Introduction

Hydropower is a renewable energy resource because it uses the Earth's water cycle to generate electricity. Water evaporates from the Earth's surface, forms clouds, precipitates back to earth, and flows toward the ocean. The movement of water as it flows downstream creates kinetic energy that can be converted into electricity. 2700 TWH is generated every year. Hydropower supplies at least 50% of electricity production in 66 countries and at least 90% in 24 countries.

Out of the total power generation installed capacity in India of 1,76,990 MW (June, 2011), hydro power contributes about 21.5% i.e. 38,106 MW. A capacity addition of 78,700 MW is envisaged from different conventional sources during 2007-2012 (the 11th Plan), which includes 15,627 MW from large hydro projects. In addition to this, a capacity addition of 1400 MW was envisaged from small hydro up to 25 MW station capacity. The total hydroelectric power potential in the country is assessed at about 150,000 MW, equivalent to 84,000 MW at 60% load factor. The potential of small hydro power projects is estimated at about 15,000 MW.

Hydro is a Greek word, which means water. Hydro electricity is the conversion of the mechanical energy in flowing water into electricity. Hydro electricity is generated when the force of falling water from dams, rivers or waterfalls is used to turn turbines, which then drives generators that produce electricity. The energy produced is directed to a substation, where transformers "step up" the voltage before its transmission to the electricity grid.

Technology
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.

Process of energy generation in Hydroelectric Power Plant
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.

Advantages of hydropower
• Hydropower is a 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.
• It is a renewable source of energy with no consumables involved; there is very little recurring cost and hence no high long term expenditure. It is cheaper as compared to electricity generated from coal and gas fired plants. It also reduces the financial losses due to frequency fluctuations and it is more reliable as it is inflation free due to not usage of fossil fuel.
• Hydropower stations are preferred solution for meeting peak loads in grids due to its unique capabilities of quick starting and closing.
• The operational needs of hydro & thermal stations are complimentary and the balanced mix helps in optimal utilization of the capacity. Seasonal load curves of regional grids match with the pattern of hydro power generation. During summer/monsoon season when the generation at hydro power plants is high, the load factor of the system is high due to heavy agricultural load. During winter, the thermal stations operating at base load and hydro stations working as peak load stations will take care of weather beating loads.

Challenges related to hydropower
• The hydropower generation is highly capital-intensive mode of electricity generation.
• Due to the fact that hydropower projects are primarily located in hilly areas, where forest cover is comparatively better than plain areas, diversion of forest land is sometimes unavoidable.
• Submergence of land, thereby loss of flora and fauna and large scale displacement, due to the hydropower projects

Hydropower potential in India
The hydropower potential of India is around 1,45,000 MW and at 60% load factor, it can meet the demand of around 85,000 MW. The estimated potential for power generation from Small hydropower projects is about 20,000 MW.