Power Systems
The power station that does not requier any moving part is

 Wind power generation.
  Thermonic convertor.
 Solar power generation.
 Tidal power generation.

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Power Systems
Gross head of an hydroelectric power station is

 the height of water level in the river where the storage is provided.
  the difference of water level between the level in storage and tail race.
 the height of water level in the river where the tail race is provided.
 all of above.

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