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Design for the Environment/Batteries for Electric Cars

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Batteries for Electric Cars store the energy used to power the vehicle. They contribute to the performance, price and range of the car, the key success factors for electric vehicles.[1] Comparing lead acid batteries, ultracapacitors and flywheel systems in electric car applications, ultracapacitors appear to be the superior option, excelling in the criteria above and also in environmental performance.

Project Information

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MIE315/415 Section 2 Group B15
  • Michael Hamilton (Mhamilton)
  • Ammar Khalid (Ammar Khalid)
  • Shaheryar Khan (shaheryar)
  • Jay Leng (Jayseraph)

Highlights and Recommendations

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Ultracapacitors offer superior functional, environmental and economic performance compared to both lead acid batteries and flywheels. The flywheel exhibits better functional performance than the lead acid battery, but is much more expensive and has a much greater impact on the environment. Also, given that there are many years of experience using lead acid batteries in automotive applications, where flywheels are relatively unproven in this environment we would recommend the lead acid battery over the flywheel. However, the ultracapacitor outperforms both of these alternatives in all dimensions analyzed.

Based upon the EIOLCA the ultracapacitor has the least environmental impact of the three alternatives. Over its life cycle it uses the least energy, is reponsible for the least amount of global warming potential and causes the least amount of air pollutions, toxic releases and transfers. Its superior environmental performance was confirmed by the SLCA as the ultracapacitor scored the highest with 65 of 100 points. Cost analysis also finds that it is the least expensive alternative. Furthermore, its energy density and specific energy are substantially greater than either other alternatives, as described in the functional analysis. However, there is some uncertainty about its ability to achieve the performance claimed by its developer. This will become known soon, as ultracapcitors are expected to be used in electric cars by the end of 2009.[2]

Details about the Streamlined Life Cycle Assessment

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The streamlined life cycle assessment (SLCA) rates the environmental performance of each of a product's life cycle stages along five dimensions: materials choice, energy use, solid residue, liquid residue and gaseous residue. Summing the ratings for each cell in the matrix creates a score, the maximum possible being 100. As shown in the table below, the ultracapacitor scored the highest with a 65. The lead acid battery and flywheels scored 59 and 57 respectively. The only stage in which the ultracapacitor performed significantly better than the other options was the delivery stage. This is primarily because the ultracpacitor is much lighter than the other alternatives. However, this type of analysis does not consider the relative importance of each stage. For example, as shown in the EIOLCA the greatest impact of all alternatives originate from the resource provisioning, manufacturing and use phases. The score is also relatively subjective as firm criteria are available only for the maximum and minimum scores in each cell. Therefore, the small difference in the scores of the three alternatives is not in itself a strong indicator of superior environmental performance.

Streamlined Lifecycle Analysis (SLCA) Results Table
Lifecycle Stage Materials Choice Energy Use Solid Residue Liquid Residue Gaseous Residue Stage Score
Resources
Lead Acid Battery
Ultracapacitor
Flywheel System
1
3
3
1
2
1
1
1
2
1
0
2
1
0
1
5
6
9
Manufacturing
Lead Acid Battery
Ultracapacitor
Flywheel System
1
3
3
2
1
2
2
1
2
2
2
2
2
4
2
9
11
11
Delivery
Lead Acid Battery
Ultracapacitor
Flywheel System
4
4
3
2
2
2
2
2
2
3
4
1
2
4
2
13
16
10
Use
Lead Acid Battery
Ultracapacitor
Flywheel System
4
4
2
2
2
2
4
4
4
4
4
4
4
4
4
18
18
16
Disposal
Lead Acid Battery
Ultracapacitor
Flywheel System
3
2
2
2
2
2
3
3
2
3
4
3
3
3
2
14
14
11
Total
Lead Acid Battery
Ultracapacitor
Flywheel System










59
65
57

Lead Acid Batteries

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Total SLCA score of lead-acid battery is 59. The product use stage gets the highest score, because it won’t generate any residues during the product use stage. The total score of EOL (end of life) stage is also high because the 90% of used lead-acid batteries are being recycled[3]. The pre-manufacturing stage gets the lowest score due to the intensive energy use and industrial hazardous residues generation [4], which is also the main reason for the low score of SLCA of lead-acid battery.

Ultracapacitors

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The overall score for the Ultracapacitor Streamlined Life Cycle Analysis is 65. The product performed well in terms of product use, product delivery and end of life stages. During product use, no solid, liquid or gaseous residues are generated since product uses barium titanate ceramic powder (dielectric)with double coating layers of Aluminosilicate glass and aluminum oxide. Moreover, energy storage at about 4-6 minutes consumes significantly lower amount of electricity. For product delivery stage, cardboard a re-useable material will be used for shipping purposes and could be shipped back during the next shipment for further use. Finally, no liquid residue results since barium titanate powder is closely intact inside the double coating layer. End of life stage scores well because all materials used can be identified and separated upon recycling [5]. In addition, the product has a life of up to a million cycles without material degradation which is well above the life limit of a car; hence, this product could be placed into the other car once the car life comes to an end making it an environmentally friendly product [6]. EESU did not perform well for the pre-manufacturing stage because virgin materials nickel and copper have been used since recycled material use would result in a lower quality of the product and product may not perform as predicted; however, the composition of virgin materials is kept lowest to reduce the production of large amount of solid, liquid and gaseous toxic residues.

Flywheel Systems

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The overall score for the flywheel Streamlined Life Cycle Analysis is 57. The product performed well in terms of material choice for the pre-manufacturing, manufacturing and delivery stages. The flywheel system is constructed using a carbon fiber composite flywheel, aluminum casing and magnetic bearings. The material used to package the finished flywheel system most likely includes foam (cushioning), cardboard (box), and adhesive tape for sealing the box. Both foam and cardboard are recyclable and currently there is a functioning recycling infrastructure available. [7]. The system was ranked high for production of residues during the use stage because there are no solid, liquid or gaseous residues produced as the flywheel system operates. The system did not rank well for energy use during the product life cycle because the system operation energy use is dependent on the user and the amount of time the flywheel system is charged for, manufacturing the system is energy intensive and delivery has significant energy requirements because of the distances involved as we will be having the flywheel energy storage systems delivered from the California offices of U.S. Flywheel Systems Inc. [8].

Details about the Economic Input-Output Life Cycle Assessment

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The economic imput-output life cycle assessment uses information on the US economy to estimate the environmental impact of a product based on its cost. Many criteria are considered, including total energy use, global warming potential, conventional air pollution and toxic releases and transfers. The ultracapacitor outperformed the other alternatives in each of these criteria. The use phase is very similar for all alternatives and the impact of the delivery phase is very small. The differentiator is based upon the resource extraction and manufacturing phases, for which the impacts are calculated based upon the price. The ultracapacitor is the least expensive option, which has a strong influence on the results of this analysis. The results of the EIOLCA are shown in the table below.

Economic Input-Output Life Cycle Analysis (EIOLCA) Results Table
Alternative Total Energy Use [TJ] Global Warming Potential [MTC02E] SO2[mt] CO[mt] NO2[mt] VOC [mt] Lead [mt] PM10 [mt] Total Releases [kg] POTW Transfers [kg] Offsite Transfers [kg]
Lead Acid Battery 0.199 17.7 0.082 0.046 0.041 0.007 0 0.009 41.955 0.858 3.443
Ultracapacitor 0.177 15.5 0.076 0.023 0.037 0.004 0 0.002 20.543 0.394 1.661
Flywheel System 0.342 34.3 0.158 0.069 0.078 0.011 0 0.011 75.22 1.619 6.249

Lead Acid Batteries

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Our EIOLCA found total energy use to be 0.199 TJ, global warming potential (GWP) to be 17.7 MTCO2E and total toxic releases to be 0.271 kg. The product use stage yields high output in energy use and GWP, since the vast majority of energy and greenhouse gas comes from electricity generation and supply during the use stage of the lead-acid battery. The resource extraction and manufacturing stage yields the highest toxic release due to the usage of metal lead during manufacturing stage.

A considerable amount of conventional pollutants are generated from the lead-acid battery life cycle. Product use results in higher quantities of the pollutant emissions than do the other life stage because the electricity generation such as coal-fired power plant produces large SO2 and NO2 emissions. The major CO emissions result from the product delivery sector due to the truck exhaust gases during the delivery process.

Ultracapacitors

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In our analysis, an Economic Input Output Life Cycle Analysis was conducted on the EESU for the pre-manufacturing/manufacturing stage, product delivery stage and the product use stage. However, the effect of end of life stage was significantly negligible due to the product’s ability to last up to million cycles whereas an average car’s life is six years; thus, product could be replaced into a new car. For an EESU, the total energy use and the total GWP for the above mentioned included sectors were found to be 0.177 TJ and 15.516 MTCO2E. Both the highest amount of energy used and greenhouse gases emission occur during the product use phase where power generation and supply sector contributes the most. The reason being the amount of electricity required to charge the vehicle daily for a period of six years as well as energy required for power generation. For the coal-fired power plants, the generation of electricity requires extraction of coal during which methane is released into the environment, the transportation of coal (rail, truck) releases carbon monoxide into the atmosphere, “The burning of coal at the plant produces oxides of carbon, usually carbon dioxide in a complete combustion, along with oxides of sulfur, mainly sulfur dioxide (SO2), and various oxides of nitrogen (NOx)”[9]. Hence, the total amount of conventional pollutants were SO2[mt]=0.076, CO[mt]=0.023, NOx[mt]=0.037 and VOC [mt] = 0.004. As mentioned above, the most pollutant gases are emitted during the product use due to electricity generator power plants. These plants mainly use coal-fired systems which are the main reason for SO2 and NOx emissions. However, Carbon monoxide is emitted during the product delivery due to truck transportation where fuel burning takes place. Finally, the total toxic releases was 20.543kg.

Flywheel Systems

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 An Economic Input Output Life Cycle Analysis (EIOLCA) was conducted on the system for the Premanufacturing/Manufacturing stage, Product Delivery stage and the Product Use stage. The Disposal stage was excluded because if we were to incorporate the product disposal stage it would require a separate analysis where data would be required on the test analysis of the flywheel system to determine how many cycles it can sustain and the flywheel energy storage system would also be required to fail to determine nature of scrap material, quantity and after effects however modes of failure can not be predicted. For the flywheel system the total energy use for the above mentioned sectors (Premanufacturing/Manufacturing stage, Product Delivery stage, Product Use stage) was calculated to be 0.342 TJ. The main contributor to this value is the power generation and supply sector during the product use stage that requires daily electricity recharging use. The product use stage has the most greenhouse gas emissions which is understandable considering the daily energy consumption and requirement. The generation of electricity requires extraction of coal during which methane is released into the environment, the transportation of coal (rail, truck) releases carbon monoxide into the atmosphere, “The burning of coal at the plant produces oxides of carbon, usually carbon dioxide in a complete combustion, along with oxides of sulfur, mainly sulfur dioxide (SO2), and various oxides of nitrogen (Nox)” [10]. The total GWP value was calculated to be 34.3 MTCO2E. Similarly the amount of some major toxic releases obtained were SO2[mt]=0.158, CO[mt]=0.069, NO2[mt]=0.078 w and the total toxic releases amount was found to be 75.22kg. (All values obtained using the EIOLCA model available online)[11]

Details about the Functional Analysis

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Range is a key requirement for electric cars. As such, the functional analysis focussed on the storage capacity of each battery, since the range of the car is proportional to the energy available to it. Specifcally, the energy density (energy relative to volume) and specific energy (energy relative to volume) of each were considered. The ultracapacitor had the greatest specific energy at 341 Wh per kg compared to 41 and 90 Wh per kg for the lead acid battery and flywheel respectively. The ultracpacitor also had the greates energy density at 1583 Wh per liter compared to 107 and 1583 Wh per L for the lead acid battery and flywheel respectively.

Lead Acid Batteries

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The lead-acid battery is an electrical storage device that is based on a reversible chemical reaction between lead and sulphuric acid. It has a capacity of six or more volts which is enough to power a vehicle [12]. To power a Ford TH!NK City A306, twenty-two 110 Ah 12V lead-acid battery of model UB121100 from Universal Power Group Inc. were selected. Each battery has a capacity of 1.32kWh and has average 650 recharge cycles[13].

Ultracapacitors

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Ultracapacitor are energy storage devices that could store tremendous amount of energy, and have the ability to provide both high power and high energy [14]. The car model we have chosen to base our analysis on is the Ford Th!nk City A306. Th!nk City’s electric battery requires 28.3kWh of energy storage for each recharge [15]. Thus, the model chosen to meet our electric car Th!nk City power demand is EEstor’s Electrical Energy Storage Unit (EESU). EESU could store up to 52kWh of energy [16]; hence, the energy storage capability of an EESU meets or exceeds the demand of the Th!nk City. The total mass of a single EESU is 336lb which includes 272lb of dielectrics, 34lb of nickel and 30lb of copper, and each unit charges within 4-6 minutes with a peak power output of 74.6kW. An EESU has over million numbers of cycles which makes it relatively more environmentally friendly.

Flywheel Systems

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To power the TH!NK we need 8 flywheel energy storage systems. The flywheel energy storage system consists of the flywheel, aluminum storage system and magnetic bearings. For the flywheel system the number of cycles is almost infinite barring catastrophic failure.[17], [18]

Jack Bitterly Flywheel System: TH!NK Requirement: Design:
Total Mass = 90 lbs ~ 41kg Total Energy Required = 28.3 kWh I = kmr^2 = 0.2671
Flywheel Alone = 50 lbs ~23kg Energy needed = 28.3 kWh/0.90 = 31.44 kWh
Flywheel Diameter = 12 inches = 0.3048m # of flywheels required = 31.44kWh/4.1kWh ~ 8
Flywheel Thickness = 3 inches = 0.0762m
Each wheel stores 4.1 kilowatt-hours of energy
Flywheel conversion efficiency ~90%

Details about the Cost Analysis

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In order to account of the true cost of each alternative over its lifetime we compared the present values of their costs. The ultracapacitor was the least expensive with a present value of $4,036 followed by the lead acid battery at $7,193 and the flywheel at $18,705. In all cases the analysis was performed in real (2008) dollars using a discount rate of 3.62%. The alternatives were also compared on their price per kWh stored. The ultrapacitor performed much better than the alternatives, costing $40 per kWh compared to $169 and $295 per kWh for the lead acid battery and flywheel respectively.

Lead Acid Batteries

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The 22 lead-acid batteries are considered as a unique product for the whole life cycle cost analysis. During the analysis, all cash flows are in 2008 US dollars for a consistency. Some costs are calculated in EIOLCA such as the cost for resource and manufacturing, product delivery and product use. Some other costs such as installation and service are calculated by skilled worker’s wage and estimated time. For the life stage of manufacturing, delivery and initial installation, all costs are put into the current year 2008. The 6 years after 2008 are the use stage of the lead-acid battery. Each year has a product use cost, accompany with the service cost. At the end of the battery life (year 2014), the recycling cost will be incurred. The Net Present Value (NPV) was found to be $7193.13 (2008 US dollar). The calculation of the NPV is based on the equation PV (Present Value) = FV (Future Value)/ (1+i) n. Using all the costs in different years and the real discount rate 3.62%, we can calculate the NPV.

Ultracapacitors

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The purchase price of an EEstor Ultracapacitor is $2100 (2007 dollars) [19][20]. The delivery cost is calculated to be $15.31 (2006 dollars) for a single EEstor unit. The energy cost of a product during the product use phase is based on Th!nk City’s average life of six years. The Th!nk City needs 28.3 kWh of energy storage for a full charge which could cover a distance up to 180 kilometers [21]. Hence, 0.157 kWh/ km. The cost for electricity used for every kWh is 10.28 cents [22]. We are assuming that the EESU will be charged daily for the period of six years which is the average life of a vehicle and an average vehicle travels 11100 miles per year (17863.7184km) [23]. Since, Th!nk City needs 28.3kWh of storage energy every recharging cycle, we get {(0.157kWh/km x 17863.7184 km) x (10.28cents)} = $288.3 (2007 dollars)for one year. Applying “CPI Inflation Calculator” results in $294.36 (2008 US dollar). As mentioned in the functional analysis, EESU can be used for over a million cycles, whereas, it will be used in the Th!nk City for only 2190 cycles based on six years of daily use; hence, after the car’s life is over, EESU can be taken out and sent back to the manufacturer where it can be reused. Thus, only removal cost occurs at the end of life stage which will be considered to be the same as the installation cost of $13.61(2008 dollars) explained below. Indirect costs should also be considered. Assuming that for installation an electric battery, it takes a skilled automotive worker about half an hour and the average wage for the skilled worker is $27.22/hr [24]; hence, $13.61 (2008 dollars). Finally, service cost is considered to be an indirect cost as well. Assuming the battery is serviced every year for 2 hour including installation and removal time, it will cost $27.22 x 2 = $54.44 (2008 US dollars) each year for up to six years.

Flywheel Systems

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The average life of a car is 6 years and an average vehicle travels 18990.2592 kilometers in 6 years [25]. 1 flywheel system costs $818.36 (obtained using CPI Inflation Calculator and converting 1996 US Dollar value of $800 to 1997 US Dollar Value) [26], [27] so $818.36 x 8 = $ 6546.88 (1997 US Dollars) which is $8,635.07 (2008 US Dollars) [28]. The manufacturer of the flywheel energy storage system is U.S. Flywheel Systems [29]. The cost to deliver 889 flywheel systems is $7,792.44 (2008 US Dollars) [30]. The cost of electricity used for every kWh is 10.28 cents [31].The cost therefore is {(0.157kWh/km x 18 990.2592 km) x (10.28cents)} = $306.5 (2007 dollars) per year. The average cost/time ratio for a skilled automotive installer is $27.22/hr [32]. The estimated install time is 20 minutes. Thus, the cost of initial installation of the 8 flywheel systems in 160 minutes is $72.59 (2008 US dollars). We also assume each flywheel system should take a routine 30 minute service each year during the use phase. Therefore to check 8 flywheel systems would require 240 minutes and using the average cost/time ratio $27.22/hr obtained above, we can get the service cost of $108.88 (2008 US dollar) each year. Using a real discount rate of 3.62% the Net Present Value is calculated to be $18,704.78.

2008 2009 2010 2011 2012 2013 2014
Resource & Manufacturing $8,635.07
Product Delivery $7,792.44
Product Use $306.50 $306.50 $306.50 $306.50 $306.50 $306.50 $306.50
Other $72.59 $108.88 $108.88 $108.88 $108.88 $108.88 $108.88
Total $16,500.10 $415.38 $415.38 $415.38 $415.38 $415.38 $415.38
PV Factor 1 0.965 0.931 0.899 $0.867 0.837 0.808
NPV $18,704.78 The net present value obtained using a real discount rate of 3.62%

References

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  1. ↑ IMechE (Institution of Mechanical Engineers) and Fluid Machinery Group Staff Ed.,“Alternatively Fuelled Vehicles,” John Wiley & Sons, 2000
  2. ↑ Zenn Motor Company Inc. (March 2008) ZENN MOTOR COMPANY DETAILS PLANS FOR HIGHWAY CAPABLE ZENN POWERED BY EESTOR's Electrical Energy Storage Unit (EESU). Zenn Motor Company Press Release. Retrieved April 8, 2008, from the World Wide Web: http://www.zenncars.com/
  3. ↑ Natural Resource Canada. (2008) Automotive Recycling Archives [Internet], Available from: http://www.nrcan.gc.ca/ms/canmet-mtb/mmsl-lmsm/rnet/autoarte.htm [Accessed 28 Feb 2008]
  4. ↑ Wikipedia (2006) Sulfuric acid [Internet], Available from: http://en.wikipedia.org/wiki/Sulfuric_acid [Accessed 22 Mar 2008]
  5. ↑ Patent Storm. (April 2006), Electrical-Energy-Storage Unit (EESU) utilizing ceramic and integrated-circuit technologies for replacement of electrochemical batteries [Internet], [Retrieved Feb.28, 2008], Available at: http://www.patentstorm.us/patents/7033406-fulltext.html
  6. ↑ Ultracapacitor. Ultracapacitor-The Technology [Internet], [Retrieved Jan. 27, 2008], Available at: http://www.ideaspike.com/ultracaps.shtml
  7. ↑ Nitro PDF Software. Corrugated Cardboard [Online Document], [Retrieved 17 Mar 2008], Available at: http://www.pdfdownload.org/pdf2html/pdf2html.php?url=http%3A%2F%2Fwww.gvrd.bc.ca%2Frecycling-and-garbage%2Fpdfs%2Ffacts-cardboard.pdf&images=yes
  8. ↑ NASA. News, [Internet Document], Available at: http://www.nasa.gov/centers/glenn/news/pressrel/2000/00-017.html [Accessed 20 Mar, 2008]
  9. ↑ Wikipedia. Environmental Effects of Coal [Internet], Available at: http://en.wikipedia.org/wiki/Environmental_effects_of_coal#Coal_burning [Accessed 20 Mar 2008]
  10. ↑ Wikipedia. Environmental Effects of Coal [Internet], Available at: http://en.wikipedia.org/wiki/Environmental_effects_of_coal#Coal_burning [Accessed 20 Mar 2008]
  11. ↑ Carnegie Mellon University Green Design Institute. (2008) Economic Input-Output Life Cycle Assessment (EIO-LCA) model [Internet], Available from: http://www.eiolca.net/ [Accessed 22 Feb, 2008]
  12. ↑ Lead-Acid Battery Info. (2007) Lead-acid Battery Resources [Internet], Available from: http://www.leadacidbatteryinfo.org/resources.htm [Cited 25 Jan 2008]
  13. ↑ Wikipedia (2006) Lead-acid Battery [Internet], Available from: http://en.wikipedia.org/wiki/Lead-acid_battery [Accessed 23 Mar 2008]
  14. ↑ US department of energy. (May 2006), Technologies [Internet], [Retrieved Feb. 13, 2008], Available at: http://www.eere.energy.gov/de/supercapacitors.html
  15. ↑ Th!nk. Technical data [Internet],[Retrieved Feb. 23, 2008], Available at: http://en.think.no/think/Think-Models-Concepts/TH!NK-i-cityi/ Specifications/Technical-data
  16. ↑ The Energy Blog. (January 2007), EEstor Ultracapacitor Shuns Publicity [Internet], [Retrieved Feb.23, 2008], Available at: http://thefraserdomain.typepad.com/energy/2006/01/eestor_ultracap.html
  17. ↑ W. Hively “Reinventing the wheel - Jack Bitterly is developing the flywheel automobile engine” Discover, [Online Document] Aug. 1996, [Retrieved 28 Jan 2008], Available at HTTP:http://findarticles.com/p/articles/mi_m1511/is_n8_v17/ai_18471043/pg_1
  18. ↑ Discover Magazine, Wheel [Internet Article], Available at: http://discovermagazine.com/1996/aug/reinventingthewh842 [Accessed 20 Mar, 2008]
  19. ↑ The Energy Blog. (January 2007), EEstor Ultracapacitor Shuns Publicity [Internet], [Retrieved Feb.23, 2008], Available at: http://thefraserdomain.typepad.com/energy/2006/01/eestor_ultracap.html
  20. ↑ Patent Storm. (April 2006), Electrical-energy-storage unit (EESU) utilizing ceramic and integrated-circuit technologies for replacement of electrochemical batteries [Internet], [Retrieved Feb.28, 2008], Available at: http://www.patentstorm.us/patents/7033406-fulltext.html
  21. ↑ Th!nk. Technical data [Internet],[Retrieved Feb. 23, 2008], Available at: http://en.think.no/think/Think-Models-Concepts/TH!NK-i-cityi/ Specifications/Technical-data
  22. ↑ Toronto Hydro. (March 2008), Residential Rates [Internet], [Retrieved March 7, 2008], Available at: http://www.torontohydro.com/electricsystem/residential/rates/index.cfm
  23. ↑ US department of energy. (June 2007), Transportation Energy Data Book [Internet], [Retrieved March 7, 2008], Available at: http://cta.ornl.gov/data/index.shtml
  24. ↑ Bureau of Labor Statistics (2008) Automotive Worker Earnings [Internet], [Retrieved March 23, 2008] Available at: http://www.bls.gov/oco/ocos181.htm#earnings
  25. ↑ US department of energy. (June 2007), Transportation Energy Data Book [Internet], Available at: http://cta.ornl.gov/data/index.shtml [Retrieved March 7, 2008]
  26. ↑ W. Hively “Reinventing the wheel - Jack Bitterly is developing the flywheel automobile engine” Discover, [Online Document] Aug. 1996, [Retrieved 28 Jan 2008], Available at HTTP:http://findarticles.com/p/articles/mi_m1511/is_n8_v17/ai_18471043/pg_1
  27. ↑ Discover Magazine, Wheel [Internet Article], Available at: http://discovermagazine.com/1996/aug/reinventingthewh842 [Accessed 20 Mar, 2008]
  28. ↑ CPI Inflation Calculator. Inflation Calculator [Internet], Available at: http://data.bls.gov/cgi-bin/cpicalc.pl
  29. ↑ NASA. News, [Internet Document], Available at: http://www.nasa.gov/centers/glenn/news/pressrel/2000/00-017.html [Accessed 20 Mar, 2008]
  30. ↑ Agricultural Marketing Services. (2008) Truck Transportation [Internet], Available from: http://www.ams.usda.gov/tmdtsb/grain/QuarterlyUpdates/4thQuarter06.pdf [Accessed 20 Mar 2008]
  31. ↑ Toronto Hydro. (March 2008), Residential Rates [Internet], Available at: http://www.torontohydro.com/electricsystem/residential/rates/index.cfm [Retrieved March 7, 2008]
  32. ↑ Bureau of Labor Statistics (2008) Automotive Worker Earnings [Internet], Available from: http://www.bls.gov/oco/ocos181.htm#earnings [Accessed 23 Mar 2008]
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