17. Did you know . . . ? 5

GUIDE: Batteries in a portable world. 17. Did you know . . . ? 5

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Applications — The fuel cell is being considered as an eventual replacement for the internal combustion engine for cars, trucks and buses. Major car manufacturers have teamed up with fuel cell research centers or are doing their own development. There are plans for mass-producing cars running on fuel cells. However, because of the low operating cost of the combustion engine, and some unresolved technical challenges of the fuel cell, experts predict that a large scale implementation of the fuel cell to power cars will not occur before 2015, or even 2020.

Large power plants running in the 40,000kW range will likely out-pace the automotive industry. Such systems could provide electricity to remote locations within 10 years. Many of these regions have an abundance of fossil fuel that could be utilized. The stack on these large power plants would last longer than in mobile applications because of steady use, even operating temperatures and absence of shock and vibration.

Residential power supplies are also being tested. Such a unit would sit in the basement or outside the house, similar to an air-conditioning unit of a typical middle class North American home. The fuel would be natural gas or propane, a commodity that is available in many urban settings.

Fuel cells may soon compete with batteries for portable applications, such as laptop computers and mobile phones. However, today’s technologies have limitations in meeting the cost and size criteria for small portable devices. In addition, the cost per watt-hour is less favorable for small systems than large installations.

Let’s examine once more the cost to produce 1kW of power. In Figure 17-5 we learned that the investment to provide 1kW of power using rechargeable batteries is around $7,000. This calculation is based on 7.2V; 1000mAh NiCd packs costing $50 each. High energy-dense batteries that deliver fewer cycles and are more expensive than the NiCd will double the cost.

The high cost of portable power opens vast opportunities for the portable fuel cell. At an investment of $3,000 to $7,500 to produce one kilowatt of power, however, the energy generated by the fuel cell is only marginally less expensive than that produced by conventional batteries.

The DMFC, the fuel cell designed for portable applications would not necessarily replace the battery in the equipment but serve as a charger that is carried separately. The feasibility to build a mass-produced fuel cell that fits into the form factor of a battery is still a few years away.

The advantages of the portable fuel cell are: relatively high energy density (up to five times that of a Li-ion battery), liquefied fuel as energy supply, environmentally clean, fast recharge and long runtimes. In fact, continuous operation is feasible. Miniature fuel cells have been demonstrated that operate at an efficiency of 20 percent and run for 3000 hours before a stack replacement is necessary. There is, however, some degradation during the service life of the fuel cell. Portable fuels cells are still in experimental stages.

Advantages and limitations of the fuel cell — A less known limitation of the fuel cell is the marginal loading characteristic. On a high current load, mass transport limitations come into effect. Supplying air instead of pure oxygen aggregates this phenomenon.

The issue of mass transport limitation is why the fuel cell operates best at a 30 percent load factor. Higher loads reduce the efficiency considerably. In terms of loading characteristics, the fuel cell does not match the performance of a NiCd battery or a diesel engine, which perform well at a 100 percent load factor.

Ironically, the fuel cell does not eliminate the chemical battery — it promotes it. Similar to the argument that the computer would make paper redundant, the fuel cell needs batteries as a buffer. For many applications, a battery bank will provide momentary high current loads and the fuel cell will serve to keep the battery fully charged. For portable applications, a supercapacitor will improve the loading characteristics and enable high current pulses.

Most fuel cells are still handmade and are used for experimental purposes. Fuel cell promoters remind the public that the cost will come down once the cells are mass-produced. While an internal combustion engine requires an investment of $35 to $50 to produce one kilowatt of power, the equivalent cost in a fuel cells is still a whopping $3,000 to $7,500. The goal is a fuel cell that would cost the same or less than diesel engines.

The fuel cell will find applications that lie beyond the reach of the internal combustion engine. Once low cost manufacturing is feasible, this power source will transform the world and bring great wealth potential to those who invest in this technology.

It is said that the fuel cell is as revolutionary in transforming our technology as the microprocessor has been. Once fuel cell technology has matured and is in common use, our quality of life will improve and the environmental degradation caused by burning fossil fuels will be reversed. However, the maturing process of the fuel cell may not be as rapid as that of microelectronics.

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