Plug-in Hybrids

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 electric vehicle with a weight penalty (the ICE). The long range and additional power of the ICE power train is available when needed.

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 30-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 double that of its electric-only range.

Plug-in Prius, 100+ MPG

Types

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 have demonstrated 10 miles (15 km) of EV-only and 20 miles (30 km) of double mileage mixed-mode range. A company planning to offer conversions to consumers named EDrive systems will be using Valence Li-ion batteries and have 35 miles (55 km) of electric range. Another company offering a plug-in module for the Toyota Prius is Hymotion. All of these systems leave the existing HSD system mostly unchanged and would be fairly simple to apply to other hybrid configurations. A conversion to plug-in mode involves replacing the stock NiMH battery with a higher capacity battery pack and an on-board AC powered charger to recharge the larger pack from mains power. Reprogramming of the system controller computer is required to encourage deep discharge of the batteries.

The cost of electricity for a PHEV is about $0.03/mi ($0.019/km) from standard household outlets. 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 the possibility is fairly remote, General Motors or DaimlerChrysler could potentially effect a marketing coup by producing a markedly more versatile and fuel-efficient hybrid; a PHEV.

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) will drive you the same distance as a gallon of gasoline. During the year 2006, 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, strong interest is budding in 2006 to such a level that the architecture has even been 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.

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).

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 stetch 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.

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. Finally, if the local source of electricity comes from burning fossil fuels, the benefits in terms of reduced CO₂ emissions could be lost.

Issues for wide-scale commercialisation

Unlike a conventional hybrid electric vehicle current PHEV implementations use the full charge cycle of its battery, which reduces the life of the battery. Mass-produced Hybrid electric vehicles by design avoid a complete or near complete discharge of the battery. Current PHEV implementations aren't practical on a large scale because of reduced battery life, which is not true of commercial hybrids.

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

1. Battery life
2. Capacity to store electric energy. Affects range, acceleration, and top speed
3. Heat dissipation of larger capacity batteries
4. Weight issues with increased batteries: slower acceleration, reduced gas mileage, increased strain on system components such as brakes, etc...
5. Costs
6. Safety

For example, if the current Prius were made plug-in capable its range would only be a few miles with low acceleration and low top speed. To solve this one can:

1. Increase the number of batteries: Adds weight but only increases range mildly.
2. Use the full charge/discharge of a battery: Reduces the life of the battery.
3. Use alternative battery technology: Currently expensive, but under heavy research. Life expectancy unknown. For lithium-ion (Li-on) batteries Toyota reports a heat dissipation issue.hybrid-cx_jf_0530flint.html

The next version of the Prius is rumored to use Li-on batteries[1]. This Guardian article suggests it will have plug-in capability with 9 mile range[2].

Prototypes and Conversions

A number of interesting prototypes have been created, mostly at the UC Davis Hybrid Center by teams led by Prof. Andy Frank, but there are no production vehicles available at this time (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.

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.

CalCars, a non-profit advocacy and technology development group in California, has converted one 2004 Prius into what it calls a "PRIUS+" as proof of concept. It is now working with EDrive Systems, a new Southern California company that plans to install aftermarket conversions for 2004-2006 Priuses with a target fuel efficiency of 230 mpg (1.0 L/100 km).hybrid_tinkerers;_ylt=Ajsg5s42ZReOhSpJhVs7Zo0DW7oF;_ylu=X3oDMTBiMW04NW9mBHNlYwMlJVRPUCUl And 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.

Battery electric vehicle

A battery electric vehicle with a range extending trailer called pusher trailers or genset trailers might also be considered a plug-in hybrid. 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 infastructure.

External links

• CalCars.org
• Description of DaimlerChrysler's plug-in hybrid Sprinter van

News

• GM working on plug-in hybrid
• Report from the Advanced Automotive Battery Conference
• Forbes: Plug-ins aren't practical

After Market Conversions

• EDriveSystems.com
• Hymotion.com

Related Groups

• Electric and Plug-In Hybrid Electric Vehicles Wiki
• HybridConsortium.org
• PlugInPartners.com
• Oil Crisis Executive Simulation
• Flexible Fuel Electric (Plug-In) Hybrids