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Unlike ordinary combustion engines, fuel cells can run with high efficiency in both small and large systems, even when not running at full load. This makes possible a wide range of applications for fuel cells. The applications can be divided into the following areas: portable power, transport, space, decentralized energy supply, stationary power plants and energy storage. The different types of fuel cells are suited for different applications.
Portable power
Today batteries are used to power mobile phones (cell phones) and laptop computers. The batteries have comparatively short lifetimes, and recharging takes a considerable amount of time. In a fuel cell system, the energy density may be up to ten times larger than in a battery, giving the possibility of a much longer operation time. Small DMFC (Direct Methanol Fuel Cell) systems are being developed where refueling is made simply by replacing the empty methanol container. Companies such as Casio, NEC and Toshiba have demonstrated such systems for laptop computers. They are expected to be commercially available within a few years.
Two DMFC prototypes from Toshiba.
The upper picture shows a system for a laptop computer.
With its 20 cm3 fuel container the system can deliver 20 watt for approx. 8 hours.
The lower picture shows a 100 milliwatt unit for, e.g., an MP3 player.
It goes with a 2 cm3 fuel container. Photo: Copyright Toshiba.
Transport
A large part of the solid polymer fuel cell (PEMFC) research and development is directed towards a system which can replace the internal combustion engine in a car. Most major car manufacturers have R&D programs on fuel cells, and DaimlerChrysler and General Motors, among others, have built and demonstrated prototype fuel cell vehicles. However, on a purely cost basis such systems will hardly be able to compete with an internal combustion engine. A complete drive system will include a tank for fuel storage (presumably using hydrogen for fuel, else the system must also include a reformer to transform the fuel into hydrogen), a fuel cell unit and an electrical motor. But the price of the electrical motor alone is comparable to the price of an internal combustion engine. Furthermore, unsolved problems remain with regard to hydrogen storage. The push for fuel cell vehicles will therefore to a large extent originate in environmental considerations. Another important aspect favouring fuel cells will be energy supply security, e.g., being independent of imported oil and gasoline. The time frame for a large-scale switch to fuel cells within the car industry is likely to be at least 20 years. However, the promises of fuel cells, which include significantly improved air quality in large cities, make the development a high priority with the car manufacturers.
The concept vehicle Necar from DaimlerChrysler, based on the Mercedes Benz A class. The fuel cell system, placed beneath the cabin floor, can deliver 75 kW, and the car has a range of approx. 450 km (280 miles). Photo: Copyright DaimlerChrysler.
Fuel cells may acheive a faster breakthrough in a more specialized segment of the transportation sector, namely as auxiliary power supplies (APUs) for air condition and other electrical appliances in the cars. In trucks and ships, fuel cells will be an attractive alternative to the polluting and inefficient diesel generators that are used today to generate power when the main engines aren't running (e.g., when the driver of a refrigeration truck rests). Solid oxide fuel cells (SOFCs) will be well suited for such applications.
Space
On American spacecrafts fuel cells have been used since the 1960s as a pollution free power source. The Gemini project used PEMFC, but since the Apollo launches, Alkaline Fuel Cells (AFCs) have been used. They are still used on the present-day space shuttle. For space applications cost is not the decisive factor. Rather, it is the high power density and the lack of emissions: the only "waste product" from the cells is pure water, used for drinking water for the astronauts.
12 kW fuel cell system made for NASA by UTC Fuel Cells. Each space shuttle carries three of these units to supply electricity and water. Photo: Copyright UTC Fuel Cells.
Decentralized energy supply
An interesting perspective for fuel cells is a more decentralized energy supply than today. High temperature fuel cells such as SOFC produce both electricity and heat. This makes it possible to have a single-house unit replacing both the heater and the electrical grid. Such systems will most likely first come into use in remote areas off the grid. However, in the longer term a completely new organization of the energy sector could be made possible, where a large part of all energy production takes places decentrally. If a household uses less electricity than the unit produces, the surplus can simply be sent out on the grid. The drawing below shows the schematics of a natural gas fueled unit for a single household.
Schematics of a fuel cell unit that supplies both electricity and
heat for a single house. It uses natural gas as a fuel.
Stationary power plants
Power plants in sizes from 200 kW (to supply, e.g., a hospital or a hotel) to several MW are promising possibilities. High temperature fuel cells such as molten carbonate fuel cells (MCFCs) and SOFCs make it possible either to have combined heat and power or to use the heat to drive a gas turbine, resulting in a very high electrical efficiency.
Energy storage
A fuel cell is in principle an electrolysis apparatus "in reverse". And actually, most types of fuel cells can be inverted and made to work as an electrolyzer, splitting water into hydrogen and oxygen, by applying an external voltage to the cell. SOFCs will be particularly well suited for this application. Such an SOEC (Solid Oxide Electrolysis Cell) could play an important role in a future society where a large part of the electricity is produced by wind turbines and solar energy. One of the problems of these kinds of sustainable energy is that they can not be turned on at will – being only produced when the wind is blowing or the sun is shining. However, by coupling an SOEC system to, e.g., a wind turbine, the energy production from the turbine can be smoothed out: When a wind surplus exists, the surplus is used to electrolyze water to oxygen and hydrogen; and when the wind doesn't blow, the hydrogen is used to produce electricity in a fuel cell unit. You can read more about our high temperature electrolysis research here.
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