Wednesday, June 3, 2020

Electricity from hydropower- clean and renewable alternative

Electricity from hydropower is generated since centuries. It is a non-conventional energy source. Hydropower is used to generate the electricity. Generating electricity from hydropower require large volume of water and rapid movement of water. It is a clean energy source as the water is in moving state continuously. Also no other chemicals are added for generating electricity from hydropower. No air borne or dissolved pollutants are produced. Electricity from hydropower is generated by transforming hydraulic energy into mechanical energy.

Electricity from hydropower

Why there is need of generating electricity from hydropower?

Generating electricity from hydropower is much healthier for environment as compared to another conventional energy sources.
Increasing demand due to increasing pollution is a major factor.
Free availability of water sources.
Most important and unique factor is its reusability.

Comparison between hydroelectric power plant and thermal power plant

Hydroelectric power plant has high initial cost due to the construction of infrastructure such as dams, spillways etc. and its location is far from load centres whereas thermal power plant has low initial cost and its location is nearby to load centres.
Hydroelectric power plant has low operation, maintenance and repair cost because there is no fuel cost, it requires less maintenance and less staff whereas thermal power plant has high operation, maintenance and repair cost.
Life expectancy of hydroelectric power plant is more than thermal power plants.
Transmissions losses are there in hydroelectric power plants due to long distance between the residential areas and power plants whereas in thermal power plants there are less loss.
Hydroelectric power plant produces no pollution and wastes whereas thermal power plants causes air pollution and stream pollution. Ash and smoke are the waste products from thermal power plants.
Hydropower generators have high power efficiency whereas thermal power plants has lower efficiency.
There are secondary benefits like irrigation, flood control, water supply from hydroelectric power plants but thermal power plants do not have any secondary benefits.

Classification of hydroelectric power plants

Hydroelectric power plants can be classified into different types based on various criteria.

Classification based on storage

1. Run-of river plants- such plants utilize the river flow which do not have any storage in the upstream. A low head dam is constructed. A low head dam is a barrier across the width of the river due to which certain properties of water gets changed and also it affects the water level. Such plants are constructed over perennial rivers. Sometimes, tail water rises to high level making the plant inoperative.
2. Storage or reservoir plants- in such plants, a storage like dam is constructed to store water in favourable season and to fulfil the demands in dry season. Such plants are more flexible than run of river plants. It is designed for seasonal storage. It has the ability to meet base load power and peak load power. It is generally built over non perennial rivers and the plant is at the toe of the dam.
3. Pumped storage plants- it is the most developed technique.  These are peak load plants. In this type of plant extra storage is made available by pumping back the water which has already used for generating electricity from hydropower. The pumped storage water generates power only during the peak load period. During the off peak period, water is pumped back to the head water pool from the tail water pool. The pumps are usually run with secondary power available from some other plants in the system.
4. Tidal plants- such plants are of recent origin. Tidal plants works on the principle of high tide and low tide. A basin is created at the shore and is separated from the sea through a wall like barrier. Low head turbines are installed in openings of this walls. During high tide, water flows from sea to the basin and generates electricity from hydropower. Similarly during low tides, the water gets returned back from the basin to the sea. This backflow of water can also contribute for generation of electricity from hydropower, but the turbines should be designed for either direction of flow. 

Classification based on load characteristics

1. Base load plants- such plants are capable of supplying continuous power throughout the year. Run-of river plants and storage plants are base load plants.
2. Peak load plants-such plants are capable of generating electricity from hydropower during the peak load. Pumped storage plants are peak load plants. 
Run-of river plants can be either base load plants or peak load plants depending upon the type of pondage

Classification based on head characteristics.

1. Low head plants- a low head plant uses head less than 15 m. Run-of-river plants are low head plants. A weir or barrage is constructed across the width of river and the power house may be constructed in continuation with the barrage or sometimes, the barrage is above the power house and water is transferred through canals.
2. Medium head plants- a medium head plant uses heads between 15 to 60 m. Such plants are used to store water and also to obtain the required head. 
3. High head plants- such plants uses the head above 60 m. Dam needs to be constructed at sufficient height to store and ensure the supply of water throughout the year. To maintain high heads three methods are adopted:
Construction of high dams.
Utilisation of Natural falls.
Conveying water to lower valley.

Classification based on plant capacity

1. Microhydel plants- capacity less than 5MW.
2. Medium capacity plants- capacity between 5MW and 100MW.
3. High capacity plants- capacity between 101 and 1000MW.
4. Super hydro plants- capacity greater than 1000MW.

Classification based on type of fall

1. Concentrated fall plants- in this type of plant, the power house is located close to dam or weir. The purpose is to consume the entire created head as concentrated head.
2. Divided fall plants-in this type of plant, the power house is located away from the dam or weir. It is located in the downstream to utilise a steep fall available for increasing operation head.