1. Technology Comparison

This report aims to give a clear and neutral comparison between the different technologies, and their efficiencies. \

2. Technology Options

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2.1 ICE

\ ICEs (internal combustion engines), use the combustion of petrol or diesel to drive the engine. It is the engine that drives all conventional cars. Petrol engines are about 18-20% [1] efficient and diesel engines are about 37%, with peak efficiency about 45% [2]. Diesel engines are more efficient as they use high compression ratios to ignite the fuel.

[{Image src= ‘smartcar.jpg’ align = ‘center’ width = ‘400px’ height = ‘250px’ caption = ‘The smart diesel, the most efficient conventional car being produced in the world, it is capable of 86mpg.[3]’}]

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2.2 Hybrids

Hybrids have two motors, a petrol one and an electric one. They also have two stores of energy; the battery, and petrol tank. This makes the car very heavy. The wheels can be powered by either motor, depending on how the car is being driven.

The battery can be recharged in several ways: by the mains for a plug in hybrid, by the petrol engine, or through regenerative braking, although this contributes a smaller propertion of the energy stored.

[{Image src= ‘prius.jpg’ align = ‘center’ width = ‘400px’ height = ‘250px’ caption = ‘The Toyota Prius, one of the most famous hybrids. Plug in hybrids are also available’}]\

Hybrids can be used in exactly the same way as conventional cars.Despite the fact that they capture some of the energy lost in braking, through regenerative braking, hybrids are heavy, so efficiency still is not high. Also, they will not be a sustainable option for the future as they still use petrol and diesel.

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2.3 E-REV

E-REVs, extended range electric vehicles, are similar to hybrids in many ways; they both run off either petrol or a battery. However the wheels are only driven by an electric motor. The petrol goes to a generator which converts it into electricity to drive the electric motor. The E-REV runs off just the battery until it is drained after which it will use the generator to create electricity to drive the electric motor.

[{Image src=’ampera.jpg’ align = ‘center’ width = ‘400px’ height = ‘250px’ caption = ‘The Vauxhall Ampera is the European version of the Chevy Volt. Vauxhall Ampera claim 175mpg, [4] this figure is based on the petrol used, doesn’t include the battery energy’}]

E-REV can be used like conventional cars, and have good range and speeds. However they are inefficient, a battery car or a petrol car would be more efficient than the combined car. E-REV are not a sustainable option for the future as they use petrol.

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2.4 BEV\

Battery Electric Vehicles, store the energy in the battery which is used to drive the electric motor. The power train is very simple.

The energy is stored in the battery, with very little being discharged when the car is not being used. The charging of a battery is about 90% [5] efficient, so more energy will be used than is stored in the battery. The discharge of batteries is also 90% [6] efficient, and all the energy which is stored in the battery cannot be used without damaging the battery, 20% needs to remain in the battery[7].

[{Image src= ‘miev.jpg’ align = ‘center’ width = ‘400px’ height = ‘250px’ caption = ‘The Mitsubishi i MiEV, BEV range of 80 miles and a top speed of 81 mph[8]. the battery takes 8 hours to recharge completely.’}]

The BEV is a realistic option for the future, as it could in theory be sustainable into the future if all the electricity in the world was made from renewable sources. They emit 0 tail gas emissions. However they don’t have a very good range, using a bigger battery would just reduce the efficiency of the car. The battery takes 8 hours [9] to recharge which makes it unsuitable for long journeys.

In the foreseeable future it is unlikely that electricity will completely change to be renewable. If the demand on electricity increases more fossil fuels will have to be used to meet the immediate demand. Lighting, heating and cooking should all take priority for electricity over transport.

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2.5 Hydrogen fuel cell vehicles

Hydrogen can be used to create electricity through hydrolysis in a fuel cell. The electricity is then used to power the electric motor which drives the car. This is a much lighter option to a battery, meaning that less power is needed to run the car. However the fuel cell is only about 50% efficient [10], and very expensive.\

[{Image src = ‘riversimplecar.jpg’ width = ‘400px’ Height = ‘250px’ align = ‘center’ caption = ‘The Riversimple local car, with a max speed of 50mph,and a range of 240 miles [11], is a 2 seater car designed to be used locally’}] \

Hydrogen fuel cell vehicles are also a realistic option for the future. Hydrogen could be created by photoelectric chemical water splitting, or from biological production by algae. Electricity is not needed in the production of hydrogen. Hydrogen cars have a good range and only take 5 minutes to refuel which makes them good for longer journeys.

However currently the infrastructure is not in place to fuel hydrogen cars. It will be expensive to create. Fuel cells are expensive. Hydrogen is currently being created by steam reforming from natural gas.
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3. Efficiency Comparison

It is important to be able to compare all the different vehicles. A way of unifying across all categories is to calculate the CO2 emitted from well to wheel (WTW) per km driven by the car. This method makes it easy to assess the environmental impact of the car this way. The units which are often used to measure the energy use, in order to compare across energy sources is MJ/100km. This is km driven by the vehicle.

The Concawe report was carried out by the representatives of EUCAR (European Council for Automotive R&D). It gives a neutral way of assessing all the different technologies.

The WTW emissions of several cars will be assessed. The cars have been chosen, because they are the most representative of each technology, and have the most developed designs. \

This is calculated by working out the tank to wheel values and the well to tank values and adding them up.
The well to tank values calculated were based on manufacturers values for mpg. If those figures weren’t available the efficiency was calculated from the range and the energy stored.
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||Type of technology ||vehicle||TTW gCO2/km||WTT g CO2/km||WTW g CO2/km||Range (Miles)||Energy Stored (MJ)||Fuel type |ICE|Smart Diesel|86.7|16.5|103.2|670|1355|Diesel | |Ford Focus|211.9|36.3|248.2|511|1782|Petrol | |Audi A2 3L|15.57|81.6|97.2|687.5|1214|Diesel |Hybrid|Toyota Prius|93.4|15.6|109|619|1747|Petrol |E-REV|Vauxhall Ampera|52.6|7.4|60|350|1029|Petrol | |Chevy Volt Const charge|202.6|31.9|234.5|300|1765|Petrol |BEV|Mitsubishi i MiEV|0|57.3|57.3|80|57.6|Electricity | |Nissan Leaf|0|69.4|69.4|100|86.4|Electricity | |Think|0|64|64|100|79.2|Electricity |Hydrogen fuel cell|Honda clarity|0|120.2|120.2|240|470|Hydrogen | |Riversimple|0|30.5|30.5|240|120|Hydrogen
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These values have been calculated from the manufacturers values for the cars efficiency. The following pathways have been used for each of the fuel types.
\Diesel and Petrol — Concawe Reports Conventional fuel path
Hydrogen — Compressed hydrogen trucked 4000km
Electricity — Suggested EU mix 129.2 grams of CO2 per MJ of Electricity.

[{Image src = ‘CO2graph.jpg’ align = ‘center’ Height = ‘400px’ width = ‘500px’ Caption = ‘CO2 per km calculated from manufacturers figures.}] \

##4. Fuel efficiency Validation
The efficiency values stated by Vauxhall for the Ampera, appear to be unrealistic based on the weight, size of the car, and the losses in the complex power train.
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Battery only TTW efficiency\

• The Vauxhall Ampera has a lithium ion battery pack total capacity of 16kwh.
• Lithium ion batteries can only be discharged to 20% of their capacity.
• The total useable battery energy is therefore 46.08MJ.
• The Vauxhall Ampera battery only range is 40 miles or 64.36km
• Therefore on petrol alone the TTW efficiency is 72MJ/100km which is equivalent to 128mpg.
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Petrol only TTW efficiency\

\\ •	The Vauxhall Ampera has a 30L fuel tank holding 971.7MJ\\ •	IT has a range of 310 miles on just petrol\\ •	TTW petrol efficiency of 194.8MJ/100km which is 47mpg.\\ \\ The differences in efficiencies of the vehicles come from the efficiency of the power train in the different modes.\\ \\ [{Image src = 'EREVefficiency.jpg' width = '600px' height  = '200px' align = 'center'}]  \\ \\ ###	Comparison of Calculated and Manufacturer Fuel Efficient Values\\ \\

Vauxhall Ampera values calculated in different ways.
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• Just on battery 128mpg
• Just on Petrol 47.0 mpg
• Total range (petrol equiv) 50.1mpg
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• Manufacturers value 230mpg

It is likely that the Vauxhall Ampera values have been created in a similar way to the Chevy Volt values. These are the statistics off the Chevy Volt website [12].

This shows a wide range of efficiencies. It is not stated how these values have been calculated.
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One way to calculate 150mpg when travelling 60 miles

• 40 miles on battery using no petrol.
• 20 miles on petrol at 50 mpg.
• Therefore using 0.4 gallons of petrol to travel 60 miles.
• Equivalent to 150mpg this is the figure quoted.

\The Vauxhall Ampera efficiency values could have been worked out in a similar way to the Chevy Volt. Assuming 40 miles is within the range of a daily commute, therefore considering several journeys on just the battery (not considering the energy stored), and one journey using the petrol range extender.
\When asked how the 175mpg had been calculated they responded “I can advise, given the sensitive nature of your enquiry, it is not possible to supply this information, as it is for internal use only.” This is an interesting response as these figures have been published on the Vauxhall Ampera website, so have been available for the public.
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Battery electric Vehicle Efficiencies

WTW Processes for BEV

[{Image src = ‘BEVefficiency.jpg’ align = ‘center’ width= ‘700px’ height = ‘300px’}]

The red arrows show the WTT processes, the blue arrows show the TTW processes.\

Often the WTT processes aren’t taken into account when calculating the CO2 produced by BEV.
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Losses in the complete BEV Power-train.\

The EU mix for electricity which is used in the Concawe reports produces 129.2g of C02 per MJ of electricity, at the socket.

The efficiency of charging the battery, transforming from the mains to the battery is about 90%. This should be included in the WTT calculations. Therefore the g of CO2 per MJ is actually 143.5g.

The discharge efficiency of a battery is about 90% as well according to Tesla. An electric motor is about 90% efficient also. This process will be typical of all BEV.\

Battery Capacity\

Automotive manufacturers give the capacity of batteries in KWH. The total Capacity of the battery can’t be used without damaging the battery. Therefore normally the battery is just discharged to 20%. Therefore when working out the efficiency based on the range and the battery capacity, only 80% of the capacity should be used.
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Newly calculated BEV grams of CO2\

Values for battery electric vehicles have been calculated, assuming charging the battery from 20% until full, and that the total grams of CO2 per MJ is 142.3g. They work out to be similar if the full capacity of the battery was taken into account.
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The Mitsubishi i MiEV
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Full capacity of battery\ 57.3g
(not taking into account charging)
80% charged with 10% charge efficiency 51.68g
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The cenex ‘Electric Vehicle deployment’ Report 115g


The cenex report is based on a study which drove Mitsubishi i MiEV’s 500 miles, with 8 different drivers. The study happened in march 2009, the vehicles were mainly used for commuting activities. The data collected showed that the Mitsubishi actually produced 115g of CO2 per km based on the current UK concentration of CO2. (0.537kg/KWH equiv to 149.2 g/MJ)
\115g is based on real driving, which shows that the driving cycles don’t give a realistic value for the efficiency of the car in normal use.

[{Image src = ‘newefficiencies.jpg’ align = ‘center’ width= ‘500px’ height = ‘300px’ caption = ‘Comparison of realistic values of CO2 produced for all vehicles’}]


This graph has been created using the combined and steady state values for the Vauxhall Ampera and the Chevy Volt. The electric vehicles values have been based on the charge efficiency being 90%, and only charging the battery 80% of the total capacity.


This shows clearly, that the electric vehicles, and also the Riversimple car produce much less CO2 than conventional cars or the EREV. The graph shows that the EREV and the Hybrids currently aren’t any better than the most efficient ICE. This would suggest that they would not be a wise choice for the future, they would not even be a good way to bridge the gap, between a conventional car and an electric or hydrogen one, as they actually produce more CO2 so in terms of environmental impact they are a step back.\

References\

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All pictures from green.autoblog.com\

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1 C Johnson, 2010, Physics in an Automotive engine, available at: < [http://mb-soft.com/public2/engine.html|pagename]> [accessed 25 August 2010]

2 U.S. EPA NVFEL, 2004, medium and heavy duty diesel vehicle modelling using fuel consumption methodology, available at: <[http://www.epa.gov/otaq/models/ngm/may04/crc0304c.pdf|pagename]> [accessed 25 August 2010]
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1. The smart people, 2010, the smart way to save money, available at: http://www.thesmartpeople.co.uk/intro.htm [accessed 26 August 2010]
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2. Vauxhall, 2010, What’s the output? available at: <[http://www.vauxhallampera.co.uk/vauxhall/#/technology|pagename]> [accessed 26 August]// //
3. Delta Q Technologies corp, [online], available at:<[http://www.delta-q.com/white-papers/QuiQ-HighEfficiencyGridFriendlyBatteryCharger.pdf|pagename]> [accesses 26 August 2010]// // 6.Tesla, 2010, Using energy efficiently, available at: http://www.teslamotors.com/goelectric/efficiency [accessed 26 August]// // 7.National semiconductor,2010, Characteristics of rechargeable batteries, available at:http://www.national.com/appinfo/power/files/f19.pdf [accessed 26 August]
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4. Mitsubishi I MiEV, 2010,Introduction of the i MiEV, available at: http://www.mitsubishi-cars.co.uk/imiev/introduction.aspx#imievContentContainer [accesses 26 August 2010]
   
   9.Cabled, 2010, FAQ, accessed at:< http://cabled.org.uk/faq/-list-/how-long-does-it-take-to-recharge-a-car/#faq> [accessed 26 August 2010]
   
   10.The online fuel cell resource, 2000, fuel cell benefits, accessed at : http://www.fuelcells.org/basics/benefits.html [accessed 26 August 2010]
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5. Riversimple, 2010, How it works, accessed at: http://www.riversimple.com/Content.aspx?mode=menu&type=7&key=93d46e65-ebbd-47f1-8ad1-ae168dfc10f3 [accessed 26 August 2010]
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6. Chevy Volt concept car.,2010,Overview, accessible at: http://www.chevy-volt.net/chevrolet-volt-specs.htm [accessed 26 August 2010]
   
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