Pump as Turbine (PAT) Systems

Typical hydropower systems convert the energy of falling water to mechanical energy with a turbine.  In some cases, it may be more appropriate to replace the turbine with a centrifugal water pump, and run it in reverse.  The words 'pump' and 'turbine' are used interchangeably in this manual, as are the words 'motor' and 'generator'.  Using a pump as a turbine has numerous benefits for rural pico-hydro projects in the developing world.  Since centrifugal water pumps can usually be found locally, one avoids paying expensive import taxes, and since the pump is a familiar technology to local pump and motor technicians, it can be serviced if problems arise.  This is far easier than finding renewable energy technicians specializing in pico-hydro turbines.  Furthermore, pumps are manufactured to operate under a wide range of conditions, are easy to install, and spare parts for these pumps are easy to find.

System Components

• The Intake

  This is where the water flows into the system.  It should be designed so that it remains clear of debris.

• The Trashrack

  A metal or fabric mesh covering the intake such that material is blocked from entering the pipe.

• The Weir

  A structure designed to divert the flow of water into the intake.  It also maintains the level of the water at the intake,

• The Channel

  If the stream is far away from the point of use, this diverts water a relatively large distance to the inlet of the penstock pipe.  This component is not usually necessary, although if an irrigation channel is available, that may be used.

• The Forebay

  A basin located just before the penstock pipe that may serve as a settling basin to remove waterborne debris that may otherwise damage the turbine impeller over time.  This part is probably unnecessary for most systems, as it is more difficult to build a forebay tank of adequate size than to replace the impeller in the turbine.

• The Penstock Pipe

  This vital piece of equipment serves to carry the water from the intake to the turbine.

• The Powerhouse

  This structure protects the turbine, generator, and electrical equipment.  How big it is and where it is located depends upon the size of the equipment and the characteristics of the site.

• The Pump As Turbine

  This transforms the energy of falling water into mechanical energy.

• The Motor As Generator

  This transforms mechanical energy into electrical energy.

• The Tailrace

  A short, open canal that leads the water from the powerhouse back into the stream from which the water came. This may not be necessary if the turbine outlet is located near enough to the stream.