Micro hydro scheme components and classification

A run-of-river scheme diverts part of the stream flow through a channel and penstock to a turbine and returns it to the river, with little or no storage.

Layout

  river  weir/intake
   ~~~~>[==]--> canal --> [forebay/
                           settling tank]
                              \  penstock
                               \  (gross
                                \  head)
                         [powerhouse]
                         turbine+gen --> load
                           tailrace--> river

Components

• Diversion weir and intake: raises the water level, directs flow into the canal; trash rack and gate keep out debris and control flow.
• Headrace canal (or pipe): carries water with a small slope to the forebay.
• Settling basin (desilting tank): removes sand and silt to protect the turbine.
• Forebay: small tank at the head of the penstock; gives storage for load changes and has a trash rack, spillway and air vent.
• Penstock: steel, HDPE or PVC pipe taking water down to the turbine; designed for pressure and water hammer.
• Powerhouse: turbine (Pelton, cross-flow, Turgo, propeller, or pump as turbine), governor or electronic load controller, generator, and control panel.
• Tailrace: returns the water to the river.
• Transmission and distribution lines to users.

Classification

Class limits vary by country and textbook. Low-head sites use Kaplan or cross-flow turbines; high-head sites use Pelton or Turgo turbines.