Hydropower Systems: Construction, Turbines, and Energy Generation
Hydropower System Construction
1. Dam
A dam is built to raise the water level of a river, creating a falling water system. The reservoir stores energy in the form of potential energy. Key considerations include the dam’s ability to withstand water pressure and the use of impermeable construction materials.
2. Spillways
Spillways are designed to cope with large floods, providing pathways for floodwater to flow around the dam and prevent breaches.
Diversion or Run-of-River Systems
Run-of-river plants derive energy from water flow with minimal disruption to the flow or surroundings. These hydroelectric plants use the river’s power as it passes through, causing minimal change to the river flow, water quality, or downstream habitats.
Pumped Storage
In pumped storage facilities, water is collected in a reservoir after passing through the turbine. A reversible turbine pumps the water back to an upper reservoir during low electricity demand. This water is then released to generate power during peak demand periods.
Types of Turbines
1. Impulse Turbines
Impulse turbines use the velocity of water to move the runner. Water is discharged at atmospheric pressure, without suction on the downside of the turbine. These turbines are suitable for high head, low flow applications.
1.1. Pelton Turbine
Water jets strike cups arranged on the periphery of a wheel, causing it to rotate. The wheel is connected to a shaft, generating electricity via a generator. Pelton turbines are suited for high head, low flow applications and are available for both large and small hydropower systems.
1.2. Turgo Wheel Turbine
The Turgo wheel turbine is a modification of the Pelton turbine. The runner is shaped like a Pelton wheel cut in half, with the water stream applied on one side. The incoming and outgoing jets do not cross each other.
1.3. Cross-Flow or Ossberger Turbine
The Cross-Flow turbine is shaped like a drum and uses an elongated, rectangular section nozzle. Water flows through the blades twice. It can be used in horizontal and vertical orientations and can accommodate higher water flow and lower head than the Pelton turbine. The efficiency of Ossberger turbines is approximately 80%.
Reaction Turbines
Reaction turbines generate power from the combined action of pressure and moving water. The runner is placed directly in the water stream and are generally preferred over impulse turbines when lower head but higher flow is available.
2.1. Propeller Turbine
A propeller turbine typically has a runner with 3 to 6 blades. The pitch of the blades may be fixed or adjustable.
2.1.1. Bulb Turbine
The bulb turbine has the turbine and generator sealed and placed directly in the water stream. It is appropriate for low heads, below 25m, and can also operate in reverse flow.
2.1.2. Straflo Turbine
The Straflo turbine combines the turbine and generator, requiring less space. The generator is attached directly to the perimeter of the turbine.
2.1.3. Tube Turbine
Tube turbines allow a straight-line connection to the generator, providing a direct drive and compact configuration.
2.1.4. Kaplan Turbine
In a Kaplan turbine, both the blades and the wicket gates are adjustable, allowing for a wider range of operation. The rotor is attached to the turbine shaft and rotates at a fixed speed. The rotational speed of the generator is the same as the speed of the turbine.
2.2. Francis Turbine
The Francis turbine has a runner with fixed buckets, usually nine or more. Water is introduced just above the runner and falls through, causing it to spin. The major components include a scroll case, wicket gates, and a draft tube.
2.3. Kinetic Energy Turbine
Kinetic energy turbines generate electricity from the kinetic energy present in flowing water, using the water stream’s natural pathway. These systems can operate in rivers, tidal waters, or ocean currents and do not require large civil works or water diversion.