Hybrid Cars (Energy)
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2009 Toyota Prius. Hybrids utilize a gasoline-powered engine and an electric motor to power the vehicle. Photo: Flickr
Petroleum-electric hybrid vehicles combine the desirable properties of electric propulsion with the portability and convenient refueling of petroleum fuels. Most of the locomotives and many of the ships built during the past 50 years are diesel-electric hybrids. In such vehicles, a large diesel engine turns a generator that recharges batteries, which in turn power small electric motors connected directly to the wheels or propellers. This arrangement operates the diesel engines under the uniform loads and low revolutions per minute that optimize their fuel efficiency. It also eliminates the need for complex transmission systems between an engine and several wheels or propellers. Finally, isolating the diesel engine’s vibrations from the frame of a locomotive or hull of a ship leads to much smoother and quieter operation.
Contents
Driving Performance
Today’s hybrid cars take a different approach: They connect both a gasoline-powered engine and electric motors to the wheels. In some vehicles, the electric motors assist the gasoline engine, whereas in others the gasoline engine assists the electric motors; in most, the gasoline engine shuts down when the vehicle stops. The vehicles currently on the market use nickel-metal hydride batteries and recharge the batteries with the gasoline-powered engine and regenerative braking. Unfortunately, these batteries have small capacities (e.g., a Toyota Prius can travel 25 miles on its electric motor without a recharge), are difficult to recycle, and are guaranteed for 8 years or 100,000 miles. A replacement battery for a Toyota Prius costs as little as $1200 retail. Some hybrid electric vehicles have a lifetime replacement guarantee for the electric battery.
In city driving, a hybrid vehicle takes advantage of engine shutdown, electric motors, and regenerative braking to achieve fuel efficiencies of 30% greater than the same vehicle equipped with a gasoline powered engine alone. Efficiency gains of hybrids are far more modest under highway driving, where they depend heavily on their gasoline engines. The next generation of hybrid cars should be able to travel substantial distances (40 miles) at high speeds on electric power alone when lithium batteries, which have higher energy-storage capacities per size and weight, become more reliable and affordable.
Economics
Hybrid vehicles have the lowest life cycle dollar costs of any vehicle type, followed by internal combustion engines; electric vehicles are the most expensive in life cycle costs. (Aguirre et al, 2012) This outcome is based upon the fact that the electric vehicle battery is very expensive to manufacture, and appears to need replacement much sooner than originally forecast; the carbon life cycle energy cost of the electric vehicle is also greater than the hybrid, based upon the very high carbon manufacturing intensity, since most electric vehicle batteries are made in China, which uses 80 percent of its energy from coal burning. Chinese coal also has a much higher output of carbon dioxide and sulfur dioxide than coal burning plants in the Western World.
Most automobile manufacturers have developed prototypes of diesel-electric hybrid vehicles that achieve substantial improvements in fuel efficiency. A number of them have attained 70 mpg (30 km L–1) or better. The main impediment to such a propulsion system is cost: A diesel engine plus electric drive system adds over $5000 to the purchase price of the same vehicle equipped with a gasoline engine. At current gasoline prices, an owner would recover the additional capital costs during the life of the vehicle.
Autonomous Driving
As of 2023, virtually all of the autonomous vehicles are either all electric or hybrid, with the majority being all electric. Autonomous vehicles have accident rates over twice as high as conventional vehicles. In addition, autonomous vehicles consume vastly more energy than human drivers. (Zewe, 2023) As a result the effective energy efficiency of autonomous driving of an electric vehicle makes the electric vehicle highly energy inefficient and carbon intensive compared to a conventional internal combustion vehicle. For example, as articulated in the MIT Zewe paper: "if an autonomous vehicle has 10 deep neural networks processing images from 10 cameras, and that vehicle drives for one hour a day, it will make 21.6 million inferences each day. One billion vehicles would make 21.6 quadrillion inferences." That rate of energy consumption by autonomous servers implies that electrifying even half of the world's vehicle would add incredible amounts to the world's total carbon emissions, perhaps doubling the future carbon dioxide emissions by 2035. .
Carbon Life Cycle Analysis
Hybrid vehicles have the lowest life cycle carbon dioxide emissions, mainly due to the high carbon cost of electric vehicle manufacture. An electric vehicle battery costs about 17 tons of carbon dioxide emissions in its manufacture. (Dai et al, 2019) Due to this high carbon cost of manufacture and difficulty of electric vehicle recycling, electric vehicles actually have a higher life cycle carbon emissions than a fuel efficient internal combustion vehicie. According to data from the U.S. Department of Energy, an electric vehicle would have to driven about nine years to break even with carbon dioxide emissions from a plug in hybrid vehicle, (U.S. Dept. of Energy, 2021) based upon the large carbon footprint of manufacturing an electric vehicle battery. (This break even point does not include the considerable carbon expense of mining the materials for the electric battery, shipping costs of battery materials and extreme difficulty of properly recycling a lithium ion battery) It is unclear how long most electric vehicles will last; Optimistic views place electric vehicle life at 100,000 miles, although 46% of prospective buyers expect a lifespan of 65,000 miles.(Hardesty, 2021) At a figure of 65,000 miles the electric vehicle would massively produce more carbon in its lifetime than a hybrid vehicle (or even a moderately fuel efficient internal combustion vehicle), by needing at least two battery replacements.
The above simple life cycle analysis does not take account two important factors: (1) It assumes the entire USA or relevant electric grid is uniform in its energy composition; and (2) It ignores the inability of the electric vehicle to use waste heat available to hybrid vehicles or internal combustion vehicles As to the first point, about half of the U.S.States have a grid mix such that the electric vehicle will never recover its carbon deficit from electric battery manufacture; thus the plug in hybrid will perpetually have a lesser carbon emissions from day one through the vehicle lifetime. Regarding the second point, electric vehicles do not have the capability of utilizing waste heat in the way hybrid electric or internal combustion engines do; thus, efficiency of the electric vehicle is significantly degraded relative to both plug in hybrids as well as internal combustion vehicles. For example, when cabin heating is needed, the electric vehicle effectively consumes much more of its lithium battery (and hence adds to its carbon emissions) to produce cabin heat. Similar elevation in carbon emissions for an electric vehicle occur if air conditioning, sound system, automatic windows or other ancillary devices are deployed. With all of these factors are considered, the plug in hybrid is universally considered the lowest carbon footprint from day one through lifetime of vehicle; in fact, a moderate fuel efficient internal combustion engine outperforms the electric vehicle for minimum carbon emissions in most states.See Also
References
- Kimberly Aguirre, Luke Eisenhardt, Christian Lim, Brittany Nelson, Alex Norring, Peter Slowik, Nancy Tu, Deepak Rajagopal (2012) Lifecycle Analysis Comparison of a Battery Electric Vehicle and a Conventional Gasoline Vehicle. Prepared for California Air Resources Board
- Qiang Dai, Jarod Kelly, Linda Gaines and Michael Wang (2019) Life Cycle Analysis of Lithium-Ion Batteries for Automotive Applications. Systems Assessment Group, Energy Systems Division, Argonne National Laboratory, DuPage County, Argonne, IL 60439, USA. Batteries 2019, 5(2), 48; https://doi.org/10.3390/batteries5020048
- Chris Hardesty (2021) How Long do Electric Car Batteries Last? Autotrader
- Romm J.J. & Frank A.F. 2006, Hybrid Vehicles Gain Traction, Scientific American April 2006
- O'Dell, J. (2005) Prius Keeps Car Dealers—but Not Repairmen—Busy. L.A. Times, Los Angeles, June 1, 2005.
- U.S. Department of Energy. (2021) Emissions from Hybrid and Plug in Hybrid Vehicles
- Adam Zewe (2023) Computers that power self-driving cars could be a huge driver of global carbon emissions MIT News Office. https://news.mit.edu/2023/autonomous-vehicles-carbon-emissions-0113
This article draws from the book Global Climate Change: Convergence of Disciplines by Dr. Arnold J. Bloom and taken from UCVerse of the University of California. ©2010 Sinauer Associates and UC Regents
1 Comment
Vicki Osis wrote: 05-24-2012 10:15:41
I own a hybrid with over 100,000 miles. average mileage over its lifespan is 57 miles/gal. I now must replace the batteries at a cost of over 5,000.00. There is a cost to these cars, even though I have have saved the 5,000.00 over those miles with reduce gasoline usage. The all electric cars would have greater savings on fuel costs but those batteries also must be replaced and recharging stations are not abundant at present.