Miles per gallon gasoline equivalent
Miles per gallon gasoline equivalent (MPGe or MPGge) is a measure of the average distance traveled per unit of energy consumed.
The equivalence of this unit to energy in a gallon of gasoline is true if and only if the heat engine, generating equipment, and power delivery to the car battery are 100% efficient.
MPGe does not necessarily represent an equivalency in the operating costs between alternative fuel vehicles and the MPG rating of internal combustion engine vehicles due to the wide variation in costs for the fuel sources regionally[4][5] since the EPA assumes prices that represents the national averages.
The MPGe metric was introduced in November 2010 by EPA in the Monroney sticker of the Nissan Leaf electric car and the Chevrolet Volt plug-in hybrid.
[9][10] All new cars and light-duty trucks sold in the U.S. are required to have this label showing the EPA's estimate of fuel economy of the vehicle.
[3] In a joint ruling issued in May 2011 the National Highway Traffic Safety Administration (NHTSA) and EPA established the new requirements for a fuel economy and environment label that is mandatory for all new passenger cars and trucks starting with model year 2013.
Beginning in 1993, manufacturers of these other alternative fuel automobiles that meet the qualifying requirements can also benefit for special treatment in the calculation of their CAFE.
[17] In 1994 the U.S. National Institute of Standards and Technology (NIST) introduced gasoline gallon equivalent (GGE) as a metric for fuel economy for natural gas vehicles.
[18] During the late 1990s and early 2000s several electric cars were produced in limited quantities as a result of the California Air Resources Board (CARB) mandate for more fuel-efficient zero-emissions vehicles.
[27] The Automotive X Prize competition was intended to encourage development of automobiles that would be capable of operating 100 miles on a gallon of gasoline (mpg).
[29] As required by the 2007 Energy Independence and Security Act (EISA), with the introduction of advanced-technology vehicles in the U.S. new information should be incorporated in the Monroney label of new cars and light-duty trucks sold in the country, such as ratings on fuel economy, greenhouse gas emissions, and other air pollutants.
[3][30] The EPA rating for on board energy efficiency for electric vehicles before 2010 was expressed as kilowatt hour per 100 miles (kWh/100 mi).
[30] The proposed design and final content for two options of the new sticker label that would be introduced in 2013 model year cars and trucks were consulted for 60 days with the public in 2010, and both include miles per gallon equivalent and kWh per 100 miles as the fuel economy metrics for plug-in cars, but in one option MPGe and annual electricity cost are the two most prominent metrics.
[34][35] In November 2010, EPA introduced MPGe as comparison metric on its new sticker for fuel economy for the Nissan Leaf and the Chevrolet Volt.
[9][10] In May 2011, the NHTSA and EPA issued a joint final rule establishing new requirements for a fuel economy and environment label that is mandatory for all new passenger cars and trucks starting with model year 2013.
EPA explained that the objective is to avoid the traditional miles per gallon metric that can be potentially misleading when consumers compare fuel economy improvements, and known as the "MPG illusion".
The formula includes the inherent efficiency of the vehicle as the range capability of a specific fuel source capacity directly represents the EPA testing, it then becomes universal regardless of weight, vehicle size, co-efficient of drag, rolling resistance as these directly influence the range possible and are accounted for.
The result is number of miles the vehicle travels on alternative fuel for the same cost of a single gallon of gasoline.
Using EPA 2018 Fuel Economy Guides assumptions for national average pricing of $2.56/gal regular gasoline and $0.13/kWh[42] we can calculate a vehicle that is rated at 84 MPGe or 40 kW/100 Mi efficiency and has a 16.5 kW EV battery of which 13.5 kWh is usable for electric driving with an advertised range of 33 miles per charge.
For battery electric vehicles, the U.S. Environmental Protection Agency's formula to calculate the well-to-wheel MPGe is based on energy standards established by the U.S. Department of Energy in 2000:[2][13][14] The well-to-wheel conversion is used in calculation of corporate-average fuel economy (CAFE) but not for window sticker (Monroney) fuel economy.
For Monroney fuel economy the equation is where The formula employed by the EPA for calculating their rated MPGe does not account for any fuel or energy consumed upstream such as the generation and transmission of electrical power, or well-to-wheel life cycle, as EPA's comparison with internal combustion vehicles is made on a tank-to-wheel versus battery-to wheel basis.
The California Air Resources Board uses a different dynamometer testing than EPA, and considers reformulated gasoline sold in that state.
[10][45][47] 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 kWh of electricity being the energy equivalent of a gallon of gasoline.
The i3 REx is the most fuel economic EPA-certified current year vehicle with a gasoline engine with a combined gasoline/electricity rating of 88 mpg-e, but its total range is limited to 150 mi (240 km).
Plug-in hybrid car energy efficiency The following table compares EPA's fuel economy expressed in miles per gallon gasoline equivalent (MPGe) for the two models of hydrogen fuel cell vehicles rated by the EPA as of September 2021[update], and available in California.
[14] This methodology is used by carmakers to estimate credits into their overall Corporate Average Fuel Economy (CAFE) for manufacturing electric drive vehicles.
is computed as: This computation accounts for the well-to-wall losses resulting from the extraction of crude oil and refinement into gasoline (Tp), conversion to electricity (Tg), and the transmission grid (Tt); in summary, the total amount of useful electrical energy that can be extracted from gasoline is just 36.5% of its total theoretical stored energy.
In 2009, the Monroney sticker for the Mini E rated the wall-to-wheel energy consumption at 33 / 36 kWh/100 mi (102.1 / 93.6 mpg‑e) for the city and highway driving cycles, respectively.
For comparison, the 2017 Chevrolet Bolt EV has a rated (wall-to-wheel) consumption of 128 / 110 mpg‑e (263 / 306 Wh/mi) listed on the Monroney sticker for the urban/highway driving cycles, respectively.
[63] The petroleum-equivalent fuel economy for the Bolt, using the DoE rule to consider well-to-wall energy losses, is 284 MPGPE, computed using the same 55%/45% urban/highway split.
