Hybrid Electric Vehicles
Hybrid Electric Vehicles Today
Hybrid electric vehicles (HEVs) are on the market today. The Toyota Prius, Honda Insight, and Honda Civic are sold in many countries, and hybrid versions of the Toyota Camry, Toyota Highlander, and Ford Escape will soon be available. The Prius is manufactured at a volume of about 5000 per month, and Toyota recently announced that it is making a modest profit on these cars. The cost of HEVs is about US$5000 more than comparable conventional vehicles, and their fuel economy is about twice that of their conventional counterparts. Their emissions meet the second strictest regulations in existence: California Super Ultra Low Emission Vehicle (SULEV).
How Do They Work?
Hybrid vehicles have a conventional engine (gasoline or diesel) as well as a large battery and an electric motor, so that the wheels of the car are driven by both an internal combustion engine and an electric motor. There are various arrangements for these two motors. In the parallel hybrid car, both the conventional engine and the electric motor are attached to the driveshaft and the wheels of the car. In the series hybrid car, the conventional engine is used only to generate electricity, which then goes through a wire to an electric motor that drives the wheels. Combinations also exist; for example, the front wheels are driven by a conventional engine and the rear wheels by an electric motor.
Some hybrids, called "charge-depleting" or "plug-in," have batteries that can be charged from the electricity net. Other hybrids, called "charge-sustaining," do not have this ability — all the electricity that goes into the battery is produced by the internal combustion engine. All HEVs have a computer that is programmed to operate the car on either or both motors, depending on factors such as speed, power required, and amount of electricity left in the batteries.
The extra cost of an electric motor and battery in an HEV make sense because the internal combustion engine in a conventional car is very energy inefficient. Less than 20% of the energy of gasoline is actually used to drive the wheels of the car; most of the rest is lost as waste heat. In a conventional car, the engine is much more powerful than required to drive the car at a constant speed of say 100 km/hr because extra power is needed for accelerating the car in a reasonable time. Except when accelerating, this power is not really used, and most of the time, the engine operates inefficiently far below its capacity. The main losses of energy occur when the car is idling, braking, and driving at low speeds.
In an HEV, the electric motor assists in acceleration, which allows for a smaller and more efficient internal combustion engine. In addition, the engine does not idle: it is stopped when the car is standing still and immediately started when required. Furthermore, the electric motor acts in reverse as a generator when the car is braking, recovering the braking energy and feeding it into the battery. At low speeds, the car often uses only the electric motor, which has an efficiency of the order of 90%. At medium or high speeds, the internal combustion engine will operate (as required) at its most energy efficient point and produce more power than is needed by the car at that moment. The extra energy is fed into the battery, to be used later when required.
In a series hybrid vehicle, the internal combustion engine is not connected to the wheels of the car — it is used only to generate electricity, which powers the electric motor and is also fed into the battery at times when the car does not need all the energy produced. This internal combustion engine needs only to produce the average amount of power required by the car; it is much smaller than those in conventional cars, and it usually operates at its most efficient point and at constant speed.
In a plug-in or charge-depleting hybrid vehicle, the car battery can be charged from the electricity net, and this electricity can then be used for all or part of the next trip that the car makes. The distance that the car can drive on the electricity stored in the battery varies widely from model to model, anywhere from less than 20 km up to 80 km.
Outlook
The outlook for hybrid vehicles is very positive for a variety of reasons. The HEV can easily be designed to equal or surpass the performance of conventional cars, and it can meet or exceed customer expectations. The extra cost of the car, currently about US$5000, can be substantially reduced as manufacturing experience is acquired for the batteries, which currently cost about US$3000, and for the other components. In countries with relatively high gasoline prices, the savings in gasoline costs currently pay back the extra purchase costs of the car in about 8 years. As manufacturing volumes and gasoline prices increase, this payback period could be reduced to 3-5 years, and consumers would have an economic incentive to buy HEVs. For all these reasons, some of the major motor manufacturers strongly support hybrid vehicle technology; for example Toyota considers it to be the key enabling technology for the coming decades.
Hybrid vehicle technology can be used in most segments of the car market, including all mid- and high-priced passenger cars, city buses, and delivery trucks. It has fewer advantages for heavy trucks that drive long distances at constant speed and for low -cost small passenger cars, which are already fuel efficient and for which the extra purchase cost would be a major impediment.
Hybrid vehicle technology is a "step-out" technology in that it modifies an existing and proven technology, rather than replacing it completely with something that is totally different. This is a major advantage from the market introduction perspective: the changes can be introduced gradually, and the risk of major technical problems and high warranty costs after a few years is reduced. Another advantage is that no new infrastructure is required.
Hybrid vehicles have strong environmental advantages: they reduce noxious pollution, emissions of greenhouse gases, and energy consumption by half. They will be able to use all of the advanced fuels, such as ethanol, biodiesel, and natural gas, which will make them even more environmentally friendly. In countries where most of the electricity is generated by coal-fired power plants, hybrid vehicles will be environmentally friendlier than battery electric vehicles.
Great potential for improvement in hybrid technology still remains, not only in cost reduction but also in technical performance. (On the other hand, strategies that increase the performance of hybrid vehicles could degrade their potential fuel efficiency.)The key will be further improvements in battery performance, so that the battery will easily last for 8-10 years and the car will be able to drive on battery power for 20-30 km. (Some first-generation Prius models have already surpassed the 8-year/200,000-km threshold of battery life.)This would allow hybrid vehicles to drive on battery power with zero pollution in city centers and use their internal combustion engines only on the outskirts of a city or on long trips.
Where Do We Go from Here?
Local, state, and central governments can play a key role in supporting improved vehicle technologies and thereby achieving their clean air, greenhouse gas, and energy diversification objectives. Some car manufacturers have fulfilled their social responsibilities and introduced vehicles that are more environmentally friendly than conventional cars. It is now up to customers to buy these cars in large numbers. Conventional cars impose costs on society that are not paid by the car buyer but are borne by governments. These "external costs" are in the form of air pollution, greenhouse gases, climate change, dependence on imported petroleum, and the cost of securing oil supplies. Since governments pay these external costs, they have a strong and double justification for paying the higher purchase price of hybrid vehicles for their own fleets. Not only will their own cars reduce the external costs relative to conventional cars, but they will also help to build up market volume and allow manufacturers to reduce their costs to the point where hybrid vehicles become attractive for other car buyers.
Aside from buying hybrid vehicles for their own fleets, governments can also provide subsidies and tax incentives for buyers of hybrid vehicles, as has been enacted in the United States. In countries with an autonomous automobile industry, governments can encourage the manufacturers to continue to bring different models of hybrid vehicles to the market and support research in battery improvement and other enabling technologies.
For the short-term future (5-10 years), hybrid vehicles are the only practical way in which the environmental and energy objectives in the transportation sector can be pursued, especially because hybrid vehicles can easily be adjusted to operate on advanced or alternative fuels, such as biofuels and natural gas. For the longer term (10-20 years), the costs of fuel cells and advanced batteries might come down to a point where either fuel cell vehicles or battery electric vehicles become price competitive in certain market segments. However, depending on the primary energy that the fuel cells use, or the way electricity is generated for battery electric vehicles, there may be few or no environmental advantages compared with hybrid vehicles. It is likely that even in the longer term, future hybrid vehicles will be environmentally friendlier than the alternatives in many market segments.
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