Mr. Green Car: Fuel-cell vehicles
By Allen Penticoff
In the last Mr. Green Car, I discussed how hydrogen is made and used in internal combustion engines. In this week’s column, we’ll look at the other side of hydrogen power as fuel cell vehicles.
To briefly recap—hydrogen can be made from an electrical process from water called electrolysis. Depending on the source of the electrical power, this can be a clean process—i.e., solar panels are used to create hydrogen through electrolysis, the hydrogen is stored in compressed tanks, and then used in a fuel cell to produce electricity.
The other way to make hydrogen is “steam reformation” of hydrocarbon-based fuels, such as natural gas, ethanol or gasoline. Steam reformation of natural gas is the most common source of hydrogen. Any steam reformed hydrocarbon releases CO2 or carbon monoxide as a byproduct of the process. Research is under way searching for thermo-chemical reactions that can produce hydrogen from water. In some scenarios, the hydrogen would be produced at the point of use. A few experimental vehicles have reformed gasoline into hydrogen in the vehicle to supply fuel cells.
A fuel cell operates much like a battery, except the energy is not fixed in capacity. You can only shove so much electricity into a battery, and only get the same amount back out. In a fuel cell, which has no moving parts, as long as you can supply clean fuel, the conversion to electricity can continue indefinitely.
As the fuel, typically hydrogen, processes through the fuel cell, it creates electricity, heat, water vapor and no pollutants. Unfortunately, unless the heat and water can be captured and put to use, the efficiency of fuel cells is not very high. The Honda FCX Clarity fuel cell car claims an efficiency of 60 percent, delivering 72 mpg equivalent—which is good, compared to efficiencies of internal combustion engines in the 20 percent range.
In transportation, the fuel cell, often in parallel with a battery pack, powers an electric motor that drives the wheels. Fuel cell vehicles are essentially electric cars without big battery packs. The reason fuel cell vehicles are pursued as a transportation technology is that hydrogen fuel tanks can be built far more cheaply than equivalent battery packs. Hydrogen refueling can take place faster than electric recharging of battery packs, too.
Fuel cells suffer from a number of technological hurdles. Some get quite hot as they produce power. This can be a benefit in a stationary power unit to heat a building; however, in a vehicle, it is not practical to put the heat to work. The more power drawn from the fuel cell, the more its voltage drops. Therefore, a fairly large fuel cell must be put together so there is sufficient power when high loads (highway speeds) are called for.
Cost is a major hurdle. Platinum is used in fuel cells, an expensive metal that can become contaminated by carbon monoxide in some fuel cells. A variety of fuel cell types are in production and in research, including a bacteria/iron/sulfur fuel cell that does not need platinum and could potentially be very inexpensive to produce. Obtaining hydrogen is problematic for fuel cell vehicles right now. In a chicken-or-egg problem, the infrastructure won’t develop without the vehicles, and the vehicles won’t be practical without the supply infrastructure. Some states and countries have developed heavily subsidized “hydrogen highways” to meet the needs of the few hydrogen-powered vehicles on the road today.
Other hurdles are, until recently, fuel cells would not start in below-freezing temperatures. They also have had life limit issues that require rebuilding far more often than an ordinary engine would. Many fuel cells’ lives are far shorter than anticipated.
Buses are an area where fuel cell technology can shine, and a few have been placed in service. Since urban buses typically refuel at the same depot at the end of each day, the distribution network can be very local and practical. Fuel cells would be ideal for school buses to reduce pollution in school zones.
Honda is in limited production of its pretty FCX Clarity sedan, which is in the hands of 100-some corporate lessees ($600 per month). It has a range of 280 miles, and can refill the tank in five minutes. It stores braking and deceleration energy in a Li-ion battery, making it a hybrid as well as a fuel cell-powered vehicle.
Chevrolet has been involved with fuel cell vehicles since 1966, and Chrysler had the experimental 2001 Natrium mini-van fuel cell that made hydrogen onboard by reacting sodium borohydride with borax, which produced no carbon dioxide. Presently, General Motors has made 100 Chevy Equinox FC vehicles available for road testing. The Equinox fuel cell can start in temperatures down to minus 13 degrees and has a life expectancy of 50,000 miles.
Ford has been working on fuel cell vehicles as well. Thirty fuel-cell Focus FCVs have been built, as has an Explorer and the Flexible Series Edge, which is a plug-in hybrid that uses a smaller fuel cell to recharge the batteries for extended range. Ford has dropped its FCV program, shifting to a pure electric Focus (2011) and Transit (2010).
Other automakers, particularly Mercedes, have been involved in fuel-cell vehicle development as well, since the H2Mobility plan for Germany calls for hydrogen fueling stations to be in place in that country for a commercial rollout of hydrogen vehicles in 2015. Most manufacturers still in the game see 2015 as a target for broad introduction of fuel-cell vehicles, according to Kevin Kantola of HydrogenCarsNow.com.
Despite $1.5 billion in federal spending since 2001, Energy Secretary Steven Chu tried to pull the plug on much of the funding in 2009, citing lack of hydrogen refueling infrastructure as putting off practical fuel-cell vehicles for 20 to 30 years. Congress pushed back, restoring $190 million to those companies still interested in pursuing the fuel-cell technology. Only time will tell if fuel-cell vehicles will be commonplace.
From the April 7-13, 2010 issue