Lecture 7 2015-2016

Renewable Energy SystemsDavid Buchla | Thomas Kissell | Thomas Floyd

Copyright © 2015 by Pearson Education, Inc.All Rights Reserved

Renewable Energy

Systems11

Dr. Caroline Dong



11Energy from Water

11-1 ENERGY IN MOVING WATER

11-2 HYDROELECTRIC DAM OPERATION

11-3 WATER TURBINES

11-4 TIDAL POWER GENERATION

11-5 WAVE POWER GENERATION

Chapter Outline



11-1 Energy in Moving Water

Hydroelectric energy is a useful renewable energy source.

Most hydropower comes from converting falling water to electricity.

Some power comes from moving streams, rivers, and ocean tides.

Worldwide, it accounts for over 6% of all energy and 17% of electricity production.

3



Moving water has kinetic energy that can be converted to useful work directly or by using it to generate electricity.

Hydroelectric is the most efficient method of large-scale power generation; it has and efficiency of 80% to 95% for large installation with high flow rates but less in installations with a low flow rate.


© nstanev/Fotolia

4




The amount of kinetic energy in a moving substance was given by the equation:

5

21

2KEW mv

WKE = kinetic energy in J

m = mass in kg

v = velocity in m/s.



Water behind a dam or any object above a reference point posses potential energy, which is the energy of position. Potential energy is given by the equation:


PEW mgh

What is the potential energy in joules of the car

and driver? The car and driver weigh 1400 lbs.

40 feet

1 lb = 0.454 kg; 1 ft = 0.305 m

2

1400 lb0.454 kg 9.8 m 0.305 m

40 ft 76 kJlb s ft

PEW mgh

6




What is the speed of the car in the previous example if 70% of

the energy is transformed to kinetic energy? The car had a

potential energy of 76 kJ and a mass of 636 kg.

0.70 0.70 76 kJ 53.2 kJKE PEW W

21

2

2 53.2 kJ212.9 m/s (29 mi/h)

636 kg

KE

KE

mvW

Wv

m

When energy is transformed from potential to kinetic energy, some will be lost to friction (heat).

7




Water behind a dam posses potential energy which is converted to kinetic energy as it falls. Each cubic meter weighs 1000 kg and the distance it falls relative to a reference is called the head.

Head is a height of water created by a vertical difference in elevation.

A 1 m drop corresponds to 9794 Pa.

In hydropower applications, the head is measured from the top of the water level to the inlet at the turbine.

8




The distance is considered the gross head. The net head is the equivalent height after equivalent friction losses in piping are subtracted.

To calculate the gross energy stored in a pond or reservoir, the volume and the average height are used.

9




Assume the head on a dam is 30 m.

(a)What is the WPE for one m3 of water at the top of the reservoir?

(b)If this passes a turbine in 1 s, what total power does it

represent? (Ignore friction).

2

9.8 m1000 kg 30 m 294 kJ

sPEW mgh

(a)

294 kJ 294 kW

1 sP

W

t (b)

10




2

2eq

vh

g

ph

h = height in meters,

p = pressure in N/m2,

= specific weight of water (9807 N/m3)

v = velocity in m/s

g = gravitational constant (m/s2)

The energy in moving water can be thought of as potential energy plus the kinetic energy, Summarizing:

1) potential energy due to elevation,

2) potential energy due to pressure and

3) kinetic energy due to motion.

The equivalent head, heq is:

11




12

2

2eq

vh

g

ph

ℎ𝑝 =𝑝

𝛾

ℎ𝑘𝑒 =𝑣2

2𝑔ℎ𝑒𝑞 = ℎ + ℎ𝑝 + ℎ𝑘𝑒




The volumetric flow rate, Qv, is measured in m3/s or ft3/s. The product of specific weight, , and Qv is the weight passing the turbine per time, which is mg/t.

eq

eq

mghW mgP h

t t t

Power is energy per time, so the power in moving water

can be written in terms of equivalent head:

By substitution:

v eqP Q h

© r

eb

/Fo

tolia

13




Example:

A small stream has a head of 8 m from the diverter to the turbine. The volumetric flow rate is determined to be 0.05 m3/s.

Calculate the total power available to the turbine (ignore the pipe friction).

Answer:

Gamma = 1000 kg /m3 * 9.807 m/s2 =9807 N/m3

P = 9.807 N/m3 * 0.05 m3/s * 8m = 3.92 kW

14



11-2 Hydroelectric Dam Operation

Compared to thermal plants, hydroelectric plants are more efficient in converting energy to electricity.

Most hydroelectricity, by far, is generated in conventional hydroelectric dams.

Other types of power dam:

• Run-of-the-river

• Microhydroelectric dams

• Pumped storage system

15




In a conventional hydroelectric generating system,

stored water is allowed to flow through a penstock and

used to spin a turbine/generator, generating electricity.

Large dams will have multiple penstocks and turbines.

16




The process in Conventional Hydroelectric Dam:

• A large screen is located in front of the inlet gate to keep debris from damaging the turbine.

• The inlet gate controls the amount of water that flows through a penstock.

• Penstock directs the water to the turbine blades to spin the shaft at a high speed

• The shaft is connected to a generator.

• After giving up most of its energy, the water passes through a channel called the tailrace to a relatively shallow storage area called the afterbay.

17




Water is stored behind the dam.

As more water is stored, its level becomes higher, and its ability to produce electrical energy increases.

The dam has spillways that are built into it to allow water to be released and to avoid overfilling the reservoir during rainy periods.

Water in the spillway does not go through the penstock and past the turbine, so its energy is lost.

It is important that the water level is not allowed to increase to the point where water runs over the dam because this can damage the dam.

18




A very useful concept for renewable energy systems in

mountainous areas is pumped storage.

A pumped storage system is a system of two dams,

each with a reservoir. One is located at a much higher

elevation than the other.

If the idea is applied to renewable systems, the storage

water can be used when the resource is not available.

Currently it is mostly used to help power companies

level loads.

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19




• During low-peak electrical hours, water is pumped from the lower reservoir into the higher reservoir.

• During the highest peak times, when electrical energy is needed on the grid, water is released from the upper reservoir, where it flows down through penstocks to turbines, as in a traditional hydroelectric dam, producing electricity.

20




Raccoon Mountain pumped storage plant in Tennessee:

21




The Cabin Creek pumped storage power plant is located in Colorado and consists of two reservoirs connected by a tunnel. It has a total installed generating capacity of 320 megawatts in two reversible pump-turbine units.

22




A very large pumped storage plant is the Helms

Pumped Storage Plant, located high in a remote area

of the Sierra Nevada Mountains. This is the largest

hydroelectric and pumped storage facility in the

California electric system and consists of three units. The

rotors alone weigh 1 million pounds and are 20 feet in

diameter and 10 feet high.

Helms produces 1,212 MW by

moving water from the upper

reservoir, which is CourtrightLake to a reservoir that is 1700

feet below at Lake Wishon.

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• The generator in a pumped storage facility can act as a motor. Technically, it is called a motor/generator.

• When water from the lower reservoir is to be pumped to the higher reservoir, power from the grid is applied to the motor generator rather than just an ac generator or alternator.

• The pump generating system is used to provide extra electrical power at the peak times when it is needed.

• Energy can be stored in various ways, but pumped water storage is one of the most effective.

24




Run-of-the-River systems (ROR) are hydroelectric systems that primarily use the kinetic energy in flowing rivers to generate electricity.

When a dam is part of the system, storage area behind it is called pondage.

Two types of ROR:

• Without pondage; no storage of water and subject to seasonal river flows

• With pondage; can provide regular water flow.

25




The photo shows a small

run-of-the-river system in

King Cove, AK, which

helped offset expensive

power from diesel

generators.

This plant generates only 800 kW of power. Very

small systems like this are

useful in remote villages

and in developing countries.

So

urc

e: N

REL

26




Compared to conventional dams, ROR dams are considered environmental friendly, as they have onya small effect on river flow, and they do not have large reservoirs with their accompanying environmental impact.

Even with its smaller capacity, an ROR system with pondage can help with flood control to a limited extent.

27




Micro- and small hydroelectric dams

• Small hydroelectric dams generate between 100 kW and 10 MW.

• Small hydroelectric systems can be connected directly to the grid, or they can be used to provide electrical power to a building or business with grid power backup when the water level is not high enough to produce all the power that is needed.

• Microhydroelectric system: <100 kW

28




Microhydroelectric system is designed to prevent harm to fish or other wildlife in the system.

It is now being used in developing countries to provide small amounts of electrical power for refrigeration or pumping and purifying water.

Picohydroelectric system: < 5 kW

Picohydroelectric systems typically operate the same as larger ROR systems but without pondage.

It is inexpensive and it can be installed around the world, in developing countries.

29



11-3 Water Turbines

Turbine: A rotary engine that extracts energy from a fluid and converts it to useful work.

Water turbine is to transfer the kinetic energy in moving water into turning the shaft.

The key to high efficiency is to minimize losses such as those resulting from turbulence, vibration, or heat.

The minimize the turbulence, the turbine blades must be smooth and the turbine must be well balanced with low friction bearings.

30



11-3 Water Turbines

Water turbines are defined by the form of energy they convert to mechanical motion.

Turbines are classified to:

• Impulse turbine

• Reaction turbine

Most turbines are a mixture of both.

31



11-3 Water Turbines

1. An impulse turbine is a rotary engine that changes

the direction of a high velocity fluid, thus converting

kinetic energy into mechanical rotating energy.

Impulse turbines are primarily

used in applications with high

pressure heads and relatively

lower flow rates.

32



11-3 Water Turbines

Pelton and Turgo turbines are examples of impulse

turbines. Notice the double cups on these Pelton

turbines, a innovation by William Doble, an employee of

Pelton.

The double cups split the

water flow in half, which transfers most of the

momentum of the water to

the wheel.

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Hyd

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11-3 Water Turbines

2. Reaction turbines are the second type; they develop

torque from the pressure of water and are

submerged at all times. It primarily converts potential

energy into mechanical rotating energy.

In a reaction turbine, the rotating blades are

completely encased in a pressure encasement and the

fluid flows through a fixed guide mechanism onto

rotating both potential energy due to its pressure and

kinetic energy due to its motion, but the primary mover

is the pressure drop, which creates the reaction force.

34



11-3 Water Turbines

Impulse and reaction turbines are further divided into specific types of turbines:

• Fourneyron Turbine

• Francis Turbine

• Kaplan Turbine

• Pelton Turbine

• Turgo Turbine

• Crossflow water turbines

35



11-3 Water Turbines

Fourneyron turbine

The reaction turbine was built by Benoit Fourneyron; from 1827 onwards he designed the first water turbines with good efficiency. From 1834 to 1883 this turbine was used to drive the machines in a Black Forest cotton mill.

The turbine was connected to a pressure pipe with a 108 m head which gave it an unusually high speed.

The water flows in from above through a vessel. The distributor at the bottom of the vessel deflects the water outwardly into the runner.

36

http://www.deutsches-

museum.de/en/collections/machines/power-

engines/water-turbines/fourneyron-turbine-1834/



11-3 Water Turbines

Francis Turbine

The Francis turbine is the most widely used reaction turbine and is used in moderate-head, high-volume applications.

Water from behind a dam flows through the guide vanes on the side of the turbine, spins the runner, and exits through the bottom tailrace tube.

37

Runner for the Francis Turbine



11-3 Water Turbines

38

The Kaplan turbine is a propeller type reaction turbine used in low-head applications such as run-of-the river systems.



11-3 Water Turbines

A typical installation of Kaplan

Turbine:

• There is pressure on the

upstream side of the turbine

runner and suction on the

downstream side.

• On the outlet side of the

turbine is the draft tube, which connects the turbine

to the tailrace.

• The tailrace is the channel

leading away from the turbine.

39



11-3 Water Turbines

Pelton turbine

The runner has a number of cup-shape containers connected around its circumference.

40



11-3 Water Turbines

A cross-flow turbine is an impulse turbine used in smaller

hydro plants with relatively large flow. They can operate

effectively with a low head.

Source: OSSBERGER GmbH + Co.

41



11-3 Water Turbines

Reaction Turbines Impulse turbines

Fourneyron Pelton

Francis Turgo

Kaplan Crossflow

42



11-4 Tidal Power Generation

There is a huge amount of power in ocean tides, which move

primarily by the influence of the moon, so are quite predictable

and occur every 12 h and 25 min.

The moon’s gravity produces a tidal bulge on one side of the earth

and centrifugal force causes a second tidal bulge at the same

time on the opposite side.

43



When the sun, moon, and earth all align, a stronger gravitational pull occurs on the oceans, and higher and lower tides called spring tides are produced.

Spring tide: it occurs at new moon and again at full moon (twice a lunar month).

Neap tide: at first and third quarter, the net gravitational force of the sun and the moon is not as pronounced, so lesser tides than normal.

The currents associated with the tides depend on the particular location on earth.

Currents from tides can vary from 0 to over 2 m/s.

44




A few locations in the world can take advantage of a

natural estuary, harbor or river by trapping water

behind a barrage dam and taking advantage of the

inflowing and/or outflowing water to generate power.

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Po

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The Annapolis Tidal Power Station is located

in the Bay of Fundy and

is the only such station

in North America. It is

rated at 20 MW; power

varies depending on

the tides. It has been in operation since 1984.

45




The turbines at Annapolis Tidal Power Station use a

unique but older design called a Straflo turbine. It is

similar to a Kaplan turbine but with larger blades. The

Straflo is a rim generator, in which the rotor is attached

to the periphery of the blades of the runner. At the end

of the rotor rim is a water seal.

46




The energy in the water behind a barrage can be

calculated from considering gravitational potential energy. Recall that WPE is given by PEW mgh

Substituting rAh for mass, and using ½ the maximum

height of the tidal basin to account for average height,

we obtain: 21 1

2 2PEW Ah gh Aghr r

WPE is the energy stored in J

h is the maximum height of the vertical tide in m

A is the horizontal area of the barrage basin in m2

ρ is the density of seawater = 1025 kg/m3

(Fresh water density = 1000 kg/m3)g is the gravitational constant = 9.8 m/s2.

47



Example:

Determine the theoretical energy stored in a barrage if the height of the tide is 3 m in a barrage with an area of 300,000 m2.

Answer:

Density: 1025 kg/m3; A = 300,000 m2; h = 3 m

Wpe = ½ (1025 kg/m3)(300,000 m2)(9.8 m/s2)(3 m)^2

= 1.36 E10 J = 13,600 MJ

48

21 1

2 2PEW Ah gh Aghr r




Another method for generating power from the tides is

a tidal stream generator, which is anchored to the

bottom. The generator can generate power from

incoming (flood) or outgoing (ebb) tide.

49




A crossflow turbine is another form of tidal stream

generator with the advantage of moving in the same

direction regardless of the direction of the tidal currents.

The generator (in center) can generate power from

incoming (flood) or outgoing (ebb) tides.

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Advantages to tidal stream power include predictability and the generates are located under water – no visual impact and no sound. There are many sites around the world that can benefit from tidal stream generators.

Disadvantage:

• Initial expense

• Fish, seals, marine life

• Changing sediments

51



11-5 Wave Power Generation

Water waves are created by wind moving across

large stretches of water, creating waves that are a

combination of transverse and longitudal so

individual waves move in an elliptical pattern. some

definitions for waves are:

52




Energy converters are classified into three basic

types.

Point absorbers that have an upper and lower section that move relative to each other.

Attenuators that have relative motion between large floating sections.

Terminating devices that can trap the up and down motion to generate winds in a tube.

Source: NREL Source:Pelamis Wave Power Ltd.

53




54

Mass per unit length of a half of a sinusoid is:𝑚

𝑙=𝜌𝐴𝜆

𝜋Height of the center of gravity is:

ℎ =𝜋𝐴

8




The potential energy per unit length is 𝐸

𝑙=𝑚

𝑙𝑔Δℎ =

𝜌𝐴𝜆𝑔

𝜋

𝜋𝐴

4=1

4𝜌𝐴2𝜆𝑔

The wave’s kinetic energy is equal to its potential energy, so the total energy is:

𝐸

𝑙=𝜌𝐴2𝜆𝑔

2

The wavelength is related to its period:

𝜆 =𝑔𝑇2

2𝜋

Thus the wave energy is :𝐸

𝑙=𝐴2𝑔2𝜌𝑇2

4𝜋55




The power per unit length is given as:𝑃

𝑙=𝐴2𝑔2𝜌𝑇

4𝜋

Substituting A = H/2 into the above equation, giving𝑃

𝑙=𝐻2𝑔2𝜌𝑇

16𝜋

Substituting the values of density, gravitational constant, giving

𝑃

𝑙= 1.96 𝑘𝑊/(𝑚3/𝑠)𝐻2𝑇

56



Selected Key Terms

Attenuator

Francis turbine

Impulse turbine

Kaplan turbine

With respect to wave energy devices, it is a

device that extracts energy from wave power by

converting relative motion between large semi-

submerged cylindrical sections to electricity.

A reaction type water turbine that directs water from the outer circumference towards the center

of a runner. Water flows through a scroll case

which is a curved tube that diminishes in size with

a shape similar to a snail shell.

A reaction type water turbine that uses propellers

with adjustable blades. The turbine is usually

placed in a spiral casing called a volute.

A rotary engine that changes the direction of a

high velocity fluid, thus converting kinetic energy

into mechanical rotating energy.



Selected Key Terms

Oscillating water column

Pelton turbine

Point absorber

Reaction turbine

A fixed device for producing electrical power

from waves. It consists of a large tube that

extends over a cliff and into the ocean. Wave action causes water to rise in the tube and

displace air, which rotates a wind turbine.

An impulse turbine in which water moves under it

(impulse) rather than water falling over it. It is

among the most efficient types of water turbines.

A rotary engine that develops torque by reacting

to the pressure of a fluid moving through the

turbine, thus primarily converting potential energy

into mechanical rotating energy.

A floating wave energy converter that is in a

fixed in position. It bobs up and down from wave motion. The motion with respect to a fixed

reference is captured and the energy converted

to electricity.



Selected Key Terms

Run-of-the-river (ROR)

Tidal barrage system

Tidal stream generator (TSG)

A hydroelectric system that uses river flow to

generate electricity. The system may include a

small dam with storage for water but many do not.

A system designed to convert tidal power into

electricity by trapping water behind a dam,

called a tidal barrage dam, and generating

power from the inflow and/or the release of

water.

An electrical generating system that uses a water

turbine to turn a generator and produce

electrical power when a stream of water caused

by tides or a river flow past it.



true/false quiz

1. In the equation, P = Qvheq, the

stands for the volumetric flow rate.



true/false quiz

2. The potential energy in water behind

a dam is converted to kinetic energy

to spin a turbine and generator.



true/false quiz

3. Run-of-the-River systems primarily use

the kinetic energy in flowing rivers to

generate electricity.



true/false quiz

4. Impulse turbines are primarily used in

applications with low heads and

relatively high flow rates.



true/false quiz

5. The turbine pictured

here is a Kaplan

turbine.



true/false quiz

6. A cross-flow turbine can work in low

head hydro plants or in tidal streams.



true/false quiz

7. The tides are primarily caused by the

gravitational pull of the sun on the

earth.



true/false quiz

8. A barrage dam is used to trap tidal

waters and use the flow to generate

electricity.



true/false quiz

9. The vertical distance from the trough

of a wave to the crest is called the

amplitude.



true/false quiz

10. One type of wave energy converter

is called an attenuator.



true/false quiz

Answers:

1.F

2.T

3.T

4.F

5.F

6.T

7.F

8.T

9.F

10. T



Multiple Choice Quiz

1. Water stored behind a hydroelectric dam is an example of

A. Kinetic energy

B. Potential energy

C. Electrical energy

D. All of these

71



2. A good turbine for a ROR system is:

A. Pelton

B. Kaplan

C. Crossflow

D. Francis

72



3. The unit for torque in the SI system is the

A. kilogram-meter

B. Kilogram-meter/second

C. Newton

D. Newton-meter

73



4. A pumped storage system has

A. A single reservoir that allows water to flow through a penstock to turn a turbine

B. Two reservoirs; water is pumped from the lower one to the higher one during low usage times

C. Two reservoirs; power is generated when pumped from the lower one to the higher one

D. A single reservoir that has its water pumped past a turbine, which turns a generator

74



5. An oscillating water column uses

A. A tube or chamber and waves that cause air to compress and flow past a turbine blade that rotates and turns a generator

B. Water from a reservoir to flow through a penstock and turn a turbine and generator

C. Hydraulic cylinders to pump oil through hydraulic motors to turn generators

D. A barrage to produce electrical power

75



6. Total equivalent head includes

A. Head due to elevation

B. Pressure equivalent head

C. Kinetic energy equivalent head

D. All of the above

76



1. B

2. B

3. D

4. B

5. A

6. D

77



Example:

A small river, 40 m wide and 6 m deep, flows at a velocity of 2 m/s. If 20% of the flow of the river is diverted through a run-of-the river hydroelectric system that generates electricity at an efficiency of 90%, what is the output in power?

Answer:

Q = 2 m/s * 40 m * 6 m = 480 m3/s

20% Q = 96 m3/s

P = ½ (m/t)v2 = ½ (ρQ)v2 = ½ (1000 kg/m3 * 96 m3/s) * (2m/s)^2 = 192,000 W

90% efficiency considered, the output is 173 kW 78



Example:

What is the equivalent head if the velocity of a river is 3 m/s?

Answer:

hke = v2/2g = (3 m/s)^2 / 2 / 9.8 m/s2 = 0.45 m

79



Example:

What is power generated if the elevation head of a dam is 20 m, the velocity of the flow in reservoir is 4 m/s, the sectional area is 600 m2, and the efficiency of power generation is 85% ?

Answer:

h = 20 m; hke = v2/2g = (4 m/s)^2 / 2 / 9.8 m/s2 = 0.816 m

heq = 20+0.816 = 20.816 m

P = (1000 kg /m3) * (9.8 m/s2) * (4 m/s) * (600 m2) * 20.816 m * 85% = 416 MW

80

Lecture 7 2015-2016

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Transcript of Lecture 7 2015-2016