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Alternative Fuels for Transportation
11.6 Fueling Options for Fuel-Cell Vehicles
Besides the fuel cell stack, another subsystem influencing the vehicle cost
and performance is the fuel storage. The key issue in the use of fuel cells for
automotive applications is the availability of hydrogen fuel. Without a widespread network of hydrogen stations, no large scale introduction of fuel-cell
cars is feasible and, without a substantially large network of fuel-cell cars,
large investments in the hydrogen infrastructure is unlikely. Onboard storage of hydrogen is critical to the success of FCVs to address the issues concerning driving ranges comparable to gasoline cars, low-storage volume, low
weight, and low cost.
The state-of-the-art hydrogen storage options include compressed hydrogen, liquid hydrogen, and metal hydrides. U.S. DoE has published targets for
onboard hydrogen storage devices (Ross 2006). The energy storage density
for hydrogen (in MJ/l) amounts to 2.8 for hydrogen as gas at 345 bar to a
value between 7 and 12 for metal hydrides, 8.4 for liquid hydrogen, and 31.1
for gasoline.
DoE has established a series of targets as indicated below.
• Gravimetric energy density: 2 kWh/kg
• Volumetric energy density: 1.5 kWh/l
• H 2 storage capacity (mass fraction) of 6 wt% (on a system basis)
• Operating temperature: –30°C to + 50°C
• Refueling time <5min
• Refueling rate: 1.5 kg H 2 /min
• Recoverable amount of hydrogen: 90%
• Cycle life: 500 times (requirements for the physical properties of
storage materials)
• Cost targets: U.S. $5/kWh (storage materials without peripheral
components)
There are four options for onboard hydrogen storage; namely (a) liquid
hydrogen at 20–30 K, 0.5–1 MPa, (b) compressed gaseous hydrogen at 35–70
MPa and at room temperature, (c) solid-state storage using hydrides or highsurface materials, and (d) porous solid adsorption of molecular hydrogen.
The first two methods have reached the engineering prototype stage while
with the last two methods much remains in finding the optimum system for
further development.
Liquid hydrogen can be stored onboard the vehicle as demonstrated by
BMW. In these vehicles, most of the hydrogen is supplied to an ICE with a part
going to a fuel-cell that provides the electrical power for air-conditioning, and
Alternative Fuels for Transportation
11.6 Fueling Options for Fuel-Cell Vehicles
Besides the fuel cell stack, another subsystem influencing the vehicle cost
and performance is the fuel storage. The key issue in the use of fuel cells for
automotive applications is the availability of hydrogen fuel. Without a widespread network of hydrogen stations, no large scale introduction of fuel-cell
cars is feasible and, without a substantially large network of fuel-cell cars,
large investments in the hydrogen infrastructure is unlikely. Onboard storage of hydrogen is critical to the success of FCVs to address the issues concerning driving ranges comparable to gasoline cars, low-storage volume, low
weight, and low cost.
The state-of-the-art hydrogen storage options include compressed hydrogen, liquid hydrogen, and metal hydrides. U.S. DoE has published targets for
onboard hydrogen storage devices (Ross 2006). The energy storage density
for hydrogen (in MJ/l) amounts to 2.8 for hydrogen as gas at 345 bar to a
value between 7 and 12 for metal hydrides, 8.4 for liquid hydrogen, and 31.1
for gasoline.
DoE has established a series of targets as indicated below.
• Gravimetric energy density: 2 kWh/kg
• Volumetric energy density: 1.5 kWh/l
• H 2 storage capacity (mass fraction) of 6 wt% (on a system basis)
• Operating temperature: –30°C to + 50°C
• Refueling time <5min
• Refueling rate: 1.5 kg H 2 /min
• Recoverable amount of hydrogen: 90%
• Cycle life: 500 times (requirements for the physical properties of
storage materials)
• Cost targets: U.S. $5/kWh (storage materials without peripheral
components)
There are four options for onboard hydrogen storage; namely (a) liquid
hydrogen at 20–30 K, 0.5–1 MPa, (b) compressed gaseous hydrogen at 35–70
MPa and at room temperature, (c) solid-state storage using hydrides or highsurface materials, and (d) porous solid adsorption of molecular hydrogen.
The first two methods have reached the engineering prototype stage while
with the last two methods much remains in finding the optimum system for
further development.
Liquid hydrogen can be stored onboard the vehicle as demonstrated by
BMW. In these vehicles, most of the hydrogen is supplied to an ICE with a part
going to a fuel-cell that provides the electrical power for air-conditioning, and