→Electric and plug-in hybrid electric vehicles: re-arranged to put the EPA value for Eg first followed by the GREET value, since section deals with EPA formula |
→Electric and plug-in hybrid electric vehicles: removing blatant OR by Blake1960: This article is NOT about energy efficiency well-to-wheels |
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: <math> MPGe = \frac { E_G} {E_M*E_E} = \frac{ 34,024 } {E_M}</math> |
: <math> MPGe = \frac { E_G} {E_M*E_E} = \frac{ 34,024 } {E_M}</math> |
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The above formulas employed by the EPA for calculating their reported MPGe do not account for any fuel or energy consumed during the creation or transmission of electrical power, which is required to charge BEVs and PHEVs |
The above formulas employed by the EPA for calculating their reported MPGe do not account for any fuel or energy consumed during the creation or transmission of electrical power, which is required to charge BEVs and PHEVs, as the comparison with gasoline-powered vehicles is made on a tank-to-wheels basis. |
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:<small>When comparing gasoline vehicles with electric vehicles, it is essential to consider the efficiency of the respective ‘‘upstream’’ processes in the two fuel cycles. ...the critical difference is that a gasoline vehicle burns its fuel on-board the vehicle, and an electric vehicle burns its fuel (the majority of electricity in the U.S. is generated at fossil fuel burning power-plants) off-board the vehicle. In both cases, the burning of fuels to produce work is the least efficient step of the respective energy cycles.</small> |
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Per the Department of Energy, the gasoline-equivalent energy content of electricity (E<sub>g</sub>) is calculated as follows: |
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: E<sub>g</sub> = (T<sub>g</sub> * T<sub>t</sub> * C)/T<sub>p</sub> |
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:E<sub>g</sub> = (0.328 * 0.924 * 33,705)/0.830 = 0.365 * 33,075 = 12,307 Wh/gal |
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:where: |
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:T<sub>g</sub> = U.S. average fossil-fuel electricity generation efficiency = 0.328 |
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:T<sub>t</sub> = U.S. average electricity transmission efficiency = 0.924 |
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:T<sub>p</sub> = Petroleum refining and distribution efficiency = 0.830 |
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: C = Watt-hours of energy per gallon of gasoline conversion factor = 33,705 Wh/gal |
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See the section entitled [[Miles_per_gallon_gasoline_equivalent#Well-to-wheel|Well-to-Wheel]] below for more information on this issue. |
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====Examples==== |
====Examples==== |
Revision as of 12:55, 16 February 2011
Miles per gallon gasoline equivalent (MPGe or MPGge) is a measure of distance traveled per unit energy consumption. This indicator is meant to be useful for comparing the energy consumption of alternative fuel vehicles and plug-in electric vehicles to those of gasoline-powered vehicles in terms of fuel economy expressed as miles per US gallon, a unit familiar to consumers in the United States. MPGe is based on the energy content of the fuel or energy stored in the vehicle. However, overall energy consumption of an alternative fuel or advanced technology vehicle also will have to consider the energy consumed to produce the fuel and deliver it to the vehicle, yielding the so-called well-to-wheel measure of energy efficiency, depending on the purpose of the energy comparison.
Description
The miles per gallon gasoline equivalent is based on the energy content of gasoline. The energy obtainable from burning one US gallon is 115,000 BTU. Thus one mile per gallon gasoline equivalent is equal to 115,000 BTU per mile.[1] For alternative fuels, energy required to manufacture the fuel may also be considered. For electrical power, the energy of any fuels used to generate the electricity and the transmission efficiency must be considered.
To convert the mile per gallon rating into other units of distance per unit energy used, the mile per gallon value can be multiplied by one of the following factors to obtain other units:
1 MPGe = 8.55 miles/ million BTU ≈ 0.0292 miles/kW·h ≈ 0.0182 km/kW·h ≈ 0.005 km/MJ
Conversion to MPGe
MPGe is determined by converting the vehicle consumption per unit distance, as determined through computer modeling or completion of an actual driving cycle, from its native units into a gasoline energy equivalent. Examples of native units include W·h for electric vehicles, kg-H2 for hydrogen vehicles, gallons for biodiesel vehicles, cubic feet for compressed natural gas, pounds for propane or Liquefied petroleum gas vehicles, and gallons for liquefied natural gas vehicles. Special cases for specific alternative fuels are discussed below, but a general formula for MPGe is:
Depending on the purpose, total energy consumption for the vehicle may also need to include the energy used in the production of whatever energy carrier (fuel) is used for the vehicle and the energy used in filling the "tank". For example, with electrically powered vehicles, a full accounting of total energy consumption would include the efficiency factor for conversion of primary fuels into electricity (the energy of the fuel used to generate and transmit electricity) and the efficiency factor of charging the battery from the electrical plug.
Basic values for the energy content of various fuels are given by the defaults used in the Department of Energy GREET (Greenhouse gases, Regulated Emissions, and Energy used in Transportation) model [2], as follows:
Note: 1 KWH is equivalent to 3,412 BTU
Fuel | Unit | Btu/Unit | KWH/Unit |
---|---|---|---|
gasoline | gallon | 116,090 | 34.02 |
diesel | gallon | 129,488 | 37.95 |
biodiesel | gallon | 119,550 | 35.04 |
ethanol | gallon | 76,330 | 22.37 |
E85 | gallon | 82,000 | 24.03 |
CNG | 100 SCF | 98,300 | 28.81 |
H2-Gas | 100 SCF | 28,900 | 8.47 |
H2-Liq | gallon | 30,500 | 8.94 |
LPG | gallon | 84,950 | 24.9 |
methanol | gallon | 57,250 | 16.78 |
The energy content of a particular fuel can vary somewhat given its specific chemistry and production method. For example, in the new efficiency ratings that have been developed by the United States Environmental Protection Agency (EPA) for battery electric vehicles (BEVs) and plug-in hybrid electric vehicles (PHEVs) – see below – the energy content of a gallon of gasoline is assumed to be 114,984 BTUs.[citation needed]
History and usage
The origin of the general form of MPGe is uncertain.[citation needed] For the special case of a single alternative fuel, MPGe reduces to what is known as gasoline gallon equivalent (GGE), which was first introduced for compressed natural gas (CNG). In 1994, the U.S. National Institute of Standards and Technology (NIST) defined "gasoline gallon equivalent (GGE) means 5.660 pounds of natural gas."[3] In April 2007, as part of Draft Competition Guidelines released at the New York Auto Show, MPGe was announced as the main figure of merit for the Progressive Insurance Automotive X Prize, a competition developed by the X Prize Foundation for super-efficient vehicles that can achieve at least 100 MPGe.[4] In February 2009, Consumer Reports announced that, as part of a partnership with the X Prize Foundation, they plan to report MPGe as one of several measures that will help consumers understand and compare vehicle efficiency for alternative fuel vehicles.[5] In November, 2010, the EPA began including MPGe as one figure of merit on its new sticker for Fuel Economy and Environmental Comparisons (see below).
Electric and plug-in hybrid electric vehicles
Increasingly popular today are vehicles fueled by electrical energy obtained from the grid (via a wall plug) and stored in an on-board battery – including both pure battery electric vehicles (BEVs), which use only electricity, and plug-in hybrid electric vehicles (PHEVs), which use electricity together with a liquid fuel obtained from a pump or other source and stored in an on-board fuel tank. For PHEVs, the liquid fuel is commonly but not necessarily gasoline (it might be diesel, biodiesel, ethanol, etc.)
For such electric vehicles, the EPA's formula for MPGe is
where
- energy (BTU) per gallon of gasoline = 116,090
- gallons of liquid fuel consumed per mile (with for pure BEVs)
- energy (BTU) per gallon of liquid fuel consumed (not necessarily gasoline)
- plug-to-wheels electrical energy consumed per mile (Wh/mi)
- energy per Watt-hour of electricity (BTU/Wh) = 3.412
And for pure BEVs (), so it reduces to
This is based on the EPA value for . If the GREET value for is used, the result is
The above formulas employed by the EPA for calculating their reported MPGe do not account for any fuel or energy consumed during the creation or transmission of electrical power, which is required to charge BEVs and PHEVs, as the comparison with gasoline-powered vehicles is made on a tank-to-wheels basis.
Examples
In November 2010 the EPA began including "MPGe" in its new sticker for Fuel Economy and Environmental Comparisons (see example shown for the Chevrolet Volt). They rated the Nissan Leaf electric car with a combined fuel economy of 99 MPGe,[6] and rated the Chevrolet Volt PHEV with a combined fuel economy of 93 MPGe in all-electric mode, and an overall fuel economy rating of 60 mpg[convert: ambiguous unit] combining power from electricity and gasoline.[7][8] For both vehicles EPA calculated the MPGe rating under its five-cycle tests using the formula displayed earlier with a conversion factor of 33.7 kW-hr of electricity being the energy equivalent of a gallon of gasoline.[9]
Conversion using GGE
The same method can be applied to any other alternative fuel vehicle when that vehicle's energy consumption is known. Generally the energy consumption of the vehicle is expressed in units other than W·h/mile, or Btu/mile so additional arithmetic is required to convert to a gasoline gallon equivalent (GGE) of 115,000 BTU/mile.[citation needed]
Hydrogen example with GGE
The 2008 Honda FCX Clarity is advertised to have a vehicle consumption of 72 mi/kg-H
2.[10] Hydrogen has an energy density of 120 MJ/kg (113,738 BTU/kg),[11] by converting this energy density to a GGE, it is found that 1.012 kg of hydrogen is needed to meet the equivalent energy of one gallon of gasoline. This conversion factor can now be used to calculate the MPGe for this vehicle.
- ,
The above ignores the energy required to create the hydrogen fuel.
Life cycle assessment
Tank-to-wheel
MPGe when listed alone, as with MPG, does not describe a vehicle's full cycle, or well-to-wheel, fuel efficiency. Rather, the EPA presents MPGe in the same manner as MPG [citation needed]; therefore, the value preceding MPGe is presented as the tank-to-wheel energy consumption, but this ignores the energy (fuel) required to generate the electricity for battery powered electric vehicles. The tank-to-wheel consumption is the EPA rating reported on the Monroney sticker for gasoline and diesel powered vehicles.[citation needed] For battery powered electric vehicles the Monroney sticker reports what is defined as MPGe plug-to-wheel energy consumption[12], which does not include any of the energy (fuel) required to generate electricity.
Well-to-wheel
To calculate a vehicle's well-to-wheel (WTW) consumption, the vehicle consumption is multiplied by a lumped well-to-tank efficiency factor (efuel), to account for the production and distribution of all fuel and/or energy as applicable. The United States Department of Energy (DOE) reports that the lumped average energy efficiency of electrical production and transmission in the United States, eelectricity, is 0.303 (30.3%), while the efficiency of refining and distributing petroleum, egasoline, is 0.830 (83.0%).[13]
For example, a gasoline powered vehicle rated at 30 MPG tank-to-wheel would have a well-to-wheel rating of 24.9 MPGe as follows:
- ,
An electric powered vehicle rated at 93 MPGe would have a well-to-wheel rating of 28.2 as follows:
- ,
Comparison to Monroney sticker
It is also important to determine if the vehicle consumption quoted for a particular vehicle is that of the EPA combined drive cycle. If not, the quoted value can not be directly compared to the value listed on another vehicle’s Monroney sticker.
See also
- Alternative propulsion
- Corporate Average Fuel Economy (CAFE)
- Energy density
- Energy conversion efficiency
- Fuel efficiency in transportation
References
- ^ Bioenergy Conversion Factors
- ^ GREET model retrieved 2011 01 20
- ^ "Handbook 44 Appendix D - Definitions" (PDF). National Institute of Standards and Technology. 2007. Retrieved 2009-01-02.
- ^ "Press Release: Automotive X Prize Announces Draft Guidelines for Competition to Inspire Super-Efficient Vehicles". X Prize Foundation. Retrieved 2010-12-01.
- ^ "Press Release: Consumer Reports to Adopt MPGe Measure for Fuel Economy". X Prize Foundation. Retrieved 2010-12-07.
- ^ Nick Bunkley (2010-11-22). "Nissan Says Its Electric Leaf Gets Equivalent of 99 M.P.G." New York Times. Retrieved 2010-11-23.
- ^ David Bailey and Kevin Krolicki (2010-11-24). "Chevy Volt tops Prius in fuel economy rating". Reuter. Retrieved 2010-1124.
{{cite news}}
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(help) - ^ "Volt receives EPA ratings and label: 93 mpg-e all-electric, 37 mpg gas-only, 60 mpg-e combined". Green Car Congress. 2010-11-24. Retrieved 2010-1124.
{{cite web}}
: Check date values in:|accessdate=
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(help) - ^ Fred Meier (2010-11-24). "Volt is rated 93 mpg on electricity alone, 37 mpg on gas generator". USA Today. Retrieved 2010-1124.
{{cite news}}
: Check date values in:|accessdate=
(help) - ^ Honda FCX Clarity Fuel Cell Vehicle Lease Program Begins with First Customer Delivery, Honda, 2008, retrieved 2008-12-02
- ^ HFCIT Hydrogen Storage: Basics, United States Department of Energy, 2007, retrieved 2008-12-02
- ^ http://www.transportation.anl.gov/pdfs/HV/460.pdf
- ^ Electric and Hybrid Vehicle Research, Development, and Demonstration Program; Petroleum-Equivalent Fuel Economy Calculation; Final Rule (PDF), retrieved 2008-12-02