Comparison of Energy Efficiency and CO2 of Gasoline and Electric Vehicles
- May 11, 2017
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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 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%, i.e., EVs are 3.2 times more efficient. But that is not even close to reality.
E10 fuel (90% gasoline/10% ethanol) has a source energy, which is reduced due to exploration, 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 exploration, extraction, processing and transport, to become the primary energy fed to power plants, which convert that energy into electricity, which after various losses, arrives at user meters. As a result, the energy fed to the meter has to be multiplied by 2.8776 to obtain source energy. After these factors are applied, the EV and E10 vehicles have values as shown in the below table. The below table is based on US 2013 CO2 emissions of 2053 million metric ton to match the available 2013 electricity generation data. See Table 8.
|kWh/65 miles, to wheels||16.67||16.67||16.67||16.67|
|Btu/65 miles, to wheels||56878||56878||56878||56878|
|miles in one hour||65||65||65||65|
|Btu/65 miles, T-t-W||260265||214336||182185||140143|
|eff, SE basis||0.173||0.210||0.247||0.321|
|gal/65 miles, T-t-W||2.321||1.912||1.625||1.250|
|Btu/65 miles, SE basis||328948||270899||230264||177126|
|lb CO2/gal, SE basis||23.95||23.95||23.95||23.95|
|lb CO2/mile, SE basis||0.86||0.70||0.60||0.46|
|g CO2/km, SE basis||241||199||169||130|
|g CO2/km, T-t-W||191||157||134||103|
|L of E10/100 km, T-t-W||8.40||6.92||5.88||4.52|
|kWh/65 miles, to wheels||16.67|
|kWh/65 miles, M-t-W||24.371|
|Btu/65 miles, M-t-W||83155|
|Btu/65 miles, SE basis||239287|
|lb CO2/kWh, SE basis||1.2712|
|lb CO2/mile, SE basis||0.477|
|g CO2/km, SE basis||134|
|Energy efficiency, SE basis|
|EV better than E10, %||27.3||11.7|
|EV worse than E10, %||3.9||35.1|
|CO2, SE basis|
|EV better than E10, %||44.3||32.3||20.4|
|EV worse than E10, %||3.5|
Effect of a “Cleaner” Grid in 2016: If the 2016 CO2 emissions of 1821 MMt were used, and the 2016 electricity generation data were assumed to be about the same as in 2013, then the above 1.2712 would become 1.1275 and the EV CO2 emissions would become 0.423 lb/mile (119 g/km). Only E10 vehicles with about 45 mpg (5.23 L/100 km), or better, would have less CO2 emissions than an EV with a real-world, annual average meter to wheel of 0.375 kWh/mile (0.233 kWh/km). See below table and sections and Table 9.
High-efficiency Vehicles More Efficient Than Electric Vehicles: The table shows high-efficiency E10 vehicles, including hybrids, such as the 52 mpg, 4.52 L/100 km Toyota Prius, have greater energy efficiency than EVs, and less CO2 emissions than EVs, on an SE basis. It would be much less costly and quicker to significantly increase the US hybrid fleet, than to build out the EV fleet, which is still in its infancy, and would require major, expensive changes to supporting infrastructures.
Tesla Model S: An upstate New York owner of a Tesla Model S measured the house meter kWh, vehicle meter kWh, and miles for one year. There was significant kWh/mile variation throughout the year. His annual average was 0.392 kWh/mile, M-t-W. The Model S has regenerative braking as a standard feature. The above analysis used an annual average of 0.375 kWh/mile, M-t-W, which means I used a higher EV efficiency than measured by this owner.
Data as measured by owner in New York State. See URL
|Tesla, Model S|
|Electricity cost, c/kWh||19|
|Miles in one year||15243||c/mile|
|kWh, vehicle meter||5074||6.3|
|kWh/mile, vehicle basis||0.333|
|kWh/mile, vehicle basis||0.301||Apr-Oct|
|kWh/mile, vehicle basis||0.290||Jul|
|kWh/mile, vehicle basis||0.371||Nov-Feb|
|kWh/mile, vehicle basis||0.400||Jan|
|kWh, house meter||5969||7.4|
|kWh/mile, house meter basis||0.392|
Tesla Model S Driving Ranges on Non-urban Interstate Highways Under Varying Conditions
Interstate Highway speed limits; non-urban, contiguous 48 states; 12 states @ 65 mph, 20 states @ 70 mph, 14 states @ 75 mph, 1 state @ 80 mph (Texas). See: www.ghsa.org
Tesla Model S 85 kWh. Range advertised by Tesla as 300 miles at 55 mph
Sources: www.teslamotors.com and Tesla battery engineer claims.
Table 1. Ideal driving conditions: no AC, no heat, level terrain, 300 lbs aboard, windows rolled up, constant speed, no wind.
Table 2. Ideal driving conditions, but using average AC, and average heat
Table 3. Assuming additional 15% energy consumption due to non-ideal driving conditions, heavier AC and heavier heat
Debunking the Phony EPA Fuel Consumption Numbers – all numbers are on a source energy basis:
– An E10 vehicle, 28 mpg, uses 2.321 gal x 112114 Btu/gal = 260265 Btu of E10 to go 65 miles in one hour (tank-to wheel basis), per Table 6, or 328948 Btu, on a SE basis.
– An EV uses 24.371 kWh x 3412 Btu/kWh = 83155 Btu to go 65 miles in one hour (meter-to-wheel basis), or 239287 Btu, on an SE basis.
The EPA mpg gasoline equivalent is based on the energy content of gasoline. The energy obtainable from burning one US gallon of gasoline is 115,000 Btu, or 33.705 kWh, or 121.3 MJ. If a different fuel, such as E10, is used, then the Btu of that fuel is used to determine EPA MPGe.
EPA EV mileage = total miles/(fuel energy/energy/gal) = 65/(83154/112114) = 87.6 MPGe. The EPA deliberately ignores the US electrical system upstream SE factor and the E10 upstream SE factor. If the US SE factor were applied, the real mileage would be 87.6/2.8776 = 30.4 mpg, similar to the 28 mpg of the E10 vehicle, as one would expect.
The car manufacturers are in on the deal, because they are allowed to take those low MPGe numbers and average them into their CAFE mpg, making it look lower than it really is to befuddle the public, which is somewhat of a sham.
The official explanation of the EPA is that people are familiar with miles/gallon, and EPA decided to call it “miles/gallon equivalent”. Engineers may not be befuddled, but Joe Blow likely is. Just ask some average people what it means. They have no idea. That means what EPA came up with was confusing.
US-DOE/Argonne National Laboratories GREET Program: ANL wrote the Greenhouse gases, Regulated Emissions, and Energy use in Transportation, GREET, computer program. The program enables comparing the well-to-wheel efficiency of gasoline and electric vehicles. If I had used the program, the inputs would have been a fuel mix to power plants for determining the CO2 of the EV, and E10 for determining the CO2 of the E10 vehicle.
However, lacking sufficient familiarity with the GREET program, and always wanting to see equations, instead of just accepting printed results, readily available EIA data regarding CO2 emissions from the US electricity generating system, and EIA data regarding the generation of electricity, and data from various other sources, referenced in this article, were used to perform the analysis of this article.
NOTE: The article, “Is Ethanol a Cost Effective Solution to Climate Change?” shows, after a detailed analysis of the GREET computer program, the Argonne analysts relied on less-than-fully accurate international data bases, and overestimated well-to-wheel fossil fuels consumption (and associated CO2 equivalent emissions) of petroleum fuels by up to about 9%.
Quick Charging of Batteries: Because low-voltage (110V+) charging of batteries takes a long time, higher voltage (220V+) charging is often used, because it reduces charging times. However, that negatively impacts:
– Overall charging efficiencies, which increases energy consumption and costs
– Battery aging, which requires earlier battery replacement, because of a loss of storage capacity, kWh, which negatively affects driving range
– Delivering energy at required rates, which negatively affects acceleration and uphill driving.
New England and EVs: With snow and ice, and hills, and dirt roads, and mud season, all-wheel drive vehicles, such as the Subaru Outback, SUVs, ¼-ton pick-ups, minivans, are a necessity in rural areas. There are a few EVs, such as the Tesla Model S, $80,000-$100,000, which offer road-clearance adjustment and all-wheel drive as options. Here is a list of EVs and Plug-in Hybrids. Very few have all-wheel drive and some of them cost 1.5 to 3 times as much as a Subaru Outback.
Driving an EV in winter, with 5 cm of snow, uphill, at low temperature, say – 10 C, with the heat pump heating the battery and the passenger cabin, would be slow going, unless the EV has a large capacity, kWh, battery. The additional stress causes increased battery aging and capacity loss.
Batteries likely will come down in cost, because of mass production, and weight, due to clever packaging (which would decrease rolling resistance), but the lithium-ion chemistry is pretty well maxed out, according to Musk, CEO of Tesla.
People switching from E10 vehicles to EVs likely will not happen anytime soon. There are no compelling CO2 reasons, as shown by the above table, unless the government compels people to do so, which would be a folly, as there are so many, less expensive ways, to reduce CO2. In fact, it would be best, if the government stopped interfering with the energy business.
Efficiency of US Light Duty Vehicles: LDVs are cars, SUVs, ¼-ton pick-ups, and minivans. The average efficiency of LDVs has not changed much these past 15 years. Even though new vehicle efficiency increased during the past 15 years, it caused just a very minor increase in the efficiency of all LDVs. See table. A similarly slow increase could be expected if EVs were to replace E10 vehicles.
However, if more LDVs were required to be hybrids (such as the Toyota Prius), which could be more rapidly implemented by manufacturers, then an efficiency increase of at least 25% could be expected during the next 15 years, etc. Toyota has a proven line-up of high-efficiency hybrids in various sizes and shapes. Other manufacturers could have the same.
|mile/gal||mile/gal||L/100 km||L/100 km||%|
A Better Future Pathway: Future E10 vehicles likely would become more efficient, more quickly, and at much less cost, especially by increased use of hybrids, than:
– EVs could improve their efficiency, because lithium-ion technology is “just about maxed-out”, according to CEO Musk of Tesla. Such future EVs likely would become less costly, but not much more efficient.
– The US electrical system could reduce its CO2 intensity, kg CO2/kWh, such as with additional capacity, MW, build-outs of renewables and enlargements of the US electrical system. With higher-efficiency E10 vehicles, no such highly visible build-outs and enlargements would be needed. In fact, the capacity of the existing E10 fuel supply systems would be more than adequate for decades.
CO2 can be much less expensively reduced by:
– Making E10 vehicles more efficient
– Increased use of hybrid vehicles, such as Toyota Prius hybrids
– Increased building efficiency (having energy surplus buildings)
– Replacing existing nuclear plants with new nuclear plants, and, in New England,
– Getting more, low-cost, near-zero-CO2, hydro energy from Hydro-Quebec.
The Source-to-Wheel Efficiency of an E10 Vehicle
Per US-EPA, the energy of the gasoline is allocated, in percentages, approximately as shown in Table 1.
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. The wind resistance is 454 newton. See Table 2.
|Wind resistance||454||N||102.063||lb force|
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 = 0.5 of tire radius, 0.2032 m. The cosine (a) is about 1. The rolling resistance is 123 N. See Table 3.
|0.5 of tire radius||a||0.203||m||0.667||ft|
|Rolling resistance||123||N||27.549||lb force|
Wind + Rolling Resistance: The useful power to the wheels, kW, was calculated using f, the total of wind and rolling resistance, 577 N; d, the distance travelled in one hour, 104.607 km; 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.
|Wind + Rolling||f||577||N||129.612||lb force|
|Work done||f*d||60,331,767||N.m = J||44,482,152||ft.lb force|
The Fuel: The vehicle is assumed to use E10, a mixture of 90% gasoline and 10% ethanol. Its lower heating value is 31.25 MJ/L. In engines, the LHV must be used. See Tables 5 and 6.
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. See Table 7.
NOTE: The UK, cleanairchoice and GREET claim the factor is 1.203, 1.23 and 1.2568, respectively. In this analysis 1.2639 was used which attributes more CO2eq to E10 vehicles, which makes EVs look better, in comparison. See Table 2 in second URL and Page 8 in third URL.
Source Factor for US Electrical System: Various fuels, extracted from the earth, are fed to US electrical 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.
Table 7 shows the well-to-pump source factor for E10 is about 1.2639. The well-to-user source factor for gas and the mine/well-to-meter source factor for electricity are about 1.090 and 2.8776, respectively.
Also there is the energy consumed for O&M and on-going replacements/upgrading of the infrastructures used for exploration, extraction, processing and transport of the source energy that is converted to primary energy for the US economy. The US electrical system uses about 40% of all primary energy.
This results in an upstream factor of the US electrical system of about 1.08, i.e., the equivalent of about 8% of the source energy is used to obtain the primary energy fed to power plants. That 8% usage causes CO2 emissions. See Table 8. Excluded is the embodied energy of all the required infrastructures.
The Source-to-Wheel Efficiency of an EV
The US economy was supplied with about 25,451.00 TWh of primary energy in 2013. See Table 8. In this analysis, I used the 2013 emission data in conjunction with the 2013 electricity generation data.
The EIA 2013 emissions data is higher than at present, due to gas replacing coal. It is ironic, I could find the 2016 GERMAN electricity generation data, but not the 2016 US data.
|US Primary energy||25451.00|
|Electrical primary energy||10180.40|
|Self-use, % of Generation||3.82||161.55|
|Net generation to grid||4065.97|
|Imports, % of net generation||1.15||46.74|
|T&D, % of To grid||6.50||267.33|
|To electric meters||3845.38|
|System efficiency, PE basis||0.3777|
|System efficiency, SE basis||0.3475|
|Inverter AC to DC||0.950|
|Battery and charger||0.800|
|Motor and drivetrain||0.900|
German 2016 Electrical Data: Here are the corresponding numbers for Germany. In 2016, domestic electricity consumption = gross generation (648.4), less self-use (30), less net exports (53.7), less transmission and distribution (30), less pumped storage and misc. (19.4), = about 515.3 TWh at user meters. (CO2 of the gross generation) / (515.3 TWh) = grid CO2 intensity at the meter, which should be multiplied by the kWh drawn by an EV. However, this CO2 is based on primary energy grid intensity. It has to be adjusted by a factor to get source energy grid intensity, similar to the Table 8 procedure.
CO2 Emission Reduction Due to less Coal and More Natural Gas Combustion: The URL shows the unusually rapid decrease of CO2 emissions during 2015 and 2016. Such a rapid decrease likely will not occur during the next few years, as natural gas prices likely will increase due to exports, and as changes in EPA rules likely will cause fewer coal plants to close. A “cleaner” US grid would mean EVs would compare more favorable with E10 vehicles regarding emissions. See Table 9.
|To meters, TWh||3845.38|
|lb CO2/kWh, PE basis||1.0440|
|lb CO2/kWh, SE basis||1.1275|
Photo Credit: Frank Hebbert via Flickr