Plug-In Hybrids: The New Focus for the Future of Transportation

In contrast, the Plug-In Hybrid can use as much as 90% of their driving energy from electricity using the currently available electric sources already in our society, ie the standard outdoor plugs at 120 volts and 1.5 KW in the US and 220 volts at 2 KW in much of the rest of the world. The rest of the energy for these automobiles can come from liquid fuels such as gasoline, Diesel or ethanol from biomass. In addition, the vehicles can be charged directly from small wind and solar systems on top of our homes and workplaces. Of course, large wind and Solar systems could also be used much more effectively. Since wind and solar generators are intermittent, they need an energy storage mechanism to be effective. The batteries of the PHEV's can provide this storage capability at no cost to the Utility companies.

The reason the PHEV is so attractive now is that at the current cost of gasoline is $2.50 and rising whereas the average cost of electricity is stable at about 8 cents/kWh. This translates to about the equivalent of 75 cents a gallon of gasoline when used in a PHEV. In addition, in most places in the US, outdoor plugs are available everywhere in our society. Thus, in contrast, to the much touted hydrogen economy, there is no need for massive infrastructure development and construction. The PHEV allows us to immediately transition from our dependence on oil for transportation to one where we can begin to transition to cleaner and more efficient electricity without a need for new infrastructure.

A major difference between the PHEV and the Electric Cars of the past is that the PHEV does not have to be charged since the car is designed to operate the same whether the batteries are fully charged or at its maintenance state of charge, SOC, about 20% to 30%. With this reserve SOC the batteries are always available for extra power when needed. In addition, most cars in the US and the world are used about 3 to 4 hours a day, meaning it is parked somewhere for 20 to 21 hours a day. Thus the PHEV can be plugged in somewhere to charge its batteries most of the day. We have constructed vehicles that use about 200 to 300 watt-hrs /mile. Thus a 60-mile range requires 12 to 18 kWh. Or at 1.5 kW from the 120 volt plug 9 to 12 hours is required to achieve 60 miles of range for a small car to a full size SUV.

In terms of practical applications to our vehicles, we have designed and constructed at UC Davis eight vehicles in the last 15 years that show that the concept applies equally to small cars up to full size SUVs that do everything a conventional vehicle does in the US including towing trailers while running mostly on electricity from the wall plug or from wind or solar systems. In fact, we have shown that a 60 mile All Electric Range PHEV full size SUV generates less than one half the CO2 emissions of a compact car and uses less than one quarter the liquid fuel of a compact sedan. In addition, these PHEV's have one quarter or less of the moving parts and weigh no more than the conventional car because they have much smaller engines (about one third the conventional) and much simpler and lighter transmissions. This technology can be transferred to industry for high volume manufacturing now.

The reality today is that the car companies have been focused on ever-larger trucks and vehicles that get lower and lower fuel economy but do meet stricter emission standards. They are however emitting more CO2. The PHEV can reverse these trends since the vehicles that we have constructed show not only zero emission operation on a daily basis but when using gasoline only, the fuel economy is more than double the conventional car. If a vehicle travels 40 miles a day commuting to and from work and the vehicle travels 15,000 miles a year the effective gasoline mileage for a PHEV is over 250 miles a gallon. Or compared to conventional car, the PHEV will use about 1/10th the liquid fuel. This fact makes bio-fuels such as ethanol from cellulostic materials and biodiesel practical since we can supply 1/10th of our current oil energy use from croplands and waste agricultural products. In addition, as batteries improve, the electric range of the PHEV can increase reducing the need for liquid fuel further.

Finally, the bigger battery packs of the PHEV can be used to power the house or provide relief for the need for peak power in the middle of the day. The key to this direction of energy flow from the vehicle back to the grid or V2G is to do it at a low power level so that the efficiency of energy transfer is high. Then to affect the overall grid, we would use more vehicles, ie if there is a need for 1MW of electricity at a certain time, it could be supplied by 1000 vehicles at one KW or by 100 vehicles at 10 KW. We are saying that 1000 vehicles is the choice because of efficiency and infrastructure cost.

Conclusions:

The PHEV concept is now ready for development by the major car companies, since all the necessary technology is available. A few of these technologies need further development to bring the cost and durability to a level demanded by the car companies and the consuming public. These requirements mean that the batteries, the CVT, and all the powertrain components must be maintenance free and warranted for 15 years and 150,000 miles, and they must be within the range of the cost of a conventional vehicle of today while providing a profit to the car companies and their suppliers. In addition the public must be educated to demand that these vehicles be built to reduce the risk to the car companies for their investment in the PHEV concept.

It would appear that the low cost of electric energy (1/3 to 1/4) compared to liquid fuels, the fact that the electric drive technology can provide even greater performance than conventional gasoline engines, the fact that big battery pack can begin the integration of the transportation and the stationary energy sector, and the availability of home fueling would be enough incentive to attract the current price difference. However, a car company needs to be assured that they will be able to recover their initial investment in the technology and ultimately make a profit in a short term.

The best way to do this is to make the information about the benefits of the PHEV available to the public and to have the public demand be voiced in "soft orders" which basically says "build them, we will buy them!!" to the car companies. The effort by Austin Energy, EPRI, CalCars various magazines and newspapers is beginning to get the message about PHEV's out. Our US president recently mentioned biofuels and the PHEV as a necessary part of our strategy to immediately begin to reverse the trend of increased oil consumption. This will hopefully get our industry to begin to take the potential up coming oil crisis seriously. This is the "New Game" that we all need to focus on today!

About the author...

Professor Andrew Alfonso Frank is Director of Hybrid Vehicle Research at the University of Californai-Davis. He holds the following degrees: B.S. (1955), University of California, Berkeley, M.S. (1958), University of California, Berkeley, M.S. (1965), University of Southern California, Ph.D. (1968), University of Southern California, Mechanical and Aeronautical Engineering.