Energy consumption of cars: Difference between revisions
imported>Paul Wormer (New page: The '''energy consumption of cars''' is mainly due power lost to the following three processes: # Friction with air # Breaking # Accelerating Less important is the loss due to rolli...) |
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The '''energy consumption of cars''' is mainly due | The '''energy consumption of cars''', either with internal combustion engine or with electric motor, is mainly due to the following three processes: | ||
# Friction with air | # Friction with air | ||
# Breaking | # Breaking | ||
# Accelerating | # Accelerating | ||
Less important is the loss due to rolling resistance. The | Less important is the loss due to rolling resistance. The first process depends only on the size of the car and is independent of its weight (mass). The second and third process depend on the weight of the car and through its weight on its engine. An electric motor is in general lighter than a combustion engine, but this is offset to some extent by the weight of the batteries, especially when these are old-fashioned lead-acid batteries. Application of modern lightweight Li-ion batteries gives the electric car an advantage in breaking and accelerating over the gasoline car. Another energy advantage of the electric car is the easy application of regenerative breaking, some of the kinetic energy that would be lost in heating up the breaks can be re-funneled into the batteries. | ||
An important difference between electric- and combustion-engine cars is the thermodynamic efficiency of the generation of | An important difference between electric- and combustion-engine cars is the thermodynamic efficiency of the generation of their propelling power. Electric power is usually generated in big (500 to 1000 MW) power stations fed by fossil fuels and operating at an efficiency of about 40%, which means that about 40% of the [[heat of combustion]] of the fuel (coal, natural gas, oil, etc.) is converted into electric energy. The relative small combustion engines of cars, on the other hand, operate at an efficiency of around 25%. | ||
The relative small | |||
Other | Other energy losses—but that are difficult to quantify—are in the production of gasoline (or other fuels such as diesel used in combustion engines), the transport of electricity from power station to electric outlet, and losses in the charging of the batteries of electric cars. | ||
'''(To be continued)''', see [http://www.withouthotair.com/download.html David MacKay] | '''(To be continued)''', | ||
see [http://www.withouthotair.com/download.html David MacKay] | |||
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From MacKay: | |||
A car driven 100km uses about 80kWh of energy. | |||
Gasoline: 10 kWh/l = 3600*10 kJ/l = 36 MW/l = 45-49 MW/kg | |||
Gasoline's’s density: 0.74 - 0.8; Diesel’s is 0.820–0.950. | |||
A typical car going at an average speed of 50km/h and consuming one litre per 12km has an average power consumption of 42kW. [PW: 50/12 * 10 = 41.7 kW, checks. If car drives 100 km it consumes 84kWh.] | |||
The power consumption of a typical electric car is about 5kW. (p. 58) ??? | |||
Mass of *electric* car and occupants is 740kg, without any batteries. We’ll add 100kg, 200kg, 500kg, or perhaps 1000kg of batteries. Speed of 50km/h (30mph); a drag-area of 0.8 m2; a rolling resistance of 0.01; a distance between stops of 500m; an engine efficiency of 85%; and that during stops and starts, regenerative braking recovers half of the kinetic energy of the car. Charging up the car from the mains is assumed to be 85% efficient. | |||
Electric car: 13 kWh per 100km. (p. 261) [PW: drives 2 h 50 km/h: 6.5 kWh/h = 6.5 kW, 7x cheaper than gasoline ?] | |||
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Revision as of 11:15, 19 December 2009
The energy consumption of cars, either with internal combustion engine or with electric motor, is mainly due to the following three processes:
- Friction with air
- Breaking
- Accelerating
Less important is the loss due to rolling resistance. The first process depends only on the size of the car and is independent of its weight (mass). The second and third process depend on the weight of the car and through its weight on its engine. An electric motor is in general lighter than a combustion engine, but this is offset to some extent by the weight of the batteries, especially when these are old-fashioned lead-acid batteries. Application of modern lightweight Li-ion batteries gives the electric car an advantage in breaking and accelerating over the gasoline car. Another energy advantage of the electric car is the easy application of regenerative breaking, some of the kinetic energy that would be lost in heating up the breaks can be re-funneled into the batteries.
An important difference between electric- and combustion-engine cars is the thermodynamic efficiency of the generation of their propelling power. Electric power is usually generated in big (500 to 1000 MW) power stations fed by fossil fuels and operating at an efficiency of about 40%, which means that about 40% of the heat of combustion of the fuel (coal, natural gas, oil, etc.) is converted into electric energy. The relative small combustion engines of cars, on the other hand, operate at an efficiency of around 25%.
Other energy losses—but that are difficult to quantify—are in the production of gasoline (or other fuels such as diesel used in combustion engines), the transport of electricity from power station to electric outlet, and losses in the charging of the batteries of electric cars.
(To be continued),
see David MacKay