22 Hydropower Generation-II

Somvir Bajar and Anita Singh

Objectives:

1.      To understand different types of hydropower plants.

2.      To explain the different components of hydropower plant

3.      To explain the impacts of hydropower plant.

22.1 Introduction

The power derived from the force or energy of moving water is called as hydropower or water power or hydraulic power. Hydro-power word is made up of two words hydro (is a Greek word meaning water) and power (is the energy present in water). When water falls from a height, then the potential energy of water is converted into kinetic energy and this is the base of hydropower production.

22.2    Classification of hydropower plant

Hydropower projects can be classified by a number of ways which are not mutually exclusive as per IEA hydropower agreement (2000). Fig. 1shows the classification of hydropower projects depending upon size, head, purpose and storage capacity.

22.2.1 Hydropower projects depending on size: Depending upon the size, the hydropower plant can be classified as below (Kumar et al. 2011):

Large hydropower project: Large hydropower project produces more than 500 MW electricity.

Medium hydropower project: Medium hydropower projects produces more than 100 MW electricity.

Small hydropower project: Small hydropower projects produces 1-100 MW electricity.

Mini hydropower project: Mini hydropower projects produces less than 1MW electricity.

Micro hydropower project: Micro hydropower projects produces from 5kW to 100 KW electricity.

Pico hydropower project: Pico hydropower projects produces electricity under 5kW.

22.2.2.  Hydropower   projects   depending  on  Head:     depending  upon   the  head  of   water,             the hydropower projects can be classified as (The Bureau of Indian Standards code IS: 4410 (Part10)-1988 “Glossary of terms relating to river valley projects: Hydroelectric power station including water conductor system)

1.    Low head power station: A power station operating under heads less than 30 m.

2.    Medium head power station: A power station operating under heads less than 30 m to 300 m. The limits are not exactly defined and sometimes the upper limit may be taken as 200 to 250 m.

3.    High head power station: A power station operating under heads above 300 m.

22.2.3. Hydropower projects depending upon the storage capacity: Depending upon the storage capacity, hydropower projects are of mainly three types as follows:

22.2.3.1. Run-of-river project: Run-of-river project utilizes natural flow of the water with no or small storage. The water flow within the natural range is utilized for hydropower generation. Fig. 2 shows the run-of-river type hydropower project and its components. This type of project requires rivers with little dry weather, so that electricity can be produced throughout the year. Depending upon the head, run-of-river projects again divided into two types: low head run-of-river project and high head run-of-the-river project. Low head run-of-river project used for large rivers with gentle gradient like Kamaushi hydropower power project in Japan. High head run-of-river project can be sited at water falls like Nore power station in Norway. Depending upon the flow diversion system, run-of-river hydropower plants are of two different types: in-stream or cross-watershed. In in-stream diversion system, the local topography plays an important role. A portion of the water from the stream is diverted for energy production. In cross-watershed, the water from another rivers are diverted across the catchment area to increase the flow of water, so that more electricity can be produced.

22.2.3.2. Reservoir type project: In this type of hydropower project, a reservoir is either naturally present or constructed to store the water. This type of reservoir provides water throughout the year for electricity production. The reservoir store water which can be used throughout the year for power generation. Landscape of the area plays an important role in this type of hydropower projects. One of the best thing of this type of hydropower project is storage of potential energy of water in the reservoir and whenever required this potential energy can be converted into electricity by hydropower plant.

Fig. 3 shows the reservoir type hydropower plant and its components.

22.2.3.3. Pumped storage project: In this type of storage system, there are two reservoirs upper reservoir and lower reservoir. Fig.4 shows the pumped storage type hydropower plant and its components. The upper reservoir is also called as the head-water pond which is present at height and the lower reservoir is also called as the tail-water pond present at low level. In this type of hydropower power project, energy is produced during peak load by flow of water from upper reservoir to lower reservoir, and in this process the water is collected in the lower reservoir. During off-peak hours, the water is pumped from lower reservoir to upper reservoir by using excess electricity available in the power grid. This type is considered as one of the best and most efficient technologies available for energy storage. These hydropower projects are site specific, example Lam Ta Khong, Thailand; Tehri dam, India; Raccoon mountain pumped storage plant, USA.

22.2.4. Hydropower plants depending upon the purpose: If hydropower plant constructed only for one purpose i.e. electricity production, then it is called as single purpose hydropower project. Water used in hydropower project can be used for other purposes like flood mitigation, irrigation, navigation, aquaculture, recreational requirements etc., and then such project is called as multipurpose hydropower project.

22.3. Hydropower Plant and its components

Fig. 5 shows the important components of a hydropower plant.

22.3.1. Catchment area and water reservoir:

The area behind the dam, where rain water is collected and drains into the river and stream is called catchment area. Water reservoir is present behind the dam at height to store water collected from catchment area. The main purpose of the reservoir is to store water and provide throughout the year for power generation. In rainy season, there is more water, so reservoir store water and supply during dry season. The height of the reservoir is higher than rest of the dam, to store more potential energy. A reservoir may be natural (like a lake in the mountain) or artificial (like construction of dam).

22.3.2. Dam

Dam is made to impound water for any of the following purposes like for irrigation, flood control, energy generation, recreation etc. A dam is most important component of hydropower project. A dam is built on a river, where water is available throughout the year in abundant quantity. Main function of a dam is to provide the head of water and to create storage or pondage. There are different types of dams depending upon the structure (like arch dams, gravity dams, arch-gravity dams, barrages, embankment dams), size (like saddle dam, weir, check dam, dry dam, diversionary dam, underground dam, tailings dam), material (like steel dams, timber dams), and other types like natural dams, cofferdams.

22.3.3. Gates and valves:

Gates and valves are used to control the water flow rate entering into the intake. There are different types of gates (like radial gate, sluice gate, wheeled gate, plain sliding gates, crest gates, rolling or drum gates) and valves (line needle valve and butterfly valve) to control the water flow. These gates and valves control the water flow, boom screens and trash rack control the passing debris. When control gates are opened, water flow through the penstock under the influence of gravity.

22.3.4. Inlet water ways

The main function of inlet water ways is to carry water from dam to power house. There are different kinds of inlet water ways like penstock, tunnel, flume, forebay and surge tank. A penstock is made up of reinforced concrete or steel. The main function of the penstock is to convey water to turbine from the reservoir. Penstocks are may be closed pressure pipes or open conduits. The water in penstock have both kinetic and potential energy due to its motion and its height, respectively. The amount of water flowing through the penstock and height of the water reservoir plays most important role in hydropower plant as the total amount of power generation depends on these two factors.

When there is difficult to have a pipe line or canal, tunnel is made by cutting the mountains to carry water. Surge tanks are additional water storage space near the power units. When there is more distance between the reservoir and the power unit, surge tanks are used. Fore bay is also a type of regulating reservoir type and also known as head pond. Spillways are used for discharging of the surplus water from the storage reservoir. Spillways plays most important role during the flood conditions.

22.3.5. Power house

The water from penstock enters into the power house, where turbine, alternators and the auxiliary plant are present. In power house, the energy of the water is converted into the electric energy. Every power house have two main parts- substructure (having hydraulic and electrical equipment’s) and superstructure (having all operating equipment’s). There are different types of turbines like Pelton turbine, Francis turbine, Kaplan turbine and Propeller turbine. In any hydropower plant these three factors- height of the reservoir, quantity of water and total power generation capacity decide which type of turbine is used. Penstocks carry the water to power house where the kinetic energy and potential energy of water is converted into rotational energy by rotating the blades of the turbine. In power house turbine coupled with generator are present. The rotating blades, rotates the shaft of the turbine, which is enclosed in the generator, produces alternating current in the coil of the generator. Rotation of turbine is most important and crucial step in electricity production as the rotation of the turbine shaft inside the generator produce magnetic field which is converted into electricity by electromagnetic field induction.

22.4. Impacts of hydropower

Hydropower projects have both negative and positive impacts, like any other energy project, on the regional level, inter-regional level, national level and global level. Hydropower projects have socioeconomic, health, institutional, environmental, ecological and cultural impacts. According to the World Commission on Dams (WCD) report- “ a simple accounting for the direct benefits provided by large dams- the provision of irrigation water, electricity, municipal and industrial water supply, and flood control often fails to capture the full set of social benefits associated with these survives” (WCD, 2000). Indirect impacts are called multiplier impacts. The impacts of hydropower projects are as follows (Kumar et al., 2011; Kaunda et al., 2012):

22.4.1 Hydrological regimes: A hydropower project may affect the natural flow of the river; magnitude and timing of discharge; physical and biological changes like water level, timing and temperature. The aquatic and terrestrial habitats are affected by the change in annual flow pattern of a river.

22.4.2 Reservoir creation: Creation of reservoir means converting a terrestrial region into an aquatic region. The topography and landscape of the areas play an important role in finding the suitable site for creation a reservoir. Storage of water from a river to reservoir means converting the flowing water into standing water, and this affects the aquatic species and habitat. The reservoir creation affects the fish habitat, as reservoir supports fish species which grow in standing water. The water level fluctuation in the reservoir often leads to erosion of the reservoir shoreline and along the downstream riverbanks. The erosion may be controlled by various ways like bank restoration, riparian vegetation enhancement etc.

22.4.3 Water quality: The hydropower plant reservoir and operation of hydropower plant affects the water quality both positively and negatively. Water quality issues and its management are shown in fig. 6.

22.4.4 Sedimentation/siltation: Sedimentation affects the reservoir by decreasing its storage capacity due to deposition of sediments with time. The silt may be deposited in both the dead storage and in the live storage. Factors like hydrologic characteristics (slope, current velocity, water depth); material available in the catchment and type and nature of sediments present in the riverbed, decides the sediment carrying capacity of a river. When a dam is built up, the flow of the water is reduced and the sediment carrying capacity is also decreased. With the decrease in water flow, deposition of the sediments increases, and may raise the riverbed and increase the chances of flood. Along with flood, other impacts of sedimentation/ siltation are increased evaporation losses, increased backwater flooding and damage to turbine. Kondolf et al. (2014) classified strategies for sediment management from the perspective of sustaining reservoir capacity. There are different types of management strategies for reservoir sediments like- sediment bypassing and off-channel reservoir storage; sediment sluicing; drawdown flushing; flushing sediments for dams in series; pressure flushing; turbidity current vending; dredging and mechanical removal of accumulated sediments. Upstream sediments is also a big problem and different approaches for upstream sediment managements like catchment erosion control; checkdams; sediment traps; wraping etc.

22.4.5 Biological diversity: The biological diversity is affected by the hydropower projects. In hydropower plant, the flow of the river is either diverted or water is stored in a reservoir (which convert the flowing water into standing water), and both cases affect the biodiversity. When a dam is built up, a terrestrial area is submerged which affect the regional biodiversity, especially the indigenous species. Fig. 7 shows the effect of hydropower plant on wildlife, environmental disturbances caused by hydropower plant and preventive measures to protect biodiversity.

22.4.6 Barrier for fish migration and navigation: Construction of dam creates obstacle in fish migration and navigation. Construction of dam changes the natural flow of water and may reduce access to spawning grounds and rearing zones. Dam construction effects both migratory fish population as well as non-migratory fish populations by affecting the flow of water and by fragmentation, respectively.

22.4.7 Involuntary population displacement: As per WCD (2000) all hydropower projects does not require resettlement or displacement. Displacement of people, due to construction of hydropower plant on that site, affects their social and economic life. During resettlement programme, the affected people must be involved and in resettlement area, basic necessities must be provided to these people.

22.4.8 Affected people and vulnerable group: The local people are the most affected and vulnerable group in construction of hydropower plant. A complete socio-economic study must be carried out of the site selected for construction of hydropower plant, to find out which people are more affected by the hydropower plant.

22.4.9 Public health: Construction of dam leads to storage of water and standing water may leads to waterborne disease like malaria, dengue or yellow fever, in warmer climatic zones. In some areas, mercury level may increase in water due to liberation of mercury from soil through the action of bacteria, which may enter into the food chain. So, proper health care services must be provided in such areas.

22.4.10 Cultural heritage: During selection of site for hydropower plant, attention must be paid to the importance of site from history, archaeological, religious, cultural and aesthetic point of view. Possible measures to minimize the negative impacts of hydropower plant as per IPCC (2000) are:

•      On-site protection

•      Conserving and restoring

•      Relocation or recreating important physical and cultural resources

•      Creating a museum with the help of local communities

•      putting transmission lines and power stations underground in areas of exceptional natural beauty

22.5 Dam failure studies

Lake Delhi Dam- Lake Delhi dam was constructed in 1929 for hydroelectric power generation in Iowa (USA). In July, 2010, high rainfall cause overtopping of the dam and its eventual failure on July 24, 2010. This dam failure leads to property damage of more than 1 million dollars with no fatalities.

Teton Dam failure- Teton dam was located in southeastern Idaho (USA) and constructed in 1975. The primary purpose of the dam was flood control and hydropower. The dam experienced catastrophic failure on June 5, 1976 during its first filling and caused 11 fatalities and property damage of 400 million dollars.

Anita Dam failure- Anita dam is located in Montana (USA) and constructed in 1996 with primary purpose of flood control. But the dam failed on March 26, 1997 leads to 10,000 dollars property loss with no fatalities.

Kaddam project Dam failure- Kaddam project dam was built in Adilabad, Andhra Pradesh (India) in 1957-58 and the dam failed in August, 1958 due to overtopping of water.

Kalika Dam- Kalika dam in Kachch, Gujrat (India) was constructed during 1952-55 and the dam failed and embankment collapsed due to the weak foundation bed in 1959.

Kodaganar Dam- Kodaganar dam, Tamil Nadu (India) was constructed in 1977 and failed due to overtopping of flood water.

Machhu II dam- machhu II (irrigation scheme) dam was built near Rajkot, Gujrat (India) in August, 1972 with primary function for irrigation. The dam failed on August 1, 1979, because of abnormal floods and inadequate spillway capacity.

Fundao tailing dam- The Fundao dam was one of the mega structures of the Germano mining complex, located in the southeastern Brazil and began operating in 2008. The total collapse of the dam took place on November 5, 2015 between 3:00 pm and 4:00 pm.

References:

• Indian standard- Glossary of terms relating to river valley projects, part 10 hydroelectric power station including water conductor system (first revision) IS:4410 (part 10)-1988
• International Energy Agency (IEA). Implementing Agreement for Hydropower Technologies and Programmes, Annex III, Hydropower and the environment: Present Context and Guidelines for Future Action, Subtask 5 Report, Volume III, Appendices, May 2000
• IPCC (2000). Special Report on Emissions Scenarios. N. Nakicenovic and R. Swart (eds.), Cambridge University Press, 570 pp.
• Kaunda, C.S., Kimambo, C.Z., Nielsen, T.K. (2012) Hydropower in the context of sustainable energy supply: a review of technologies and challenges. ISRN Renewable energy, doi: 10.5402/2012/730631
• Kondolf, G.M., Gao, Y., Annandale, G.W., Morris, G.L., Jlang, E., Zhang, J., Cao, Y., Carling, P., Fu, K., Guo, Q., Hotchklss, R., Peteull, C., Sumi, T., Wang, H-W., Wang, Z., wel, Z., Wu, B., Wu, C., Yang, C.T, (2014) Sustainable sediment management in reservoirs and regulated rivers: experiences from five continents. Earth’s Future, 2, 256-280. Doi:10.1002/2013EF000184
• Kumar, A., T. Schei, A. Ahenkorah, R. Caceres Rodriguez, J.-M. Devernay, M. Freitas, D. Hall, A. Killingtveit, Z. Liu, 2011: Hydropower. In IPCC Special Report on Renewable Energy Sources and Climate Change Mitigation [O. Edenhofer, R. Pichs-Madruga, Y. Sokona, K. Seyboth, P. Matschoss, S. Kadner, T. Zwickel, P. Eickemeier, G. Hansen, S. Schlomer, C. von Stechow (eds)], Cambridge University Press, Cambridge, United Kingdom and New York, NY, USA.
• WCD (2000). Dams and Development – A New Framework for Decision-Making.World Commission on Dams, Earthscan, London, UK, 356 pp.