Electric power generation based on rotating prime movers and electric generators, is a mature technology, but there is continuously being evaluated alternatives to the traditional synchronous generator.
The fuel cell technology is an area of great interest and research effort, mainly in the automotive industries.
A fuel cell is an electrochemical device that combines a fuel, e.g. hydrogen, and oxygen from the air to produce electricity, heat and water.
Fuel cells operate without combustion, hence, a hydrogen fuel cell is
virtually pollution free. Since the fuel is converted directly to electricity, a fuel cell can operate at much higher efficiencies than internal combustion engines, extracting more electricity from the same amount of fuel.
The fuel cell itself has no moving parts – making it a quiet and reliable source of power. The fuel cell is composed of an anode (a negative electrode that repels electrons), an electrolyte membrane in the center, and a cathode (a positive electrode that attracts electrons).
There is a range of various concepts under evaluation, such as; Phosphoric Acid, Proton Exchange Membrane or Solid Polymer, Molten Carbonate, Solid Oxide, Alkaline, Direct Methanol Fuel Cells, Zinc Air Fuel Cells, and
Protonic Ceramic Fuel Cells.
Common for any of these alternatives is that the technology at present has a high production and maintenance cost – with high energy price.
The dynamic capability should still be improved, and with the present low power density of the unit the use is in practice limited to smaller power ratings. There are reported some experimental vessel designs using fuel cell power generation, and is commonly assumed and expected that fuel cell will become commercially feasible within some time, but not in the very close future.
The fuel cell generates DC voltage and one could imagine two alternatives for distribution:
DC distribution and DC load
Most of the converter principles for propulsion drives are based on rectifying the AC supply before converting to variable frequency.
The problem is mainly related to switching and
protection of the distribution system, since interruption of high DC currents is difficult. The conversion to different voltage levels and supply of consumers that need AC supply will also become expensive. DC distribution has mainly been evaluated, and to some extent been used, in military applications.
DC-AC conversion of the power
With this solution, the problems with voltage distribution and supply will be reduced, but for higher power levels, the solution is yet expensive.
DC distribution could also enable the use of compact and lightweight high-speed permanent magnet exited generators. As the power density of a rotating machine increase by its nominal rotational speed, there would be
significant savings in weight and volume if speed could be increased from typically 500-900 RPM to 15000 RPM.
The disadvantage will be a high frequency output with uncontrolled and varying voltage that would require large power conversion installations.
The fuel cell and power electronics developments open for large shifts in applied technology.
The electric power generation, distribution, and propulsion technology, which has been applied until recently are lagging state-ofthe-art industrial and automotive research and application, but these technologies will make progress step by step just similar to development of other new technologies.
