Classify hydroelectric power plants based on their hydraulic characteristics. Briefly explain any two types with neat sketi;iles
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Hydropower is a mature technology, with well-proven solutions and good reliability. A hydropower plant includes components from civil, mechanical and electrical engineering. During planning and operation it is also very important to include information about the hydrology, hydraulics, environmental engineering together with information of the social and political issues, in order to find an optimal solution.
A hydropower plant typically consists of an intake, a waterway (‘head race’), a penstock, the power station with electrical and mechanical equipment (‘Elmek’) and finally a waterway (‘tailrace’) to the outlet. It may or may not include a dam and a reservoir for water storage. The three main components of Elmek equipment are turbine(s), generator(s) and transformer(s). In addition, there will be many other components such as gates and valves, electronic equipment for controlling the operation of the station, power cables, switchyard and grid connections.
A hydropower plant is nearly always tailored to utilise the available water and head, and many different types of turbines have been developed; the most common is the Pelton and Francis turbine for high and medium head situations and the Kaplan turbine for lower head and large flow systems.
Hydropower schemes can broadly be classified into four main types: run-of-river (ROR), storage (reservoir-based), pumped storage hydro (PSH) and in-stream (hydrokinetic) technologies.
21.3.1 Run-of-River
Hydropower plants mainly generate electricity from the available flow in a river. Some short-term storage (a pond) may be included, allowing for some adaptation to the consumption, but the generation profile will generally follow the inflow profile.
21.3.2 Storage Hydro
Hydropower projects with a reservoir can store water for later use, typically by saving water during the high-flow season (spring, rainy season) and releasing water during the low-flow season (winter, dry season). A reservoir gives a higher flexibility and allow the hydropower plant to adapt better to the demand profile, both in the short term (hours, days) and seasonally.
21.3.3 Pumped Storage
A pumped storage hydropower plants consist of a reversible power plant and two reservoirs, connected by a pipe or a tunnel. The main purpose is to store energy by pumping water up into the upper reservoir during low-demand periods and generate (peaking) power by releasing the water back to the turbine during high-demand periods.
21.3.4 Hydrokinetic
This technology is less developed and less used than the other three, but offers promise to extend the range of possible sites for hydropower development to rivers and canals where it can harness energy directly from flowing water, rather than from a hydraulic head created by dams or other control structures.
21.3.5 Underground Power Plants
Tunnels and rock caverns are important construction elements in most large-scale hydropower projects, as headrace and tailrace tunnels, access tunnels, powerhouse, surge shafts, power cables shafts and ventilation tunnels or shafts. In Norway, nearly all large-scale hydropower plants have been built underground since 1960 [2]. If the rock is of good quality, most of the tunnels, penstocks and rock caverns can be used unlined, saving on time in construction and saving on expensive concrete lining.
21.3.6 Large and Small Hydro
It has become popular to classify hydropower plants either as ‘small’ or ‘large’, depending on installed capacity. There seem to be a belief that ‘small is beautiful’ and that small hydro schemes are more environmental friendly. In some countries small hydro schemes are accepted for development and receive subsidies while larger hydro schemes are not subsidised. If one looks at the impact per kilowatt hour the picture becomes more complicated, one large hydropower plant could easily have less impact (per kilowatt hour) than many small plants of the same capacity combined. This was discussed thoroughly in Ref. [1] where the conclusion was that the use of classification according to size should be avoided, both because there is no clear connection between size and impact, and also because the definition of what is ‘small’ and ‘large’ varies widely from one country to another, as given in Table 21.4. There have even been attempts to classify small hydro as ‘renewable’, and large hydro as ‘not renewable’. This is of course nonsense and should be avoided. Both small and large hydropower plants are equally renewable, but they could have different impacts and be more or less sustainable. It is therefore better to discuss whether the project is sustainable and classify the project(s) according to a sustainability index. This is discussed in the next section.
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A hydropower plant typically consists of an intake, a waterway (‘head race’), a penstock, the power station with electrical and mechanical equipment (‘Elmek’) and finally a waterway (‘tailrace’) to the outlet. It may or may not include a dam and a reservoir for water storage. The three main components of Elmek equipment are turbine(s), generator(s) and transformer(s). In addition, there will be many other components such as gates and valves, electronic equipment for controlling the operation of the station, power cables, switchyard and grid connections.
A hydropower plant is nearly always tailored to utilise the available water and head, and many different types of turbines have been developed; the most common is the Pelton and Francis turbine for high and medium head situations and the Kaplan turbine for lower head and large flow systems.
Hydropower schemes can broadly be classified into four main types: run-of-river (ROR), storage (reservoir-based), pumped storage hydro (PSH) and in-stream (hydrokinetic) technologies.
21.3.1 Run-of-River
Hydropower plants mainly generate electricity from the available flow in a river. Some short-term storage (a pond) may be included, allowing for some adaptation to the consumption, but the generation profile will generally follow the inflow profile.
21.3.2 Storage Hydro
Hydropower projects with a reservoir can store water for later use, typically by saving water during the high-flow season (spring, rainy season) and releasing water during the low-flow season (winter, dry season). A reservoir gives a higher flexibility and allow the hydropower plant to adapt better to the demand profile, both in the short term (hours, days) and seasonally.
21.3.3 Pumped Storage
A pumped storage hydropower plants consist of a reversible power plant and two reservoirs, connected by a pipe or a tunnel. The main purpose is to store energy by pumping water up into the upper reservoir during low-demand periods and generate (peaking) power by releasing the water back to the turbine during high-demand periods.
21.3.4 Hydrokinetic
This technology is less developed and less used than the other three, but offers promise to extend the range of possible sites for hydropower development to rivers and canals where it can harness energy directly from flowing water, rather than from a hydraulic head created by dams or other control structures.
21.3.5 Underground Power Plants
Tunnels and rock caverns are important construction elements in most large-scale hydropower projects, as headrace and tailrace tunnels, access tunnels, powerhouse, surge shafts, power cables shafts and ventilation tunnels or shafts. In Norway, nearly all large-scale hydropower plants have been built underground since 1960 [2]. If the rock is of good quality, most of the tunnels, penstocks and rock caverns can be used unlined, saving on time in construction and saving on expensive concrete lining.
21.3.6 Large and Small Hydro
It has become popular to classify hydropower plants either as ‘small’ or ‘large’, depending on installed capacity. There seem to be a belief that ‘small is beautiful’ and that small hydro schemes are more environmental friendly. In some countries small hydro schemes are accepted for development and receive subsidies while larger hydro schemes are not subsidised. If one looks at the impact per kilowatt hour the picture becomes more complicated, one large hydropower plant could easily have less impact (per kilowatt hour) than many small plants of the same capacity combined. This was discussed thoroughly in Ref. [1] where the conclusion was that the use of classification according to size should be avoided, both because there is no clear connection between size and impact, and also because the definition of what is ‘small’ and ‘large’ varies widely from one country to another, as given in Table 21.4. There have even been attempts to classify small hydro as ‘renewable’, and large hydro as ‘not renewable’. This is of course nonsense and should be avoided. Both small and large hydropower plants are equally renewable, but they could have different impacts and be more or less sustainable. It is therefore better to discuss whether the project is sustainable and classify the project(s) according to a sustainability index. This is discussed in the next section.
Read full chapter
The Recent Tre
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