PRIMRE/PTOs

Power Take-Off (PTO) is the mechanism that converts the motion of the prime mover into a useful form of energy such as electricity. A list of PTOs have been created for marine energy devices, drawing on terminology from the International Electrotechnical Commission (IEC) standards and literature:

• Direct Drive Generator – A prime mover, designed to collect the marine energy resource, is connected to an electrical or magnetic generator, either directly or with a gearbox. An example is a turbine attached to the same shaft as rotating magnets that induce current on coils.
• Hydraulic Generator – A prime mover, designed to collect the marine energy resource, compresses a hydraulic fluid to drive a generator. An example is when energy capture is based on the motion of waves, such as a point absorber.
• Hydro Turbine – A device is designed to manipulate water as a working fluid to drive a turbine and/or generator, such as using a difference in water height between two points to drive either reaction turbines (e.g., Kaplan or Francis turbines) or impulse turbines (e.g., Pelton turbines). For example, dams, barrages, lagoons, and overtopping devices can be classified as hydro turbines.
• Air Turbine – A device is designed to manipulate air as a working fluid to drive a turbine and/or generator, such as compressing air to drive a turbine (e.g., Wells Turbine). And example is an oscillating water column.
• Membrane – Converts chemical potential energy to electrical energy using difference in salinity concentrations across a membrane. An example is for salinity gradient technology.
• Alternative PTO – Unique PTO that generates electricity but does not fit into the other categories.
• Direct Use – Some devices bypass electricity generation and directly accomplish an end goal. Examples are direct desalination, mineral extraction or Seawater Air Conditioning (SWAC).

Many PTOs have unique design elements, particularly within marine energy, so these classifications are quite broad. PTO classifications are primarily based on the function of the prime mover, which is the physical component that acts as the interface between the marine resource and the energy converter from which energy is captured. PTO is often the primary design consideration for a marine energy device. The following diagram shows the potential PTO pathways.