There are basically five types of power plants: 

• Pelton turbines - It is impulse turbine which is normally used for more than 250 m of water head.
• Francis - This is a reaction turbine which is used for head varying between 2.5m to 450m 
• Kaplan – It is propeller type of plant with adjustable blades which are used for heads varying between 1.5 m to 70 m
• Propeller – It is used for head between 1.5 to 30 m
• Tubular – This is used for low and medium height projects. Normally for head less than 15 m.

Major components of a Hydroelectric Power Plant 

• Dam/Barrage 
• Head works i.e. power intake, head regulator and desilting chambers etc.
• Head race tunnels/channels 
• Surge shaft/surge chambers 
• Pressure shaft/Penstock
• Underground and surface power house 
• Tailrace channel or tailrace tunnel.

Classification of Hydro Projects based on Installed Capacity

• Micro: upto 100 KW
• Mini: 101KW to 2 MW 
• Small: 2 MW to 25 MW 
• Mega:
  • Hydro projects with installed capacity >= 500 MW 
  • Thermal Projects with installed capacity >=1500 MW

How energy is generated in Hydroelectric Power Plant?

• A hydroelectric power plant consists of a high dam that is built across a large river to create a reservoir, and a station where the process of energy conversion to electricity takes place. 
• The first step in the generation of energy in a hydropower plant is the collection of run-off of seasonal rain and snow in lakes, streams and rivers, during the hydrological cycle. The run-off flows to dams downstream. The water falls through a dam, into the hydropower plant and turns a large wheel called a turbine. The turbine converts the energy of falling water into mechanical energy to drive the generator After this process has taken place electricity is transferred to the communities through transmission lines and the water is released back into the lakes, streams or rivers. This is entirely not harmful, because no pollutants are added to the water while it flows through the hydropower plant.
• Hydropower is called renewable source of energy because it uses and not consumes the water for generation of electricity, and the hydropower leaves this vital resource available for other uses. 
• Three Gorges project in China on Yang-Yang river is the largest power station in the world having installed capacity of around 22,500 MW.
• The oldest Hydropower power plant is in Darjeeling District in West Bengal. Its installed capacity is 130KW and was commissioned in the year 1897.

Hydro Potential of India 

• India is endowed with economically exploitable and viable hydro potential assessed to be about 84,000 MW at 60% load factor (1,48,701 MW installed capacity). In addition, 6782 MW in terms of installed capacity from Small, Mini, and Micro Hydel schemes have been assessed. Also, 56 sites for pumped storage schemes with an aggregate installed capacity of 94,000 MW have been identified. However, only 27.51 % of the potential has been harnessed so far.

Hydro Initiative 

• On 24th May, 2003, Hon’ble Prime Minister of India launched a scheme, formulated by Central Electricity Authority (CEA), for preparation of Preliminary Feasibility Report (PFRs) of 162 New Hydro Electric Schemes totaling to over 50,000 MW. All the PFRs were targeted to be completed by September, 2004. 
• CEA was entrusted with the overall responsibility for the scheme
• Preparation of PFRs involves conceptual planning, preparation of project and equipment layouts, infrastructure requirement, environmental and geological studies, power evacuation arrangement, cost estimates and economic evaluation.
• PFRs of all the 162 schemes have been prepared ahead of schedule. The schemes are located in 17 states/UTs.

Advantages of Hydro power 

• A renewable source of energy - saves scarce fuel reserves. 
• Non-polluting and hence environment friendly. 
• Long life - The first hydro project completed in 1897 is still in operation at Darjeeling is still in operation. 
• Cost of generation, operation and maintenance is lower than the other sources of energy. 
• Ability to start and stop quickly and instantaneous load acceptance/rejection makes it suitable to meet peak demand and for enhancing system reliability and stability. 
• Has higher efficiency (over 90%) compared to thermal (35%) and gas (around 50%). 
• Cost of generation is free from inflationary effects after the initial installation. 
• Storage based hydro schemes often provide attendant benefits of irrigation, flood control, drinking water supply, navigation, recreation, tourism, pisciculture etc.
• Being located in remote regions leads to development of interior backward areas (education, medical, road communication, telecommunication etc.)