Hydroelectric

Hydroelectric dams and run-of-the-river systems

Depending on their configurations, hydroelectric station can be divided into 2 major types. i.e. hydroelectric dam type and the run-of-the-river type.

Hydroelectric dam type

This type of hydroelectric station involves the construction of a dam to store water in a reservoir to create the water head difference. Water flows by gravity through a channel (called penstock) to reach a turbine at a lower level to make it spin. The spinning turbine then drives an electric generator to produce electricity.

Above: Typical hydroelectric dam

Although hydroelectric dams are usually built for large hydro stations of hundreds and even thousands of mega watts in capacity, they are also built for small hydro stations.

Hydroelectric dams can store water, and then release the water for power generation when needed. Thus this type of system is more suitable than other intermittent renewable energy sources to provide peak load power. Besides, dams also serve other practical functions of flood control, irrigation and navigation.

However, there are concerns over the construction of hydroelectric dams. Constructing a dam will cause flooding of the upstream areas. Besides, dams block the way of migrating fish such as salmons. A fish ladder can be built to allow salmons to migrate upstream.

Run-of-the-river type

This type of hydroelectric station is normally located on swift flowing streams or rivers, and extracts the energy from the water as it passes through the station. Run-of-the-river stations are usually built on small dams or diversion weirs, and in some occasions these structures are not required.

Water collected by the diversion weir falls by gravity through a penstock to drive a turbine at a lower level, which is coupled to a generator to produce electricity. The water then joins back to the normal river channel. Since such systems do not involve significant amount of water storage, they have much smaller impact on the surrounding environment than the hydroelectric dam systems.

Above: Picture showing the configuration of a run-of-the-river system

Run-of-the-river systems are usually mini or micro hydro systems, and small hydro systems in the lower end of the capacity range. Since this type of system does not store a large amount of water, the electricity output will be affected by the seasonal flow of the river.