Dr. P. K. Jena in Bhubaneswar, September 14, 2021: Energy needs in industrial, transport, agricultural and domestic sectors are being met mainly from fossil fuels. Presently, about 74% of energy being utilized is obtained from fossil fuels and the rest from renewable energy sources like hydro power, solar, wind and bio products. The most important advantage of using renewable energy resources is to avoid emission of green house gases like carbon dioxide, oxides of nitrogen and sulphur and particulate matters to the atmosphere.

These green house gases are responsible for global warming and climate change which have brought a lot of disasters to human beings and other living beings on the earth. Out of all renewable energy sources, the hydro power is the most important one. Since long, construction of dams in rivers and streams and other water bodies to reserve water has been an integral part of human civilization, as these control floods, providing water for drinking and agricultural purposes and generating hydro power.

The water stored in the dam at suitable sites of the river is allowed to fall from a certain height on turbines and in this process the energy present in water is converted into mechanical energy and subsequently to electrical energy by putting a generator along with the turbine. In this process, no water is lost. The water going out of the system is used for agricultural, industrial and domestic purposes. Similarly, by storing rain water at suitable land sites, it is also possible to harness energy as and when required. In this way the potential energy stored in water is converted to electrical energy without loss of any water as shown below.

Some of the advantages of hydro electric power plants are:

 The supply of electric power can be maintained constantly.
 The water can be stored and used when electricity demand is high.
 The longevity of dams is quite long which helps to generate electricity at low cost.
 The hydro electric power is renewable and eco friendly.
 The dam area can be converted as a tourist attraction spot.

However, there are certain disadvantages of hydro power plants particularly when water stored is quite large as given below.

 The constructions of big dams are quite expensive and it has to be constantly maintained.
 Time to time desilting of dam has to be done.
 The rehabilitation problems of the people in the area are quite delicate and expensive.
 The dam has to be operated for many years as the returned on the cost invested for construction of dam is obtained after long time.
 Sometimes the dam blocks the river water resulting in irregular supply of water at downstream.
In addition to these in recent years, the constructions of large dams are avoided because of the following reasons.
 Alteration of water quantity and quality occur in downstream areas.
 Water quality and bio-diversity are very much affected by increased erosion and sedimentation due to deforestation of the catchment areas.
 Large reservoirs produce significant amount of green house gases like carbon dioxide, methane etc.
 Many times benefits of large dams are not enjoyed by local communities or displaced families.

In view of these problems, in recent years, small hydro power plants are being encouraged. Some of the advantages of small hydro power plants are:

 The socio economic impart are very little in comparison to large hydro power plants.
 In micro dam investment is low, much durable and sometimes it can last for 50 years or more without much investment.
 It is considered to be cost effective.
 Maintenance cost is quite low.
 If small hydro power produces excess electricity, some power companies can bye the same.
 It is possible to supplement the small hydro power with intake from the power grid.

There are mainly four types of Hydro Power:

1. Run-off-river Hydro Power:
In this case, the flowing water from a river is allowed through a narrow canal or pen stock to spin the turbine, which is connected to a generator to produce electricity. The run-off-river system provides a continuous supply of electricity with some fluctuation depending on the water flow.

2. Storage Hydro Power:
In this case, the water is stored in a reservoir with the help of a dam. When water is released from the reservoir, the turbine rotates and the connected generator produces electricity. This type of hydro power system provides base load as well as the ability to shutdown and start up at short notice according to the demand. This system because of enough storage capacity, operates independent of hydrological inflow.

3. Pumped Storage Hydro Power:
In this system, water is pumped from a lower reservoir to an upper reservoir. The water is released back to the lower reservoir through turbine which is attached with the generator to produce electricity.

4. Off-Shore Hydro Power:
In this case, tidal current of the waves of the sea rotates the turbine which is connected to a generator to produce electricity. However, this technology has to be fully developed.

At present in the world, electric generation from hydro power, solar, wind and bio-fuel are 16%, 2%, 4% and 3% respectively of the total electricity produced and the rest are from fossil fuels. In the year 2009, 16.5% of electricity produced in the world was contributed by hydro power. According to World Energy Council 2010 report, about 160 countries have hydro power. However, the production of hydro power in the top ten countries accounts for about 70% of the hydro power electricity produced in the world as given in Table – 1.

Hydro Electricity Production and share of world, total electricity production in top ten countries and the rest of the world in 2010, adapted from World Energy Council is given below.

Hydro power contributes approximately 62.10% of the total electricity produced by renewable energy sources. At present, the world’s installed capacity of hydro power is 1292 GW. It is hoped that, because hydro power is predictable and has high efficiency with flexibility and reliability, many more hydro power units should come up in future. International Energy Association predicted that, hydro power would continue to become main renewable energy sources in future years

Large hydro power is associated with a number of problems like displacement of people, submergence of land in the catchment area, risk of dam malfunctioning, damage to eco system etc. In view of these, nowadays small hydro power units are being preferred. It is reported that, utilizing hydro power for electric generation in place of the amount of coal used at present, it is possible to prevent release of about 148 million tons of particulate matters, 62 million tons of sulphur dioxide and 8 million tons of nitrogen oxide to the atmosphere every year. In view of this and considering a number of merits of small hydro power, it is suggested that, more efforts should be made to set up large numbers of small hydro power units to meet our increasing demands of electricity while keeping our environment clean and healthy.

• Former Director General, Council of Scientific & Industrial Research, India.