Electric Vehicles Definition
An electric vehicle (EV), also referred to as an electric drive vehicle, is a vehicle which uses one or more electric motors for propulsion. Depending on the type of vehicle, motion may be provided by wheels or propellers driven by rotary motors, or in the case of tracked vehicles, by linear motors. Electric vehicles can include electric cars, electric trains, electric trucks, electric lorries, electric airplanes, electric boats, electric motorcycles and scooters, and electric spacecraft.
An electric car is an alternative fuel automobile that uses electric motors and motor controllers for propulsion, in place of more common propulsion methods such as the internal combustion engine (ICE). Electricity can be used as a transportation fuel to power battery electric vehicles (EVs). EVs store electricity in an energy storage device, such as a battery. The electricity powers the vehicle's wheels via an electric motor. EVs have limited energy storage capacity, which must be replenished by plugging into an electrical source.
Electric vehicles are different from fossil fuel-powered vehicles in that they can receive their power from a wide range of sources, including fossil fuels, nuclear power, and renewable sources such as tidal power, solar power, and wind power or any combination of those. However it is generated, this energy is then transmitted to the vehicle through use of overhead lines, wireless energy transfer such as inductive charging, or a direct connection through an electrical cable. The electricity may then be stored onboard the vehicle using a battery, flywheel, supercapacitor, or fuel cell. Vehicles making use of engines working on the principle of combustion can usually only derive their energy from a single or a few sources, usually non-renewable fossil fuels. A key advantage of electric or hybrid electric vehicles is their ability to recover braking energy as electricity to be restored to the on-board battery (regenerative braking) or sent back to the grid (V2G). At the beginning of the 21st century, increased concern over the environmental impact of the petroleum-based transportation infrastructure, along with the spectre of peak oil, led to renewed interest in an electric transportation infrastructure. As such, vehicles which can potentially be powered by renewable energy sources, such as hybrid electric vehicles or pure electric vehicles, are becoming more popular.[
Electric cars have the potential of significantly reducing city pollution by having zero tail pipe emissions. Vehicle greenhouse gas savings depend on how the electricity is generated. With the U.S. energy mix using an electric car would result in a 30% reduction in carbon dioxide emissions. Given the current energy mixes in other countries, it has been predicted that such emissions would decrease by 40% in the UK, 19% in China, and as little as 1% in Germany.
Electric cars are commonly powered by on-board battery packs, and as such are battery electric vehicles (BEVs). Although electric cars often give good acceleration and have generally acceptable top speed, the poorer energy capacity of batteries compared to that of fossil fuels means that electric cars have relatively poor range between charges, and recharging can take significant lengths of time. However, for everyday use, rather than long journeys, electric cars are very practical forms of transportation and can be inexpensively recharged overnight. Other on-board energy storage methods that may give more range or faster recharge are areas of research.
Electric cars are expected to cause a revolution in the auto industry given advantages in city pollution, less dependence on foreign oil imports, and expected rise in gasoline prices.
Electric cars are a variety of electric vehicle (EV); the term "electric vehicle" refers to any vehicle that uses electric motors for propulsion, while "electric car" generally refers to road-going automobiles powered by electricity. While an electric car's power source is not explicitly an on-board battery, electric cars with motors powered by other energy sources are generally referred to by a different name: an electric car powered by sunlight is a solar car, and an electric car powered by a gasoline generator is a form of hybrid car. Thus, an electric car that derives its power from an on-board battery pack is called a battery electric vehicle (BEV). Most often, the term "electric car" is used to refer to pure battery electric vehicles, such as the REVAi and GM EV1.
In an electric vehicle (EV), a battery or other energy storage device is used to store the electricity that powers the motor. EV batteries must be replenished by plugging in the vehicle to a power source. Some electric vehicles have onboard chargers; others plug into a charger located outside the vehicle. Both types, however, use electricity that comes from the power grid. Although electricity production may contribute to air pollution, EVs are considered zero-emission vehicles because their motors produce no exhaust or emissions.
There are currently no light-duty electric vehicles available from the major auto manufacturers. Neighborhood electric vehicles (NEVs), on the other hand, are being manufactured by a variety of companies. These small vehicles are commonly used for neighborhood commuting, light hauling, and delivery. Their use is limited to areas with 35 mph speed limits or for off-road service on college campus or at airports or resort areas.
Because they are limited to speeds of 25 mpg or less, NEVs are not considered light-duty vehicles and are not eligible for fleet credit under the Energy Policy Act of 1992 Standard Compliance option and Federal Fleet Requirements. However, their versatility in moving people through limited commute areas makes them useful in a variety of applications. Other useful EVs in niche applications include electric scooters and bikes.
Comparison with internal combustion engine vehicles
An important goal for electric vehicles is overcoming the disparity between their costs of development, production, and operation, with respect to those of equivalent internal combustion engine vehicles (ICEVs).
Given the Tesla Roadster's plug-to-wheel mileage of 280 W·h/mi and an arbitrary electricity price of $0.10/kW·h, driving a Tesla Roadster 40 miles a day would cost $1.12. For comparison, driving an internal combustion engine-powered car the same 40 miles, at a mileage of 25 mpg, would use 1.6 gallons of fuel and, at a cost of $3 per gallon, would cost $4.80. This is approximately 4 times more expensive than charging the electric car. This cost advantage varies depending on the costs of gasoline and electricity, the mileages of the vehicles, and the type of driving being considered.
The Tesla uses about 13 kW·h/100 km (0.47 MJ/km; 0.21 kW·h/mi), the EV1 used about 11 kW·h/100 km (0.40 MJ/km; 0.18 kW·h/mi).
Nissan estimates the 5 year operating cost to $1,800 and $6,000 for a gasoline car. The documentary film Who Killed the Electric Car? shows a comparison between the parts that require replacement in a gasoline powered cars and EV1s, with the garages stating that they bring the electric cars in every 5,000 mi (8,000 km), rotate the tires, fill the windshield washer fluid and send them back out again. Even the hydraulic brakes require less maintenance because regenerative braking itself also slows the vehicle, as it does with a hybrid.
Current electric car infrastructure is not capable of completing a long trip in the same amount of time as a gasoline car due to more frequent and long recharge times. According to the documentary film Who Killed the Electric Car? the EV1 was "only" suitable for 90% of consumers.
Range issues can be solved by towing a generator on long trips, renting a gasoline car, in two car houses by using the other car, and by improvements to the electrical infrastructure. Charging stations are being created with 80% recharge in 30 minutes.
Replaceable standard battery packs is also an option. The battery would be charged at the energy station and the vehicle's depleted battery would be replaced with the fully charged one, for a fee. Because of the weight (several hundred kilos), the vehicle and the energy station need to be adapted with a simple lift-and-slide-in mechanism to facilitate the replacement. It should not take longer time to switch batteries than filling up a gasoline car. A small car would use one battery pack, while a larger car might use several of the standardized battery packs.
Carbon dioxide emissions
Electric cars produce no pollution at the tailpipe, but their use increases demand for electricity generation. Generating electricity and producing liquid fuels for vehicles are different categories of the energy economy, with different inefficiencies and environmental harms, but both emit carbon dioxide into the environment that must be accounted for in a "well to wheel" comparison. An electric car's WTW emissions are much lower in a country like Canada, which electricity supply is dominated by hydro and nuclear, than in countries like China and the US that rely heavily on coal.
An EV recharged from the existing US grid electricity emits about 115 grams of CO2 per kilometer driven (6.5 oz(CO2)/mi), whereas a conventional US-market gasoline powered car emits 250 g(CO2)/km (14 oz(CO2)/mi) (most from its tailpipe, some from the production and distribution of gasoline). The savings are questionable relative to hybrid or diesel cars, (according to official British government testing the most efficient European market cars are well below 115 grams of CO2 per kilometer driven), but would be more significant in countries with cleaner electric infrastructure. In a worst case scenario where incremental electricity demand would be met exclusively with coal, a 2009 study conducted by the WWF, World Wildlife Foundation, and IZES found that a mid-size EV would emit roughly 200 g(CO2)/km (11 oz(CO2)/mi), compared with an average of 170 g(CO2)/km (9.7 oz(CO2)/mi) for a gasoline powered compact car. This study concluded that introducing 1 million EV cars to Germany would, in the best case scenario, only reduce CO2 emissions by 0.1%, if nothing is done to upgrade the electricity infrastructure or manage demand.
Like any other vehicles, EVs themselves of course differ in their fuel efficiency and their total cost of ownership, including the environmental costs of their manufacture and disposal.
According to the US Department of Energy, most electricity generation in the United States is from fossil sources, and half of that is from coal. Coal is more carbon-intensive than oil. Overall average efficiency from US power plants (33% efficient) to point of use (transmission loss 9.5%) is 30%. Accepting a 70% to 80% efficiency for the electric vehicle gives a figure of only around 20% overall efficiency when recharged from fossil fuels. That is comparable to the efficiency of an internal combustion engine running at variable load. The efficiency of a gasoline engine is about 16%, and 20% for a diesel engine. This is much lower than the efficiency when running at constant load and optimal rotational speed, which gives efficiency around 30% and 45% respectively. The electric battery suffers from similar decrease in efficiency when running at variable load, which accounts for the modest increased efficiency of hybrid vehicles. The actual result in terms of emissions depends on different refining and transportation costs getting fuel to a car versus a power plant. Diesel engines can also easily run on renewable fuels, biodiesel, vegetable oil fuel, with no loss of efficiency. Using fossil based grid electricity substantially negates the in-vehicle efficiency advantages of electric cars. The major potential benefit of electric cars is to allow diverse renewable electricity sources to fuel cars.
According to the US Department of Energy, CO2 emissions for electricity generated from coal result in 2.05 lb (0.93 kg) of CO2 per kW·h or roughly 0.5 lb(CO2)/mi (0.14 kg(CO2)/km). CO2 emissions from electricity produced from all types of fuel using the mix of sources in the US as of 2008 results in 1.35 lb (0.61 kg) of CO2 per kW·h or 0.337 pounds of CO2 per mile (0.095 kg(CO2)/km) from an electric vehicle with a 0.250-kilowatt-hour-per-mile (0.155 kW·h/km; 0.56 MJ/km) energy consumption (typical). Gasoline used in Internal Combustion Engine automobiles produces 19.5 lbCO2/US gal (2.34 kg(CO2)/L) directly and an undetermined amount of CO2 in refining the crude oil, and transporting the gasoline to retail point of sale. With a US fleet average of 21.3 mpg-US (11.0 L/100 km; 25.6 mpg-imp) in 2008, this would indicate a CO2 production of 0.915 lb/mi (0.258 kg/km) driven. Electric powered automobiles, even using the most CO2 intensive coal produced electricity, produce half the emissions of gasoline powered automobiles.
If solar, wind, hydro, or nuclear electric generation, or carbon capture for fossil fuel powered plants were to become prevalent, electric vehicles could produce less CO2, potentially zero. Based on GREET simulations, electric cars can achieve up to 100% reductions with renewable electric generation, against 77% with a B100 car. At present only a 32% reduction of CO2 is available for electric cars recharging from non-renewable utilities on the US Grid, because of the majority use of fossil fuels in generation, and inefficiency in the grid itself.
Acceleration and drivetrain design
Electric motors can provide high power to weight ratios, and batteries can be designed to supply the large currents to support these motors.
Although some electric vehicles have very small motors, 15 kW (20 hp) or less and therefore have modest acceleration, many electric cars have large motors and brisk acceleration. In addition, the relatively constant torque of an electric motor, even at very low speeds tends to increase the acceleration performance of an electric vehicle relative to that of the same rated motor power internal combustion engine. Another early solution was American Motors’ experimental Amitron piggyback system of batteries with one type designed for sustained speeds while a different set boosted acceleration when needed.
Electric vehicles can also use a direct motor-to-wheel configuration which increases the amount of available power. Having multiple motors connected directly to the wheels allows for each of the wheels to be used for both propulsion and as braking systems, thereby increasing traction. In some cases, the motor can be housed directly in the wheel, such as in the Whispering Wheel design, which lowers the vehicle's center of gravity and reduces the number of moving parts. When not fitted with an axle, differential, or transmission, electric vehicles have less drivetrain rotational inertia.
When the foot is lifted from the accelerator of an ICE, engine braking causes the car to slow. An EV would coast under these conditions, and applying mild regenerative braking instead provides a more familiar response.
A gearless or single gear design in some EVs eliminates the need for gear shifting, giving such vehicles both smoother acceleration and smoother braking. Because the torque of an electric motor is a function of current, not rotational speed, electric vehicles have a high torque over a larger range of speeds during acceleration, as compared to an internal combustion engine. As there is no delay in developing torque in an EV, EV drivers report generally high satisfaction with acceleration.
For example, the Venturi Fetish delivers supercar acceleration despite a relatively modest 220 kW (295 hp), and top speed of around 160 km/h (100 mph). Some DC motor-equipped drag racer EVs, have simple two-speed transmissions to improve top speed. The Tesla Roadster prototype can reach 100 km/h (62 mph) in 4 seconds with a motor rated at 185 kW (248 hp).
Great effort is taken to keep the mass of an electric vehicle as low as possible, in order to improve the EV's range and endurance. Despite these efforts, the high density and weight of the electric batteries usually results in an EV being heavier than a similar equivalent gasoline vehicle leading to less interior space, worse handling characteristics, and longer braking distances. However, in a collision, the occupants of a heavy vehicle will, on average, suffer fewer and less serious injuries than the occupants of a lighter vehicle; therefore, the additional weight brings safety benefits despite having a negative effect on the car's performance. An accident in a 2,000 lb (900 kg) vehicle will on average cause about 50% more injuries to its occupants than a 3,000 lb (1,400 kg) vehicle. In a single car accident, and for the other car in a two car accident, the increased mass causes an increase in accelerations and hence an increase in the severity of the accident. Some electric cars use low rolling resistance tires, which typically offer less grip than normal tires.
Proponents of electric cars usually tout an increased efficiency as the primary advantage of an electric vehicle as compared to one powered by an internal combustion engine. The energy efficiency comparison is difficult to make because the two vehicles operate on different principles. Vehicles powered by internal combustion engines operate by converting energy stored in fossil fuels to mechanical energy through the use of a heat engine. Heat engines operate with very low efficiencies because heat cannot be converted directly into mechanical energy. Electric vehicles convert stored electric potential into mechanical energy. Electricity can be converted into mechanical energy at very high efficiencies. A quick analysis will show electric vehicles are significantly more efficient. However, electricity (in a form usable for humans) does not naturally exist in nature. The electricity used for electric cars may be created by converting fossil fuels to electricity using a heat engine (with a similar efficiency as an automotive engine), converting nuclear energy to electricity using a heat engine, or through dams, windmills, or solar energy. Each of these conversion processes operate with less than 100% efficiency and those involving heat engines operate at relatively low efficiencies.
When comparing the efficiencies of an electric vehicle to a gasoline vehicle, the efficiency of the source of generating the electric energy must be included in the comparison. For example, it is incorrect to say that an electric vehicle charged each night from a gasoline powered generator is more efficient than a gasoline powered vehicle.
An electric car's efficiency is affected by its battery charging and discharging efficiencies, which ranges from 70% to 85%, and its engine and braking system. The electricity generating system in the US loses 9.5% of the power transmitted between the power station and the socket, and the power stations are 33% efficient in turning the calorific value of fuel at the power station to electrical power. Overall this results in an efficiency of 20% to 25% from fuel into the power station, to power into the motor of the grid-charged EV, comparable or slightly better than the average 20% efficiency of gasoline-powered vehicles in urban driving, though worse than the about 45 % of modern Diesel engines running under optimal conditions (e.g. on motorways).
Production and conversion electric cars typically use 10 to 23 kW·h/100 km (0.17 to 0.37 kW·h/mi). Approximately 20% of this power consumption is due to inefficiencies in charging the batteries. Tesla Motors indicates that the vehicle efficiency (including charging inefficiencies) of their lithium-ion battery powered vehicle is 12.7 kW·h/100 km (0.21 kW·h/mi) and the well-to-wheels efficiency (assuming the electricity is generated from natural gas) is 24.4 kW·h/100 km (0.39 kW·h/mi). The US fleet average of 10 l/100 km (24 mpg-US) of gasoline is equivalent to 96 kW·h/100 km (1.58 kW·h/mi), and the Honda Insight uses 32 kW·h/100 km (0.52 kW·h/mi) (assuming 9.6 kW·h per liter of gasoline).
The greater efficiency of electric vehicles is primarily because most energy in a gasoline-powered vehicle is released as waste heat. With an engine getting only 20% thermal efficiency, a gasoline-powered vehicle using 96 kW·h/100 km of energy is only using 19.2 kW·h/100 km for motion.
The waste heat generated by an ICE is frequently put to beneficial use by heating the vehicle interior. Electric vehicles generate very little waste heat and resistance electric heat may have to be used to heat the interior of the vehicle if heat generated from battery charging/discharging can not be used to heat the interior. Electric vehicles used in cold weather will show increased energy consumption and decreased range on a single charge.
Hazard to pedestrians
Electric cars produced much less roadway noise as compared to vehicles propelled by a internal combustion engine. However, the reduced noise level from electric engines may not be beneficial for all road users, as blind people or the visually-impaired consider the noise of combustion engines a helpful aid while crossing streets, hence electric cars and hybrids could pose an unexpected hazard. Tests have shown that this is a valid concern, as vehicles operating in electric mode can be particularly hard to hear below 20 mph (30 km/h) for all types of road users and not only the visually-impaired. At higher speeds the sound created by tire friction and the air displaced by the vehicle start to make more audible noise. The US Congress and the European Commission are exploring legislation to establish a minimum level of sound for electric and hybrid electric vehicles when operating in electric mode, so that blind people and other pedestrians and cyclists can hear them coming and detect from which direction they are approaching.
It is generally possible to equip any kind of vehicle with an electric powertrain.
Hybrid electric vehicle
A hybrid electric vehicle combines a conventional (usually fossil fuel-powered) powertrain with some form of electric propulsion. Common examples include hybrid electric cars such as the Toyota Prius.
On- and off-road electric vehicles
Electric vehicles are on the road in many functions, including electric cars, electric trolleybuses, electric bicycles, electric motorcycles and scooters, neighborhood electric vehicles, golf carts, milk floats, and forklifts. Off-road vehicles include electrified all-terrain vehicles and tractors.
Railborne electric vehicles
The fixed nature of a rail line makes it relatively easy to power electric vehicles through permanent overhead lines or electrified third rails, eliminating the need for heavy onboard batteries. Electric locomotives, electric trams/streetcars/trolleys, electric light rail systems, and electric rapid transit are all in common use today, especially in Europe and Asia.
Since electric trains do not need to carry a heavy internal combustion engine or large batteries, they can have very good power-to-weight ratios. This allows high speed trains such as France's double-deck TGVs to operate at speeds of 320 km/h (200 mph) or higher, and electric locomotives to have a much higher power output than diesel locomotives. In addition they have higher short-term surge power for fast acceleration, and using regenerative braking can put braking power back into the electrical grid rather than wasting it.
Maglev trains are also nearly always electric vehicles.
Airborne electric vehicles
Since the beginning of the era of aviation, electric power for aircraft has received a great deal of experimentation. Currently flying electric aircraft include manned and unmanned aerial vehicles.
Seaborne electric vehicles
Electric boats were popular around the turn of the 20th century. Interest in quiet and potentially renewable marine transportation has steadily increased since the late 20th century, as solar cells have given motorboats the infinite range of sailboats. Submarines use batteries (charged by diesel or gasoline engines at the surface), nuclear power, or fuel cells run electric motor driven propellers.
Spaceborne electric vehicles
Electric power has a long history of use in spacecraft. The power sources used for spacecraft are batteries, solar panels and nuclear power. Current methods of propelling a spacecraft with electricity include the arcjet rocket, the electrostatic ion thruster, the Hall effect thruster, and Field Emission Electric Propulsion. A number of other methods have been proposed, with varying levels of feasibility.
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