The early electric cars used the old lead-acid batteries. Todays hybrids are provided with more robust nickel-metal units. The EVs of the future are likely to be provided with lithium-ion batteries, found in todays laptops and cellphones. In this area much work remains to be done to increase their safety and life to 100,000 miles of driving and to reduce their cost.
New battery developments include the ultra-capacitor hybrid barium-titanate powder design patented by EEStor, Austin, Texas. (The company is very publicity shy and has no operating website, but details about its system are available at www.technologyreview.com/Biztech/18086/?a=f.) These devices can absorb and release charges much faster than electrochemical batteries. They weigh less, and some projections suggest that in electric cars they might provide 500 miles of travel at a cost of $9 in electricity.
The direction of hybrid car design is also influenced by battery developments. Today, Toyotas Prius uses the heavy and range-limited nickel-metal hydride battery, basically because it is safe. The Prius recaptures energy during breaking and runs on electric power in stop and start traffic, but its all-electric mode of operation is limited. GM plans to increase the electric mode of operation of the Chevrolet Volt, which is designed as a plug-in hybrid that can be recharged overnight. GM plans to use high-energy density lithium-ion batteries to obtain an all- electric range of 40 miles and hopes that these batteries will be safe and reliable by 2010.
Another battery development involves high temperature and larger units. NGK Insulators Ltd. in Japan uses sodium sulfur batteries operating at 427 °C (800 °F) and have a capacity to deliver one mW for 7 hours from a battery unit, which is about the size of a bus. Such units could be used on filling stations that are not connected to the grid.
Hydrogen Fuel Cell Hybrids
In the cars with high-efficiency fuel cells, the fuel is hydrogen and the motor is electric. Fuel-cell efficiency is about 60%, while the efficiency of gasoline internal combustion engines is only 25%. This high efficiency of the fuel cells makes them prime candidates for use in the electric cars of the future. (Figure 1)
A hydrogen filling station in Japan consists of two 300-cubic meter tanks and five filling stations for dispensing hydrogen in both as high-pressure gas and as liquid.
GMs Volt and Fords Dayglo and Edge fuel-cell hybrids are likely to operate with lithium-ion batteries and fuel tanks for high-pressure hydrogen gas containing 4.5 kg to 10 kg of hydrogen and get about 60 miles per kilogram of hydrogen.
One version of the hydrogen fuel tanks, Quantum Technologies TriShield composite cylinders can hold up to 3 kilograms of hydrogen at 5,000 PSIG, which is sufficient for a 200-kilometer journey in a standard sedan.
Hydrogen Internal Combustion Engine
Because of its lower volumetric energy density, when liquid hydrogen is used as transportation fuel, the hydrogen fuel tanks need to be three times the size of todays gasoline tanks to provide the same driving range. Today, a typical passenger car has a range of 575 miles and is provided with an 18-gallon tank, while an 18-wheeled semi-trailer has a 750-mile driving range and requires two 90 gallon tanks. Actually, the volume of the hydrogen tanks can be somewhat smaller, because hydrogen internal combustion (IC) and fuel cell engines are more efficient than the gasoline burning ones (gasoline: 25%, hydrogen IC: 38%, hydrogen fuel cell: 45% to 60%).
BMW, DaimlerChrysler, GM, Honda and Toyota are placing some 100 carsboth IC and fuel-cell unitsinto the hands of ordinary drivers to gain experience and to collect data. The prototype units cost about $1 million each. The manufacturers aim for a pilot commercialization phase by 2010-2012 at a unit cost of $250,000, full production by 2013 at a unit cost of $50,000. The cost will drop as the volume of production increases.
The list of vehicles that can run on hydrogen is constantly growing. Quantum Fuel Technologies Worldwide converted Toyota Priuses to hydrogen fuel. BMW is marketing its 7 Series, 12-cylinder, 260 horsepower car with an internal combustion (IC) engine that can burn liquid hydrogen or run on gasoline. The BMW-750 hl burns liquid hydrogen in an IC engine. The Ford E-450 shuttle bus burns 5,000 PSI hydrogen gas in an IC engine.
Iceland offers hydrogen-fueled rental cars via Hertz. In Japan, as part of its national hydrogen program, a 200,000 m3 tanker ship has been designed for transporting hydrogen. A hydrogen-fueled commuter train, using hydrogen at 35 mPa (5000 PSIG or 350 bars) operates in Japan, fueling a 125 kW Forza PEM fuel cell by Nuvera (www.rtri.or.jp).
Hydrogen buses operate in Montreal and Bavaria; a hydrogen-powered passenger ship sails in Italy; and the 2008 Olympics in Beijing will feature hydrogen vehicles. Russia has flown a jet fueled partly by hydrogen. In the U.S., DARPA, NASA and the Air Force are jointly developing a hydrogen-fueled earth-orbit airplane. Two teams are converting light planes to hybrid fuel cell/battery electric engines.
Hydrogen Filling Stations
As of this writing, according to a survey by Fuel Cell Today, there are 160 hydrogen fuel stations world wide. In the U.S., there are 170,000 gas stations. During the transition from oil to hydrogen, 12,000 filling stations would be needed to supply 70% of the population.
High-pressure hydrogen tanks are made of carbon fiber. Cryogenic (liquid) hydrogen tanks are double-walled with the space between the walls evacuated to provide good thermal insulation.
Hydrogen filling stations are already in operation in Japan, Germany and in the U.S. in Vermont, Florida and California. Some of these are gas-and-liquid dispensing stations, such as the one designed by Air Products at the University of California in Irvine. In Burlington, Vermont, the Department of Public Works hydrogen fuel station uses wind energy to produce 12 kg/day of hydrogen. Air Products and Chemicals participated in the design of this wind-to-hydrogen generator. Figure 1 illustrates a hydrogen tank farm.
In Orlando, Fla., Ford airport buses are served at a Chevron energy station, where 115 kg/day of hydrogen is generated by H2Gen Innovation units. In Munich, a fuel station designed by Linde can dispense hydrogen in both liquid and gaseous forms. At that fuel station, hydrogen is stored above ground in a 17,600 liter tank and is dispensed at a rate of 50 liters/minute. Gaseous hydrogen is produced from liquid hydrogen by evaporation followed by two steps of compression to 350 bars (5000 psig) at 15 °C.