The major applications for fuel cells are as stationary electric power plants (including cogeneration units), as a transportation power source

for vehicles, and as portable power sources, besides an electric power source for space vehicles or other closed environments.

Stationary power applications are very favorable for fuel cell systems. Stationary applications mostly require continuous operation, so start­up time is not a very important constraint. Thus, high-temperature fuel cells such as the MCFC and SOFC systems are also suitable for this application in addition to the PAFC and PEMFC systems. The fuel source for stationary applications is most likely to be natural gas, which is relatively easy to reform in the internal reformer of high-temperature fuel cells or in the external reformer for low-temperature fuel cells. An advantage of using natural gas is that the distribution infrastructure for natural gas already exists. Promising applications for stationary fuel cell systems include premium power systems (high-quality uninterruptible/ back-up power supply systems); high-efficiency cogeneration (heat and electricity) systems for residences, commercial buildings, hospitals, and

industrial facilities; and distributed power generation systems for util­ities. Although some demonstration and commercial stationary fuel cell power plants in sizes from a few kilowatts to 11 MW are in operation, widespread commercialization can be expected only if their installation cost drops down from the present cost of $4000/kW to about $400-700/kW (or about $1000/kW for some premium applications).

The recent surge of interest in fuel cell technology is because of its potential use in transportation applications, including personal vehicles. This development is being sponsored by various governments in North America, Europe, and Japan, as well as by major automobile manufac­turers worldwide, who have invested several billion dollars with the goal of producing a high-efficiency and low-emission fuel cell power plant at a cost that is competitive with the existing internal combustion engines. With hydrogen as the onboard fuel, such vehicles would be zero-emission vehicles. With fuels other than hydrogen, an appropriate fuel processor to convert the fuel to hydrogen will be needed. Fuel cell — powered vehicles offer the advantages of electric drive and low mainte­nance, because of the few critical moving parts. The major activity in transportation fuel cell development has focused on the polymer elec­trolyte fuel cell (PEFC), and many of the technical objectives related to the fuel cell stack have been met or are close to being met. The current development efforts are focused on decreasing cost and resolving issues related to fuel supply and system integration.

Besides exotic areas of applications such as space vehicles or sub­marines, another very promising area of application for fuel cells is portable power systems. Portable power systems are small, lightweight systems that power portable devices (e. g., computers, laptops, cellular phones, and entertainment electronic devices), camping and recreational vehicles, military applications in the field, and so forth. These devices need power in the range of a few watts to a few hundred watts. Fuel cell systems based on DMFC or PEMFC technology are well suited for many of these applications. The convenience of transporting and storing liquid methanol makes DMFC systems very attractive for this application. A small container of methanol or a cylinder of compressed hydrogen can be used as a fuel supply. When the fuel is depleted, a new fuel container may be installed in its place after removing the old one.

In recent years, there has been a lot of interest in electric power gen­eration using renewable energy sources such as wind energy, solar energy, and tidal energy. A major problem with these energy sources is that all are intermittent in nature. Combining the renewable energy — based power generation system with a fuel cell system would solve this problem to a great extent. A hybrid wind/solar energy-fuel cell system can use wind/solar power for generating hydrogen using the electroly­sis of water, and store it in cylinders at high pressure. This hydrogen can then be used as the fuel for the fuel cell stack. The stored hydrogen can also be used to fuel the fuel cell vehicles and so forth. In a grid — connected wind/solar energy—hydrogen system, wind/solar power whenever available provides electricity for hydrogen production. The grid power is used during off-peak periods for low-cost electricity and hydrogen production; whereas during peak-demand periods or no/low wind/solar energy periods, the fuel cell can generate electricity using the stored hydrogen. These hybrid systems could be configured in several ways.

9.4 Conclusion

Fuel cell systems are one of the most promising technologies to meet our future power generation requirements. Fuel cell systems provide a very clean and efficient technology for electrical and automotive power sys­tems. With cogeneration efficiencies higher than 80%, fuel cells prom­ise to reduce primary energy use and environmental impact. Fuel cells are a very good alternative for rural energy needs, especially in remote places where there are no existing power grids or power supply is unre­liable. The application of fuel cells into the transportation sector will reduce greenhouse emissions considerably; if fuels from renewable energy sources are used, it would nearly eliminate greenhouse gas emis­sions. Utility companies are beginning to locate small, energy-saving power generators closer to loads to overcome right of way problems and transmission line costs. The modular design of fuel cells suits this dis­tributed generation strategy very nicely as new modular units can be added when the demand increases. This reduces the financial risk for utility planners. Biofuel cells are very attractive for implant devices as they can use glucose in blood to power these devices, eliminating the need for surgery for maintenance and battery replacement. Use of digester gas as a fuel in biofuel cells makes them very attractive for power generation from garbage and other organic waste. This will also help in waste disposal, a big problem in the agriculture and food industry.

All fuel cell technologies (PEMFC, DMFC, AFC, PAFC, MCFC, SOFC, and MFC) discussed in this chapter are in a very advanced stage of development and are very near to commercialization. Although a number of demonstration units of different types of fuel cells are oper­ating all over the world and many PAFC and AFC units have been com­mercially sold and are successfully operating, fuel cells are still awaiting widespread commercialization due to their high cost and limitation in the choice of the fuel used. These barriers will be overcome in the next few years, and fuel cells will become a preferred power source with widespread applications.