A plug in hybrid electric vehicle (PHEV) is a hybrid electric vehicle with the ability to recharge its energy storage with electricity from an off-board power source such as a grid. PHEVs have the potential to displace a significant amount of fuel in the next 10 to 20 years. It is estimated that they can reduce fuel consumption by up to 45% relative to that of a comparable combustion engine vehicle. However, the PHEV technique is still expensive compared to techniques which improve internal combustion engines, and additional infrastructure investments are needed for the recharging infrastructure. Moreover, the lifespan of the batteries has not been established, yet, for these types of vehicles.
A plug in hybrid electric vehicle (PHEV) is a hybrid electric vehicle with the ability to recharge its energy storage with electricity from an off-board power source such as a grid. (Pesaran et.al, 2009) The PHEV can run either on its Internal Combustion Engine (ICE) or on its battery.
A full electric vehicle uses its energy far more efficiently than a vehicle with an Internal Combustion Engine (ICE) and can drive about 2.5 times further with the same energy. For this reason it is expected that the electric vehicle will replace the ICE vehicle in the long run. However, in the coming 20 years or so vehicles will probably still be equipped with IC engines, possibly in combination with electric engines, because per unit of weight an ICE vehicle can still drive about 40 times further. In this 20 year period the IC engine is expected to improve substantially (Sharpe et al. 2009).
The key advantage of PHEV technology relative to full Battery Electric Vehicles (BEV) is the fuel flexibility. PHEVs have no limitation of the driving range and if the recharging infrastructure is spatially or temporally unavailable, it doesn’t restrict the use of the vehicle. A possible drawback of the PHEV is that it contains two systems to propel the vehicle, making it more costly to build than a BEV. However, the car manufacturing industry expects that PHEVs will be introduced to the market first, and that the switch to BEV could be made when the PHEVs are found to be economically and technological viable. (Gilijamse,2009).
A main problem of the usage of PHEVs is the space required for the battery and the mass increase of the vehicle due to the batteries. However, for most commuters a relatively small 40 kilometer battery package will be sufficient to travel to work and back. The batteries can be recharged at night when the electricity demand is low.
The mass and volume of a 15 kilometer (the maximum distance it can drive electrically) battery is about 60 kg and 40 liters. The mass and volume of a 40 kilometer battery is about 120 kg and 80 liters. (Pesaran et al. 2009) In contrast, full electric vehicles need battery packages of more than 500 kg to obtain an action radius of about 160 kilometers.
To make the widespread use of PHEVs feasible, an infrastructure of recharging stations is needed. This infrastructure needs to be standardized in way that every brand of Plug-in Hybrid Electric Vehicle can be recharged at every recharging station.
Batteries need to improve in a numbers of aspects – durability, life-expectancy, energy density, power density, temperature sensitivity, reductions in recharge time, and reductions in cost. Battery durability and life-expectancy are probably the biggest hurdles technically to mass commercial viability of EVs and PHEVs (IEA, 2011).
New battery chemistries with increased energy densities will enable important changes to battery design. Energy storage systems will require less active material, fewer cells, and less cell and module hardware. These advancements will result in lighter, smaller and cheaper batteries and hence EVs and PHEVs (IEA, 2011).
Plug-in hybrid vehicles (PHEVs) have the potential to displace a significant amount of fuel in the next 10 to 20 years. The main barriers to the commercialization of PHEVs are the cost, weight, safety, volume and lifespan (combined shallow/deep cycle life and calendar life) of the batteries. It is expected that more and more car manufactures will bring plug in vehicles to the market in the coming years.
PHEVs are potentially an important technology for reducing fossil fuel consumption and CO2 emissions. Globally PHEVs could satisfy a large proportion of daily driving demand. In the UK, for example, 97% of trips are estimated to be below 80 km, in Europe 50% of trips are less than 10 km and 80% less than 25 km, and in the U.S. 60% of trips are less than 50 km and 85% less than 100 km. However, there is only a handful of demonstration projects of PHEVs worldwide and no manufacturer produces PHEVs on a commercial scale yet meaning market penetration is almost zero.
The Energy Technology Perspectives (ETP) 2010 BLUE Map scenario sets ambitious targets for the PHEV market. Technologies for Light Duty Vehicles (LDVs) are expected to evolve rapidly over the coming decades and massive market penetration of PHEVs after 2010 is part of the IEA BLUE Map scenario. PHEV sales per year are expected to reach 5 million by 2020, 25 million by 2030 and sales are only expected to decline after 2040 as Electric Vehicles gain more market share (IEA, 2011). Figure 1 below depicts this evolution in the LDV market:
A PHEV uses stored electrical energy to propel the vehicle which reduces fuel consumption by the combustion engine. This provides an opportunity to drive primarily in electric mode and reduce emissions in congested cities around the world.
The main air pollutants in congested cities are nitric oxide (NOx) and small particulate matter PM10 and PM2.5 (10 and 2.5 are the average particle diameter in micrometer)
In the electric mode the vehicle does not emit any NOx locally. The global emissions of NOx depend on the way the electricity has been produced. Also the local emissions of small particulate matter is lowered significantly: In the electric mode there is no contribution from the exhaust PM10. However, braking still causes the formation of some small particulate matter PM2,5. However, hybrid cars use regenerative braking in which part of the kinetic energy lost during braking can be recovered. Using regenerative braking, the electric motors reverse the current, which slows down the vehicle. At the same time, it generates electricity to be returned to battery system. Regenerative braking can lower the formation of small particulate matter PM2,5 significantly (~ 60%) in comparison with conventional vehicles with solely an internal combustion engine.
Studies estimate that a PHEV with usable electrical energy storage equivalent to 30 kilometers of electric travel would reduce fuel consumption by 36 - 45% relative to that of a comparable combustion engine vehicle assuming that the PHEV drives in full electric mode in the city and as a hybrid on rural roads and on the highway (Pesaran et al. 2009, CalCars, 2009). The final CO2 emission reduction depends strongly on the source of the electricity used. A larger deployment of renewable energy sources would lower the CO2 emission of the PHEV further.
The hybridization of the vehicle (not plug-in) adds costs, a full hybrid light passenger car offers 20% reduction potential for about US$ 4000 additional manufacturer’s cost. (Sharpe, 2009) Additionally PHEVs require a bigger battery which adds extra to the costs. The price of the battery system price is about $1700 for a 15 kilometer battery and about $3400 for a 60 kilometer battery. The specified distance is the distance for which the vehicle can drive in full electric mode. This brings the additional cost of a PHEV to $ 5700 to $ 7400 compared to a conventional vehicle with an internal combustion engine. However, the costs of the lithium ion battery are expected to decrease in the near future. The 2007 prices for high energy batteries on a per kWh basis range from $800/kWh to $1000/kWh (Pesaran, 2009). The mid- and long term research and development cost goals of the battery are $500/kWh in 2012 and $300/kWh in 2016.
A big advantage of PHEVs is that the fuel costs are considerably lower the ones of a conventional ICE powered car. However, it depends strongly on the local fuel and electricity prices whether it is worth to invest the extra $ 5700 to $ 7400 compared to a conventional vehicle with an internal combustion engine.
In addition, there is a need for investment into the recharging infrastructure. This infrastructure needs to be standardized in a way that every brand of Plug-in Hybrid Electric Vehicle can recharge at every recharging station. A simple recharging point at a private house or at an office costs about $1800. However, a public recharging station, with the necessary electronics to make contact with the bank costs about $18.000. (Roeterdink, 2010)
[This information is kindly provided by the UNEP Risoe Centre Carbon Markets Group .]
Project developers of projects deploying plug-in hybrid electric vehicles can use the following CDM methodology: AMS-III.C.: Emission reductions by electric and hybrid vehicles .
The California Cars Initiative (CalCars), (2009). All About Plug-In Hybrids (PHEVs). available at http://www.calcars.org/vehicles.html 
Gilijamse, J. (2009). Elektrische Auto: inhaalslag van de Duitse auto-industrie, available at http://www.twanetwerk.nl/default.ashx?DocumentId=12362 
International Energy Agency (IEA) (2011). Technology Roadmap: Electric and plug-in hybrid electric vehicles. IEA, 2011. Available at http://www.iea.org/publications/freepublications/publication/EV_PHEV_Roadmap.pdf 
Pesaran A.A., Markel, T., Tataria, H.S. and Howel, D. (2009): Battery Requirements for Plug-In Hybrid Electric Vehicles, NREL/CP-540-42240. July 2009.
Roeterdink, W.G., Uyterlinde, M.A., Kroon, P. and Hanschke, C.B. (2010). Groen Tanken: Inpassing van alternatieve brandstoffen in de tank- en distributie infrastructuur. ECN-E—09-082
Sharpe, R. and Smokers, R.T.M. (2009). Assessment with repect to long term CO2 emission targets for passenger cars and vans. available at http://ec.europa.eu/environment/air/transport/co2/pdf/Report%20LT%20targets.pdf