What You’ll be Driving in 10 Years
July 16, 2007
ANN ARBOR, Mich.
By Zoran Filipi
In his 2007 State of the Union Address, President Bush set a national goal of replacing more than 75% of US oil imports from the Middle East by 2025. To achieve this formidable target, the research community and automakers need to develop cleaner, cheaper, and more reliable alternative energy sources and to change the way we power our automobiles.
Sensing the urgency, private foundations are stimulating creative minds with competitions such as the Automotive X Prize. A multimillion-dollar purse will be awarded to teams that win a series of races in a production-ready vehicle capable of exceeding 100 mpg. Is this possible? Well, there is a prototype vehicle capable of demonstrating 140 miles per gallon of fuel in urban driving today1! It’s called a plug-in hybrid.
The basic idea of a plug-in hybrid is to combine environmental advantages of the electric vehicle with range-extension capability of the internal combustion (IC) engine. In other words, plug-in hybrid vehicles (PHEVs) use electrical energy stored in the batteries to drive the vehicle, and an on-board IC engine for backup and extension of range once the battery charge is depleted. The combination of two energy sources, i.e. the battery and the IC engine, eliminates range concerns that led to the demise of pioneering electric vehicle concepts such as GM’s EV1.
Of course, the total energy consumption is more than what’s indicated with miles per gallon of gas, but using electricity from a battery allows the replacement of fossil fuels with different sources of energy. In particular, generating electricity from renewable energy sources such as wind and solar, supports a vision of sustainable and clean energy for transportation. How do you charge the battery? By plugging into a 120V outlet socket in your garage!
The PHEV concept owes much of its appeal to the fact that electric energy consumption goes through tremendous fluctuations during the course of 24 hours. The peak consumption usually occurs in the early afternoon, and requires cranking up the production and bringing additional costlier power plants on–line. The valley of consumption occurs in the wee hours of the night, as the demand drops to less than half of the peak consumption. Consequently, there is a huge potential to generate power for charging PHEV batteries over night.
A recent study by the Pacific Northwest National Laboratory (PNNL) has shown that filling in the power consumption valley by charging a large number of PHEVs could in an ideal case replace ~70% of fuel for light-duty vehicles. A more realistic scenario of charging only between 6 p.m. and 6 a.m. yields roughly 43% of energy needed for U.S. light-duty fleet. The cost of electrical energy during night hours is very low, 7-10 cents per kWh, thus making it very attractive to consumers.
The future may appear to be around the corner, but there are still challenges that need to be addressed before PHEV can be ready for prime time. The main challenge is battery technology. The plug-in concept requires increased energy density and high power limit of the battery. Energy storage based on the current NiMH technology would lead to unacceptably high volume and weight of the battery. However, Lithium-ion batteries hold a promise of increasing both the energy density and power limits by a factor of two or more. Recent breakthroughs in developing new electrode materials enabled laboratory demonstrations of battery packs suitable for PHEVs.
The remaining issues are cost, abuse tolerance, and lifespan of the battery. The current cost of a Li-Ion battery is estimated at about $1000/kWh and the long term goal that would facilitate speedy introduction of PHEVs is $250/kWh. The typical use of the PHEV means daily deep discharges, and this creates conditions detrimental to battery life. However, feverish research and development activities at university laboratories, including UM, National Labs and private companies are a guarantee that achieving the technology targets is just a matter of time.
Recent advances in battery technology have compelled Google to announce their RechargeIT initiative aimed at accelerating the adoption of plug-in hybrid electric vehicles and vehicle-to-grid (V2G) applications. The latter is an extension of the basic idea where PHEV might at critical times send energy to the grid for regulation of high-frequency fluctuations or short-term mitigation of spikes in consumption. The V2G concept can be a life-saver in emergencies or in case of natural disasters.
Another challenge for PHEVs is determining the suitable All Electric Range (AER) of the vehicle. Currently, numbers between 10 and 40 miles are being considered by engineers working on PHEV concepts. The range affects the important tradeoff: higher AER provide more fuel savings, but increases the weight and cost of the battery. PHEVs will not be a solution for every transportation need and class of vehicles, but is perfectly suited for urban commutes. When it comes to fleets of small delivery vehicles, zero-emission during AER operation will be an added bonus in densely populated urban areas.
The big picture depends on the sources of energy for electric power generation. In today’s mix, the nuclear and hydro power plants satisfy the base consumption, and coal and natural gas is used for peak loads. Increased use of nuclear power and renewable sources of energy for filling-in the valley is needed for significant reduction of GHG emissions. Still, even if the current mix of US power plants is utilized for increased production needed to charge PHEV batteries, the overall carbon-dioxide emission from light-vehicle fleet would be reduced by 27% according to analysis published by PNNL.
Two decades ago, GM’s EV1 may have been ahead of its time, but it still managed to attract environmentally conscientious consumers. The PHEV concept offers a second chance, but this time the electric vehicle will have a practical range and utility required for everyday use. The public interest and government incentives for development of alternative technologies capable of replacing the foreign oil are stimulating vigorous activity at both the small start-ups developing battery materials and large OEMs exploring PHEV system design and technology options. GM has already introduced its concept PHEV Volt, and Ford, Toyota and Honda have all announced PHEV development programs. So, the future is closer than we think.
Listen to a Podcast
Zoran Filipi discusses how plug-in hybrid electric vehicles work and why they offer a promising cleaner technology. Listen to audio (4MB mp3) »
About the Author
Zoran Filipi is Research Associate Professor of Mechanical Engineering and Assistant Director of the Automotive Research Center at the University of Michigan. His research interests include internal combustion engines, modeling and computer simulation of engine processes and systems, integration of powertrain and vehicle systems, and hybrid propulsion.
About MMPEI
The Michigan Memorial Phoenix Energy Institute is charting a path to a clean, secure and affordable energy future by developing and coordinating energy research and education in the physical and social sciences at the University of Michigan. For more information, please visit www.mmpei.umich.edu, email mmpei@umich.edu, or call (734) 763 7401.
1A recent test of the prototype Toyota Prius PHEV carried out by the Idaho National Laboratory has demonstrated 140 mpg over first 30 miles of urban driving.
