COMPARISON OF ENERGY EFFICIENCY AND CO2 OF GASOLINE AND ELECTRIC VEHICLES – Citizens' Task Force on Wind Power - Maine

Many articles have been written about the comparison of the energy efficiency of gasoline and electric vehicles. Most such articles have various flaws. This article will avoid these flaws and will show, electric vehicles are only slightly more energy efficient than gasoline vehicles, on a source energy-to-wheel basis, which is the most rational way to make the comparison.

Many studies fail to use the lower heating value of the fuel, or fail to use the correct heating value of the fuel.

Many studies calculate meter-to-wheel efficiencies of electric vehicles of about 70%, which compare favorably with the tank-to-wheel efficiencies of gasoline vehicles of about 22%. Proponents of EVs say EVs are 70/22 = 3.2 times better. That is not even close to reality.

E10 has a source energy, which is reduced due to extraction, processing and transport, to become the primary energy fed to E10 vehicles. As a result, the energy fed to the tank has to be multiplied by 1.2639 to obtain source energy.

Electrical energy has a source energy, which is reduced due to extraction, processing and transport, to become the primary energy fed to power plants, which convert that energy into electricity. As a result, the energy fed to the meter has to be multiplied by 2.995 to obtain source energy.

After these factors are applied, the EV and E10 vehicles have source-to-wheel efficiencies of about 22.8% and 17.3%, respectively, i.e., EVs are just 22.8/17.3 = 1.31 times better.

Also, the CO2 emissions of an EV are about 62.30 x 1.323 = 82.44 lb, versus about 55.59 lb of an E10 vehicle, i.e., about 82.44/55.59 = 1.48 times greater.

The Source-to-Wheel Efficiency of a Gasoline Vehicle

Per US-EPA, the energy of the gasoline is allocated, in percentages, approximately as shown in Table 1.

http://www.fueleconomy.gov/feg/atv.shtml

At a steady velocity, on a level road, and with no wind from any direction, the propelling force of the engine offsets the external resisting forces acting on the vehicle, which are wind and rolling resistance.

Wind Resistance: The wind resistance of a medium-size vehicle was calculated using 0.5*c*A*d*V^2, where; c is drag coefficient, 0.32; A is cross-sectional area of vehicle, 2.600 m2; d is air density, 1.293 kg/m3, V is velocity, 104.607 km/h (65 mph). The wind resistance is 454 newton (101.389 lbf). See Table 2.

Rolling Resistance: The rolling resistance was calculated using m*g*f*cos (a), where; m is mass, 1250 kg; g is gravity, 9.807 m/s2; f is tire deformation, 0.01 m, a is 0.5 of tire radius, 0.2032 m. The cos (a) is about 1. The rolling resistance is 123 N (27.367 lbf).

Wind + Rolling Resistance: The useful power to the wheels, in kW, was calculated using f, the total of wind and rolling resistance, 577 N (128.756 lbf); d, the distance travelled in one hour 104,607 m; J = N.m, the work done, 60,331,767; t, the time 3600 seconds; W = J/s = 16759, or 16.67 kW. See Table 4.

The Fuel: The vehicle is assumed to have an EPA combined of 28 mpg, using E10, a mixture of 90% gasoline and 10% ethanol. Its higher heating value, HHV, is 126.98 MJ and its lower heating value is 118.28 MJ. In engines, the LHV must be used. See Tables 5 and 6.

http://www.straferight.com/forums/general-chit-chat/178951-ethanol-vs-gasoline.html

http://hydrogen.pnl.gov/tools/lower-and-higher-heating-values-fuels

https://en.wikipedia.org/wiki/Gasoline_gallon_equivalent

http://www.afdc.energy.gov/fuels/fuel_comparison_chart.pdf

Source-to-Wheel Efficiency: The tank-to-wheel efficiency is the useful power of Table 4 divided by the supplied power in Table 6.

* The well-to-tank upstream factor accounts for the energy used for exploration, extraction, processing and transport of the E10 fuel. For exploration and extraction mostly diesel is used, for processing mostly diesel, gas and electricity are used, and for transport mostly diesel is used. See Table 7. Gas and electricity have source factors of about 1.09 (from well-to-power plant) and 2.995 (from well/mine-to-meter), respectively.  Excluded is the embedded energy of all the infrastructures required to provide the US transportation system with various fuels. 

https://www.vcalc.com/wiki/MichaelBartmess/CO2+from+Diesel+Fuel

http://www.cleanskies.org/wp-content/uploads/2011/06/staple_swisher.pdf

http://www.afteroilev.com/Pub/CO2_Emissions_from_Refining_Gasoline.pdf

http://energyoutlook.blogspot.com/2008/08/back-door-on-co2.html

http://www.reuters.com/article/2009/07/28/oil-cost-factbox-idUSLS12407420090728

http://www.accenture.com/SiteCollectionDocuments/PDF/MOD-019_CarbonAccountingPoV_083010_LR.pdf

The Source-to-Wheel Efficiency of an Electric Vehicle

The US economy was supplied with about 25,451.00 TWh of primary energy in 2013. About 40% of that energy, or 10,180.40 TWh, was supplied to the US electricity generating systems, which generated 4065.97 TWh of electricity, for a conversion rate of 0.399. The self-use was 161.54 TWh (about 3.97%), imports were 46.74 TWh, fed into grids was 3951.17 TWh, which reduced by transmission and distribution losses of 256.83 TWh (about 6.5%), resulted in 3694.34 TWh fed to meters. The ratio of primary energy divided by electricity to meters was 0.3629, the system efficiency. See Table 8.

https://en.wikipedia.org/wiki/Energy_in_the_United_States

* The upstream factor accounts for the energy used for exploration, extraction, processing and transport of the various fuels to power plants. For exploration and extraction mostly diesel is used, for processing mostly diesel, gas and electricity are used, and for transport mostly diesel is used. See Table 7. Gas and electricity have source factors of about 1.09 (from well-to-power plant) and 2.995 (from well/mine-to-meter), respectively. Excluded is the embedded energy of all the infrastructures required to provide the US electricity system with various fuels.

CO2 Emissions of Gasoline Vehicles: Table 6 shows driving at a steady 65 mph for one hour uses 2.321 gallon of E10, which, according to Table 7, results in emissions of 23.95 x 2.321 = 55.59 lb CO2, on a source energy basis. See table 10.

CO2 Emissions of Electric vehicles: Based on the EV using 0.32 kWh/mile and traveling at a steady 65 mph for one hour, it uses 20.8 kWh. According to Table 8, the US electricity generating system efficiency is 0.3339, on a source energy basis. The EV source energy is 20.8/0.3339 = 62.30 kWh. See table 10.

The US grid CO2 was about 2053 million metric ton, on a primary energy basis, or 4888.17 billion lb, on a source energy basis.  The US generation to meters was 3694.34 TWh, for an emission intensity of 1.323 lb CO2/kWh. See table 10.

The EV emissions are 62.30 x 1.323 = 82.44 lb CO2, about 82.44/55.59 = 1.48 times greater than of a gasoline vehicle. See Table 10.

https://www.eia.gov/todayinenergy/detail.php?id=18511