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Hybrid Vehicles

Toyoto Prius  -- Regenerative Braking

Toyoto has sold more than 52,000 first-generation Priuses in the United States and more than 125,000 worldwide since 1997.  The first of the roughly 36,000 Priuses that Toyota expects to sell in the United States in 2004/2005 arrived at dealerships in October 2004,

Gasoline electric hybrids employ both a gasoline engine and an electric motor or motors to propel a  vehicle. The efficiency comes mainly from harnessing energy that is lost in conventional vehicles every time you use the brakes. Acceleration requires the most energy, in the form of gasoline. Cruising at a steady speed requires far less. So momentum represents energy, which is wasted when you come to a stop. You have to expend more gas to get moving again. Through a system called regenerative braking, the same motor that propels the car serves as a generator during coasting and braking. Rotated by the wheels, the motor charges the high-voltage battery pack. That captured energy is then used to help propel the vehicle back up to cruising speed. For this reason, no current hybrid ever needs to be plugged in and charged up.  AAEA supports plug-in hybrids though because larger batteries with more storage capability will decrease the use of gasoline and significantly increase electric use mileage. 

Further efficiency comes from the fact that the added power and torque of the electric motor allows the gasoline engine to be smaller and otherwise more efficient than it would have to be if it did all the work. As stated before, cruising doesn’t take nearly as much power as acceleration does. In practice, it’s the gas engine that keeps a hybrid vehicle moving at highway speeds, and the electric motor aids acceleration and is most useful in stop-and-go city-style driving where it most effectively captures and reuses energy, sometimes propelling the vehicle by itself. The gas engine shuts off and restarts automatically.  This is why the Prius’ fuel economy is lopsided — 60 mpg city/51 mpg highway, an improvement over the first model’s EPA-estimated 52/45.

Honda’s Insight and Civic Hybrid do not have the lopsided fuel-economy figures. This is because they are mild hybrids in which the electric motor cannot propel the car by itself. The engine shuts off only when the car comes to a complete stop. The Hondas are parallel hybrids where the Prius, now as in the first generation, is a series/parallel hybrid, which means the engine, motor or both can propel the car.

Hybrid Sales Up

According to J.D. Powers and Associates, 38,000 hybrids were sold in the United States in 2002 and about 54,000 were sold in 2003. JD&P projects sales to be about 107,000 in 204 and 211,000 in 2005. Toyota predicts it will sell 300,000 such hybrids alone by 2005.

According to R.I. Polk & Co., a research company in Southfield, Michigan, 43,435 hybrid vehicles were sold in 2003.  Honda, which introduced the first hybrid v ehicle in the U.S. in 1999, led hybrid sales in 2003 with 23,048

Factories use the same production line for hybrids as they do their traditional cars.  This new technology needs some federal tax credit assistance to get over the barriers to mass production and commercialization.  Hybrids can get up to 50% better gas mileage than cars powered by regular internal combustion engines.

Hybrid Electric Vehicles Significantly Reduce Emissions and Fuel Consumption Compared to Conventional Vehicles, Study Says  

Palo Alto, Calif. - December 11, 2002 - Results of a study sponsored by the Electric Power Research Institute (EPRI) indicate that hybrid electric vehicles (HEVs) produce significantly lower total fuel-cycle ("well to wheel") emissions and substantially reduce consumption of petroleum-based fuels when compared to equivalently sized conventional vehicles (CVs). These benefits further increased for those HEVs with plug-in capability and greater all-electric mileage ranges, and in comparison with sport utility vehicles (SUVs). The study, carried out by the Hybrid Electric Vehicle Working Group (HEVWG) under EPRI direction, is the first research available to the public to compare the benefits and impacts and HEVs and CVs.

Members of the HEVWG include the California Air Resources Board, the Department of Energy, General Motors Corporation, Ford Motor Company, South Coast Air Quality Management District, the University of California Davis Hybrid Vehicle Center, Southern California Edison, New York Power Authority, Southern Company, Long Island Power Authority, and Sacramento Municipal Utilities istrict.

Emissions considered were the so-called urban smog precursors-nitrogen oxide (NOx) and hydrocarbons (HC) - and greenhouse gas emissions-primarily carbon dioxide (CO₂). Total emissions include emissions from vehicle manufacturing and recycling, fuel production, facility construction and decommissioning, and vehicle operation (tailpipe and evaporative emissions). Vehicles included several kinds of HEVs, with and without plug-in capability, and different vehicle platforms, including compact and mid-sized sedans and mid-sized and full-sized SUVs with internal combustion engines.

Vehicles studied included CVs and three types of HEV design:
·       HEV 0-hybrid vehicles with a small battery for power assist and regenerative braking but no plug-in capability and no all-electric mileage range.

·       HEV 20-hybrid vehicles with plug-in capability and sufficient battery capacity to provide about 20 miles of all-electric range.

·       HEV 60- hybrid vehicles with plug-in capability and sufficient battery capacity to provide about 60 miles of all-electric range.

Researchers compared vehicles for factors such as environmental impact, performance, fuel savings, and customer preference. Environmental impacts were compared on the basis of emissions over the full fuel-cycle ("well to wheels"). This analysis takes into account all emissions associated with the extraction, processing, distribution, and final use of the energy used to propel the vehicles.

For CVs, these emissions include all those that result from extracting crude oil, processing oil into a vehicle fuel, distributing the fuel, fueling the vehicle, and the vehicle's tailpipe and evaporative emissions during operation. For HEV 0, the perspective is the same as for a CV because it only uses gasoline as fuel, although substantially less due to its higher efficiency. For plug-in HEVs, the "well to wheels" analysis must also take into account the emissions produced by the power plants that provide the electricity for charging the vehicles' batteries.

Results for the smog precursors (NOx and HC) are shown in Figure 1. The analysis assumed an average driving schedule and nightly battery charging. As can be seen, smog precursors are lower for all HEVs due to their improved fuel economy. Emissions decrease with increasing degree of hybridization. Plug-in HEVs provide additional benefits because, on a gram per vehicle mile basis, emissions from power plants are much lower than that from the same vehicle running on gasoline.

In the mid-sized SUV category, an HEV 0 can reduce smog-forming gases by 19%, an HEV 20 by 37%, and an HEV 60 by 54% when compared to a conventional SUV. In the full-size SUV category, the HEV 0 reduces smog-forming gases by 20%, the HEV 20 by 40%, and the HEV 60 by 55% when compared to a conventional SUV.

Figure 1. Smog Precursor Emissions (table available upon request)

Results for CO₂ emissions are shown in Figure 2. HEVs can substantially reduce greenhouse gas emissions due to their improved fuel economy alone, and these benefits grow with increasing all-electric range and its utilization. In the mid-size SUV, an HEV 0 reduces greenhouse gases by 31%, an HEV 20 by 46%, and an HEV 60 by 60% relative to a comparable conventional SUV. The full-size SUV shows a 30% reduction in greenhouse gases for the HEV 0, a 50% reduction for the HEV 20, and a 60% reduction for the HEV 60 relative to a conventional SUV.

Figure 2. Greenhouse Gas Emissions  (table available upon request)

HEVs can also significantly reduce petroleum consumption. In the mid-size SUV, an HEV 0 can reduce petroleum consumption by 31%, an HEV 20 by 60%, and an HEV 60 by 85%. In addition, a properly designed full-size SUV HEV 60 can exceed 80 mpeg in an all-electric mode without resorting to expensive lightweight construction or extreme body aerodynamics. It can also exceed 55 mpegg (miles per equivalent gasoline gallon) in normal driving if charged every night.

Figure 3. Annual Gasoline Consumption (table available upon request)

The findings are published in two free EPRI reports entitled Comparing the Benefits and Impacts of Hybrid Electric Vehicle Options (#1000349), and Comparing the Benefits and Impacts of Hybrid Electric Vehicle Options for Compact Sedan and Sport Utility Vehicles (#1006892). These reports are available to the public from the EPRI Customer Assistance Center at (800) 313-3774 or askepri@epri.com <mailto:askepri@epri.com>. For technical information contact Robert Graham, (650) 855-2556, rgraham@epri.com <mailto:rgraham@epri.com>.

EPRI, headquartered in Palo Alto, Calif., was established in 1973 as a non-profit center for public interest energy and environmental research.  EPRI's collaborative science and technology development program now spans nearly every area of power generation, delivery and use.  More than 1,000 energy organizations and public institutions in 40 countries draw on EPRI's global network of technical and business expertise. Visit the EPRI website at www.epri.com <http://www.epri.com>.

Tables available electronically from Christine Hopf-Lovette, chopf@epri.com <mailto:chopf@epri.com>