Plug-in hybrid

Hybrids Plus plug-in hybrid Toyota Prius conversion with PHEV-30 (30 mile or 48 km all-electric range) battery packs

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

The cost for electricity to power plug-in hybrids for all-electric operation has been estimated at less than one quarter of the cost of gasoline.[1] Compared to conventional vehicles, PHEVs can reduce air pollution, dependence on petroleum, and greenhouse gas emissions that contribute to global warming. Plug-in hybrids use no fossil fuel during their all-electric range if their batteries are charged from nuclear or renewable energy sources. Other benefits include improved national energy security, fewer fill-ups at the filling station, the convenience of home recharging, opportunities to provide emergency backup power in the home, and vehicle to grid applications.[2]

As of September 2008, production plug-in hybrid passenger vehicles are not yet for sale. However, Toyota,[3] General Motors,[4] Ford,[5] Chinese automaker BYD Auto,[6] California startups Fisker Automotive[7] and Aptera Motors,[8] and Volkswagen[9] have announced their intention to introduce production PHEV automobiles. BYD's PHEV-60 F3DM hatchback is expected to be available in China by November, 2008,[10] with the BYD F6DM sedan soon to follow. The PHEV-6 Toyota Prius will be offered beginning with commercial fleets in 2009.[11][12] The luxury Fisker Karma PHEV-50 sports car is slated for late 2009, and GM's PHEV-40 Chevrolet Volt and Saturn Vue and the Volkswagen Golf PHEV50km plug-ins are expected in 2010.[13][14] Conversion kits and services are available to convert production model hybrid vehicles to plug-ins.[15][16] Most PHEVs on the road in the U.S. are conversions of 2004 or later Toyota Prius models, which have had plug-in charging added and their electric-only range extended.

On October 3, 2008, the U.S. enacted the Energy Improvement and Extension Act of 2008 as part of the bailout of the U.S. financial system. The law provides tax credits for purchases of plug-in hybrid vehicles until less than a year after the first 250,000 are sold, worth $2,500 plus $417 for each kilowatt-hour of battery capacity over 4 kilowatt-hours, up to $7,500 for cars under 10,000 pounds (4536 kg), or more for larger vehicles.[17][18]

Contents

Terminology

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 without using its internal combustion engine, or about 32 kilometers, so it may also be designated as a PHEV32km.[19]

Graphic car big plug.jpg

The Energy Independence and Security Act of 2007 defines a plug-in electric drive vehicle as a vehicle that:

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

The Institute of Electrical and Electronics Engineers (IEEE) defines PHEVs similarly, but also requires that the hybrid electric vehicle can drive at least ten miles (16 km) in all-electric mode (PHEV-10 / PHEV16km), while consuming no gasoline or diesel fuel.[20]

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.[21]

History

For more details on this topic, see History of plug-in hybrids.

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

The July 1969 issue of Popular Science featured an article on the General Motors XP-883 plug-in hybrid. The concept commuter vehicle housed six 12-volt lead-acid batteries in the trunk area and a transverse-mounted DC electric motor turning a front-wheel drive.[22] The car could be plugged into a standard North American 120 volt AC outlet for recharging.

In 2003, Renault began selling the Elect'road, a plug-in series hybrid version of their popular Kangoo, in Europe. It was sold alongside Renault's "Electri'cite" electric-drive Kangoo battery electric van. The Elect'road had a 150 km (93 mi) range using a nickel-cadmium battery pack and a 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.[23] 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 litres (2.6 US 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.[24] 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,[23] the Elect'road was redesigned in 2007.

Lithium-ion battery pack, with cover removed, in a CalCars "PRIUS+" plug-in hybrid converted Toyota Prius converted by EnergyCS

In September 2004, the California Cars Initiative (CalCars) converted a 2004 Toyota Prius into a prototype of what it called the PRIUS+. With the addition of 130 kg (300 lb) of lead-acid batteries, the PRIUS+ achieved roughly double the fuel economy of a standard Prius and could make trips of up to 15 km (9 mi) using only electric power. The vehicle, which is owned by CalCars technical lead Ron Gremban, is used in daily driving, as well as a test bed for various improvements to the system.[25]

On July 18, 2006, Toyota announced that it "plans to develop a hybrid vehicle that will run locally on batteries charged by a household electrical outlet before switching over to a gasoline engine for longer hauls."[3] Toyota has said it plans to migrate to lithium-ion batteries in future hybrid models,[26] but not in the next-generation Prius, expected in fall 2008.[27] 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.[27]

On November 29, 2006, GM announced plans to introduce a production plug-in hybrid version of Saturn's Greenline Vue SUV with an all-electric range of 10 mi (16 km).[4] The model's sale is anticipated by fall 2009,[27] and GM announced in January 2007 that contracts had been awarded to two companies to design and test lithium-ion batteries for the vehicle.[28] GM has said that they plan on introducing plug-in and other hybrids "for the next several years".[4]

In January 2007, GM unveiled the Chevrolet Volt, which is expected to initially feature a plug-in capable, battery-dominant series hybrid architecture which they are calling E-Flex.[29] 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.[30] General Motors presented the Volt as a PHEV-40 that starts its engine when 40% of the battery charge remains, and which can achieve a fuel economy of 50 miles per US gallon (21 km/l/60 mpg-imp), even if the vehicle's batteries are not charged.[31]

On July 9, 2007, Ford Motor Company CEO Alan Mulally said he expects Ford to sell plug-in hybrids in five to ten years, the launch date depending on advances in lithium-ion battery technology. Ford will provide Southern California Edison with 20 Ford Escape Hybrid sport utility vehicles reconfigured to work as plug-ins by 2009, with the first by the end of 2007.[5]

On July 25, 2007, Japan's Ministry of Land, Infrastructure and Transport certified Toyota's plug-in hybrid for use on public roads, making it the first automobile to attain such approval. Toyota plans to conduct road tests to verify its all-electric range. The plug-in Prius was said to have an all-electric range of 13 km (8 mi).[32] But later prototypes shown at the 2008 Paris Auto Show had an electric-only range of "just a little over six miles."[33]

On August 9, 2007, General Motors vice-president Robert Lutz announced that GM is on track for Chevrolet Volt road testing in 2008 and production to begin by 2010. Announcing an agreement with A123Systems, Lutz said GM would like to have their planned Saturn Vue plug-in on the roads by 2009.[14] The Volt has an all-electric range of 40 mi (64 km).

On September 5, 2007, Quantum Technologies[34] and Fisker Coachbuild, LLC announced the launch of a joint venture in Fisker Automotive.[35] Fisker intends to build a US$ 80,000 luxury PHEV-50, the Fisker Karma, anticipated in late 2009.[7]

In September 2007, Aptera Motors announced their Typ-1 two-seater. They plan to produce both an electric Typ-1e and a plug-in hybrid Typ-1h with a common three-wheeled, composite body design. As of May 2008, over two thousand pre-orders have been accepted, and production is expected to begin in late 2008.[8]

On October 9, 2007, Chinese manufacturer BYD Automobile Company (which is owned by China's largest mobile phone battery maker) announced that it would be introducing a production PHEV-60 sedan in China in the second half of 2008. BYD 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 batterys - LiFeP04 - based batteries instead of lithium-ion, and can be recharged to 70% of capacity in just 10 minutes.[6]

On October 27, 2007, Venture Vehicles announced it would produce two versions of the three-wheeled VentureOne, an electric model with a range of 120 miles, and a 100 mpg PHEV version.

In January 2008, a privately-run waiting list to purchase the Chevy Volt reached 10,000 members. The list, administered by Lyle Dennis, was started one year prior.[36] Dr. Yi Cui and colleagues at Stanford University's Department of Materials Science and Engineering [37] have made a discovery to use silicon nanowires to give rechargeable lithium ion batteries 10 times more charge.[38][39] On January 7, 2008, Bob Lutz, the Vice Chairman of General Motors said, "The electrification of the automobile is inevitable".[40] On January 14, 2008, Toyota announced they would start sales of lithium-ion battery PHEVs by 2010.[41][42][43]

On March 27, 2008, the California Air Resources Board modified their regulations, requiring automobile manufacturers to produce 58,000 plug-in hybrids during 2012 through 2014.[44] This requirement is an asked-for alternative to an earlier mandate to produce 25,000 pure zero emission vehicles, reducing that requirement to 5,000.[45]

On June 26, 2008, Volkswagen announced that they would be introducing production plug-ins based on the Golf compact. Volkswagen uses the term 'TwinDrive' to denote a PHEV.[9]

In September 2008, Mazda was reported to be planning PHEVs.[46] On September 23, 2008, 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 in to production.[47][48][49][50]

On October 3rd, 2008, the U.S. Congress passed the Energy Improvement and Extension Act of 2008 as part of Public Law 110-343. The legislation provides tax credits for the purchase of plug-in hybrid vehicles worth $2,500 plus $417 for each kilowatt-hour of battery capacity over 4 kilowatt-hours, up to $7,500 for cars under 10,000 pounds, $10,000 for larger vehicles under 14,000 pounds, $12,500 for bigger trucks under 26,000 pounds, or $15,000 for larger trucks and equipment. The tax credit will be phased out two calendar quarters after the first 250,000 such vehicles are sold, down to 50% for the next six months and 25% for another half year after that.[17][18]

In mid-October, 2008, the Wall Street Journal reported that BYD Auto's PHEV-60 F3DM hatchback will be available by November in China.[10] It will sell for equivalent of USD $22,000 and has a 110 km electric-mode driving range.[51]

Technology

Powertrains

For more details on this topic, see Hybrid vehicle drivetrains.
The Chevrolet Volt concept car is a series plug-in hybrid, meaning that its mechanical engine power is exclusively converted to electricity, not used directly.

PHEVs are based on the same three basic powertrain architectures as conventional electric hybrids:[52]

Series hybrids (also called extended range electric vehicles (EREV)[53]) 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 include the Renault Kangoo Elect'Road, Toyota's Japan-only Coaster light-duty passenger bus, Daimler AG's hybrid Orion bus, the Chevrolet Volt production car, the Opel Flextreme concept car, and many diesel-electric locomotives. With an appropriate balance of components this type can operate over a substantial distance with its full range of power without engaging the ICE. As is the case for other architectures, series hybrids can operate without recharging as long as there is liquid fuel in the tank.[54]

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.[55]

Series-parallel hybrids have the flexibility to operate in either series or parallel mode. Hybrid powertrains currently used by Ford, Lexus, Nissan, and Toyota, which some refer to as “series-parallel with power-split,” can operate in both series and parallel mode at the same time. As of 2007, most plug-in hybrid conversions of conventional hybrids utilize this architecture.[56]

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:[57]

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.[58]

Blended mode is a type of charge-depleting mode normally employed by vehicles which do not have enough electric power to sustain high speeds without the help of the internal combustion portion of the powertrain. A blended control strategy typically increases the distance from stored grid electricity compared to a charge-depleting strategy.[59] 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.[60] 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.

The redesigned Renault Kangoo Elect'road operates in blended mode, using engine and battery power simultaneously.

Mixed mode describes a trip in which a combination of the above modes are utilized.[61] For example, a PHEV-20 Prius conversion may begin a trip with 5 miles (8 km) of low speed charge-depleting, then get onto a freeway and operate in blended mode for 20 miles (32 km), using 10 miles (16 km) worth of all-electric range at twice the fuel economy. Finally the driver might exit the freeway and drive for another 5 miles (8 km) without the internal combustion engine until the full 20 miles (32 km) of all-electric range are exhausted. At this point the vehicle can revert back to a charge sustaining-mode for another 10 miles (16 km) until the final destination is reached. Such a trip would be considered a mixed mode, as multiple modes are employed in one trip. This contrasts with a charge-depleting trip which would be driven within the limits of a PHEV's all-electric range. Conversely, the portion of a trip which extends beyond the all-electric range of a PHEV would be driven primarily in charge-sustaining mode, as used by a conventional hybrid.

Electric power storage

Further information: Electric vehicle battery, Charging station

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.[62] Design issues and trade-offs against battery life, capacity, heat dissipation, weight, costs, and safety need to be solved.[63] Advanced battery technology is under development, promising greater energy densities by both mass and volume,[64] and battery life expectancy is expected to increase.[65]

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.[66]

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.[67] 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.[68] 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."[69]

Lithium iron phosphate (LFP) is a kind of cathode material of lithium iron phosphate batteries that is getting attention from the industry. Valence Technologies sells the only large format lithium iron phospate battery currently available. The most important merit of this battery type is safety and high-power. LiFePO4 is one of three major compounds and technology in LFP family. The other two are Nanophosphate, and NanoCocrystallineOlivine.

In France, Électricité de France (EDF) and Toyota are installing recharging points for PHEVs on roads, streets and parking lots.[70] EDF is also partnering with Elektromotive, Ltd.[71] to install 250 new charging points over six months from October 2007 in London and elsewhere in the UK.[72] Recharging points also can be installed for specific uses, as in taxi stands. Project Better Place has begun in October 2007 and is working with Renault on development of exchangeable batteries (battery swapping).[73]

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[15][74] [75]. The UltraBattery combines a supercapacitor and a 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).[76]

Conversions of production hybrids

For more details on this topic, see Electric vehicle conversion.
15 lead-acid batteries, PFC charger, and regulators installed into WhiteBird, a PHEV-10 conversion of a Toyota Prius

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

Many early plug-in hybrid electric vehicle conversions have been based on the 2004 or later model Toyota Prius.[77] Some of the systems have involved replacement of the vehicle's original NiMH battery pack and its electronic control unit. Others, such as Hymotion, the CalCars Prius+, and the PiPrius, piggyback an additional battery back onto the original battery pack, this is also referred to as Battery Range Extender Modules (BREMs).[78] Within the electric vehicle conversion community this has been referred to as a "hybrid battery pack configuration".[79] 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.[25]

EDrive Systems use Valence Technology Li-ion batteries and have a claimed 40 to 50 miles (64 to 80 km) of electric range.[80] 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).[81] 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.[74][15]

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.[82] It includes a "conversion interest" page.[83] 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.[84] of Petaluma, California offers components and assemblies to build the Prius+, the plug-in conversion invented by CalCars [85]. Their lead-acid battery box assembly form 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 in a strong welded steel enclosure with a plastic powder coat finish. That "PbA Battery Box Assembly" is also available without batteries. It provides about 10 miles (16 km) of EV mode range.[86] 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.[87] 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.[88] Poulsen Hybrid[89] is developing a conversion kit that will add through-the-road plug-in hybrid capability to conventional vehicles by externally mounting electric motors onto 2 of the wheels.[90]

Advantages

Energy resilience and petroleum displacement

Main article: Energy resilience

Each kilowatt hour of battery power used will displace up to 50 US gallons (190 l) of petroleum fuels (gasoline or diesel fuels.)[91] Also, electricity is multi-sourced and, as a result, it gives the greatest degree of energy resilience.[92]

Range anxiety elimination

PHEVs, compared with all-electric vehicles, is one method of eliminating "range anxiety" (as is the use of a generator trailer [93]), giving the confidence and peace of mind that the driver will not be stranded by a depleted battery.[94]

Fuel efficiency

Main article: Energy efficiency

Claimed fuel economy for PHEVs depends on the amount of driving between recharges. If no gasoline is used the MPG equivalent depends only on the efficiency of the electric system. A 120 km (70 mile) range PHEV-70 may annually require only about 25% as much gasoline as a similarly designed PHEV-0, depending on how it will be driven and the trips for which it will be used.[2] The furthest all-electric range in a PHEV planned for mass production is the PHEV-60 BYD F6e.

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.[58] 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.[95] 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.[96]

Greenhouse gas emissions

Main article: Greenhouse gas

Another advantage of PHEV adoption is a predicted reduction in carbon emissions. Increased drivetrain efficiency results in significant reduction of greenhouse gas emissions, even taking into account energy lost to inefficiency in the production and distribution of grid power and charging of batteries. A study by the American Council for an Energy Efficient Economy (ACEEE) predicts that, on average, a typical American driver is expected to achieve about a 15% reduction in net CO2 emissions compared to the driver of a regular hybrid, based on the 2005 distribution of power sources feeding the U.S. electrical grid.[97] The ACEEE study also predicts that in areas where more than 80% of grid-power comes from coal-burning power plants, local net CO2 emissions will increase,[97] while for PHEVs recharged in areas where the grid is fed by power sources with lower CO2 emissions than the current average, net CO2 emissions associated with PHEVs will decrease correspondingly.

A large-scale June 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.[98] 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 CO2 emissions using a portfolio of existing techniques, including efficient vehicles.

GM Vice Chairman Bob Lutz has said the Chevy Volt will emit 40 grams of carbon dioxide per kilometer. That is well below the proposed European Union emission standards of 120-130 g/km.[99]

Martin Eberhard, who co-founded pure electric vehicle maker Tesla Motors, says "if you do the math, you´ll find that an electric car, even if you use coal to make electricity, produces less pollution per mile than burning gasoline in the best gasoline-powered car."[100] The Minnesota Pollution Control Agency found that if Minnesota's fleet of vehicles making lengthy trips were replaced by plug-in hybrids, CO2 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 CO2 emissions.[101] 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.[102]

Operating costs

George W. Bush is shown the PHEV Mercedes-Benz Sprinter van in the U.S. Postal Service

A 2006 research estimate in California found that the operating costs of plug-ins charged at night was equivalent to US$0.75 per U.S. gallon (3.8 L) of gasoline.[1] The cost of electricity for a Prius PHEV is about US$0.03 per mile (US$0.019 per km), based on 0.26 kW·h/mi (129 mpg) and a cost of electricity of US$0.10 per kilowatt hour.[103][104] During 2008, many government and industry researchers are focusing on determining what level of all-electric range is economically optimum for the design.[105]

Smog

The Ontario Medical Association announced that smog is responsible for an estimated 9,500 premature deaths in its province every year.[106] Plug-in hybrids in emission-free electric mode may contribute to the reduction of smog.[96]

Vehicle-to-grid electricity

Main article: Vehicle-to-grid

PHEVs and fully electric cars may allow for more efficient use of existing electric production capacity, much of which sits idle as operating reserve most of the time. This assumes that vehicles are charged primarily during off peak periods (i.e., at night), or equipped with technology to shut off charging during periods of peak demand. Another advantage of a plug-in vehicle is their potential ability to load balance or help the grid during peak loads. This is accomplished with vehicle to grid technology. By using excess battery capacity to send power back into the grid and then recharge during off peak times using cheaper power, such vehicles are actually advantageous to utilities as well as their owners. Even if such vehicles just led to an increase in the use of night time electricity they would even out electricity demand which is typically higher in the day time, and provide a greater return on capital for electricity infrastructure.[19]

In October 2005, five Toyota engineers and one Asian AW engineer published an IEEE technical paper detailing a Toyota-approved project to add vehicle-to-grid capability to a Toyota Prius.[107] Although the technical paper described "a method for generating voltage between respective lines of neutral points in the generator and motor of the THS-II (Toyota Hybrid System) to add a function for generating electricity", it did not state whether or not the experimental vehicle could be charged through the circuit, as well. However, the vehicle was featured in a Toyota Dream House, and a brochure for the exhibit stated that "the house can supply electricity to the battery packs of the vehicles via the stand in the middle of the garage", indicating that the vehicle may have been a plug-in hybrid.[108]

A converted plug-in hybrid electric vehicle in the Washington International Renewable Energy Conference 2008

In November 2005, more than 50 leaders from public power utility companies across the United States met at the Los Angeles Department of Water and Power headquarters to discuss plug-in hybrid and vehicle-to-grid technology. The event, which was sponsored by the American Public Power Association, also provided an opportunity for association members to plan strategies that public power utility companies could use to promote plug-in hybrid technology. Greg Hanssen and Peter Nortman of EnergyCS[109] and EDrive[110] attended the two-day session, and during a break in the proceedings, made an impromptu display in the LADWP parking lot of their converted Prius plug-in hybrid.[111]

In September 2006, the California Air Resources Board held a Zero Emission Vehicle symposium that included several presentations on V2G technology.[112] In April 2007, Pacific Gas and Electric showcased a PHEV at the Silicon Valley Leadership Alternative Energy Solutions Summit with vehicle-to-grid capability, and demonstrated that it could be used as a source of emergency home power in the event of an electrical power failure.[113] Regulations intended to protect electricians against power other than from grid sources would need to be changed, or regulations requiring consumers to disconnect from the grid when connected to non-grid sources will be required before such backup power solutions would be feasible.[114]

Federal Energy Regulatory Commissioner Jon Wellinghoff coined the term "Cash-Back Hybrids" to describe payments to car owners for putting their batteries on the power grid. Batteries could also be offered in low-cost leasing or renting or by donation (including maintenance) to the car owners by the public utilities, in a vehicle-to-grid agreement.[115]

Disadvantages

Cost, weight, size, and disposal of batteries

Main article: Electric vehicle battery

Disadvantages of plug-in hybrids include the additional cost, weight, and size of a larger battery pack. The dual drive train may also require additional resources.

General Motors may allow buyers of its Chevy Volt electric car to rent the vehicle's battery, offsetting some cost.[116] Also used PHEV batteries can be sold to electric utilities to be employed at electrical substations.[68][117] Not everyone will be able to lease or sell their battery packs, but the economics are changing with oil price increases since 2003.

Other companies are working on battery lease plans. Think Car USA plans to lease the batteries for its City electric car to go on sale next year. Project Better Place is trying to create a system for consumers to "subscribe" to a service that offers recharging stations and battery exchange. [118]

Lithium Iron Phosphate batteries from Valence Technologies[119] were used in the first plug-in hybrids from Calcars.org[120] has now taken over where Calcars left off and is providing a Valence powered conversion for the Toyota Prius priced at $12,000. Hymotion also offers a conversion for USD $10,000 but their conversion is only 5KW where oemtek's is 9KW.

Electrical outlets outside garages

Main article: Charging station

Many people living in apartments, condominiums, and townhouses do not have garages. With only on-street parking available, they will need access to electrical outlets to take advantage of all-electric operation. New electrical outlets near their places of residence, or in commercial or public parking lots or streets will need to be installed for them to gain the full advantage of PHEVs.[121]

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.[102] 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.[122] 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.[123]

Tiered rate structure for electric bills

Some utilities offer electric vehicle users a rate tariff that provides discounts for off-peak usage, such as overnight recharging. Pacific Gas and Electric offers a special, discounted rate for electric vehicle customers, the "Experimental Time-of-Use Low Emission Vehicle rate."[124] That tariff gives people much cheaper rates if they charge at night. Off-peak rates can lower the break-even point. The numbers in the next paragraph below would change to USD $1.96, $3.17 and $3.80 per gallon, respectively, for the listed PG&E electric vehicle summer tariff; conversely, such tariffs raise prices for recharging during peak hours to USD $5.04, $6.25, and $6.88 per gallon, respectively, in the summer, but less in winter. Customers under such tariffs could see significant savings by being careful about when the vehicle was charged, perhaps by using an automated timer to restrict charging to off-peak hours.

Electric utility companies generally do not utilize flat rate pricing. For example, Pacific Gas and Electric normally charges $0.10 per kilowatt-hour (kWh) for the base tier, but additional tiers are priced as high as $0.30 per kWh to customers without electric vehicles.[125][126] 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 much of the benefits.[127] Without an off-peak charging tariff, household electricity customers who consumed 131%–200% of baseline electricity at $0.220 per kWh would only see benefits if gasoline was priced above $2.89 (USD/gal); those that consumed 201%–300% of baseline electricity at $0.303 per kWh would only see benefits if gasoline was priced above $3.98, and households that consumed over 300% of baseline electricity at $0.346 per kWh would only see benefits if gasoline was priced above $4.55 (USD/gal.)[128]

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. In other words, the marginal cost of incremental electricity consumption must be accounted for when comparing it to other forms of energy.

Production, commercialization, public support, deployment and pilot projects

Further information: Automotive market
The number of US survey respondents willing to pay US$4,000 more for a plug-in hybrid car increased from 17% in 2005 to 26% in 2006.

PHEVs are hitting the mainstream.[129] With 2008 sales down 24% in the first eight months of 2008 and continuing prospects of an industry-wide slowdown, all the carmakers that have the resources to do so are likely to accelerate their plans for plug-ins. The prospects of PHEV tax credits and loans to re-tool are additional carrots.[130]

PHEVs have been sold as commercial passenger vans,[131] utility trucks,[132][133] general and school buses,[134][135] motorcycles,[136] scooters,[137] and military vehicles.[138] Hybrid Electric Vehicle Technologies, Inc converts diesel buses to plug-in hybrids, under contract for the Chicago Transit Authority. Fisher Coachworks is developing a plug-in hybrid, the Fisher GTB-40, which is expected to get about 10-12 mpg, about twice the mileage of a normal hybrid bus.[139]

At least fourteen car companies of all sizes are exploring or planning to offer a plug-in,[140] including a modular kit car model (XR-3 Hybrid).[141] After hearing an explanation of PHEVs, 49% of U.S. consumers surveyed in 2006 said they would consider purchasing one. That is about the same level of interest as standard hybrid technology.[142]

Interest in plug-in hybrids increased in 2006 to such a level that the architecture was included as an area of research in President George W. Bush's advanced energy initiative and mentioned in his 2007 State of the Union Address. Incentives for the development of PHEVs are included in the Energy Independence and Security Act of 2007.[143]

The two major U.S. presidential candidates have spoken in support of plug-in hybrids,[144] but the Energy Improvement and Extension Act of 2008 contains a tax credit for plug-in hybrid electric vehicles, higher than either Presidential candidate has proposed [145]. The credit is a base $2,500 plus $417 for each kWh of battery pack capacity in excess of 4 kWh to a maximum of $15,000 for any vehicle with a GVW of more than 26,000 pounds (12,000 kg) [146].

Public deployment includes:

Organizations

Organizations that support plug-in hybrids:

Patent encumbrance of large NiMH batteries in transportation

In 1994, General Motors acquired a controlling interest in Ovonics's battery development and manufacturing, including patents controlling the manufacturing of large nickel metal hydride (NiMH) batteries. In 2001, Texaco purchased GM's share in GM Ovonics. A few months later, Chevron acquired Texaco. In 2003, Texaco Ovonics Battery Systems was restructured into Cobasys, a 50/50 joint venture between Chevron and Energy Conversion Devices (ECD) Ovonics.[155] Chevron's influence over Cobasys extends beyond a strict 50/50 joint venture. Chevron holds a 19.99% interest in ECD Ovonics.[156] Chevron also maintains veto power over any sale or licensing of NiMH technology.[157] In addition, Chevron maintains the right to seize all of Cobasys' intellectual property rights in the event that ECD Ovonics does not fulfill its contractual obligations.[157] On September 10, 2007, Chevron filed a legal claim that ECD Ovonics has not fulfilled its obligations. ECD Ovonics disputes this claim.[158] Since that time, the arbitration hearing was repeatedly suspended while the parties negotiate with General Motors over the sale of Cobasys back to GM. No agreement has been reached with GM. [159]

In her book, Plug-in Hybrids: The Cars that Will Recharge America, published in February 2007, Sherry Boschert argues that large-format NiMH batteries are commercially viable but that Cobasys refuses to sell or license them to small companies or individuals. Boschert reveals that Cobasys accepts only very large orders for these batteries. When Boschert conducted her research, major auto makers showed little interest in large orders for large-format NiMH batteries. However, Toyota employees complained about the difficulty in getting smaller orders of large format NiMH batteries to service the existing 825 RAV-4EVs. Since no other companies were willing to make large orders, Cobasys was not manufacturing nor licensing any large format NiMH battery technology for automotive purposes. Boschert concludes that "it's possible that Cobasys (Chevron) is squelching all access to large NiMH batteries through its control of patent licenses in order to remove a competitor to gasoline. Or it's possible that Cobasys simply wants the market for itself and is waiting for a major automaker to start producing plug-in hybrids or electric vehicles."[160]

Recently-signed Cobasys contracts demonstrate that the company is willing to use its NiMH technology in the automotive industry, specifically for use with hybrid electric vehicles. In December 2006, Cobasys and General Motors announced that they had signed a contract under which Cobasys provides NiMH batteries for the Saturn Aura hybrid sedan.[161] In March 2007, GM announced that it would use Cobasys NiMH batteries in the 2008 Chevrolet Malibu hybrid as well. Cobasys remains unwilling to sell NiMH batteries in smaller quantities to individuals or companies interested in building or retrofitting their own PHEVs.

Electro Energy Inc., working with CalCars, converted a Prius using its own bipolar NiMH batteries. Plug-In Conversions uses Nilar NiMH batteries and the EAA-PHEV open source control system in its Prius PHEV conversions. These organizations maintain that these developments are allowable because their NiMH battery technologies are not covered by Cobasys' patents.

See also

  • Alternative fuel vehicle
  • Cleanova (a Kangoo derivative)
  • Electric transportation technology
  • FreedomCAR
  • Genset trailer
  • Glossary of automotive design
  • Hybrid tax credit
  • Hypercar
  • Inductive charging
  • List of plug-in hybrid electric vehicles
  • Low-energy vehicle
  • Mitigation of global warming
  • Plug In America
  • PHEV Center

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External links

Groups promoting plug-ins
Conferences and events
News
Video