Traction batteries for electric vehicles, which run on voltages of several hundred volts, must be well protected. Electrical components are packed into a thin-walled yet stable metal housing. Housings of this kind are equipped with at least one pressure compensation valve mostly in the form of microporous film. A second valve is a safety measure: It only opens if damage to one or several battery cells results from a malfunction, and the buildup of gases has to be released. A smart pressure compensation element, the "DIAvent", combines both functions into a single component.
Electric vehicles are about 2.5 times more energy efficient than their counterparts which are powered solely by internal combustion engines. This high energy efficiency is the main reason why electric vehicles can contribute to lower the CO2 emission and energy consumption of traffic substantially. Electric vehicles have zero tailpipe exhaust emissions and thus contribute substantially to a better air quality. Additionally, electric vehicles are inherently silent and can help to reduce the noise levels in cities. However, the market share of electric vehicles is currently still very small and consists mainly of small vehicles intended for urban transport. Purchase costs of electric vehicles are high compared to similar sized ICE vehicles. These high purchase costs are predominantly caused by the high costs of the battery pack needed in the vehicle. Moreover a recharging network with sufficient coverage is not yet available in most countries.
Electric vehicles are propelled solely by electric motors. There are three main types of electric vehicles:
- Battery electric vehicles
- Series Hybrid vehicles (see also description of Hybrid Electric Vehicles)
- Hydrogen Fuel cell vehicles. (see also description of fuel cells for mobile applications)
The Battery Electric Vehicle does not have an internal generator to produce electricity, all the electricity has to be obtained from the power grid. Examples are the Citroen EVie, Mitsubishi iMiev and the Think (van Agt, 2010).
The Series Hybrid vehicle can obtain its electricity from the power grid but has additionally a small internal combustion engine which serves as a generator to recharge the battery and offers an extended driving range. The combustion engine does not directly propel the vehicle. Examples are the Opel Ampera, GM Volt and the Volvo Recharge. The third group of electric vehicles are hydrogen fuel cell vehicles. These vehicles can also obtain their electricity from the power grid but in addition, the fuel cell can serve as a generator to recharge the battery, which also extends the driving range. Examples are the Honda Clarity and the Toyota FCHV. In the following we focus on battery electric vehicles.
There are three main technical differences between a car run on an internal combustion engine and an electric car:
- The internal combustion engine is exchanged for an electric motor.
- The electric motor is powered by a controller.
- The controller in turn is connected to rechargeable batteries, by which it is powered.
In addition, whilst an internal combustion engines contains lots of tubes, e.g. to transport the fuel, an electric engine contains a large amount of electric wiring. (Brain, 2005).
It is technically possible to convert a gasoline-powered vehicle to an electric vehicle; however, the associated costs are relatively high. (US Department of Energy, 2010) An explanation of how this conversion works can be found here.
Feasibility of technology and operational necessities
The main barriers for a wider user of electric vehicles are related to the batteries and to the recharging infrastructure. Batteries for use in electric cars are still expensive and have relatively limited driving ranges. Most existing EV need to be recharged after a maximum of 150 to 300 km. Completely recharging the batteries may take 4 to 8 hours. (US Department of Energy, 2010b). The widespread use of electric vehicles requires an extensive recharging infrastructure. The absence of this infrastructure may lead to reluctance to buy electric vehicles due to the fear of getting stranded with empty batteries.
The main technical obstacles which hamper the introduction are how to standardize the cords and connectors used for recharging, the decision to employ an on- or off-board charger and to development of an accurate state of charge meter for the battery. (Markel, 2010).
Status of the technology and its future market potential
The market share of battery electric vehicles is still very limited and comprises mainly of small vehicles intended for urban transport (van Agt, 2010). By the end of 2012 there was over 180,000 global stock of electric vehicles and global sales more than doubled from 2011 to 2012. However, this share only account for approximately 0.02% of total passenger cars globally (IEA, 2013). 38% of this stock is concentrated in the United States with Japan accounting for 24% and China next with 6.2% of the total.
Moreover, the purchase costs for electric vehicles are still relatively high due to the high costs of the required battery pack. To lower the purchase costs of the vehicle only relatively small battery packs are installed, limiting the driving range, which makes electric vehicles currently only suitable for urban transport. Nevertheless, the technology used in electric cars is largely proven and a breakthrough can be expected when the costs and weight of the battery pack are lowered sufficiently. Contribution of the technology to economic development (including energy market support)
Depending on where a country sources its gasoline and how it produces electricity, electric vehicles may improve energy security, as they may lower the dependency on imported gasoline.
Contribution of the technology to protection of the environment
The energy efficiency of electric cars is about 2.5 times better than their fossil fuel counterparts, which is the main reason why electric cars can lower the greenhouse gas emissions of road traffic and reduce the demand for oil. The actual greenhouse gas emission associated with the use of battery electric vehicles depends largely on the way the required electricity has been produced. Employing coal fired electricity plants to generate the electricity will marginally lower the CO2 emissions of an electric vehicle compared to similar sized vehicles with an internal combustion engine. However, using renewable electricity will lower the greenhouse gas emissions considerably. Electric vehicles might even provide a way to make the electricity sector more sustainable, if the batteries in the vehicles could be used to store the variable output of wind and solar-based power generation (Nieuwenhout et al, 2009).
Electric vehicles have no tail-pipe emission of air pollutants such as NOx and soot, which means that they can substantially contribute to improving local air quality, especially in urban areas. The global improvement of the air quality however, is determined by the way the electricity used is produced, e.g. fossil fuel fired power plants can have substantial emissions of NOx and soot when no appropriate measures are taken.
Road traffic is responsible for the majority of noise in cities. Electric vehicles are very quiet and can help to reduce noise levels in cities.
In the long-term electric vehicles are important for countries seeking to decarbonise the transport sector. Figure ? below highlights the important role that the transport sector will play in a future energy system that would limit the rise in global temperatures to 2⁰C by 2050 under the IEAs “2DS” scenario. In this scenario the transport sectors potential share of CO2 reductions would be 21% by 2050. To meet this target 75% of all vehicle sales by 2050 would need to be plug-in electric.
Financial requirements and costs
The high cost of an electric vehicle over the conventional alternative is mainly determined by the costs of the lithium ion battery pack. Recent developments in lithium-ion batteries make it likely that these additional costs can be reduced from the current level of about €15,000 in prototypes to an expected level of around €3,000 in 2020. This requires the battery to be about €200-250 per kWh (Nieuwenhout et al, 2009). The 2007 prices for high energy batteries range from €800/kWh to €1000/kWh (Pesaran et al, 2009). The medium term cost goals of these batteries are €500/kWh in 2012 and €300/kWh in 2016. BYD’s first commercial electric car, the E6 model, is expected to be available for sale in the US for 40’000 USD in 2010. (People’s Daily Online, 2010)
In addition, there is a need for investment into the recharging infrastructure. This infrastructure needs to be standardized in a way that every brand of electric vehicle can recharge at every recharging station. A simple recharging point at a private house or at an office site costs about $ 1800,-. However, a public recharging station, with the necessary electronics to make contact with the bank is estimated to cost about $ 18.000,-. (Roeterdink, 2010).
Clean Development Mechanism market status
Project developers of projects deploying electric vehicles can use the following CDM methodology: AMS-III.C.: Emission reductions by electric and hybrid vehicles.
- Bloomberg News (2010): BYD Scales Back Its Electric-Car Plans, Morning Post Reports. March 15, 2010. available at http://www.bloomberg.com/apps/news?pid=newsarchive&sid=aNMr8oxbgSKo
- van Agt, Jeroen (2010): Overview of electric cars, available at http://www.olino.org/us/articles/2008/10/26/overview-of-electric-cars
- Brain, Marshall (2002): How Electric Cars Work, available at HowStuffWorks.com, http://auto.howstuffworks.com/electric-car.htm
- IEA, 2013. Global EV Outlook. Understanding the Electric Vehicle Landscape to 2020.
- Nieuwenhout, F., Kolokathis, C., Özdemir, Ö. and Schoots, K. (2009): Financial and economic analysis of electric vehicles and heat pumps. ITM WP3
- People’s Daily Online (2010): BYD electric car to be sold in US for $40,000. May 19, 2010. Available at http://english.peopledaily.com.cn/90001/90778/90860/6990705.html
- Pesaran, A.A., Markel, T., Tataria, H.S. and Howell, D.(2009): Battery Requirements for Plug in Hybrid Electric Vehicles.
- Roeterdink, W.G., Uyterlinde, M.A., Kroon P. and Hanschke, C.B. (2010): Groen Tanken: Inpassing van alternatieve brandstoffen in de tank- en distributie infrastructuur. ECN report E—09-082
- US Department of Energy, Alternative Fuels and Advances Vehicles Data Centre (2010): Electric Vehicle Availability. Available at http://www.afdc.energy.gov/afdc/vehicles/electric_availability.html
- US Department of Energy, www.fueleconomy.gov (2010b): Electric Vehicles (EVs). Available at http://www.fueleconomy.gov/feg/evtech.shtml
Author affiliation: Energy research Centre of the Netherlands (ECN), Policy Studies
Due to the growing energy density of battery systems in Electric Vehicle, the developers of lithium ion batteries must satisfy ever higher safety requirements. It is especially crucial to keep a single damaged cell from overheating the entire battery module. The goal is greater range without the battery growing in size and weight. If neighboring healthy cells also heat up due to the heat buildup, a chain reaction can result that, in the worst case, could lead the entire battery system to explode.
The traction battery is the core of an Electric Vehicle. In all circumstances, it is essential to protect its high-voltage components from moisture and dirt, even in long-term operation. At the same time, it must be possible to open battery housings for maintenance. That’s why automakers are turning to housings with a large cover that allows good access to all components. But the cross-section and dimensions of such seals must be adapted exactly to a specific battery. Changes are impossible without fabricating a new tool.
Electric vehicles have high-voltage battery packs rated at over 200 volts to generate enough power to drive their motors. These high-voltage battery packs contain many low-voltage battery cells connected in series. The Battery Monitoring Unit monitors the voltage and temperature of the individual low-voltage battery cells. In other words, this unit constantly assesses the state of the battery cells. BMU detects a battery's voltage, current, temperature, and other parameters to enable high-voltage batteries to be used safely and efficiently.