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Plug-in hybrid electric vehicle

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

A plug-in hybrid electric vehicle (PHEV) is a hybrid which has additional battery capacity and the ability to be recharged from an external electrical outlet. In addition, modifications are made to the vehicle's control software. The vehicle can be used for short trips of moderate speed without needing the internal combustion engine (ICE) component of the vehicle, thereby saving fuel costs. In this mode of operation the vehicle operates as a pure battery electric vehicle with a weight penalty (the ICE). The long range and additional power of the ICE power train is available when needed.

Given suitable infrastructure, PHEVs could also be recharged while the user drives. The PHEV establishes contact with an electrified rail, plate or overhead wires on the highway via an attached conducting wheel or other similar mechanism (see Conduit current collection and Ground-level power supply). The PHEV's batteries are recharged by this process - on the highway - and can then be used normally on other roads.

This provides the advantage of virtually unrestricted highway range. Since most destinations are within 100 km of a major highway, this reduces the need for expensive battery systems.

The technology for such infrastructure is old and well established - (see Conduit current collection, Ground-level power supply,trams, electric rail, trolleys, third rail). Electricity and infrastructure costs can be funded by toll revenue, gasoline taxes or other sources.

PHEVs are commonly called "grid-connected hybrids", "gas-optional hybrids" (GO-HEVs), "full hybrids", and are sometimes called HEV-30 (for instance, to denote a hybrid with a thirty-mile (50 km) electric range, compared to a HEV-0 (a non-plug-in hybrid). However, Ford, GM, and Toyota have all used the term "Full Hybrid Technology" to describe configurations that allow electric-only operation at low speeds (yet not PHEVs). Two other PHEV names used by a major U.S. automotive supplier and in a 1999 SAE paper are "energy hybrids" and "true hybrids". PHEVs can also operate in a mixed-mode where both gas and external electricity are used simultaneously to increase gas mileage for a particular range, usually at least double that of its electric-only range, but highly dependent upon the stage length between rechargings.

History

In 1969 Popular Science did an article on the General Motors XP-883 This prototype was a commuter car with a plug in hybrid drive system. It housed six 12 Volt lead acid batteries in the trunk area and had a transverse mounted DC electric motor mounted to a front wheel drive trans-axle. The gasoline powered engine was connected to the trans-axle via a worm gear.[1] The car could be plugged into a standard 110 Volt AC outlet for recharging. Although not very fast, or a very long range, hybrids were off and rolling.

In about 1990, Prof. Andy Frank of the University of California at Davis used student teams to begin building operating prototype Plug-in hybrid electric vehicles. His work attracted industry support and funding from Nissan, Koyo Seiko, GM, Saturn, Ford, Visteon, JATCO, Ovonics, DARPA, SMUD, SCE, DOE, and others. The UC Davis PHEVs won several DOE/USCAR "Future Car" and "Future Truck" national competitions.

In 1994, the Esoro H301 was built in Switzerland.<ref>http://www.esoro.ch/english/content/kernk/nhanst/h301/h.htm</ref> Four such prototypes are still on the road.

By 2000, the Electric Power Research Institute (EPRI) sponsored the broad-based Hybrid Electric Vehicle Alliance (HEVA) under the leadership of Bob Graham, to promote and develop OEM commercialization of PHEVs. Alliance members include major automakers, national labs, utilities, and UC Davis. The HEV Working Group (HEVWG) published its landmark studies and reports on PHEV attractiveness. Dr. Frank received new support from CEC, SCAQMD, Yolo-Solano AQMD, CARB, and other governmental agencies. In 2001, the U.S. Department of Energy created the National Center of Hybrid Excellence at UC Davis, with Dr. Frank as Director, and Frank also obtained substantial GM funds to hybridize and plug-in GM's EV1, and EPRI funded Dr. Frank's work.

In 2002, entrepreneurs, environmentalists and engineers created the California Cars Initiative, a non-profit PHEV advocacy and technology development group. In 2003, Dr. Frank's vehicles are shown at the Paris International Auto Show and demonstrated to about 200 Renault engineers at a corporate event at their Paris HQ. During the same year, Toyota shipped a UC Davis Coulomb PHEV to Toyota City to demonstrate it to about 250 engineers and executives at two of Toyota's primary Tier 1 suppliers, Koyo Seiko, and Aisin AW (Aisin builds the Toyota Prius transmission system, which also is used in the Ford Escape and Nissan Hybrid).

In 2003, Renault produced "Elect'Road," a PHEV variant of its "Electri'cite" Kangoo battery electric van (50-80 km range) with a small gasoline "limp-home" engine able to drive 100 km before refueling. Renault discontinued the Elect'Road after selling about 500, mainly in France, Norway and a few in the UK, for about 25,000 euros.

By 2004, Dr. Frank's student teams had built and operated seven proof-of-concept and proof-of-demonstration prototype PHEVs, including 6-passenger sedans (Taurus and Sable), SUVs (Suburban, Explorer), two-seater sports car (EV1), and two ground-up 80 mpg sports cars, and the CalCars PRIUS+ prototype and EDrive Systems conversions were demonstrated. In 2005, DaimlerChrysler Sprinter Van PHEV prototypes were completed. <ref>CalCars' PHEV History</ref>

Types

File:Felix-car-batteries-full.jpg
Lithium-ion battery pack in the California Cars Initiative plug-in hybrid converted Toyota Prius, the PRIUS+.

As with hybrid electric vehicles, the two major classifications are series and parallel.

  • In a parallel hybrid the internal combustion engine (ICE) and the electric motor can both contribute to torque at the wheels. Coupling the ICE directly to the drive shaft bypasses inefficiencies associated with having the ICE generate electrical energy for motive power. However, parallel hybrids currently available automatically engage the ICE if the vehicle is driven beyond a particular electric only performance envelope, a matter of some concern with the Prius conversions mentioned below, since these will require conservative driving to avoid starting the ICE. Parallel implementations may use a common drivetrain for the two power sources or may be "road coupled", with different wheel sets operated by the motors.
  • In a series hybrid the ICE drives a generator to recharge the batteries and/or provide power to the electric motor, depending upon the load demand. This type is especially attractive to implementation as a plug-in hybrid, since such vehicles will ideally have an electric motor and battery capable of satisfying all performance needs of the vehicle and so will not require use of the ICE until the batteries have been discharged to a substantial level, and not at all if recharged between trips of electric-only range. In one recent (non-production) announcement<ref>http://www.autobloggreen.com/2007/01/07/detroit-auto-show-its-here-gms-plug-in-hybrid-is-the-chevy-v/</ref> (the series hybrid Chevrolet Volt), a 40% remaining charge has been proposed for at least one vehicle as the start point for the ICE, the number of miles for electric-only operation will depend upon the battery capacity relative to the vehicle drag and weight, in this particular case projected at 40 miles (64km). In such a system the ICE and generator capacity, in concert with vehicle characteristics, will determine the maximum continuous performance without external recharge. Owing to the efficient fixed-speed operation of the relatively small (1 liter displacement) ICE and regenerative energy recovery, substantial economy of operation remains even without external power recharge of the batteries, in this example projected at 50 mpg (4.7 l/100 km).

Some early non-production plug-in hybrid electric vehicle conversions have been based on the version of Hybrid Synergy Drive (HSD) found in the 2004+ model year Toyota Prius. Early Pba conversions by CalCars demonstrated 10 miles (15 km) of EV-only and 20 miles (30 km) of double mileage mixed-mode range. A company offering conversions to consumers named Hybrids Plus is using A123 Li-ion batteries and has 15 or 30 miles of electric range. A company planning to offer conversions to consumers named EDrive systems will be using Valence Li-ion batteries and have 40-50 miles of electric range. Another company offering a plug-in module for the Toyota Prius is Hymotion. All of these systems replace the original battery and its ECU (Electronic Control Unit), while leaving the existing HSD system unchanged. This technology would be fairly simple to apply to other hybrid configurations. A conversion to plug-in mode involves increasing the capacity of the battery pack (in some cases the stock NiMH battery is retained), and adding an on-board AC powered charger to recharge the larger pack from mains power. Additionally, a method is required to encourage the vehicle to make full use the greater available electrical energy.

The cost of electricity for a Prius PHEV is about $0.03/mi ($0.019/km), based on 0.262 kWh / mile and a cost of electricity of 0.10 $ / kWh. Though the Honda Integrated Motor Assist (IMA) system does not have low-speed electric-only capability, mixed-mode mileage could be greatly enhanced while displacing some of their gasoline consumption with electricity from external sources. The Advanced Hybrid System 2 (AHS2) could be offered with additional battery capacity and charging capabilities as an option, costing about $3000 if offered by the manufacturer. Although it would likely be a substantial near-term financial burden, General Motors or DaimlerChrysler could potentially change the hybrid landscape by introducing a versatile and fuel-efficient PHEV. Meanwhile, Ford's chief engineers have suggested PHEVs are in their view technically suboptimal in that they use two complete powertrains.[citation needed]||}}

Current PHEV conversions install a higher capacity battery than common hybrids like the Toyota Prius in order to extend the range. This additional cost is offset by fuel operating cost savings because just $1.00 worth of electricity from the wall (at $0.09/kW·h) is sufficient to drive the same distance as a gallon of gasoline. During the year 2007, many government and industry researchers will focus on determining what level of all-electric range is economically optimum for the design.

While PHEV concepts and research have been neglected for many years by industry and government, interest increased in 2006 to such a level that the architecture was included as an area of research in President George W. Bush's Advanced Energy Initiative. The "addiction to oil" mentioned in his 2006 State of the Union Address could be largely eliminated by PHEVs and this fact is the most dramatic advantage of the architecture. Although the technology exists today it is often classified by many to be in the initial research phases and likely to not be available for several years (largely due to patent protection to keep modern battery technology from use). [citation needed]||}}

Patent protection on battery technology

The oil company Chevron invests in key battery technologies and battery manufacturing facilities, through its subsidiary, Cobasys. According to the website ev1.org, during the development of the battery-electric vehicle (BEV) EV1, General Motors made a controlling investment in Ovonics's battery development and manufacturing, with particular interest in the patents and trade secrets controlling the manufacturing of large nickel-metal hydride (NiMH) batteries. This interest was subsequently sold to the oil company Texaco, which was acquired in its entirety by another oil company, Chevron. The book "Plug-In Hybrids, The Cars That Will Recharge America" presents the argument that large-format NiMH batteries are commercially viable and ready for mass production, but that Chevron and other oil-related interests are suppressing this technology to forestall the introduction of plug-in hybrids. However, in December, 2006 General Motors announced that they will be using Cobasys NiMH batteries in the upcoming Saturn Aura hybrid model.<ref>http://www.autobloggreen.com/2006/12/05/cobasys-providing-nimh-batteries-for-saturn-aura-hybrid/</ref>

Advantages and disadvantages

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

PHEV and fully electric cars may allow for more efficient use of existing electric production capacity, much of which sits idle as operating reserve most of the time. This assumes that vehicles are charged primarily during off-peak periods (i.e., at night), or equipped with technology to shut off charging during periods of peak demand. There is debate about whether or not PHEV or electric vehicle technology reduces pollution or simply "shifts" the pollution to another physical location. The net effect on pollution is dependent on the fuel source of the electrical grid (fossil or renewable, for example) and the pollution profile of the powerplants themselves. Identifying, regulating and upgrading "single point" pollution source such as a powerplant -- or replacing a plant altogether -- may also be more practical. From a human health perspective, "shifting" pollution away from large urban areas may be considered a significant advantage.

Another advantage of the PHEV architecture is the synergy it offers with biofuels. It has long been understood that crop production in most countries is not sufficient to supply all of the biofuel needs of society, especially when food production is the obvious primary purpose. However, PHEVs dramatically reduce the requirement for liquid fuel to as little as 20% of an equivalent HEV-0. This produces a synergy between PHEVs and biofuels whereby extreme reductions in petroleum usage are possible. For example, E85 which is composed of 85% ethanol stretches petroleum by a factor of about 2.5 today. Combining E85 as the liquid fuel with a PHEV-70 results in a petroleum stretch factor of 10 (2.5 x 4). If an HEV-0 achieves 50 mpg U.S. (4.7 L/100 km), the similar PHEV-70 would develop 500 mpgp (0.47 L/100 km) (petroleum consumption) if fueled by E85.

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

The same study predicts that in areas where more than 80% of grid-power comes from coal-burning power plants, local net CO2 emissions will increase. <ref>http://www.aceee.org/store/proddetail.cfm?CFID=1941952&CFTOKEN=35186425&ItemID=418&CategoryID=7</ref> However, given the global nature of problems associated with CO2 emissions, specifically those related to global warming, localized increases in CO2 emissions are not considered a significant problem if global CO2 emissions are decreased.

The study also predicts that widespread PHEV use in these heavily coal-dependent areas would result in an increase in local net sulfur dioxide and mercury emissions, given emissions levels from most coal plants currently supplying power to the grid. <ref>http://www.csmonitor.com/2006/0925/p03s02-usgn.html</ref> <ref>http://news.com.com/Plug+in+your+hybrid,+pollute+less/2100-11389_3-6066360.html</ref> Although "clean coal" technologies could create power plants which supply grid power from coal without emitting significant amounts of such pollutants, the higher cost of the application of these technologies may increase the price of coal-generated electricity dramatically.

Disadvantages include the weight and cost of a larger battery pack. The cost of a battery pack is especially relevant because with current technology battery packs are likely to need to be replaced before the car itself is replaced. Additionally, the mileage gain from a PHEV are highly dependent upon the way a vehicle is used, and the opportunities to recharge by plug. In the most extreme of circumstances a PHEV might get worse mileage than an HEV. For example, in a vehicle being used 24 hours a day for commercial purposes the larger battery capacity (as compared to an HEV) might lack any advantage, while the greater battery weight (than in a corresponding HEV) would reduce mileage.

Issues for wide-scale commercialization

The concept of PHEVs involves frequent charge-discharge cycles of the batteries. Because the number of charge-discharge cycles is an important determinant of the lifetime of batteries, this tends to reduce the number of miles that can be driven over the full life cycle of the batteries, relative to EVs (which go further on each charge) or HEVs (which don't fully discharge). Some argue that current PHEV implementations aren't practical on a large scale because of reduced battery life, unlike commercial hybrids. However, see "Hybrid Vehicles Gain Traction", in the April 2006 issue of Scientific American, in which the authors argue that PHEVs will soon become standard in the automobile industry.<ref>"Hybrid Vehicles Gain Traction" Scientific American, April 2006</ref>

Here are the design issues and trade-offs that need to be solved:

  1. Battery life, which should be sufficient to maintain at least 85 to 90 percent of initial operational capability for at least 150,000 miles (240,000 km)
  2. Capacity to store electric energy. Affects vehicle weight, range, acceleration, and top speed. Energy density by weight for gasoline is 60-85 times higher than for a Lithium Ion battery so a 50 litre tank of gasoline (40 kg) carries as much energy as a Lithium Ion battery weighing 2400 kg or more. However internal combustion engines are vastly inefficient compared to electric motors.
  3. Heat dissipation of larger capacity batteries, especially when batteries are fast charged, which may require active liquid cooling devices (these devices may double for cabin air cooling and heating)
  4. Weight issues with increased batteries: slower acceleration, reduced gas mileage when used for long trips, increased strain on system components such as brakes, etc..., many of which can be addressed by appropriate system design such as increased regeneration capability (to save brakes), and larger electric motor (for acceleration).
  5. Costs
  6. Safety[2], owing to the greater total energy storage, but not significantly beyond that imposed by a conventional hybrid vehicle

For example, if the current Prius were made plug-in capable using its existing small battery pack its range would only be a few miles with low acceleration and low top speed. Alternately, using unsophisticated technology, a very heavy battery would be required which would cause other design problems. These limitations are expected to be resolved within a few years by employing modern batteries. To solve this one can:

  1. Increase the number of batteries of the type currently used: Adds weight and only increases range mildly
  2. Use the full charge/discharge of a battery: Reduces the life of the existing battery
  3. Use alternative battery technology: Currently expensive, but under heavy research[3] [4] [5]. Life expectancy unknown but expected to be greater[6]. For lithium-ion (Li-ion) batteries Toyota reports a heat dissipation issue.[7][8]

The next major update to the Prius, perhaps in 2008 or later, is rumored to use Li-ion batteries[9]. This Guardian article suggests it will have a 15 km (9 mile) electric only range.[10]

Production models, prototypes and conversions

One production PHEV has gone on sale, the Renault Kangoo, in France in 2003. In addition, DaimlerChrysler is currently building PHEVs based on the Mercedes-Benz Sprinter van. Light Trucks are also offered by Micro-Vett SPA<ref>Template:Citation/core{{#if:2006|}}</ref> the so called Daily Bimodale.

A number of prototypes have been created. At the UC Davis Hybrid Center, a team led by Prof. Andy Frank Template:Citation/core{{#if:|}} have been designing and building working prototypes, the most recent of which is currently being installed into a GM Equinox for the Challenge X competition. Template:Citation/core{{#if:2006|}} Some independent researchers have demonstrated conversions of vehicles such as the Toyota Prius, while leaving the majority of the stock Hybrid Synergy Drive intact and unchanged by simply adding battery capacity and a grid charger.

Press reports on Nov 29, 2006, indicate GM's plans to introduce a production plug-in hybrid version of Saturn's Greenline Vue SUV in 2009[11]to be a PHEV-10 .

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

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

Motorcycle and small car manufacturer Suzuki has produced several prototype light sports cars capable of operation in this mode. The first of these used a 400 cc motorcycle engine to give a primarily electric vehicle a "limp home" capability. A subsequent model was more capable of general operation over a wide range of conditions and ranges.

PML built prototypes that it claims achieve 80 mpg; 0 to 60mph in 4.5 seconds; top speed of over 150mph; and a range of 1,000 miles.<ref>PML website regarding these demonstration vehicles</ref>

Battery electric vehicle

A battery electric vehicle with a range extending trailer called a hybrid adapter might also be considered a plug-in hybrid. The pusher trailers or genset trailers are two working examples of this concept. About 15 kW of power is required to maintain freeway speeds in a lightweight EV. This is about one third the power output of the Honda Insight's 1 L three cylinder ICE. One advantage of this configuration is that the ICE or other energy conversion device can be tuned to maximize efficiency by running at an ideal constant power level.

Vehicle-to-grid

Another advantage of a gridable vehicle is their potential ability to load balance or help the grid during peak loads. By using excess battery capacity to send power back into the grid and then recharge during off peak using cheaper power such vehicles are actually advantageous to utilities as well as their owners. This is accomplished with what is known as V2G or Vehicle to Grid technology. Even if such vehicles just led to an increase in the use of night time electricity they would even out electricity demand (which is typically higher in the day time) and provide a greater return on capital for electricity infrastructure.

References

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