What is hydroelectric energy?

Excessive use of conventional energy sources like petrol and diesel has contributed to the overproduction of greenhouse gas and led to the increasing phenomenon of global warming. Therefore, the use of energy from natural sources like solar energy, hydroelectric energy or hydropower energy, geothermal energy, tidal energy, and wind energy is an alternative to these conventional energy sources and accounts for clean and eco-friendly energy generations. In this article, a major emphasis has been provided on electricity generation by the use of energy from flowing water, primarily known as hydropower energy. Several hydroelectric plants are installed worldwide whose primary focus is power generation by the use of energy of flowing water.

The challenge to safeguard the environment and with the ever-increasing energy demand of the individuals, a major shift from non-renewable energy sources to renewable sources is necessary. By the term energy, it signifies the generation and consumption of electricity.

Each year, numerous power projects are undertaken by governments of several countries to meet the ever-increasing electricity demand.

Hydroelectric power plant

A power plant is an industrial-based unit that uses different conventional and non-conventional energy sources for the generation of electricity. Each power plant has numerous energy conversion devices installed that account for the energy conversion of the energy sources into electrical energy or electricity. The primary components of any power plant are turbines and generators which form the powerhouse of the power plant.

In a hydroelectric plant, the energy sources are primarily energy from flowing water or more precisely from river flow. The flow of the river carries energy that is used to operate a hydraulic turbine, these turbines are coupled to an AC generator which generates electricity. This electricity is finally delivered through power stations. The power stations contain electrical grids and transmission lines through which the electricity is delivered to households. The energy consumption is generally rated in kilowatt-hours.

Parts of hydroelectric powerplant

The basic components of a hydroelectric power plant are outlined in detail in this section.

Dam

A dam is primarily a barrier that is created around a natural water body like a flowing river or a lake. The dam serves as a large reservoir of water that can be discharged in a controlled manner by not needing numerous mechanically operated gates. The presence of a dam in a particular area also serves the purpose of safeguarding the area from river water overflow, more precisely for flood control, it can also be used for irrigation purposes and to provide an adequate supply of water to the nearby localities. Apart from flood control and irrigation purposes, a dam also supplies water for industrial use.

Dams are built with strong concrete and masonry materials. There are also other materials that are well suitable for dam constructions like masonry dams, timber dams, earthen dams, rockfill dams, and temporary steel dams. The most important uses of dams are to act as reservoirs for hydroelectric power stations. Gorges dams and Hoover dams are two of the popular dams used for many hydropower projects.

The water from the dam is not directly passed to the hydropower stations but it is first stored in a temporary reservoir known as a forebay. A forebay is a secondary water body that acts as a small reservoir that stores water to be discharged into the penstock of the hydropower plant.

Penstock

Penstock is the long conduit that connects the forebay and the inlet of the hydraulic turbines. The materials of the penstock are built with mild steel to minimize the effects of corrosion. These components of the hydro facility primarily have a circular cross-section to carry water under high pressure. The circular cross-section provides advantages to minimize circumferential stress, concentration, and scaling due to dirt and debris.

Hydraulic turbine

Turbines are one of the prime components of the hydropower facility that is used to convert the hydraulic energy of water into mechanical energy in terms of shaft rotations. These hydraulic turbines have a series of blades attached around the periphery of the shaft. The kinetic energy of the water is converted into rotational mechanical energy. The shafts of these turbines remain coupled with the armature of an electric generator.

Generator

Generator forms the major powerhouse facility of a hydropower station. The armatures of these generators have multiple copper windings and are placed in-between huge stationery magnets. The armature of the generator is rotated by the shaft of the turbine, due to the rotation, the change in magnetic flux induces an electric current in the coil windings. This electrical energy is transferred to a step-up transformer and through the transmission line into different households. A generator can be thus termed as an energy conversion device that converts mechanical energy into electrical energy.

Mechanical efficiency of a hydraulic turbine

The shaft along with the installed blades forms the runner of a hydraulic turbine. The mechanical efficiency of a hydraulic turbine denotes how much power is available at the shaft of the turbine out of the power which is transferred at the blades of the turbine due to striking water.

The ratio between the shaft power and the power generated at the turbine runner due to water is known as the mechanical efficiency of a hydraulic turbine.

The efficiency is given as

 $\vartheta =\frac{Shaft power}{Runner power}$

Where

$\vartheta$ denotes the mechanical efficiency of a hydraulic turbine. 

Context and Applications

This topic is extensively taught in different undergraduate and postgraduate degree courses of

• Bachelors of Technology in Mechanical Engineering
• Masters of Technology in Mechanical Engineering
• Bachelors of Technology in Civil Engineering
• Masters of Technology in Civil Engineering

Practice Problems

1. Which of the following acts as a temporary reservoir built near a dam?

1. Run-of-river
2. conduits
3. Forebay
4. None of these

Answer: Option c

Explanation: Forebays are the temporary reservoirs built across a dam, which stores water to transfer through penstocks into the hydraulic turbines.

2. Which of the following is true regarding the mechanical efficiency of a hydraulic turbine?

1. It is the ratio between the shaft power of the turbine and the runner power of the turbine.
2. It is the ratio between the runner power of the turbine and the shaft power of the turbine.
3. It is the ratio between the armature power of the generator and the hydraulic power at the inlet of the turbine.
4. None of these

Answer: Option a

Explanation: Mechanical efficiency is the ratio of shaft power of turbine and the runner power of the turbine.

3. Which of the following devices converts mechanical energy into electrical energy?

1. Turbine
2. Draft tube
3. Generator
4. None of these

Answer: Option c

Explanation: A generator converts mechanical energy into electrical energy.

4. Which of the following is true related to a hydraulic turbine?

1. Water at the inlet has kinetic energy
2. Water transfers the energy and causes shaft rotation
3. Hydraulic energy is converted to mechanical energy
4. All of these

Answer: Option d

Explanation: Water at the inlet to the turbine primarily has kinetic energy, which is transferred to the blades of the turbine and causes shaft rotation. A hydraulic turbine is a device that converts hydraulic energy into mechanical energy.

5. Which of the following is a conventional energy source?

1. Petrol
2. Hydroelectric energy
3. Solar energy
4. Geothermal energy

Answer: Option a

Explanation: Petrol and diesel are two of the most popular conventional energy sources.