Image 2: A crude oil vacuum distillation column as used in oil refineries
Continuous distillation, a form of distillation,
is an ongoing separation in which a mixture is continuously (without
interruption) fed into the process and separated fractions are removed
continuously as output streams. Distillation is the separation or partial separation of a liquid feed mixture into components or fractions by selective boiling (or evaporation) and condensation. The process produces at least two output fractions. These fractions include at least one volatile distillate fraction, which has boiled and been separately captured as a vapor condensed to a liquid, and practically always a bottoms (or residuum) fraction, which is the least volatile residue that has not been separately captured as a condensed vapor.
An alternative to continuous distillation is batch distillation,
where the mixture is added to the unit at the start of the
distillation, distillate fractions are taken out sequentially in time
(one after another) during the distillation, and the remaining bottoms
fraction is removed at the end. Because each of the distillate
fractions are taken out at different times, only one distillate exit
point (location) is needed for a batch distillation and the distillate
can just be switched to a different receiver, a fraction-collecting
container. Batch distillation is often used when smaller quantities are
distilled. In a continuous distillation, each of the fraction streams
is taken simultaneously throughout operation; therefore, a separate exit
point is needed for each fraction. In practice when there are multiple
distillate fractions, the distillate exit points are located at
different heights on a fractionating column. The bottoms fraction can be taken from the bottom of the distillation column or unit, but is often taken from a reboiler connected to the bottom of the column.
Each fraction may contain one or more components (types of chemical compounds). When distilling crude oil
or a similar feedstock, each fraction contains many components of
similar volatility and other properties. Although it is possible to run
a small-scale or laboratory continuous distillation, most often
continuous distillation is used in a large-scale industrial process.
Industrial application
Distillation is one of the unit operations of chemical engineering.
Continuous distillation is used widely in the chemical process
industries where large quantities of liquids have to be distilled. Such industries are the natural gas processing, petrochemical production, coal tar processing, liquor production, liquified air separation, hydrocarbonsolvents production, cannabinoid separation and similar industries, but it finds its widest application in petroleum refineries. In such refineries, the crude oil
feedstock is a very complex multicomponent mixture that must be
separated and yields of pure chemical compounds are not expected, only
groups of compounds within a relatively small range of boiling points, which are called fractions. These fractions are the origin of the term fractional distillation or fractionation.
It is often not worthwhile separating the components in these
fractions any further based on product requirements and economics.
Industrial distillation is typically performed in large, vertical
cylindrical columns (as shown in images 1 and 2) known as "distillation
towers" or "distillation columns" with diameters ranging from about 65
centimeters to 11 meters and heights ranging from about 6 meters to 60
meters or more.
Image
3: Chemical engineering schematic of Continuous Binary Fractional
Distillation tower. A binary distillation separates a feed mixture
stream into two fractions: one distillate and one bottoms fractions.
The principle for continuous distillation is the same as for normal
distillation: when a liquid mixture is heated so that it boils, the
composition of the vapor above the liquid differs from the liquid
composition. If this vapor is then separated and condensed into a liquid, it becomes richer in the lower boiling point component(s) of the original mixture.
This is what happens in a continuous distillation column. A
mixture is heated up, and routed into the distillation column. On
entering the column, the feed starts flowing down but part of it, the
component(s) with lower boiling point(s), vaporizes and rises. However,
as it rises, it cools and while part of it continues up as vapor, some
of it (enriched in the less volatile component) begins to descend again.
Image 3 depicts a simple continuous fractional distillation tower
for separating a feed stream into two fractions, an overhead distillate
product and a bottoms product. The "lightest" products (those with the
lowest boiling point or highest volatility) exit from the top of the
columns and the "heaviest" products (the bottoms, those with the highest
boiling point) exit from the bottom of the column. The overhead stream
may be cooled and condensed using a water-cooled or air-cooled condenser. The bottoms reboiler may be a steam-heated or hot oil-heated heat exchanger, or even a gas or oil-fired furnace.
In a continuous distillation, the system is kept in a steady state
or approximate steady state. Steady state means that quantities
related to the process do not change as time passes during operation.
Such constant quantities include feed input rate, output stream rates,
heating and cooling rates, reflux ratio, and temperatures,
pressures, and compositions at every point (location). Unless the
process is disturbed due to changes in feed, heating, ambient
temperature, or condensing, steady state is normally maintained. This
is also the main attraction of continuous distillation, apart from the
minimum amount of (easily instrumentable) surveillance; if the feed rate
and feed composition are kept constant, product rate and quality are also constant. Even when a variation in conditions occurs, modern process control methods are commonly able to gradually return the continuous process to another steady state again.
Since a continuous distillation unit is fed constantly with a
feed mixture and not filled all at once like a batch distillation, a
continuous distillation unit does not need a sizable distillation pot,
vessel, or reservoir for a batch fill. Instead, the mixture can be fed
directly into the column, where the actual separation occurs. The
height of the feed point along the column can vary on the situation and
is designed so as to provide optimal results. See McCabe–Thiele method.
Design
and operation of a distillation column depends on the feed and desired
products. Given a simple, binary component feed, analytical methods such
as the McCabe–Thiele method or the Fenske equation can be used to assist in the design. For a multi-component feed, computerized simulation
models are used both for design and subsequently in operation of the
column as well. Modeling is also used to optimize already erected
columns for the distillation of mixtures other than those the
distillation equipment was originally designed for.
When a continuous distillation column is in operation, it has to be closely monitored for changes in feed composition, operating temperature and product composition. Many of these tasks are performed using advanced computer control equipment.
Column feed
The
column can be fed in different ways. If the feed is from a source at a
pressure higher than the distillation column pressure, it is simply
piped into the column. Otherwise, the feed is pumped or compressed into
the column. The feed may be a superheated vapor, a saturated vapor, a partially vaporized liquid-vapor mixture, a saturated liquid (i.e., liquid at its boiling point at the column's pressure), or a sub-cooled liquid.
If the feed is a liquid at a much higher pressure than the column
pressure and flows through a pressure let-down valve just ahead of the
column, it will immediately expand and undergo a partial flash vaporization resulting in a liquid-vapor mixture as it enters the distillation column.
Improving separation
Image
4: Simplified chemical engineering schematic of Continuous Fractional
Distillation tower separating one feed mixture stream into four
distillate and one bottoms fractions
Although small size units, mostly made of glass, can be used in
laboratories, industrial units are large, vertical, steel vessels (see
images 1 and 2) known as "distillation towers" or "distillation
columns". To improve the separation, the tower is normally provided
inside with horizontal plates or trays as shown in image 5, or the column is packed
with a packing material. To provide the heat required for the
vaporization involved in distillation and also to compensate for heat
loss, heat is most often added to the bottom of the column by a reboiler, and the purity of the top product can be improved by recycling some of the externally condensed top product liquid as reflux.
Depending on their purpose, distillation columns may have liquid
outlets at intervals up the length of the column as shown in image 4.
Reflux
Large-scale industrial fractionation towers use reflux to achieve more efficient separation of products.
Reflux refers to the portion of the condensed overhead liquid product
from a distillation tower that is returned to the upper part of the
tower as shown in images 3 and 4. Inside the tower, the downflowing
reflux liquid provides cooling and partial condensation of the upflowing
vapors, thereby increasing the efficacy of the distillation tower. The
more reflux that is provided, the better is the tower's separation of
the lower boiling from the higher boiling components of the feed. A
balance of heating with a reboiler at the bottom of a column and cooling
by condensed reflux at the top of the column maintains a temperature
gradient (or gradual temperature difference) along the height of the
column to provide good conditions for fractionating the feed mixture.
Reflux flows at the middle of the tower are called pumparounds.
Changing the reflux (in combination with changes in feed and
product withdrawal) can also be used to improve the separation
properties of a continuous distillation column while in operation (in
contrast to adding plates or trays, or changing the packing, which
would, at a minimum, require quite significant downtime).
Plates or trays
Image 5: Cross-sectional diagram of a binary fractional distillation tower with bubble-cap trays. (See theoretical plate for enlarged tray image.)
Distillation towers (such as in images 3 and 4) use various vapor and
liquid contacting methods to provide the required number of equilibrium stages. Such devices are commonly known as "plates" or "trays".
Each of these plates or trays is at a different temperature and
pressure. The stage at the tower bottom has the highest pressure and
temperature. Progressing upwards in the tower, the pressure and
temperature decreases for each succeeding stage. The vapor–liquid equilibrium
for each feed component in the tower reacts in its unique way to the
different pressure and temperature conditions at each of the stages.
That means that each component establishes a different concentration in
the vapor and liquid phases at each of the stages, and this results in
the separation of the components. Some example trays are depicted in
image 5. A more detailed, expanded image of two trays can be seen in
the theoretical plate article. The reboiler often acts as an additional equilibrium stage.
If each physical tray or plate were 100% efficient, then the
number of physical trays needed for a given separation would equal the
number of equilibrium stages or theoretical plates. However, that is
very seldom the case. Hence, a distillation column needs more plates
than the required number of theoretical vapor–liquid equilibrium stages.
Packing
Another way of improving the separation in a distillation column is to use a packing material instead of trays. These offer the advantage of a lower pressure drop across the column (when compared to plates or trays),
beneficial when operating under vacuum. If a distillation tower uses
packing instead of trays, the number of necessary theoretical
equilibrium stages is first determined and then the packing height
equivalent to a theoretical equilibrium stage, known as the height equivalent to a theoretical plate (HETP), is also determined. The total packing height required is the number of theoretical stages multiplied by the HETP.
This packing material can either be random dumped packing such as Raschig rings or structured sheet metal. Liquids tend to wet the surface of the packing and the vapors pass across this wetted surface, where mass transfer
takes place. Unlike conventional tray distillation in which every tray
represents a separate point of vapor–liquid equilibrium, the
vapor–liquid equilibrium curve in a packed column is continuous.
However, when modeling packed columns it is useful to compute a number
of theoretical plates to denote the separation efficiency of the packed
column with respect to more traditional trays. Differently shaped
packings have different surface areas and void space between packings.
Both of these factors affect packing performance.
Another factor in addition to the packing shape and surface area that affects the performance of random or structured packing is liquid and vapor distribution entering the packed bed. The number of theoretical stages
required to make a given separation is calculated using a specific
vapor to liquid ratio. If the liquid and vapor are not evenly
distributed across the superficial tower area as it enters the packed
bed, the liquid to vapor ratio will not be correct in the packed bed and
the required separation will not be achieved. The packing will appear
to not be working properly. The height equivalent to a theoretical plate
(HETP) will be greater than expected. The problem is not the packing
itself but the mal-distribution of the fluids entering the packed bed.
Liquid mal-distribution is more frequently the problem than vapor. The
design of the liquid distributors used to introduce the feed and reflux
to a packed bed is critical to making the packing perform at maximum
efficiency. Methods of evaluating the effectiveness of a liquid
distributor can be found in references.
Overhead system arrangements
Images
4 and 5 assume an overhead stream that is totally condensed into a
liquid product using water or air-cooling. However, in many cases, the
tower overhead is not easily condensed totally and the reflux drum must include a vent gas
outlet stream. In yet other cases, the overhead stream may also contain
water vapor because either the feed stream contains some water or some
steam is injected into the distillation tower (which is the case in the
crude oil distillation towers in oil refineries).
In those cases, if the distillate product is insoluble in water, the
reflux drum may contain a condensed liquid distillate phase, a condensed
water phase and a non-condensible gas phase, which makes it necessary
that the reflux drum also have a water outlet stream.
Multicomponent distillation
Beside
fractional distillation, that is mainly used for crude oil refining,
multicomponent mixtures are usually processed in order to purify their
single components by mean of a series of distillation columns, i.e. the
distillation train.
Distillation train
A
distillation train is defined by a sequence of distillation columns
arranged in series or in parallel whose aim is the multicomponent
mixtures purification.
Process intensifying alternatives
The Dividing Wall Column
unit is most common process-intensifying unit related to distillation.
In particular, it is the arrangement in a single column shell of the
Petlyuk configuration that has been proved to be thermodynamically equivalent.
The crude oil fractionator does not produce products having a single boiling point; rather, it produces fractions having boiling ranges. For example, the crude oil fractionator produces an overhead fraction called "naphtha" which becomes a gasoline component after it is further processed through a catalytic hydrodesulfurizer to remove sulfur and a catalytic reformer to reform its hydrocarbon molecules into more complex molecules with a higher octane rating value.
The naphtha cut, as that fraction is called, contains many
different hydrocarbon compounds. Therefore, it has an initial boiling
point of about 35 °C and a final boiling point of about 200 °C. Each cut
produced in the fractionating columns has a different boiling range. At
some distance below the overhead, the next cut is withdrawn from the
side of the column and it is usually the jet fuel cut, also known as a kerosene
cut. The boiling range of that cut is from an initial boiling point of
about 150 °C to a final boiling point of about 270 °C, and it also
contains many different hydrocarbons. The next cut further down the
tower is the diesel oil
cut with a boiling range from about 180 °C to about 315 °C. The boiling
ranges between any cut and the next cut overlap because the
distillation separations are not perfectly sharp. After these come the
heavy fuel oil cuts and finally the bottoms product, with very wide
boiling ranges. All these cuts are processed further in subsequent
refining processes.
Continuous distillation of cannabis concentrates
A typical application for distilling cannabis concentrates is butane hash oil (BHO). Short path distillation is a popular method due to the short residence time which allows for minimal thermal stress to the concentrate. In other distillation methods such as circulation, falling film
and column distillation the concentrate would be damaged from the long
residence times and high temperatures that must be applied.
Similar to all-electric vehicles (BEVs), PHEVs displace greenhouse gas emissions from the car tailpipeexhaust to the power station generators powering the electricity grid. These centralized generators may be of renewable energy (e.g. solar, wind or hydroelectric) and largely emission-free, or have an overall lower emission intensity than individual internal combustion engines. Compared to conventional hybrid electric vehicles
(HEVs), PHEVs have a larger battery pack that can be charged from the
power grid, which is also more efficient and can cost less than using
only the on-board generator, and also often have a more powerful
electric output capable of longer and more frequent EV mode driving, helping to reduce operating costs.
A PHEV's battery pack is smaller than all-electric vehicles for the
same vehicle weight (due to the necessity to still accommodate its
combustion engine and hybrid drivetrain), but has the auxiliary option of switching back to using its gasoline/diesel engine like a conventional HEV if the battery runs low, alleviating range anxiety especially for places that lack sufficient charging infrastructure.
As of December 2019, the global stock of PHEVs totaled 2.4 million units, representing one-third of the stock of plug-in electric passenger cars on the world's roads. As of December 2019, China had the world's largest stock of PHEVs with 767,900 units, followed by the United States with 567,740, and the United Kingdom with 159,910.
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
(32 km) without using its combustion engine, so it may also be
designated as a PHEV32km.
For these cars to be battery operated, they go through charging
processes that use different currents. These currents are known as
Alternating Current (AC) used for on board chargers and Direct Current
(DC) used for external charging.
Other popular terms sometimes used for plug-in hybrids are
"grid-connected hybrids", "Gas-Optional Hybrid Electric Vehicle"
(GO-HEV) or simply "gas-optional hybrids". GM calls its Chevrolet Voltseries plug-in hybrid an "Extended-Range Electric Vehicle".
The Lohner-Porsche Mixte Hybrid, produced as early as 1899, was the first hybrid electric car. 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
term "plug-in hybrid electric vehicle" was coined by UC DavisProfessor Andrew Frank, who has been called the "father of the modern plug-in hybrid".
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. 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. In addition to its engine, it could be plugged into a standard outlet and recharged to 95% range in about 4 hours. After selling about 500 vehicles, primarily in France, Norway and the UK, the Elect'road was redesigned in 2007.
With the availability of hybrid vehicles and the rising gas
prices in the United States starting around 2004, interest in plug-in
hybrids increased. Some plug-in hybrids were conversions of existing hybrids; for example, the 2004 CalCars conversion of a Prius to add lead acid batteries and a range of up to 15 km (9 mi) using only electric power.
In 2006, both Toyota and General Motors announced plans for plug-in hybrids. GM's Saturn Vue project was cancelled, but the Toyota plug-in was certified for road use in Japan in 2007.
In 2007, Quantum Technologies and Fisker Coachbuild, LLC announced the launch of a joint venture in Fisker Automotive. Fisker intended to build a US$80,000 luxury PHEV-50, the Fisker Karma, initially scheduled for late 2009.
In 2007, Aptera Motors announced their Typ-1 two-seater. However, the company folded in December 2011.
In 2007, Chinese car manufacturer BYD Auto, owned by China's
largest mobile phone battery maker, announced it would be introducing a
production PHEV-60 sedan in China in the second half of 2008. BYD
exhibited it in January 2008 at the North American International Auto Show in Detroit. Based on BYD's midsize F6 sedan, it uses lithium iron phosphate (LiFeP04)-based batteries instead of lithium-ion, and can be recharged to 70% of capacity in 10 minutes.
In 2007 Ford delivered the first Ford Escape Plug-in Hybrid of a fleet of 20 demonstration PHEVs to Southern California Edison. As part of this demonstration program Ford also developed the first flexible-fuel plug-in hybrid SUV, which was delivered in June 2008. This demonstration fleet of plug-ins has been in field testing with utility company fleets in the U.S. and Canada, and during the first two years since the program began, the fleet has logged more than 75,000 miles.
In August 2009 Ford delivered the first Escape Plug-in equipped with
intelligent vehicle-to-grid (V2G) communications and control system
technology, and Ford plans to equip all 21 plug-in hybrid Escapes with
the vehicle-to-grid communications technology. Sales of the Escape PHEV were scheduled for 2012.
On January 14, 2008, Toyota announced they would start sales of lithium-ion battery PHEVs by 2010, but later in the year Toyota indicated they would be offered to commercial fleets in 2009.
On March 27, the California Air Resources Board
(CARB) modified their regulations, requiring automobile manufacturers
to produce 58,000 plug-in hybrids during 2012 through 2014. This requirement is an asked-for alternative to an earlier mandate to produce 25,000 pure zero-emissions vehicles, reducing that requirement to 5,000. On June 26, Volkswagen announced that they would be introducing production plug-ins based on the Golf compact. Volkswagen uses the term 'TwinDrive' to denote a PHEV. In September, Mazda was reported to be planning PHEVs. On September 23, 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 into
production.
Launched in China in December 2008, the BYD F3DM became the world's first mass-produced plug-in hybrid automobile.
The BYD Qin, released in China in December 2013, replaced the F3DM.
On December 15, 2008, BYD Auto began selling its F3DM in China,
becoming the first production plug-in hybrid sold in the world, though
initially was available only for corporate and government customers. Sales to the general public began in Shenzhen in March 2010,
but because the F3DM nearly doubles the price of cars that run on
conventional fuel, BYD expects subsidies from the local government to
make the plug-in affordable to personal buyers. Toyota tested 600 pre-productionPrius Plug-ins in Europe and North America in 2009 and 2010.
In October 2010 Lotus Engineering unveiled the Lotus CityCar, a plug-in series hybrid concept car designed for flex-fuel operation on ethanol, or methanol as well as regular gasoline. The lithium battery
pack provides an all-electric range of 60 kilometres (37 mi), and the
1.2-liter flex-fuel engine kicks in to allow to extend the range to more
than 500 kilometres (310 mi).
GM officially launched the Chevrolet Volt in the U.S. on November 30, 2010, and retail deliveries began in December 2010. Its sibling the Opel/Vauxhall Ampera was launched in Europe between late 2011 and early 2012. The first deliveries of the Fisker Karma took place in July 2011, and deliveries to retail customers began in November 2011. The Toyota Prius Plug-in Hybrid was released in Japan in January 2012, followed by the United States in February 2012. Deliveries of the Prius PHV in Europe began in late June 2012. The Ford C-Max Energi was released in the U.S. in October 2012, the Volvo V60 Plug-in Hybrid in Sweden by late 2012.
The Honda Accord Plug-in Hybrid was released in selected U.S. markets in January 2013, and the Mitsubishi Outlander P-HEV in Japan in January 2013, becoming the first SUV plug-in hybrid in the market. Deliveries of the Ford Fusion Energi began in February 2013. BYD Auto stopped production of its BYD F3DM due to low sales, and its successor, the BYD Qin, began sales in Costa Rica in November 2013, with sales in other countries in Latin America scheduled to begin in 2014. Qin deliveries began in China in mid December 2013.
Deliveries to retail customers of the limited edition McLaren P1 supercar began in the UK in October 2013, and the Porsche Panamera S E-Hybrid began deliveries in the U.S. in November 2013. The first retail deliveries of the Cadillac ELR took place in the U.S. in December 2013. The BMW i8 and the limited edition Volkswagen XL1 were released to retail customers in Germany in June 2014. The Porsche 918 Spyder was also released in Europe and the U.S. in 2014. The first units of the Audi A3 Sportback e-tron and Volkswagen Golf GTE were registered in Germany in August 2014.
In December 2014 BMW announced the group is planning to offer
plug-in hybrid versions of all its core-brand models using eDrive
technology developed for its BMW i brand plug-in vehicles (BMW i3
and BMW i8). The goal of the company is to use plug-in technology to
continue offering high performance vehicles while reducing CO2 emissions below 100g/km. At the time of the announcement the carmaker was already testing a BMW 3 Series plug-in hybrid prototype. The first model available for retail sales will be the 2016 BMW X5 eDrive, with the production version unveiled at the 2015 Shanghai Motor Show. The second generation Chevrolet Volt was unveiled at the January 2015 North American International Auto Show, and retail deliveries began in the U.S. and Canada in October 2015.
In March 2015 Audi
said they planned on making a plug-in hybrid version of every model
series, and that they expect plug-in hybrids, together with natural gas
vehicles and battery-electric drive systems, to have a key contribution
in achieving the company's CO2 targets. The Audi Q7 e-tron will follow the A3 e-tron already in the market. Also in March 2015, Mercedes-Benz
announced that the company's main emphasis regarding alternative drives
in the next years will be on plug-in hybrids. The carmaker plans to
introduce 10 new plug-in hybrid models by 2017, and its next release was
the Mercedes-Benz C 350 e, Mercedes’ second plug-in hybrid after the S 500 Plug-In Hybrid. Other plug-in hybrid released in 2015 are the BYD Tang, Volkswagen Passat GTE, Volvo XC90 T8, and the Hyundai Sonata PHEV.
Global combined Volt/Ampera family sales passed the 100,000 unit milestone in October 2015.
By the end of 2015, over 517,000 highway legal plug-in hybrid electric
cars have been sold worldwide since December 2008 out of total global
sales of more than 1.25 million light-duty plug-in electric cars.
In February 2016, BMW announced the introduction of the
"iPerformance" model designation, which will be given to all BMW plug-in
hybrid vehicles from July 2016. The aim is to provide a visible
indicator of the transfer of technology from BMW i to the BMW core brand. The new designation will be used first on the plug-in hybrid variants of the new BMW 7 Series, the BMW 740e iPerformance, and the 3 Series, the BMW 330e iPerformance.
Hyundai Motor Company made the official debut of its three model Hyundai Ioniq line-up at the 2016 Geneva Motor Show. The Ioniq family of electric drive vehicles includes the Ioniq Plug-in, which is expected to achieve a fuel economy of 125 mpg‑e (28 kW⋅h/100 mi; 17.1 kW⋅h/100 km) in all-electric mode. The Ioniq Plug-in is scheduled to be released in the U.S. in the fourth quarter of 2017.
The second generation Prius plug-in hybrid, called Prius Prime in the U.S. and Prius PHV in Japan, was unveiled at the 2016 New York International Auto Show. Retail deliveries of the Prius Prime began in the U.S. in November 2016, and is scheduled to be released Japan by the end of 2016.
The Prime has an EPA-rated all-electric range of 25 mi (40 km), over
twice the range of the first generation model, and an EPA rated fuel
economy of 133 mpg‑e (25.9 kW⋅h/100 mi) in all-electric mode (EV mode), the highest MPGe rating in EV mode of any vehicle rated by EPA.[95][96] Unlike its predecessor, the Prime runs entirely on electricity in EV mode. Global sales of the Mitsubishi Outlander P-HEV passed the 100,000 unit milestone in March 2016. BYD Qin sales in China reached the 50,000 unit milestone in April 2016, becoming the fourth plug-in hybrid to pass that mark.
In June 2016, Nissan announced it will introduce a compact range extender
car in Japan before March 2017. The series plug-in hybrid will use a
new hybrid system, dubbed e-Power, which debuted with the Nissan Gripz concept crossover showcased at the 2015 Frankfurt Auto Show.
In January 2016, Chrysler debuted its plug-in hybrid minivan, the Chrysler Pacifica Hybrid, with an EPA rated electric-only range of 48 km (30 miles). This was the first hybrid minivan of any type. It was first sold in the United States, Canada, and Mexico in 2017.
In December 2017, Honda began retail deliveries of the Honda Clarity Plug-In Hybrid in the United States and Canada, with an EPA rated electric-only range of 76 km (47 miles).
PHEVs are based on the same three basic powertrain architectures of conventional hybrids; a series hybrid is propelled by electric motors only, a parallel hybrid is propelled both by its internal combustion engine and by electric motors operating concurrently, and a series-parallel hybrid operates in either mode. While a plain hybrid vehicle charges its battery
from its engine only, a plug-in hybrid can obtain a significant amount
of the energy required to recharge its battery from external sources.
Charging systems
The
battery charger can be on-board or external to the vehicle. The process
for an on-board charger is best explained as AC power being converted
into DC power, resulting in the battery being charged.
On-board chargers are limited in capacity by their weight and size, and
by the limited capacity of general-purpose AC outlets. Dedicated
off-board chargers can be as large and powerful as the user can afford,
but require returning to the charger; high-speed chargers may be shared
by multiple vehicles.
Using the electric motor's inverter allows the motor windings to
act as the transformer coils, and the existing high-power inverter as
the AC-to-DC charger. As these components are already required on the
car, and are designed to handle any practical power capability, they can
be used to create a very powerful form of on-board charger with no
significant additional weight or size. AC Propulsion uses this charging method, referred to as "reductive charging".
Modes of operation
A plug-in hybrid operates in 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:
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.
Mixed mode describes a trip using a combination of
multiple modes. For example, a car may begin a trip in low speed
charge-depleting mode, then enter onto a freeway and operate in blended
mode. The driver might exit the freeway and drive without the internal
combustion engine until all-electric range is exhausted. The vehicle can
revert to a charge sustaining-mode until the final destination is
reached. This contrasts with a charge-depleting trip which would be
driven within the limits of a PHEV's all-electric range.
The optimum battery size varies depending on whether the aim is to
reduce fuel consumption, running costs, or emissions, but a recent study
concluded that "The best choice of PHEV battery capacity depends
critically on the distance that the vehicle will be driven between
charges. Our results suggest that for urban driving conditions and
frequent charges every 10 miles or less, a low-capacity PHEV sized with
an AER (all-electric range) of about 7 miles would be a robust choice
for minimizing gasoline consumption, cost, and greenhouse gas emissions.
For less frequent charging, every 20–100 miles, PHEVs release fewer
GHGs, but HEVs are more cost effective."
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. Design issues and trade-offs against battery life, capacity, heat dissipation, weight, costs, and safety need to be solved. Advanced battery technology is under development, promising greater energy densities by both mass and volume, and battery life expectancy is expected to increase.
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. At early
2007 gasoline and electricity prices, the break-even point is reached
after six to ten years of operation. The payback period may be longer
for plug-in hybrids, because of their larger, more expensive batteries.
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.
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. 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".
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. The CSIRO's UltraBattery combines a supercapacitor
and a lead acid 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).
There are several companies that are converting fossil fuel non-hybrid vehicles to plug-in hybrids:
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 Toyota Prius.
Some of the systems have involved replacement of the vehicle's original
NiMH battery pack and its electronic control unit. Others add an
additional battery back onto the original battery pack.
Target market
In
recent years, demand for all- electric vehicles, especially in the
United States market, has been driven by government incentives through
subsidies, lobbyists, and taxes. In particular, American sales of the Nissan Leaf have depended on generous incentives and special treatment in the state of Georgia, the top selling Leaf market.
According to international market research, 60% of respondents believe a
battery driving range of less than 160 km (99 mi) is unacceptable even
though only 2% drive more than that distance per day. Among popular current all-electric vehicles, only the Tesla (with the most expensive version of the Model S offering a 265 miles (426 km) range in the U.S. Environmental Protection Agency
5-cycle test) significantly exceeds this threshold. The Nissan Leaf has
an EPA rated range of 75 miles (121 km) for the 2013 model year.
All-electric range, in miles, for several popular model year 2013 plug-in hybrids, as observed in testing by Popular Mechanics
magazine. Providing greater all-electric range adds cost and entails
compromises, so different all-electric ranges may suit different
customers' needs.
Plug-in hybrids provide the extended range and potential for
refueling of conventional hybrids while enabling drivers to use battery
electric power for at least a significant part of their typical daily
driving. The average trip to or from work in the United States in 2009
was 11.8 miles (19.0 km), while the average distance commuted to work in England and Wales in 2011 was slightly lower at 9.3 miles (15 km).
Since building a PHEV with a longer all-electric range adds weight and
cost, and reduces cargo and/or passenger space, there is not a specific
all-electric range that is optimal. The accompanying graph shows the
observed all-electric range, in miles, for four popular U.S. market
plug-in hybrids, as tested by Popular Mechanics magazine.
A key design parameter of the Chevrolet Volt was a target of 40
miles (64 km) for the all-electric range, selected to keep the battery
size small and lower costs, and mainly because research showed that 78%
of daily commuters
in the U.S. travel 40 mi (64 km) or less. This target range would allow
most travel to be accomplished electrically driven and the assumption
was made that charging will take place at home overnight. This
requirement translated using a lithium-ion battery pack with an energy storage capacity of 16 kWh considering that the battery would be used until the state of charge (SOC) of the battery reached 30%.
In October 2014 General Motors reported, based on data collected through its OnStartelematics
system since Volt deliveries began, and with over 1 billion miles (1.6
billion km) traveled, that Volt owners drive about 62.5% of their trips
in all-electric mode.
In May 2016, Ford reported, based on data collected from more than 610
million miles (976 million km) logged by its electrified vehicles
through its telematics system, that drivers of these vehicles run an
average of 13,500 mi (21,700 km) annually on their vehicles, with about
half of those miles operating in all-electric mode. A break down of
these figures show an average daily commute of 42 mi (68 km) for Ford
Energi plug-in hybrid drivers. Ford notes that with the enhanced
electric range of the 2017 model year model, the average Fusion Energi
commuter could go the entire day using no gasoline, if the car is fully
charged both, before leaving for work and before leaving for home.
According to Ford data, currently most customers are likely charging
their vehicles only at home.
The 2015 edition of the EPA's annual report "Light-Duty Automotive Technology, Carbon Dioxide Emissions, and Fuel Economy Trends" estimates the following utility factors for 2015 model year
plug-in hybrids to represent the percentage of miles that will be
driven using electricity by an average driver, whether in electric only
or blended modes: 83% for the BMW i3 REx, 66% for the Chevrolet Volt, 45% for the Ford Energi models, 43% for the McLaren P1, 37% for the BMW i8, and 29% for the Toyota Prius PHV. A 2014 analysis conducted by the Idaho National Laboratory
using a sample of 21,600 all-electric cars and plug-in hybrids, found
that Volt owners traveled on average 9,112 miles in all-electric mode
(e-miles) per year, while Leaf owners traveled 9,697 e-miles per year,
despite the Volt's shorter all-electric range, about half of the Leaf's.
Between January and August 2014, a period during which US sales
of conventional hybrids slowed, US sales of plug-in hybrids grew from
28,241 to 40,748 compared to the same period in 2013. US sales of
all-electric vehicles also grew during the same period: from 29,917
vehicles in the January to August 2013 period to 40,349 in January to
August 2014.
Plug-in hybrids have the 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 Toyota 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.
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.
Each kilowatt hour of battery capacity in use will displace up to 50 U.S. gallons (190 l; 42 imp gal) of petroleum fuels per year (gasoline or diesel). Also, electricity is multi-sourced and, as a result, it gives the greatest degree of energy resilience.
The actual fuel economy
for PHEVs depends on their powertrain's operating modes, the
all-electric range, and the amount of driving between charges. If no
gasoline is used the miles per gallon gasoline equivalent (MPG-e) depends only on the efficiency of the electric system. The first mass production PHEV available in the U.S. market, the 2011 Chevrolet Volt,
with an EPA rated all-electric range of 35 mi (56 km) and an additional
gasoline-only extended range of 344 mi (554 km), has an EPA combined
city/highway fuel economy of 93 MPG-e in all-electric mode, and 37 mpg‑US (6.4 L/100 km; 44 mpg‑imp) in gasoline-only mode, for an overall combined gas-electric fuel economy rating of 60 mpg‑US (3.9 L/100 km; 72 mpg‑imp) equivalent (MPG-e). The EPA also included in the Volt's fuel economy label
a table showing fuel economy and electricity consumed for five
different scenarios: 30, 45, 60 and 75 mi (121 km) driven between a full
charge, and a never charge scenario. According to this table the fuel economy goes up to 168 mpg‑US (1.40 L/100 km; 202 mpg‑imp) equivalent (MPG-e) with 45 mi (72 km) driven between full charges.
For the more comprehensive fuel economy and environment label that will be mandatory in the U.S. beginning in model year 2013, the National Highway Traffic Safety Administration (NHTSA) and Environmental Protection Agency
(EPA) issued two separate fuel economy labels for plug-in hybrids
because of their design complexity, as PHEVS can operate in two or three
operating modes: all-electric, blended, and gasoline-only.
One label is for series hybrid or extended range electric vehicle (like
the Chevy Volt), with all-electric and gasoline-only modes; and a
second label for blended mode or series-parallel hybrid,
that includes a combination of both gasoline and plug-in electric
operation; and gasoline only, like a conventional hybrid vehicle.
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.
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.
In real world testing using normal drivers, some Prius PHEV
conversions may not achieve much better fuel economy than HEVs. For
example, a plug-in Prius fleet, each with a 30 miles (48 km)
all-electric range, averaged only 51 mpg‑US (4.6 L/100 km; 61 mpg‑imp) in a 17,000-mile (27,000 km) test in Seattle, and similar results with the same kind of conversion battery models at Google's RechargeIT initiative. Moreover, the additional battery pack costs US$10,000–US$11,000.
Operating costs
A study published in 2014 by researchers from Lamar University, Iowa State University and Oak Ridge National Laboratory
compared the operating costs of PHEVs of various electric ranges (10,
20, 30, and 40 miles) with conventional gasoline vehicles and non-plugin
hybrid-electric vehicles (HEVs) for different payback periods,
considering different charging infrastructure deployment levels and
gasoline prices. The study concluded that:
PHEVs save around 60% or 40% in energy costs, compared with
conventional gasoline vehicles and HEVs, respectively. However, for
drivers with significant daily vehicle miles traveled (DVMT), hybrid
vehicles maybe even a better choice than plug-in hybrids with a range of
40 mi (64 km), particularly when there is a lack of public charging
infrastructure.
The incremental battery cost of large-battery plug-in hybrids is
difficult to justify based on the incremental savings of PHEVs’
operating costs unless a subsidy is offered for large-battery PHEVs.
When the price of gasoline increases from US$4 per gallon to US$5 per gallon, the number of drivers who benefit from a larger battery increases significantly. If the gas price is US$3, a plug-in hybrid with a range of 10 mi (16 km) is the least costly option even if the battery cost is $200/kWh.
Although quick chargers can reduce charging time, they contribute little to energy cost savings for PHEVs, as opposed to Level-2 chargers.
Disadvantages of PHEVs include the additional cost, weight and size of a larger battery pack. According to a 2010 study by the National Research Council, the cost of a lithium-ion battery pack is about US$1,700/kW·h
of usable energy, and considering that a PHEV-10 requires about
2.0 kW·h and a PHEV-40 about 8 kW·h, the estimated manufacturer cost of
the battery pack for a PHEV-10 is around US$3,000 and it goes up to US$14,000 for a PHEV-40.
According to the same study, even though costs are expected to decline
by 35% by 2020, market penetration is expected to be slow and therefore
PHEVs are not expected to significantly impact oil consumption or carbon
emissions before 2030, unless a fundamental breakthrough in battery
technologies occurs.
Cost comparison between a PHEV-10 and a PHEV-40 (prices for 2010)
Notes: (1) Considers the HEV technology used in the Toyota Prius with a larger battery pack. The Prius Plug-in estimated all-electric range is 14.5 mi (23 km) (2) Assuming 15,000 miles per year.
According to the 2010 NRC study, although a mile driven on
electricity is cheaper than one driven on gasoline, lifetime fuel
savings are not enough to offset plug-ins' high upfront costs, and it
will take decades before the break-even point is achieved.
Furthermore, hundreds of billions of dollars in government subsidies
and incentives are likely to be required to achieve rapid plug-in market
penetration in the U.S.
A 2013 study by the American Council for an Energy-Efficient Economy reported that battery costs came down from US$1,300 per kilowatt hour in 2007 to US$500 per kilowatt hour in 2012. The U.S. Department of Energy has set cost targets for its sponsored battery research of US$300 per kilowatt hour in 2015 and US$125
per kilowatt hour by 2022. Cost reductions through advances in battery
technology and higher production volumes will allow plug-in electric
vehicles to be more competitive with conventional internal combustion
engine vehicles.
A study published in 2011 by the Belfer Center, Harvard University,
found that the gasoline costs savings of PHEVs over the vehicles’
lifetimes do not offset their higher purchase prices. This finding was
estimated comparing their lifetime net present value at 2010 purchase and operating costs for the U.S. market, and assuming no government subidies. According to the study estimates, a PHEV-40 is US$5,377 more expensive than a conventional internal combustion engine, while a battery electric vehicle (BEV) is US$4,819
more expensive. The study also examined how this balance will change
over the next 10 to 20 years, assuming that battery costs will decrease
while gasoline prices increase. Under the future scenarios considered,
the study found that BEVs will be significantly less expensive than
conventional cars (US$1,155 to US$7,181
cheaper), while PHEVs, will be more expensive than BEVs in almost all
comparison scenarios, and only less expensive than conventional cars in a
scenario with very low battery costs and high gasoline prices. BEVs are
simpler to build and do not use liquid fuel, while PHEVs have more
complicated powertrains and still have gasoline-powered engines.
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.
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. 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.
According to a 2009 study by The National Academy of Science,
"Electric vehicles and grid-dependent (plug-in) hybrid vehicles showed
somewhat higher nonclimate damages than many other technologies." Efficiency of plug-in hybrids is also impacted by the overall efficiency of electric power transmission. Transmission and distribution losses in the USA were estimated at 7.2% in 1995 and 6.5% in 2007. By life cycle analysis of air pollution emissions, natural gas vehicles are currently the lowest emitter.
Tiered rate structure for electric bills
The
additional electrical consumption 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 financial benefits.
Customers under such tariffs could see significant savings by being
careful about when the vehicle was charged, for example, by using a
timer to restrict charging to off-peak hours. 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 and the actual observed operational cost of electric mode
vehicle operation.
The effect of PHEVs on greenhouse emissions is complex. Plug-in hybrid vehicles operating on all-electric mode do not emit harmful tailpipe pollutants
from the onboard source of power. 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 the same way, PHEVs 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. From the perspective of a full life cycle analysis, the electricity used to recharge the batteries must be generated from zero-emission sources such as renewable (e.g. wind power, solar energy or hydroelectricity) 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.
In the case of plug-in hybrid electric vehicle when 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.
Life cycle energy and emissions assessments
Argonne
In 2009, researchers at Argonne National Laboratory adapted their GREET model to conduct a full well-to-wheels (WTW) analysis of energy use and greenhouse gas (GHG) emissions
of plug-in hybrid electric vehicles for several scenarios, considering
different on-board fuels and different sources of electricity generation
for recharging the vehicle batteries. Three US regions were selected
for the analysis, California, New York, and Illinois,
as these regions include major metropolitan areas with significant
variations in their energy generation mixes. The full cycle analysis
results were also reported for the US generation mix and renewable
electricity to examine cases of average and clean mixes, respectively
This 2009 study showed a wide spread of petroleum use and GHG emissions
among the different fuel production technologies and grid generation
mixes. The following table summarizes the main results:
PHEV well-to-wheels Petroleum energy use and greenhouse gas emissions for an all-electric range between 10 and 40 miles (16 and 64 km) with different on-board fuels.(1) (as a % relative to an internal combustion engine vehicle that uses fossil fuel gasoline)
Source: Center for Transportation Research, Argonne National Laboratory (2009). See Table 1. Notes: (1) Simulations for year 2020 with PHEV model year 2015. (2) No direct or indirect land use changes included in the WTW analysis for bio-mass fuel feedstocks.
The Argonne study found that PHEVs offered reductions in petroleum
energy use as compared with regular hybrid electric vehicles. More
petroleum energy savings and also more GHG emissions reductions were
realized as the all-electric range increased, except when electricity
used to recharge was dominated by coal or oil-fired power generation. As
expected, electricity from renewable sources realized the largest
reductions in petroleum energy use and GHG emissions for all PHEVs as
the all-electric range increased. The study also concluded that plug-in
vehicles that employ biomass-based fuels (biomass-E85 and -hydrogen) may
not realize GHG emissions benefits over regular hybrids if power
generation is dominated by fossil sources.
Oak Ridge
A 2008 study by researchers at Oak Ridge National Laboratory
analyzed oil use and greenhouse gas (GHG) emissions of plug-in hybrids
relative to hybrid electric vehicles under several scenarios for years
2020 and 2030.
The study considered the mix of power sources for 13 U.S. regions that
would be used during recharging of vehicles, generally a combination of
coal, natural gas and nuclear energy, and to a lesser extent renewable
energy. A 2010 study conducted at Argonne National Laboratory
reached similar findings, concluding that PHEVs will reduce oil
consumption but could produce very different greenhouse gas emissions
for each region depending on the energy mix used to generate the
electricity to recharge the plug-in hybrids.
Environmental Protection Agency
In October 2014, the U.S. Environmental Protection Agency published the 2014 edition of its annual report "Light-Duty Automotive Technology, Carbon Dioxide Emissions, and Fuel Economy Trends". For the first time, the 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%, PEVs began to have a
measurable impact on the U.S. overall new vehicle fuel economy and CO2 emissions.
EPA's report included the analysis of 12 all-electric passengers cars and 10 plug-in hybrids available in the market as model year
2014. For purposes of an accurate estimation of emissions, the analysis
took into consideration the differences in operation between those
PHEVs like the Chevrolet Volt that can operate in all-electric mode without using gasoline, and those that 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, on
average, of the percentage of miles that will be driven using
electricity (in electric only and blended modes) by an average driver.
The following table shows the overall EV/hybrid 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. The study used the utility factor (since
in pure EV mode there are no tailpipe emissions) and the EPA best
estimate of the CO2tailpipe emissions
produced by these vehicles in real world city and highway operation
based on the EPA 5-cycle label methodology, using a weighted 55%
city/45% highway driving. The results are shown in the following table.
In addition, the EPA accounted for the upstream CO2
emissions associated with the production and distribution of
electricity required to charge the PHEVs. Since electricity production
in the United States varies significantly from region to region, the EPA
considered three scenarios/ranges with the low end of the range
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 Rockies. The EPA estimates that the electricity
GHG emission factors for various regions of the country vary from 346 g
CO2/kW-hr in California to 986 g CO2/kW-hr in the Rockies, with a
national average of 648 g CO2/kW-hr.
The following table shows the tailpipe emissions and the combined
tailpipe and upstream emissions for each of the 10 MY 2014 PHEVs
available in the U.S. market.
Comparison of tailpipe and upstream CO2 emissions(1) estimated by EPA for the MY 2014 plug-in hybrids available in the U.S. market as of September 2014
Notes:
(1) Based on 45% highway and 55% city driving. (2) The utility factor
represents, on average, the percentage of miles that will be driven
using electricity (in electric only and blended modes) by an average
driver. (3) The EPA classifies the i3 REx as a series plug-in hybrid
National Bureau of Economic Research
Most
emission analysis use 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 study used emissions and
consumption data for 2007 through 2009, and used the specifications for
the Chevrolet Volt (all-electric range of 35 mi (56 km)). The analysis
found that marginal emission rates are more than three times as large in
the Upper Midwest compared to the Western U.S., and within regions, rates for some hours of the day are more than twice those for others.
Applying the results of the marginal analysis to plug-in electric
vehicles, the NBER researchers 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, CO2
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. This
pattern of fuel shifting explains why emission rates tend to be higher
at night and lower during periods of peak demand in the morning and
evening.
The Chevrolet Volt was the world's top selling plug-in hybrid until September 2018.
Since 2008, plug-in hybrids have been commercially available from
both specialty manufacturers and from mainstream producers of internal
combustion engine vehicles. The F3DM, released in China in December 2008, was the first production plug-in hybrid sold in the world. The Chevrolet Volt, launched in the U.S. in December 2010, was the first mass-production plug-in hybrid by a major carmaker.
Sales and main markets
There were 1.2 million plug-in hybrid cars on the world roads at the end of 2017. The stock of plug-in hybrids increased to 1.8 million in 2018, out of a global stock of about 5.1 million plug-in electric passenger cars. As of December 2017,
the United States ranked as the world's largest plug-in hybrid car
market with a stock of 360,510 units, followed by China with 276,580
vehicles, Japan with 100,860 units, the Netherlands with 98,220, and the
UK with 88,660.
Global sales of plug-in hybrids grew from over 300 units in 2010
to almost 9,000 in 2011, jumped to over 60,000 in 2012, and reached
almost 222,000 in 2015. As of December 2015, the United States was the world's largest plug-in hybrid car market with a stock of 193,770 units. About 279,000 light-duty plug-in hybrids were sold in 2016, raising the global stock to almost 800,000 highway legal plug-in hybrid electric cars at the end of 2016.
A total of 398,210 plug-in hybrid cars were sold in 2017, with China as
the top selling country with 111,000 units, and the global stock of
plug-in hybrids passed the one million unit milestone by the end of
2017.
Evolution of the ratio between global sales of BEVs and PHEVs between 2011 and 2019.
Global sales of plug-in electric vehicles
have been shifting for several years towards fully electric battery
cars. The global ratio between all-electrics (BEVs) and plug-in hybrids
(PHEVs) went from 56:44 in 2012, to 60:40 in 2015, to 66:34 in 2017, and
rose to 69:31 in 2018.
By country
The
Netherlands, Sweden, the UK, and the United States have the largest
shares of plug-in hybrid sales as percentage of total plug-in electric
passenger vehicle sales. The Netherlands has the world's largest share
of plug-in hybrids among its plug-in electric passenger car stock, with
86,162 plug-in hybrids registered at the end of October 2016, out of
99,945 plug-in electric cars and vans, representing 86.2% of the
country's stock of light-duty plug-in electric vehicles.
Sweden ranks next with 16,978 plug-in hybrid cars sold between
2011 and August 2016, representing 71.7% of total plug-in electric
passenger car sales registrations. Plug-in hybrid registrations in the UK between up to August 2016
totaled 45,130 units representing 61.6% of total plug-in car
registrations since 2011. In the United States, plug-in hybrids represent 47.2% of the 506,450 plug-in electric cars sold between 2008 and August 2016.
In November 2013 the Netherlands became the first country where a
plug-in hybrid topped the monthly ranking of new car sales. During
November sales were led by the Mitsubishi Outlander P-HEV with 2,736 units, capturing a market share of 6.8% of new passenger cars sold that month.
Again in December 2013 the Outlander P-HEV ranked as the top selling
new car in the country with 4,976 units, representing a 12.6% market
share of new car sales.
These record sales allowed the Netherlands to become the second
country, after Norway, where plug-in electric cars have topped the
monthly ranking of new car sales. As of December 2013,
the Netherlands was the country with highest plug-in hybrid market
concentration, with 1.45 vehicles registered per 1,000 people.
The following table presents the top ranking countries according
to its plug-in hybrid segment market share of total new car sales in
2013:
Top 10 countries by plug-in hybrid market share of new car sales in 2013
Note: (1) Market share of highway-capable plug-in hybrids as percentage of total new car sales in the country in 2013.
By model
According to JATO Dynamics, since December 2018 the Mitsubishi Outlander P-HEV is the world's all-time best selling plug-in hybrid. Since inception, 290,000 units have been sold worldwide through September 2021. Europe is the Outlander P-HEV leading market with 126,617 units sold through January 2019, followed by Japan 42,451 units through March 2018. European sales are led by the UK with 50,000 units by April 2020, followed by the Netherlands with 25,489 units, and Norway with 14,196, both through March 2018.
Combined global sales of the Chevrolet Volt and its variants totaled about 186,000 units by the end of 2018, including about 10,000 Opel/Vauxhall Amperas sold in Europe through June 2016, and over 4,300 Buick Velite 5s sold only in China (rebadged second generation Volt) through December 2018. Volt sales are led by the United States with 152,144 units delivered through December 2018, followed by Canada with 17,311 units through November 2018. Until September 2018, the Chevrolet Volt was the world's top selling plug-in hybrid.
Ranking third is the Toyota Prius Plug-in Hybrid (Toyota Prius Prime) with about 174,600 units sold worldwide of both generations through December 2018. The United States is the leading market with over 93,000 units delivered through December 2018. Japan ranks next with about 61,200 units through December 2018, followed by Europe with almost 14,800 units through June 2018.
The following table presents plug-in hybrid models with
cumulative global sales of around or more than 100,000 units since the
introduction of the first modern production plug-in hybrid car, the BYD F3DM, in 2008 up until December 2020:
Top selling highway legal plug-in hybrid electric cars between 2008 and 2020
Notes: (1) In addition to the Volt model sold in North America, combined sales of the Volt/Ampera family includes about 10,000 Vauxhall/Opel Ampera and 1,750 Volts sold in Europe, 246 Holden Volt sold in Australia, and 4,317 units of the Buick Velite 5 sold only in China (rebadged second generation Volt). (2) Sales in China only. BYD Qin total does not include sales of the all-electric variant (Qin EV300).
Several countries have established grants and tax credits for the purchase of new plug-in electric vehicles
(PEVs) including plug-in hybrid electric vehicles, and usually the
economic incentive depends on battery size. The U.S. offers a federal income tax credit up to US$7,500, and several states have additional incentives. The UK offers a Plug-in Car Grant up to a maximum of GB£5,000 (US$7,600). As of April 2011, 15 of the 27 European Union member states provide tax incentives for electrically chargeable vehicles, which includes all Western European countries plus the Czech Republic and Romania. Also 17 countries levy carbon dioxide
related taxes on passenger cars as a disincentive. The incentives
consist of tax reductions and exemptions, as well as of bonus payments
for buyers of all-electric and plug-in hybrid vehicles, hybrid vehicles,
and some alternative fuel vehicles.
The American Recovery and Reinvestment Act of 2009 modifies the tax credits, including a new one for plug-in electric drive conversion kits and for 2 or 3 wheel vehicles. The ultimate total included in the Act that is going to PHEVs is over $6 billion.
In March 2009, as part of the American Recovery and Reinvestment Act, the US Department of Energy
announced the release of two competitive solicitations for up to $2
billion in federal funding for competitively awarded cost-shared
agreements for manufacturing of advanced batteries and related drive
components as well as up to $400 million for transportation electrification demonstration and deployment projects. This announcement will also help meet the President Barack Obama's goal of putting one million plug-in hybrid vehicles on the road by 2015.
USDOE's FreedomCAR. US Department of Energy
announced it would dole out $30 million in funding to three companies
over three years to further the development of plug-in hybrids
USDOE
announced the selection of Navistar Corporation for a cost-shared award
of up to $10 million to develop, test, and deploy plug-in hybrid
electric (PHEV) school buses.
DOE and Sweden have a MOU to advance market integration of plug-in hybrid vehicles