Flowing water has been one of the earliest sources of energy. Water mills grind grains and can run a generator. Many water mills were in operation centuries ago. Later, the potential energy was tapped to run turbines and generate power. Initially, small hydroelectric projects were set up. Since many of these projects were in mountainous terrains, the operation of these plants depended on the availability of water. Normally, the availability of water depend on rainfall. During rainy seasons. there is more water available and during the other seasons the quantity was less. In order to even out power generation throughout the year, dams were constructed and reservoirs impounded the water. This led to major hydroelectric projects like Sharavathy. These reservoirs submerged prime forest lands thereby adding to the deforestation effect.
(i) Run of the river plants: Rivers have a flow of water. Initially hydroelectric projects have been set up to tap the energy from the flow and convert it into electricity. Run of the river plants need minimal construction, and submerge least area. Normally a small barrage is built and if there is a local head, it is exploited. Such plants can be put up in canals also. Many plants can be put up in a river. These plants normally are of small capacities and they do not need any storage area for reservoirs. They are ecologically sound. China has tapped its river water's energy potential through a series of such plants. We have a large potential for such run of the river/streams/canal schemes. Even though these plants are seasonal, a well developed grid can absorb the seasonality through a proper load generation balance with appropriate thermal generation scheduling.
(ii) Weekly and monthly pondage schemes: Whenever a large or medium head of water is available, and water can be stored in a pond or small reservoir, we can go for these schemes. Depending on the capacity of a pond, we can store water equal to a week's energy or a month's energy and the scheme is appropriately called. Such schemes handle minor variation in the flow in a river and can supply stable power reducing the fluctuations that may occur in a strict run of the river plant. There is a requirement for some area to be submerged. But this is much smaller.
(iii) Seasonal plants: We have many irrigation projects in which water flow is regulated to meet the needs of irrigation. There may not be any water in the reservoir during the lean season. In this case we can have a seasonal plant which works only when there is water flow and is shut down during the other periods. For example the Mettur tunnel scheme works for 4 months in a year and is closed down for the remaining 8 months.
Seasonal plants submerge less areas. Thereby, they are also ecologically sound. These are the best type of plants in many of our river valley schemes in forest areas. For example, let us consider the Bedthi hydro electric project in Uttara Kannada District, Karnataka state. If we put up a seasonal plant, then the plant will generate a large quantum of power and energy during monsoon and minimum during the lean period. Hence the reservoir area required will be less. We can find the ratio of reservoir area as:
(k is the ratio of power generated in monsoon to power generated in lean period), For large k, the seasonal scheme needs very much less area for submergence. If we also consider the fact that the area also produces biomass and consider it as another energy form, and we try to get maximum energy; we will reduce the submerged area still further. It may even be possible to construct a mixed hydro-thermal plant Our analyses of Bedthi hydroelectric project shows that with hydro thermal combination, and having seasonal plant the energy generated is almost twice that of year round storage plants. Earlier proposal of Bedthi hydro project is supposed to submerge 95.03 sq.km of land and generate 850 million units of electricity. Our calculation shows that by going in for run of river scheme- seasonal plants land submerged is about 5.7 sq.km. (to have two days storage) and generate same amount of electricity. And balance of 89 sq.km. hence saved can cater the fuelwood need of the region. At 6.5t/ha/yr biomass productivity, thermal energy available is about 319 million units, while the fuelwood requirement in this region is about 312 million units. Thus by this integrated approach one can meet the fuelwood requirement for domestic cooking and water heating and as well as generate electricity through hydel source.
(v) Carry over reservoir schemes: We get more rain in some years and less in some other years. If we want to store and carry over the surplus water to the next year so that the energy is not wasted, we will be designing a carry over scheme. Since this scheme needs a larger sumbergence area and since most of the area will be dry during low rainfall years, leading to higher siltation rates, thus scheme is not desirable.
So far we looked at the classification based on the type of storage of water and use of energy. Let us now look at the classification based on size.
(vi) Micro and mini hydel plants: There are a large number of streams, canals and rivulets with drops at many places. Today new technologies are available for the construction of water turbines for a small head of 2 - 3 metres. Hence it is possible to set up a large number of small plants. These are known as micro and mini plants because of their capacity. Plants with capacities upto 500 kw are called micro hydel plants and with capacities upto 50 MW as mini hydel plants. Micro hydel plants do not need any submergence, can be installed any where; (we can install a micro hydel plant in a multi storied building to use the head of water flowing from an overhead tank to flats at lower levels); costs are coming down. Hence it is desirable to allow people to put up these plants wherever possible. We should encourage setting up of many thousands of such plants in our state. China has installed lakhs of such plants. This also helps in starting rural services and industries due to the availability of electric power and energy. Power supply reliability also will improve dramatically. Cost of an installed KVA today is around 40000-50000 rupees for major projects (including transmission system) and the corresponding costs for micro and mini hydel plants will be lower around 20000 to 30000 rupees. One of the main reasons for going in for large plants was economy of scale. But with increased costs of construction of reservoirs, the economics of scale is not working. A second reason was grid operation. Operating a grid with a large number of small plants was difficult leading to frequent unstable conditions. But electronic controllers available today can solve this problem. Technically, it is now feasible to use computer control techniques to operate a grid containing a large / very large number of microhydel/mini hydel plants.
(vii) Major plants: Hydro electric projects generating power in the range of 100 MW and above are classified as major plants. They submerge large areas, store a lot of water leading to evaporation losses, deforest a large area leading to higher siltation rates. They also uproot a large number of people. In the present context, it is difficult to implement such projects. It is desirable to convert them into seasonal ones so as to tap the energy with minimal losses all around.