 mi)||$1.17||$800||Premium gasoline.|
|Gasoline only||37 mpg||35 mpg/ 40 mpg||$1.70|
|Ford C-Max Energi  Ford Fusion Energi ||2013 2014 2015 2016||Electricity and gasoline (20 mi)||88 mpg-e (37 kWh/100 mi)||95 mpg‑e (36 kW·h/100 mi)/ 81 mpg‑e (42 kW·h/100 mi)||$1.25||$750||The Energi did not use any gasoline for the first 20 miles in EPA tests, but depending on the driving style, the car may use both gasoline and electricity during EV mode. The Energi models have a combined EV/hybrid operation rating of 51 mpg-e (city 55 mpg-e/hwy 46 mpg-e). |
|Gasoline only||38 mpg||40 mpg/ 36 mpg||$1.34|
|Audi A3 e-tron ultra ||2016||Electricity only (17 mi)||86 mpg-e (38 kWh/100 mi)||-||$1.37||$900||During the first 17 mi uses some gasoline. The actual all-electric range is between 0 to 17 mi. |
|Gasoline only||39 mpg||-||$1.61|
|Cadillac ELR ||2014 2015||Electricity only (37 mi)||82 mpg-e (41 kWh/100 mi)||-||$1.33||$900||The 2014/15 ELR has a combined gasoline/electricity rating of 54 mpg-e (city 54 mpg-e/hwy 55 mpg-e). |
|Gasoline only||33 mpg||31 mpg/ 35 mpg||$1.90|
|Chrysler Pacifica Hybrid ||2017||Electricity only (33 mi)||84 mpg-e (40 kWh/100 mi)||-||$1.73||$900||During the first 33 mi uses some gasoline. The actual all-electric range is between 0 to 33 mi. |
|Gasoline only||32 mpg||-||$1.83|
|Audi A3 e-tron ||2016||Electricity only (16 mi)||83 mpg-e (40 kWh/100 mi)||-||$1.49||$950||During the first 16 mi uses some gasoline. The actual all-electric range is between 0 to 16 mi. |
|Gasoline only||35 mpg||-||$1.79|
|BMW i8  ||2014 2015 2016||Electricity and gasoline (15 mi)||76 mpg-e (43 kWh/100 mi)||-||$1.77||$1,150||The i8 does not run on 100% electricity as it consumes 0.1 gallons per 100 mi in EV mode (all-electric range = 0 mi) The i8 has a rating for combined EV/hybrid operation of 37 mpg-e. |
|Gasoline only||28 mpg||28 mpg/ 29 mpg||$2.24|
|BMW 330e ||2016||Electricity and gasoline (14 mi)||72 mpg-e (47 kWh/100 mi)||-||$1.74||$1,050||During the first 14 mi uses some gasoline. The actual all-electric range is between 0 to 14 mi.  Premium gasoline.|
|Gasoline only||31 mpg||-||$2.02|
|Porsche 918 Spyder  ||2015||Electricity only (12 mi)||67 mpg-e (50 kWh/100 mi)||-||$1.62||$1,500||Premium gasoline.|
|Gasoline only||22 mpg||20 mpg/ 24 mpg||$2.85|
|BMW 740e iPerformance ||2017||Electricity only (14 mi)||64 mpg-e (52 kWh/100 mi)||-||$2.03||$1,350||During the first 14 mi uses some gasoline. The actual all-electric range is between 0 to 14 mi. |
|Gasoline only||27 mpg||-||$2.48|
|BMW X5 xDrive40e ||2016||Electricity only (14 mi)||56 mpg-e (59 kWh/100 mi)||-||$2.23||$1,450||During the first 14 mi uses some gasoline. The actual all-electric range is between 0 to 14 mi. |
|Gasoline only||24 mpg||-||$2.61|
|Mercedes-Benz S 500 e ||2015||Electricity and gasoline (14 mi)||58 mpg-e (59 kWh/100 mi)||-||$2.13||$1,350||During the first 14 mi uses some gasoline. The actual all-electric range is between 0 to 12 mi.  Premium gasoline.|
|Gasoline only||26 mpg||-||$2.41|
|Fisker Karma ||2012||Electricity only (33 mi)||54 mpg-e (62 kWh/100 mi)||-||$2.02||$1,450||Premium gasoline.|
|Gasoline only||20 mpg||20 mpg/ 21 mpg||$3.14|
|Volvo XC90 T8 ||2016||Electricity and gasoline (14 mi)||53 mpg-e (58 kWh/100 mi)||-||$2.19||$1,400||During the first 14 mi uses some gasoline. The actual all-electric range is between 0 to 13 mi.  Premium gasoline.|
|Gasoline only||25 mpg||-||$2.51|
|Porsche Panamera S E-Hybrid ||2016||Electricity and gasoline (16 mi)||51 mpg-e (51 kWh/100 mi)||-||$2.15||$1,350||The all-electric range is between 0 to 15 mi Premium gasoline.|
|Gasoline only||25 mpg||23 mpg/ 29 mpg||$2.51|
|Porsche Panamera S E-Hybrid ||2014 2015||Electricity and gasoline (16 mi)||50 mpg-e (52 kWh/100 mi)||-||$2.18||$1,400||The all-electric range is between 0 to 15 mi The S E-Hybrid has a rating for combined EV/hybrid operation of 31 mpg-e. |
|Gasoline only||25 mpg||23 mpg/ 29 mpg||$2.51|
|Porsche Cayenne S E-Hybrid  ||2015 2016||Electricity and gasoline (14 mi)||47 mpg-e (69 kWh/100 mi)||-||$2.24||$1,550||Premium gasoline.|
|Gasoline only||22 mpg||21 mpg/ 24 mpg||$2.85|
|McLaren P1  ||2014 2015||Electricity and gasoline (19 mi)||18 mpg-e (25 kWh/100 mi)||-||$3.79||$2,200||The P1 does not run on 100% electricity as it consumes 4.8 gallons per 100 mi in EV mode (all-electric range = 0 mi)  The P1 has a rating for combined EV/hybrid operation of 17 mpg-e. |
|Gasoline only||17 mpg||16 mpg/ 20 mpg||$3.69|
|2016 Toyota Prius Eco (4th gen) ||2016||Gasoline-electric hybrid||56 mpg||58 mpg/ 53 mpg||$0.91||$550||Most fuel efficient hybrid electric car. |
|Ford Fusion AWD 2.0L   (Average new vehicle)||2016||Gasoline only||25 mpg||22 mpg/ 31 mpg||$2.04||$1,200||Other 2016 MY cars achieving 25 mpg combined city/hwy include the Honda Accord 3.5L, Toyota Camry 3.5L and Toyota RAV4 2.5L.  |
|Notes: (1) Based on 45% highway and 55% city driving. Electricity cost of US$0.13 /kWh, premium gasoline price of US$2.51 per gallon (used by the 2015 Volt, i3 REx, ELR, i8, Mercedes S500e, Karma and all Porsche models), and regular gasoline price of US$2.04 per gallon (as of 18 December 2015). Conversion 1 gallon of gasoline=33.7 kWh.|
A study published in 2014 by researchers from Lamar University, Iowa State University and Oak Ridge National Laboratory compared the operating costs of plug-in hybrid electric vehicles (PHEVs) of various electric ranges (10, 20, 30, and 40 miles) with conventional gasoline vehicles and hybrid-electric vehicles (HEVs) for different payback periods, considering different charging infrastructure deployment levels and gasoline prices. The study concluded that: 
- PHEVs save around 60% or 40% in energy costs, compared with conventional gasoline vehicles and HEVs, respectively. However, for drivers with significant daily vehicle miles traveled (DVMT), hybrid vehicles may be even a better choice than plug-in hybrids with a range of 40 mi (64 km), particularly when there is lack of public charging infrastructure.
- The incremental battery cost of large-battery plug-in hybrids is difficult to justify based on the incremental savings of PHEVs’ operating costs unless a subsidy is offered for large-battery PHEVs.
- When the price of gasoline increases from US$4 per gallon to US$5 per gallon, the number of drivers who benefit from a larger battery increases significantly. If the gas price is US$3, a plug-in hybrid with a range of 10 mi (16 km) is the least costly option even if the battery cost is $200/kW.
- Although quick chargers can reduce charging time, they contribute little to energy cost savings for PHEVs, as opposed to Level-2 chargers.
Range anxiety elimination
One of the main barriers for the general adoption of all-electric cars is the range anxiety factor, the driver's fear of being stranded by a depleted battery before reaching the final destination.  Plug-in hybrids, as opposed to pure electric cars, eliminate the range anxiety concerns because the gasoline engine serves as a back-up to recharge the battery to provide electric power to the electric motor, or to provide propulsion directly. Access to a regular fuel station guarantees that a PHEV has similar driving ranges as conventional gasoline-powered automobile. 
As of 2016, there are five plug-in hybrids in the European market capable of driving around 50 km (31 mi) (under NEDC cycle) on the battery alone, the Audi A3 e-tron, Mitsubishi Outlander P-HEV, Volkswagen Golf GTE, Volkswagen Passat GTE, and Volvo V60 Plug-in Hybrid. Other models with larger all-electric range are the Chevrolet Volt and Cadillac ELR, sold in the U.S. and Canada, and the BMW i3 REx, available in 49 countries.  
As a response to range anxiety concerns, BMW is offering an optional limited capability gasoline range extender engine for its all-electric BMW i3.  The range-extender option costs an additional US$3,850 in the United States,  €4,710 (~ US$6,300) in France, and €4,490 (~ US$6,000) in the Netherlands. The range-extender option of the BMW i3 was designed to meet the California Air Resources Board (CARB) regulation for an auxiliary power unit (APU) called REx. According to rules adopted in March 2012 by CARB, the 2014 BMW i3 with a REx unit fitted will be the first car to qualify as a range-extended battery-electric vehicle or "BEVx." CARB describes this type of electric vehicle as "a relatively high-electric range battery-electric vehicle (BEV) to which an APU is added." The unit, which maintains battery charge at about 30% after the pack has been depleted in normal use, is strictly limited in the additional range it can provide. 
According to BMW, at the beginning of the i3 release, the use of range-extender was much more than the carmaker expected, more than 60%. Over time it has decreased significantly, with some people almost never using it, and by 2016 it is being regularly used in fewer than 5% of i3s.  In early October 2014, General Motors reported, based on data collected through its OnStar telematics system, that Volt owners in North America have accumulated a total of 1 billion miles (1.6 billion km) traveled, of which, about 62.5% were driven in all-electric mode. A similar report, issued by GM in August 2016, reported that Volt owners have accumulated almost 1.5 billion miles (2.4 billion km) driven in EV mode, representing 60% of their total miles traveled. 
In a study published in June 2016, conducted by the Norwegian Institute of Transport Economics, the researchers found that plug-in hybrid owners in Norway drive on average 55% of their annual distance in charge-depleting or all-electric mode (EV mode), and the share goes up to about 63% for work trips. The share of electric travel is higher for trips to work and in the summer, and lower in the winter. The average plug-in hybrid user in the survey drives 60% of the total distance in EV mode in the summer and 53% in winter. The estimate for work trips is higher at 70% in the summer and 59% in winter. 
One of the advantages of the plug-in hybrid design is that the generator can be completely decoupled from the traction. Unlike a conventional engine, which operates over a wide variety of power settings and operational conditions, the range extender can be operated under optimum conditions at all times. High-efficiency power sources that are not suitable for normal automotive use may be perfectly suitable for PEV use. These include advanced close-cycle steam engines, stirling engines, Wankel engines, and microturbines due primarily to their light weight and small size.
The Ontario Medical Association announced that smog is responsible for an estimated 9,500 premature deaths in its province every year. Plug-in hybrids in emission-free electric mode may contribute to the reduction of smog.
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 known as charge control 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 nighttime electricity they would even out electricity demand which is typically higher in the daytime, and provide a greater return on capital for electricity infrastructure. 
Cost of batteries
Disadvantages of plug-in hybrids include the additional cost, weight, and size of a larger battery pack. According to a 2010 study by the National Research Council, the cost of a lithium-ion battery pack is about US$1,700 / kW·h of usable energy, and considering that a PHEV-10 requires about 2.0 kW·h and a PHEV-40 about 8 kW·h, the manufacturer cost of the battery pack for a PHEV-10 is around US$3,000 and it goes up to US$14,000 for a PHEV-40.  According to the same study, even though costs are expected to decline by 35% by 2020, market penetration is expected to be slow and therefore PHEVs are not expected to significantly impact oil consumption or carbon emissions before 2030, unless a fundamental breakthrough in battery technologies occurs.  
|Cost comparison between a PHEV-10 and a PHEV-40   (prices for 2010)|
| || || || || || || || |
|PHEV-10|| || || || || || || |
|PHEV-40|| || || || || || || |
|Notes: (1) Considers the HEV technology used in the Toyota Prius with a larger battery pack. The Prius Plug-in estimated all-electric range is 14.5 mi (23 km) (2) Assuming 15,000 miles per year.|
According to the 2010 NRC study, although a mile driven on electricity is cheaper than one driven on gasoline, lifetime fuel savings are not enough to offset plug-ins high upfront costs, and it will take decades before the break even point is achieved.  Furthermore, hundreds of billions of dollars in government subsidies and incentives are likely to be required to achieve a rapid plug-in market penetration in the U.S. 
A 2013 study by the American Council for an Energy-Efficient Economy reported that battery costs came down from US$1,300 per kilowatt hour in 2007 to US$500 per kilowatt hour in 2012. The U.S. Department of Energy has set cost targets for its sponsored battery research of US$300 per kilowatt hour in 2015 and US$125 per kilowatt hour by 2022. Cost reductions through advances in battery technology and higher production volumes will allow plug-in electric vehicles to be more competitive with conventional internal combustion engine vehicles.
A study published in 2011 by the Belfer Center, Harvard University, found that the gasoline costs savings of plug-in electric cars over the vehicles’ lifetimes do not offset their higher purchase prices. This finding was estimated comparing their lifetime net present value at 2010 purchase and operating costs for the U.S. market, and assuming no government subidies.   According to the study estimates, a PHEV-40 is US$5,377 more expensive than a conventional internal combustion engine, while a battery electric vehicle (BEV) is US$4,819 more expensive. The study also examined how this balance will change over the next 10 to 20 years, assuming that battery costs will decrease while gasoline prices increase. Under the future scenarios considered, the study found that BEVs will be significantly less expensive than conventional cars (US$1,155 to US$7,181 cheaper), while PHEVs, will be more expensive than BEVs in almost all comparison scenarios, and only less expensive than conventional cars in a scenario with very low battery costs and high gasoline prices. BEVs are simpler to build and do not use liquid fuel, while PHEVs have more complicated powertrains and still have gasoline-powered engines. 
Lithium iron phosphate batteries from Valence Technologies were used in the first plug-in hybrids from CalCars. They are providing a conversion for the Toyota Prius priced at US$12,000. Hymotion also offers a conversion for US$10,000 but their conversion is only 5 kW where Oemtek's is 9 kW.
Recharging outside home garages
Many authors have assumed that plug-in recharging will take place overnight at home. However, residents of cities, apartments, dormitories, and townhouses might not have garages or driveways with available power outlets, and they might be less likely to buy plug-ins unless recharging infrastructure is developed.  Electrical outlets or charging stations near their places of residence, or in commercial or public parking lots or streets or workplaces are required for these potential users to gain the full advantage of PHEVs.  Even house dwellers might need to charge at the office or to take advantage of opportunity charging at shopping centers. However, this infrastructure is not in place today and it will require investments by both the private and public sectors.
Several cities in California and Oregon, and particularly San Francisco and other cities in the San Francisco Bay Area and Silicon Valley, as well as some local private firms such as Google and Adobe Systems, already have deployed charging stations and have expansion plans to attend both plug-ins and all-electric cars. In Google's case, its Mountain View campus has 100 available charging stations for its share-use fleet of converted plug-ins available to its employees.  Solar panels are used to generate the electricity, and this pilot program is being monitored on a daily basis, with performance results published on the RechargeIT website. 
Emissions shifted to electric plants
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.
According to a 2009 study by The National Academy of Science, "Electric vehicles and grid-dependent (plug-in) hybrid vehicles showed somewhat higher nonclimate damages than many other technologies."  Efficiency of plug-in hybrids is also impacted by the overall efficiency of electric power transmission. Transmission and distribution losses in the USA were estimated at 7.2% in 1995  and 6.5% in 2007.  By life cycle analysis of air pollution emissions, natural gas vehicles are currently the lowest emitter.
Tiered rate structure for electric bills
Electric utility companies generally do not use flat rate pricing. For example, Pacific Gas and Electric (PG&E) normally charges $0.10 per kilowatt hour (kW·h) for the base tier, but additional tiers are priced as high as $0.30 per kW·h to customers without electric vehicles.   Some utilities offer electric vehicle users a rate tariff that provides discounts for off-peak usage, such as overnight recharging. PG&E offers a special, discounted rate for plug-in and other electric vehicle customers, the "Experimental Time-of-Use Low Emission Vehicle rate."  That tariff gives people much cheaper rates if they charge at night, especially during the summer months.
The additional electrical utilization required to recharge the plug-in vehicles could push many households in areas that do not have off-peak tariffs into the higher priced tier and negate financial benefits.  Without an off-peak charging tariff, one study of a certain PHEV-20 model having an all-electric range of 20 miles, gasoline-fueled efficiency of 52.7 mi/gal U.S., and all-electric efficiency of 4 mi/kW·h, found that household electricity customers who consumed 131%–200% of baseline electricity at $0.220/(kW·h) would see benefits if gasoline was priced above US$2.89/US gal; those that consumed 201%–300% of baseline electricity at $0.303/(kW·h) would only see benefits if gas was priced above $3.98; and households consuming over 300% of baseline electricity at $0.346/(kW·h) would only see benefits if gasoline was priced above $4.55 (USD/gal).  Off-peak tariff rates can lower the break-even point. The PG&E tariff would change those break-even gasoline prices to US$1.96, $3.17 and $3.80 per gallon, respectively, for the given PHEV and usage pattern in question.
Customers under such tariffs could see significant savings by being careful about when the vehicle was charged, for example, by using a timer to restrict charging to off-peak hours. Thus, an accurate comparison of the benefit requires each household to evaluate its current electrical usage tier and tariffs weighed against the cost of gasoline and the actual observed operational cost of electric mode vehicle operation.
Lithium availability and supply security
Current technology for plug-ins is based on the lithium-ion battery and an electric motor, and the demand for lithium, heavy metals and other rare elements (such as neodymium, boron and cobalt) required for the batteries and powertrain is expected to grow significantly due to the incoming market entrance of plug-ins and electric vehicles in the mid and long term. Some of the largest world reserves of lithium and other rare metals are located in countries with strong resource nationalism, unstable governments or hostile to U.S. interests, raising concerns about the risk of replacing dependence on foreign oil with a new dependence on hostile countries to supply strategic materials.   Even though the metals used in electric vehicle batteries are rare, they can be recycled. 
Currently, the main deposits of lithium are found in China and South America throughout the Andes mountain chain. In 2008 Chile was the leading lithium metal producer, followed by Australia, China, and Argentina.  In the United States lithium is recovered from brine pools in Nevada.  Nearly half the world's known reserves are located in Bolivia, and according to the US Geological Survey, Bolivia's Salar de Uyuni desert has 5.4 million tons of lithium, which can be used to make lithium batteries for hybrid and electric vehicles.  Other important reserves are located in Chile, China, and Brazil.  Regarding rare earth elements, most reserves are located in China, which controls the world market for these elements. 
Hazard to pedestrians
At low speeds, electric-drive cars produced less roadway noise as compared to vehicles propelled by internal combustion engines. Blind people or the visually impaired consider the noise of combustion engines a helpful aid while crossing streets, hence plug-in electric cars and hybrids could pose an unexpected hazard.   Tests have shown that this is a valid concern, as vehicles operating in electric mode can be particularly hard to hear below 20 mph (30 km/h) for all types of road users and not only the visually impaired. At higher speeds, the sound created by tire friction and the air displaced by the vehicle start to make sufficient audible noise. 
The Government of Japan, the U.S. Congress, and the European Parliament passed legislation to regulate the minimum level of sound for hybrids and plug-in electric vehicles when operating in electric mode, so that blind people and other pedestrians and cyclists can hear them coming and detect from which direction they are approaching.     As of March 2013, most of the hybrids and plug-in electric cars available in the United States make warning noises using a speaker system. 
Greenhouse gas emissions
The effect of PHEVs on greenhouse emissions is complex. Plug-in hybrid vehicles operating on all-electric mode do not emit harmful tailpipe pollutants from the onboard source of power. The clean air benefit is usually local because depending on the source of the electricity used to recharge the batteries, air pollutant emissions are shifted to the location of the generation plants. In the same way, PHEVs do not emit greenhouse gases from the onboard source of power, but from the point of view of a well-to-wheel assessment, the extent of the benefit also depends on the fuel and technology used for electricity generation. From the perspective of a full life cycle analysis, the electricity used to recharge the batteries must be generated from renewable or clean sources such as wind, solar, hydroelectric, or nuclear power for PEVs to have almost none or zero well-to-wheel emissions.  On the other hand, when PEVs are recharged from coal -fired plants, they usually produce slightly more greenhouse gas emissions than internal combustion engine vehicles. In the case of plug-in hybrid electric vehicle when operating in hybrid mode with assistance of the internal combustion engine, tailpipe and greenhouse emissions are lower in comparison to conventional cars because of their higher fuel economy. 
There has been much debate over the potential GHG emissions reductions that can be achieved with PHEV. A study by the Electric Power Research Institute reports that a 338 TW·h or 5.8% increase in power generation needed as a result of PHEV. In the same report the EPRI also states that CO 2 emissions could increase by 430 million metric tons. The article concludes:
- " In summary, the addition of PHEVs as a significant transportation option adds approximately 6% to the total national electricity demand in 2030 compared to the base case with no PHEVs. Due to the charging profile that results in most of this additional demand occurring during off-peak hours (late night/early morning) there is an increase in the need for baseload generation. The addition of coal-fired generation to meet this need for more baseload generation does not result in any significant differences in annual emissions of SO 2 , NO x and Hg because of the caps on those pollutants. Therefore, any reductions in emissions of SO 2 , NO x or Hg from non-electric generating sources would result in a net national decline in these emissions. However, it does result in an appreciable increase in CO 2 and PM emissions as this analysis has not assumed any limits on CO 2 or PM emissions ."
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 US electrical grid.  The ACEEE study also predicts that in areas where more than 80% of grid-power comes from coal-burning power plants, local net CO 2 emissions will increase,  while for PHEVs recharged in areas where the grid is fed by power sources with lower CO 2 emissions than the current average, net CO 2 emissions associated with PHEVs will decrease correspondingly.
A 2007 joint study by the Electric Power Research Institute (EPRI) and the Natural Resources Defense Council (NRDC) similarly found that the introduction of PHEVs into America’s consumer vehicle fleet could achieve significant greenhouse gas emission reductions. The EPRI-NRDC report estimates that, between 2010 and 2050, a shift toward PHEV use could reduce GHG emissions by 3.4 to 10.4 billion metric tons. The magnitude of these reductions would ultimately depend on the level of PHEV market penetration and the carbon intensity of the US electricity sector. In general, PHEVs can be viewed as an element in the " Pacala and Socolow wedges" approach which shows a way to stabilize CO 2 emissions using a portfolio of existing techniques, including efficient vehicles.
A 2008 study at Duke University suggests that for PHEV's to reduce greenhouse gas emissions more than hybrids a carbon pricing signal that encourages the development of low carbon power is needed.  RAND also in 2008 studied the questions of a carbon tax, carbon cap and trade systems, increasing gasoline tax, and providing renewable energy subsidies under various economic conditions and vehicle type availabilities. RAND found that subsidies were able to provide a smoother transition to new energy sources, especially in the face of energy source price volatility, because subsidies can be structured according to relative costs between renewables and fossil fuel, while taxes and carbon trading schemes alone do not take relative prices of energy into account. 
The Minnesota Pollution Control Agency found that if Minnesota's fleet of vehicles making lengthy trips were replaced by plug-in hybrids, CO 2 emissions per vehicle would likely decrease. However, unless more than 40% of the electricity used to charge the vehicles were to come from non-polluting sources, replacing the vehicles with non-plug-in hybrids would engender a larger decrease in CO 2 emissions.  Plug-in hybrids use less fuel in all cases, and produce much less carbon dioxide in short commuter trips, which is how most vehicles are used. The difference is such that overall carbon emissions would decrease if all internal combustion vehicles were converted to plug-ins.
A study by Kantor, Fowler, Hajimiragha, and ElKamel shows that fuel cell plug-in hybrid vehicles achieve twice as much reduction in greenhouse gas emissions than PHEVs and FCVs. The study uses the transportation sector in Ontario Canada as a case study, with the maximum allowable number of vehicles being that which can be supported by the electric grid. 
Argonne National Laboratory
In 2009 researchers at Argonne National Laboratory adapted their GREET model to conduct a full well-to-wheels (WTW) analysis of energy use and greenhouse gas (GHG) emissions of plug-in hybrid electric vehicles for several scenarios, considering different on-board fuels and different sources of electricity generation for recharging the vehicle batteries. Three US regions were selected for the analysis, California, New York, and Illinois, as these regions include major metropolitan areas with significant variations in their energy generation mixes. The full cycle analysis results were also reported for the US generation mix and renewable electricity to examine cases of average and clean mixes, respectively  This 2009 study showed a wide spread of petroleum use and GHG emissions among the different fuel production technologies and grid generation mixes. The following table summarizes the main results: 
|PHEV well-to-wheels Petroleum energy use and greenhouse gas emissions for an all-electric range between 10 and 40 miles (16 and 64 km) with different on-board fuels. (1) (as a % relative to an internal combustion engine vehicle that uses fossil fuel gasoline)|
|Analysis||Reformulated gasoline and Ultra-low sulfur diesel||E85 fuel from corn and switchgrass||Fuel cell hydrogen|
|Petroleum energy use reduction|| || || |
|GHG emissions reduction (2)|| || || |
|Source: Center for Transportation Research, Argonne National Laboratory (2009). See Table 1.  Notes: (1) Simulations for year 2020 with PHEV model year 2015. (2) No direct or indirect land use changes included in the WTW analysis for bio-mass fuel feedstocks.  |
The Argonne study found that PHEVs offered reductions in petroleum energy use as compared with regular hybrid electric vehicles. More petroleum energy savings and also more GHG emissions reductions were realized as the all-electric range increased, except when electricity used to recharged was dominated by coal or oil-fired power generation. As expected, electricity from renewable sources realized the largest reductions in petroleum energy use and GHG emissions for all PHEVs as the all-electric range increased. The study also concluded that plug-in vehicles that employ biomass-based fuels (biomass-E85 and -hydrogen) may not realize GHG emissions benefits over regular hybrids if power generation is dominated by fossil sources. 
Oak Ridge National Laboratory
A 2008 study by researchers at Oak Ridge National Laboratory analyzed oil use and greenhouse gas (GHG) emissions of plug-in hybrids relative to hybrid electric vehicles under several scenarios for years 2020 and 2030. Each type of vehicle was assumed to run 20 miles (32 km) per day and the HEV was assumed to have a fuel economy of 40 miles per US gallon (5.9 L/100 km; 48 mpg ‑imp ).  The study considered the mix of power sources for 13 U.S. regions, generally a combination of coal, natural gas and nuclear energy, and to a lesser extend renewable energy.   A 2010 study conducted at Argonne National Laboratory reached similar findings, concluding that PHEVs will reduce oil consumption but could produce very different greenhouse gas emissions for each region depending on the energy mix used to generate the electricity to recharge the plug-in hybrids.   The following table summarizes the main results of the Oak Ridge National Laboratory study for the 2020 scenario:
|Comparison of carbon emissions and oil consumption by plug-in hybrids relative to hybrid electric vehicles (HEVs) by U.S. regional power generation sources on 2020 |
|Region (1)||Main electricity sources||Share total generation 2020||Carbon emissions relative to HEVs||Oil consumption relative to HEVs||States included in the region (2)|
|Plug-in hybrid||All-electric mode||Plug-in hybrid||All-electric mode|
|Northwest||Natural gas Nuclear||84.3% 15.7%||−20.0%||−37.2%||−47.0%||−99.6%||Includes ID, MT, NV, OR, UT, SD, WA, and WY.|
|California||Natural gas Renewable||99.0% 1.0%||−15.3%||−26.5%||−47.0%||−99.6%|
|Florida||Natural gas Oil||96.1% 2.4%||−14.8%||−25.3%||−45.6%||−96.4%|
|New England||Natural gas Coal||70.3% 15.5%||−11.4%||−17.4%||−44.3%||−93.5%||Includes CT, MA, ME, NH, RI, and VT.|
|Lower Midwest||Natural gas Coal||88.6% 11.4%||−11.0%||−16.4%||−46.9%||−99.4%||Includes AR, KS, LA, NM, OK, and TX.|
|Southwest||Natural gas Coal||83.6% 16.1%||−9.40%||−12.8%||−46.9%||−99.4%||Includes AZ, CO, NM, NV, and TX.|
|Mid-Atlantic||Natural gas DC, DE, MD, ME, NJ, and PA.|
|Upper Midwest||Natural gas Coal||47.6% 46.0%||−0.8%||+7.2%||−46.7%||−99.0%||Includes IA, MN, MT, ND, NE, SD, and WI.|
|Southeast||Coal Natural gas||51.9% 44.9%||+2.4%||+14.4%||−46.7%||−98.9%||Includes AL, GA, LA, MS, NC, SC, and TN.|
|New York||Oil Natural gas||67.2% 29.4%||+4.3%||+19.0%||−8.6%||−10.9%|
|Greater Ohio||Coal Natural gas||65.7% 32.8%||+7.8%||+27.0%||−46.6%||−98.7%||Includes IN, KY, MI, OH, VA, and WV.|
|Greater Illinois||Coal Natural gas||75.4% 24.6%||+11.7%||+36.0%||−46.5%||−98.6%||Includes IA, IL, MI, MO, and WI.|
|Notes: (1) Regions as defined by the North American Electric Reliability Corporation. (2) Some states appear in more than one region because parts of them belong to different regions.|
Environmental Protection Agency
In October 2014, the U.S. Environmental Protection Agency published the 2014 edition of its annual report " Light-Duty Automotive Technology, Carbon Dioxide Emissions, and Fuel Economy Trends ." For the first time, the report presents an analysis of the impact of alternative fuel vehicles, with emphasis in plug-in electric vehicles because as their market share is approaching 1%, PEVs began to have a measurable impact on the U.S. overall new vehicle fuel economy and CO 2 emissions.  
EPA's report included the analysis of 12 all-electric passengers cars and 10 plug-in hybrids available in the market as model year 2014. For purposes of an accurate estimation of emissions, the analysis took into consideration the differences in operation between those PHEVs like the Chevrolet Volt that can operate in all-electric mode without using gasoline, and those that operate in a blended mode like the Toyota Prius PHV, which uses both energy stored in the battery and energy from the gasoline tank to propel the vehicle, but that can deliver substantial all-electric driving in blended mode. In addition, since the all-electric range of plug-in hybrids depends on the size of the battery pack, the analysis introduced a utility factor as a projection, on average, of the percentage of miles that will be driven using electricity (in electric only and blended modes) by an average driver. The following table shows the overall EV/hybrid fuel economy expressed in terms of miles per gallon gasoline equivalent (mpg-e) and the utility factor for the ten MY2014 plug-in hybrids available in the U.S. market. The study used the utility factor (since in pure EV mode there are no tailpipe emissions) and the EPA best estimate of the CO 2 tailpipe emissions produced by these vehicles in real world city and highway operation based on the EPA 5-cycle label methodology, using a weighted 55% city/45% highway driving. The results are shown in the following table. 
In addition, the EPA accounted for the upstream CO 2 emissions associated with the production and distribution of electricity required to charge the PHEVs. Since electricity production in the United States varies significantly from region to region, the EPA considered three scenarios/ranges with the low end of the range corresponding to the California powerplant emissions factor, the middle of the range represented by the national average powerplant emissions factor, and the upper end of the range corresponding to the powerplant emissions factor for the Rockies. The EPA estimates that the electricity GHG emission factors for various regions of the country vary from 346 g CO2/kW-hr in California to 986 g CO2/kW-hr in the Rockies, with a national average of 648 g CO2/kW-hr.  The following table shows the tailpipe emissions and the combined tailpipe and upstream emissions for each of the 10 MY 2014 PHEVs available in the U.S. market.
|Comparison of tailpipe and upstream CO 2 emissions (1) estimated by EPA for the MY 2014 plug-in hybrids available in the U.S. market as of September 2014 |
|Vehicle||EPA rating combined EV/hybrid (mpg-e)||Utility factor (2) (share EV miles)||Tailpipe CO 2 (g/mi)||Tailpipe + Total Upstream CO2|
|Low (g/mi)||Avg (g/mi)||High (g/mi)|
|BMW i3 REx (3)||88||0.83||40||134||207||288|
|Ford C-Max Energi||51||0.45||129||219||269||326|
|Ford Fusion Energi||51||0.45||129||219||269||326|
|Honda Accord Plug-in Hybrid||57||0.33||130||196||225||257|
|Toyota Prius Plug-in Hybrid||58||0.29||133||195||221||249|
|Porsche Panamera S E-Hybrid||31||0.39||206||328||389||457|
|Average gasoline car||24.2||0||367||400||400||400|
|Notes: (1) Based on 45% highway and 55% city driving. (2) The utility factor represents, on average, the percentage of miles that will be driven using electricity (in electric only and blended modes) by an average driver. (3) The EPA classifies the i3 REx as a series plug-in hybrid  |
National Bureau of Economic Research
Most emission analysis use average emissions rates across regions instead of marginal generation at different times of the day. The former approach does not take into account the generation mix within interconnected electricity markets and shifting load profiles throughout the day.  An analysis by three economist affiliated with the National Bureau of Economic Research (NBER), published in November 2014, developed a methodology to estimate marginal emissions of electricity demand that vary by location and time of day across the United States. The study used emissions and consumption data for 2007 through 2009, and used the specifications for the Chevrolet Volt (all-electric range of 35 mi (56 km)). The analysis found that marginal emission rates are more than three times as large in the Upper Midwest compared to the Western U.S., and within regions, rates for some hours of the day are more than twice those for others. Applying the results of the marginal analysis to plug-in electric vehicles, the NBER researchers found that the emissions of charging PEVs vary by region and hours of the day. In some regions, such as the Western U.S. and Texas, CO 2 emissions per mile from driving PEVs are less than those from driving a hybrid car. However, in other regions, such as the Upper Midwest, charging during the recommended hours of midnight to 4 a.m. implies that PEVs generate more emissions per mile than the average car currently on the road. The results show a fundamental tension between electricity load management and environmental goals as the hours when electricity is the least expensive to produce tend to be the hours with the greatest emissions. This occurs because coal-fired units, which have higher emission rates, are most commonly used to meet base-level and off-peak electricity demand; while natural gas units, which have relatively low emissions rates, are often brought online to meet peak demand. This pattern of fuel shifting explains why emission rates tend to be higher at night and lower during periods of peak demand in the morning and evening.
Production and sales
Since 2008, plug-in hybrids have been commercially available from both specialty manufacturers and from main-stream producers of internal combutsion engine vehicles.
Sales and main markets
As of December 2015, the global stock of highway-capable plug-in hybrid electric cars totaled 517,100 units, out of total cumulative global sales of 1.257 million light-duty plug-in electric vehicles (41.1%). The global ratio between all-electrics (BEVs) and plug-in hybrids (PHEVs) has consistently been 60:40 between 2014 and the first half of 2016, mainly due to the large all-electric market in China. In the U.S. and Europe, the ratio is approaching a 50:50 split. 
Global sales of plug-in hybrids grew from over 300 units in 2010 to almost 9,000 in 2011, jumped to over 60,000 in 2012, and reached almost 222,000 in 2015.  As of December 2015, the United States was the world's largest plug-in hybrid car market with a stock of 193,770 units, followed by China with 86,580 vehicles, the Netherlands with 78,160, Japan with 55,470 units, and the UK with 28,250.  About 279,000 light-duty plug-in hybrids were sold in 2016,  raising the global stock to almost 800,000 highway legal plug-in hybrid electric cars, out of over 2 million light-duty plug-in electric cars on the world roads at the end of 2016.  
The Netherlands, Sweden, the UK, and the United States have the largest shares of plug-in hybrid sales as percentage of total plug-in electric passenger vehicle sales. The Netherlands has the world's largest share of plug-in hybrids among its plug-in electric passenger car stock, with 86,162 plug-in hybrids registered at the end of October 2016, out of 99,945 plug-in electric cars and vans, representing 86.2% of the country's stock of light-duty plug-in electric vehicles.  Sweden ranks next with 16,978 plug-in hybrid cars sold between 2011 and August 2016, representing 71.7% of total plug-in electric passenger car sales registrations.      Plug-in hybrid registrations in the UK between up to August 2016 totaled 45,130 units representing 61.6% of total plug-in car registrations since 2011.     In the United States, plug-in hybrids represent 47.2% of the 506,450 plug-in electric cars sold between 2008 and August 2016. 
In November 2013 the Netherlands became the first country where a plug-in hybrid topped the monthly ranking of new car sales. During November sales were led by the Mitsubishi Outlander P-HEV with 2,736 units, capturing a market share of 6.8% of new passenger cars sold that month.  Again in December 2013 the Outlander P-HEV ranked as the top selling new car in the country with 4,976 units, representing a 12.6% market share of new car sales.   These record sales allowed the Netherlands to become the second country, after Norway, where plug-in electric cars have topped the monthly ranking of new car sales.   As of December 2013, the Netherlands was the country with highest plug-in hybrid market concentration, with 1.45 vehicles registered per 1,000 people. Most of the initial growth of the Dutch plug-in hybrid stock took place in 2013, with 20,164 units sold that year representing a rate of growth of 365% from 2012.   Another surge in plug-in hybrid sales took place in 2015, particularly during the last two months, with 41,226 plug-in hybrids registered in 2015.  
The dominance of plug-in hybrids in the Netherlands is reflected by the fact that, since their inception in 2011 up until October 2016, five out of the top six registered plug-in electric models are plug-in hybrids. As of 31 October 2016, among all plug-in passenger car registered in the Netherlands, the Mitsubishi Outlander P-HEV leads registrations (24,825), followed by the Volvo V60 Plug-in Hybrid (15,015), the Volkswagen Golf GTE (9,710), the Tesla Model S all-electric car (5,681), the Audi A3 Sportback e-tron (5,227), and the Mercedes-Benz C 350 e (5,092).  
The following table presents the top ranking countries according to its plug-in hybrid segment market share of total new car sales in 2013:
|Top 10 countries by plug-in hybrid market share of new car sales in 2013 |
|Ranking||Country||PHEV market share (1) (%)||Ranking||Country||PHEV market share (1) (%)|
The following table presents the top selling plug-in hybrid models with global sales of around or over 15,000 units since the introduction of the first modern production plug-in hybrid vehicle in December 2008, and summarizes sales in the top selling countries for each model through December 2015:
|Global sales of top selling highway-capable plug-in hybrids and top markets by country or region between December 2008 and December 2015|
|Model/ All-electric range||Market launch||Global sales||Top selling markets|
|Chevrolet Volt/ Opel Ampera/ Vauxhall Ampera 35 mi (56 km)||December 2010||Over 106,000||Global sales through December 2015,  including about 10,000 Amperas sold in Europe. |
|US||88,750||Chevrolet Volts through December 2015. |
|Netherlands||6,096||5,031 Amperas and 1,065 Volts registered by the end December 2015.   |
|Canada||5,415||Volts sold through December 2015. |
Government support and public deployment
Subsidies and economic incentives
Several countries have established grants and tax credits for the purchase of new plug-in electric vehicles (PEVs) including plug-in hybrid electric vehicles, and usually the economic incentive depends on battery size. The U.S. offers a federal income tax credit up to US$7,500, and several states have additional incentives.  The UK offers a Plug-in Car Grant up to a maximum of GB£5,000 (US$7,600 ).   As of April 2011, 15 of the 27 European Union member states provide tax incentives for electrically chargeable vehicles, which includes all Western European countries plus the Czech Republic and Romania. Also 17 countries levy carbon dioxide related taxes on passenger cars as a disincentive. The incentives consist of tax reductions and exemptions, as well as of bonus payments for buyers of all-electric and plug-in hybrid vehicles, hybrid vehicles, and some alternative fuel vehicles. 
Other government support
- United States
Incentives for the development of PHEVs are included in the Energy Independence and Security Act of 2007.  The Energy Improvement and Extension Act of 2008, signed into law on October 3, 2008, grants a tax credits for the purchase of PHEVs. President Barack Obama's New Energy for America calls for deployment of 1 million plug-in hybrid vehicles by 2015,  and on March 19, 2009, he announced programs directing $2.4 billion to electric vehicle development.
The American Recovery and Reinvestment Act of 2009 modifies the tax credits, including a new one for plug-in electric drive conversion kits and for 2 or 3 wheel vehicles. The ultimate total included in the Act that is going to PHEVs is over $6 billion.
In March 2009, as part of the American Recovery and Reinvestment Act, the US Department of Energy announced the release of two competitive solicitations for up to $2 billion in federal funding for competitively awarded cost-shared agreements for manufacturing of advanced batteries and related drive components as well as up to $400 million for transportation electrification demonstration and deployment projects. This announcement will also help meet the President Barack Obama's goal of putting one million plug-in hybrid vehicles on the road by 2015.
Public deployments also include:
- USDOE's FreedomCAR. US Department of Energy announced it would dole out $30 million in funding to three companies over three years to further the development of plug-in hybrids
- USDOE announced the selection of Navistar Corporation for a cost-shared award of up to $10 million to develop, test, and deploy plug-in hybrid electric (PHEV) school buses.
- DOE and Sweden have a MOU to advance market integration of plug-in hybrid vehicles
- PHEV Research Center
- San Francisco Mayor Gavin Newsom, San Jose Mayor Chuck Reed and Oakland, California Mayor Ron Dellums announced a nine-step policy plan for transforming the Bay Area into the "Electric Vehicle (EV) Capital of the U.S."  and of the world  There are partnerships with Coulomb, Better Place and others are also advancing. The first charging stations went up in San Jose  (more information in Plug-in hybrids in California).
- Washington State PHEV Pilot Project 
- Texas Governor Rick Perry's proposal for a state $5,000 tax credit for PHEVs in "non-attainment" communities
- Seattle, that includes City's public fleet converted vehicles, the Port of Seattle, King County and the Puget Sound Clean Air Agency 
GM's roadmap for plug-in ready communities includes: consumer incentives to make this early technology more affordable; public and workplace charging infrastructure; consumer-friendly electricity rates and renewable electricity options; government and corporate vehicle purchases; supportive permitting and codes for vehicle charging; and other incentives such as high-occupancy-vehicle (HOV) lanes access 
- European Union
Electrification of transport (electromobility) is a priority in the European Union Research Programme. It also figures prominently in the European Economic Recovery Plan presented November 2008, in the frame of the Green Car Initiative. DG TREN will support a large European "electromobility" project on electric vehicles and related infrastructure with a total budget of around €50 million as part of the Green Car Initiative. 
Organizations that support plug-in hybrids include the World Wide Fund for Nature, its International Director General James Leape remarked, "the cars of the future ... should, increasingly, be powered by electricity." 
CalCars (with their and) is dedicated only to the PHEV and has proposed a Prepayment Plan, where buyers would pay $1,000 to reserve a plug-in car and the federal government would match each payment with $9,000, all of which would go to carmakers.  CalCars is also promoting public funds for conversion of internal combustion engines to plug-in vehicles. 
Other supportive organizations are Plug In America, the Alliance for Climate Protection, Friends of the Earth, the Rainforest Action Network, Rocky Mountain Institute (Project Get Ready),  the San Francisco Bay Area Council,  the Apollo Alliance, the Set America Free Coalition, the Silicon Valley Leadership Group, and the Plug-in Hybrid Electric School Bus Project, 
FPL and Duke Energy has said that by 2020 all new purchases of fleet vehicles will be plug-in hybrid or all-electric. 
NiMH battery patent encumbrance
( Nickel–metal hydride batteries) suitable for use in PHEVs are tightly patented and were not licensed for use by PHEV manufacturers, thereby slowed the development of electric cars and PHEVs before the 2008 Oil Crisis.  
- Advanced Technology Vehicles Manufacturing Loan Program
- Electric transportation technology
- Electric TM4
- Fuel economy-maximizing behaviors
- Genset trailer
- Glossary of automotive design
- Green vehicle
- History of the electric vehicle
- Inductive charging
- New energy vehicles in China
- Plug In America
- Plug-in electric vehicle (PEV)
- Plug-in hybrids in California
- Plug-in hybrids in New York
- Plug-in Hybrid Electric Vehicle Research Center