Plug-in electric vehicle

A plug-in electric vehicle (PEV) is any motor vehicle that can be recharged from an external source of electricity, such as wall sockets, and the electricity stored in the rechargeable battery packs drives or contributes to drive the wheels. PEV is a superset of electric vehicles that includes all-electric or battery electric vehicles (BEVs), plug-in hybrid vehicles (PHEVs), and electric vehicle conversions of hybrid electric vehicles and conventional internal combustion engine vehicles.

Plug-in cars have several benefits compared to conventional internal combustion engine vehicles. They have lower operating and maintenance costs, and produce little or no local air pollution. They reduce dependence on petroleum and may reduce greenhouse gas emissions from the onboard source of power, depending on the fuel and technology used for electricity generation to charge the batteries. Plug-in hybrids capture most of these benefits when they are operating in all-electric mode. Despite their potential benefits, market penetration of plug-in electric vehicles has been slower than expected as adoption faces several hurdles and limitations. , plug-in electric vehicles are significantly more expensive than conventional vehicles and hybrid electric vehicles due to the additional cost of their lithium-ion battery packs. Other factors discouraging the adoption of electric cars are the lack of public and private recharging infrastructure and, in the case of all-electric vehicles, drivers' fear of the batteries running out of energy before reaching their destination due to the limited range of existing electric cars. Plug-in hybrids eliminate the problem of range anxiety associated to all-electric vehicles, because the combustion engine works as a backup when the batteries are depleted, giving PHEVs driving range comparable to other vehicles with gasoline tanks.

Several national and local governments have established tax credits, subsidies, and other incentives to promote the introduction and adoption in the mass market of plug-in electric vehicles depending on their battery size and all-electric range. The term "plug-in electric drive vehicle" is formally used in U.S. federal legislation to grant this type of consumer incentive. In China, plug-in electric vehicles are called new energy vehicles (NEVs), and only pure electric vehicles and plug-in hybrid electric vehicles are subject to purchase incentives.

, there are about 50 models of highway legal plug-in electric passenger cars available for retail sales. The Nissan Leaf is the world's top selling highway-capable all-electric car ever, with global sales of over 158,000 units, followed by the Chevrolet Volt plug-in hybrid, which together with its sibling the Opel/Vauxhall Ampera has combined sales of more than 88,000 units.

, more than 712,000 highway-capable plug-in electric passenger cars and light utility vehicles have been sold worldwide, led by the United States with a stock of over 291,000 plug-in electric cars delivered since 2008, representing 41% of global sales. Japan ranks second with about 108,000 units sold since 2009 (15%), followed by China with more than 83,000 plug-in passenger cars sold since 2008 (12%). , over 228,000 light-duty plug-in electric vehicles have been registered in the European market since 2010, representing 32% of global sales. European sales are led by the Netherlands with over 45,000 light-duty plug-in vehicles registered, followed by France with 43,600 all-electric cars and light utility vans sold since 2010, and Norway with over 43,400 plug-in electric vehicles registered. In the heavy-duty segment, China is the world's leader, with about 36,500 all-electric buses sold through December 2014.

Air pollution and greenhouse gas emissions
Electric cars, as well as plug-in hybrids operating in all-electric mode, emit no harmful tailpipe pollutants from the onboard source of power, such as particulates (soot), volatile organic compounds, hydrocarbons, carbon monoxide, ozone, lead, and various oxides of nitrogen. The clean air benefit is usually local because, depending on the source of the electricity used to recharge the batteries, air pollutant emissions are shifted to the location of the generation plants. In a similar manner, plug-in electric vehicles operating in all-electric mode do not emit greenhouse gases from the onboard source of power, but from the point of view of a well-to-wheel assessment, the extent of the benefit also depends on the fuel and technology used for electricity generation. This fact has been referred to as the long tailpipe of plug-in electric vehicles. From the perspective of a full life cycle analysis, the electricity used to recharge the batteries must be generated from renewable or clean sources such as wind, solar, hydroelectric, or nuclear power for PEVs to have almost none or zero well-to-wheel emissions. On the other hand, when PEVs are recharged from coal-fired plants, they usually produce slightly more greenhouse gas emissions than internal combustion engine vehicles and higher than hybrid electric vehicles. In the case of plug-in hybrid electric vehicles operating in hybrid mode with assistance of the internal combustion engine, tailpipe and greenhouse emissions are lower in comparison to conventional cars because of their higher fuel economy.

The magnitude of the potential advantage depends on the mix of generation sources and therefore varies by country and by region. For example, France can obtain significant emission benefits from electric and plug-in hybrids because most of its electricity is generated by nuclear power plants; California, where most energy comes from natural gas, hydroelectric and nuclear plants can also secure substantial emission benefits. The U.K. also has a significant potential to benefit from PEVs as natural gas plants dominate the generation mix. On the other hand, emission benefits in Germany, China, India, and the central regions of the United States are limited or non-existent because most electricity is generated from coal. However these countries and regions might still obtain some air quality benefits by reducing local air pollution in urban areas. Cities with chronic air pollution problems, such as Los Angeles, México City, Santiago, Chile, São Paulo, Beijing, Bangkok and Katmandu may also gain local clean air benefits by shifting the harmful emission to electric generation plants located outside the cities. Nevertheless, the location of the plants is not relevant when considering greenhouse gas emission because their effect is global.

Carbon footprint during production
A report published in June 2011, prepared by Ricardo in collaboration with experts from the UK's Low Carbon Vehicle Partnership, found that hybrid electric cars, plug-in hybrids and all-electric cars generate more carbon emissions during their production than current conventional vehicles, but still have a lower overall carbon footprint over the full life cycle. The higher carbon footprint during production of electric drive vehicles is due mainly to the production of batteries. As an example, 43 percent of production emissions for a mid-size electric car are generated from the battery production, while for standard mid-sized gasolineinternal combustion engine vehicle, around 75% of the embedded carbon emissions during production comes from the steel used in the vehicle glider. The following table summarizes key results of this study for four powertrain technologies:
 * Ricardo

The Ricardo study also found that the lifecycle carbon emissions for mid-sized gasoline and diesel vehicles are almost identical, and that the greater fuel efficiency of the diesel engine is offset by higher production emissions.

In 2014 Volkswagen published the results of life-cycle assessment of its electric vehicles certified by TÜV NORD, and independent inspection agency. The study found that emissions during the use phase of its all-electric VW e-Golf are 99% lower than those of the Golf 1.2 TSI when powers comes from exclusively hydroelectricity generated in Germany, Austria and Switzerland. Accounting for the full lifecycle, the e-Golf reduces emissions by 61%, offsetting higher production emissions. When the actual EU-27 electricity mix is considered, the e-Golf emissions are still 26% lower than those of the conventional Golf 1.2 TSI. Similar results were found when comparing the e-Golf with the Golf 1.6 TDI. The analysis considered recycling of the three vehicles at the end of their lifetime.
 * Volkswagen

Well-to-wheel GHG emissions in the U.S.
The following table compares tailpipe and upstream emissions estimated by the U.S. Environmental Protection Agency for all series production model year 2014 plug-in electric vehicles available in the U.S. market. Total emissions include the emissions associated with the production and distribution of electricity used to charge the vehicle, and for plug-in hybrid electric vehicles, it also includes emissions associated with tailpipe emissions produced from the internal combustion engine. These figures were published by the EPA in October 2014 in its annual report "Light-Duty Automotive Technology, Carbon Dioxide Emissions, and Fuel Economy Trends: 1975 Through 2014." All emissions are estimated considering average real world city and highway operation based on the EPA 5-cycle label methodology, using a weighted 55% city and 45% highway driving. For the first time, the 2014 Trends report presents an analysis of the impact of alternative fuel vehicles, with emphasis in plug-in electric vehicles because as their market share is approaching 1%, the EPA concluded that PEVs began to have a measurable impact on the U.S. overall new vehicle fuel economy and emissions.
 * Environmental Protection Agency

For purposes of an accurate estimation of emissions, the analysis took into consideration the differences in operation between plug-in hybrids. Some, like the Chevrolet Volt, can operate in all-electric mode without using gasoline, and others operate in a blended mode like the Toyota Prius PHV, which uses both energy stored in the battery and energy from the gasoline tank to propel the vehicle, but that can deliver substantial all-electric driving in blended mode. In addition, since the all-electric range of plug-in hybrids depends on the size of the battery pack, the analysis introduced a utility factor as a projection of the share of miles that will be driven using electricity by an average driver, for both, electric only and blended EV modes. Since all-electric cars do not produce tailpipe emissions, the utility factor applies only to plug-in hybrids. The following table shows the overall fuel economy expressed in terms of miles per gallon gasoline equivalent (mpg-e) and the utility factor for the ten MY2014 plug-in hybrids available in the U.S. market, and EPA's best estimate of the tailpipe emissions produced by these PHEVs.

In order to account for the upstream emissions associated with the production and distribution of electricity, and since electricity production in the United States varies significantly from region to region, the EPA considered three scenarios/ranges with the low end scenario corresponding to the California powerplant emissions factor, the middle of the range represented by the national average powerplant emissions factor, and the upper end of the range corresponding to the powerplant emissions factor for the Rocky Mountains. The EPA estimates that the electricity GHG emission factors for various regions of the country vary from 346 g /kWh in California to 986 g /kWh in the Rockies, with a national average of 648 g /kWh.

The Union of Concerned Scientists (UCS) published a study in 2012 that assessed average greenhouse gas emissions in the U.S. resulting from charging plug-in car batteries from the perspective of the full life-cycle (well-to-wheel analysis) and according to fuel and technology used to generate electric power by region. The study used the model year 2011 Nissan Leaf all-electric car to establish the analysis baseline, and electric-utility emissions are based on EPA's 2009 estimates. The UCS study expressed the results in terms of miles per gallon instead of the conventional unit of grams of greenhouse gases or carbon dioxide equivalent emissions per year in order to make the results more friendly for consumers. The study found that in areas where electricity is generated from natural gas, nuclear, hydroelectric or renewable sources, the potential of plug-in electric cars to reduce greenhouse emissions is significant. On the other hand, in regions where a high proportion of power is generated from coal, hybrid electric cars produce less equivalent emissions than plug-in electric cars, and the best fuel efficient gasoline-powered subcompact car produces slightly less emissions than a PEV. In the worst-case scenario, the study estimated that for a region where all energy is generated from coal, a plug-in electric car would emit greenhouse gas emissions equivalent to a gasoline car rated at a combined city/highway driving fuel economy of 30 mpgUS. In contrast, in a region that is completely reliant on natural gas, the PEV would be equivalent to a gasoline-powered car rated at 50 mpgUS.
 * Union of Concerned Scientists

The study concluded that for 45% of the U.S. population, a plug-in electric car will generate lower equivalent emissions than a gasoline-powered car capable of combined 50 mpgUS, such as the Toyota Prius and the Prius c. The UCS also found that for 37% of the population, the electric car emissions will fall in the range of a gasoline-powered car rated at a combined fuel economy of 41 to 50 mpgUS, such as the Honda Civic Hybrid and the Lexus CT200h. Only 18% of the population lives in areas where the power-supply is more dependent on burning carbon, and the greenhouse gas emissions will be equivalent to a car rated at a combined fuel economy of 31 to 40 mpgUS, such as the Chevrolet Cruze and Ford Focus. The study found that there are no regions in the U.S. where plug-in electric cars will have higher greenhouse gas emissions than the average new compact gasoline engine automobile, and the area with the dirtiest power supply produces emissions equivalent to a gasoline-powered car rated at 33 mpgUS.

In September 2014 the UCS published an updated analysis of its 2012 report. The 2014 analysis found that 60% of Americans, up from 45% in 2012, live in regions where an all-electric car produce fewer equivalent emissions per mile than the most efficient hybrid. The UCS study found several reasons for the improvement. First, electric utilities have adopted cleaner sources of electricity to their mix between the two analysis. The 2014 study used electric-utility emissions based on EPA's 2010 estimates, but since coal use nationwide is down by about 5% from 2010 to 2014, actual efficiency in 2014 is better than estimated in the UCS study. Second, electric vehicles have become more efficient, as the average 2013 all-electric vehicle used 0.33 kWh per mile, representing a 5% improvement over 2011 models. Also, some new models are cleaner than the average, such as the BMW i3, which is rated at 0.27 kWh by the EPA. An i3 charged with power from the Midwest grid would be as clean as a gasoline-powered car with about 50 mpgUS, up from 39 mpgUS for the average electric car in the 2012 study. In states with a cleaner mix generation, the gains were larger. The average all-electric car in California went up to 95 mpgUS equivalent from 78 mpgUS in the 2012 study. States with dirtier generation that rely heavily on coal still lag, such as Colorado, where the average BEV only achieves the same emissions as a 34 mpgUS gasoline-powered car. The author of the 2014 analysis noted that the benefits are not distributed evenly across the U.S. because electric car adoptions is concentrated in the states with cleaner power.

One criticism to the UCS study is that the analysis was made using average emissions rates across regions instead of marginal generation at different times of the day. The former approach does not take into account the generation mix within interconnected electricity markets and shifting load profiles throughout the day. An analysis by three economist affiliated with the National Bureau of Economic Research (NBER), published in November 2014, developed a methodology to estimate marginal emissions of electricity demand that vary by location and time of day across the United States. The marginal analysis, applied to plug-in electric vehicles, found that the emissions of charging PEVs vary by region and hours of the day. In some regions, such as the Western U.S. and Texas, emissions per mile from driving PEVs are less than those from driving a hybrid car. However, in other regions, such as the Upper Midwest, charging during the recommended hours of midnight to 4 a.m. implies that PEVs generate more emissions per mile than the average car currently on the road. The results show a fundamental tension between electricity load management and environmental goals as the hours when electricity is the least expensive to produce tend to be the hours with the greatest emissions. This occurs because coal-fired units, which have higher emission rates, are most commonly used to meet base-level and off-peak electricity demand; while natural gas units, which have relatively low emissions rates, are often brought online to meet peak demand.
 * National Bureau of Economic Research

Well-to-wheel GHG emissions in several countries
A study published in the UK in April 2013 assessed the carbon footprint of plug-in electric vehicles in 20 countries. As a baseline the analysis established that manufacturing emissions account for 70 g CO2/km for an electric car and 40 g CO2/km for a petrol car. The study found that in countries with coal-intensive generation, PEVs are no different from conventional petrol-powered vehicles. Among these countries are China, Indonesia, Australia, South Africa and India. A pure electric car in India generates emissions comparable to a 20 mpgUS petrol car.

The country ranking was led by Paraguay, where all electricity is produced from hydropower, and Iceland, where electricity production relies on renewable power, mainly hydro and geothermal power. Resulting carbon emissions from an electric car in both countries are 70 g CO2/km, which is equivalent to a 220 mpgUS petrol car, and correspond to manufacturing emissions. Next in the ranking are other countries with low carbon electricity generation, including Sweden (mostly hydro and nuclear power ), Brazil (mainly hydropower) and France (predominantly nuclear power). Countries ranking in the middle include Japan, Germany, the UK and the United States.

The following table shows the emissions intensity estimated in the study for those countries where electric vehicle are available, and the corresponding emissions equivalent in miles per US gallon of a petrol-powered car: