Renewable energy

Early Irrigation Waterwheel

Early Roman Water Mill

Early Norse Water Mill

World’s Largest Dams

Three gorges dam-18200MW

Three gorges dam-18200MW

Hydro electric power station • a generating station which utilizes the potential energy of water at a high level for generation of electrical energy is known as hydro-electric power station.

• water head is created by constructing a dam across a river or lake.

• water is led to water turbine

• potential

• energy is converted into kinetic energy

• kinetic energy is converted to the mechanical energy by allowing the water to flow through the hydraulic turbine runner

• becoming more popular because limited oil reserves

• importance due to flood control, storage of water for irrigation, and water for drinking.

• power developed

-

Lay out of hydro electric power plant

• The generation of electric energy from falling water is only a small process

-Hydrological cycle” or rain evaporation cycle”

This cycle is shown in figure.

Water cycle

• The input to this cycle is the solar energy.

• Due to this, evaporation of water takes.

• On cooling, these water vapours form clouds. Further cooling makes the clouds to fall down in the form of rain, and snow etc; known as precipitation

• Before a water power site is considered for development, the following factors must be thoroughly analyzed

-1. The capital cost of the total plant.

-2. The capital cost of erecting and maintaining the transmission lines and the annual power loss

-3. The cost of electric generation compared with steam, oil or gas plants which can be conveniently set up near the load center.

• Inspite of the above factors, following advantages which make these suitable for large interconnected electric system:

-1. The plant is highly reliable and its maintenance and operation charges are very low.

-2. The plant can be run up and synchronized in a few minutes.

-3. The load can be varied quickly and the rapidly changing load demands can be met without

any difficulty.

-4. The plant has no stand by losses. -5. No fuel charges. -6. The efficiency of the plant does not change

with age. -7. The cost of generation of electricity varies

little with the passage of time. • the hydro-electric power plants have the

following disadvantages also: -1. The capital cost of the plant is very high. -2. The hydro-electric plant takes much longer in

design and execution. -3. These plants are usually located in hilly areas

far away from the load center. -4. Transformation and transmission costs are

very high.

-5. The output of a hydro-electric plant is never constant due to An unpredictable change of

monsoons(A seasonal wind in southern Asia; blows from the southwest (bringing rain) in summer and from the northeast in winter) and their dependence on the rate of water flow in a river.

RUN-OFF -Defined as the total condensation of moisture that

reaches the earth in any form • includes all forms of rains, ice, and snow etc -Run-off = Total precipitation – Total evaporation • The unit of run-off are m3/s • Day-second meter • Rain-fall is measured in terms of centimeters of water

over a given area and over a given period (usually one year). • The portion of the total precipitation that flows

through the catchment area is known as “Run-off”. • The catchment area of a hydro site is the total area

behind the dam, draining water into the reservoir.

Factors Affecting Runoff 1.Nature of Precipitation

-Rains lasting a longer time results in larger run-off

-Humid atmospheres

2.Topography of Catchments Area

-Steep,

- The water will flow quickly and absorption and evaporation losses will be small

3.Geology of Area

-Rocky areas will give more run-off

4.Meteorology.

-Run-off increases with low temperature,

5.Vegetation.

-Evaporation and seepage are increased by cultivation

6.Size and Shape of Area.

- Large areas will give more run-off

Measurement of Run-Off

1.From Rain-Fall Records.

2.Empirical Formulas.

3.Actual Measurement.

HYDROGRAPH AND FLOW DURATION CURVE

• A hydrograph indicates the variation of discharge or flow with time.

• It is plotted with flows as

• ordinates and time intervals as abscissas.

• The flow is in m3/sec and the time may be in hours, days, weeks or months

THE MASS CURVE

• Indicates total volume of run-off in cubic meters upto a certain time.

• Or the mass curve is to compute the capacity of the reservoir for a hydro site.

• Abscissa can be day, month or year and cumulative volume of flow as ordinate

Storage of water

• Wide variations in flow of

• In order to ensure generation throughout the year.

Pondage

• Power demand fluctuates with time

• If power plant is away from reservoir

• Capacity of pond should be sufficient to coup with hourly changes for 24 hour.

ESSENTIAL FEATURES OF A WATER-POWER PLANT

• 1. Catchment area.

• 2. Reservoir.

• 3. Dam and

intake house.

• 4. Inlet water way.

• 5. Power house.

• 6. Tail race or

outlet water way.

2. Reservoir. -The purpose of the storing of water in the reservoir is to get a uniform power

output throughout the year 3. Dam -Are built to create head • Head -Water must fall from a higher elevation to a lower one to release its stored

energy. -The difference between these elevations (the water levels in the forebay and

the tailbay) is called head -high-head (800 or more feet) -medium-head (100 to 800 feet) low-head (less than 100 feet) 4. Inlet water way -the passages, through which the water is conveyed to the turbines from the

dam. tunnels, canals, forebays and penstocks and also surge tanks. - A forebay is an enlarged passage for drawing the water from the reservoir -Tunnels are of two types: pressure type and non-pressure type.

• 6. Tail Race or Outlet Water Way

-Tail race is a passage for discharging the water leaving the turbines

Constituents of hydro electric power plant

• Spillways

-when river flow exceeds the storage limits

• Surge tanks

-pipe to absorb sudden rises of pressure as well as to quickly provide extra water during a brief drop in pressure

-at high or medium head

• Penstocke

-A gate that controls water flow, or an enclosed pipe that delivers water to hydraulic turbines

-concrete: less than 30m

-steel : any head

-thickness increases with head or working pressure

Classification of Hydro Turbines

• Reaction Turbines – Derive power from pressure drop across turbine

– Totally immersed in water

– Angular & linear motion converted to shaft power

– Propeller, Francis, and Kaplan turbines

• Impulse Turbines – Convert kinetic energy of water jet hitting buckets

– High heads

– No pressure drop across turbines

– Pelton, Turgo, and crossflow turbines

Francis Turbine

Propeller Turbine

Kaplan turbine

Pelton wheel turbine

Turgo turbine

Turbine Design Ranges

• Kaplan

• Francis

• Pelton

• Turgo

2 < H < 40 10 < H < 350 50 < H < 1300 50 < H < 250 (H = head in meters)

Design considerations

Efficiency of Hydropower Plants

• Hydropower is very efficient

– Efficiency = (electrical power delivered to the “busbar”) ÷ (potential energy of head water)

• Typical losses are due to

– Frictional drag and turbulence of flow

– Friction and magnetic losses in turbine & generator

• Overall efficiency ranges from 75-95%

Examples • A hydro electric generating station is supplied

from a reservoir of capacity 5*106m3/sec at head of 200meters. Find the total energy available in kWh if the overall efficiency is 75%.

Solution.

Q= 5*106m3/sec

H= 200meters

Efficiency= 75%

W=(5*106)(1000), (mass of 1m3 of water is 1000kg)

Electrical energy available=W*H*efficiency, watt-sec

Ex: it has been estimated that the min run off of approximately 94m3/sec will be available at a hydro electric project with head of 39m. Determine(1) firm capacity (2) yearly gross o/p. assume efficiency of the plant to be 80%

Sol:

Weight of water available, W=94*1000=94000kg/sec, Head=39m

Work done per sec=w*H=94000*9.81*39=35963kW

(1)Firm capacity=plant efficiency*gross plant capacity=0.8*35963=28770kW

(2)Yearly gross o/p=28770*8760=252*106kWh

• Water for hydro electric station is obtained from reservoir with head of 100m. Calculate energy generated per hour per cubic meter of water if the hydraulic efficiency be 0.86 and electrical efficiency 0.92.