pumped energy storage system for the randenigala...

Master of Science Thesis

KTH School of Industrial Engineering and Management

Energy Technology TRITA-ITM-EX 2018:161

Division of Heat & Power

SE-100 44 STOCKHOLM

Pumped Energy Storage System

for the Randenigala

Hydropower Plant in Sri Lanka

Duminda Nalin Habakkala Hewage

Master of Science Thesis in Energy Technology

TRITA-ITM-EX 2018:161

Pumped Energy Storage System

for the Randenigala Hydropower Plant

in Sri Lanka

Duminda Nalin Habakkala Hewage

Approved

2018-06-26

Examiner

Miroslav Petrov - KTH/ITM/EGI

Supervisors at KTH

Amir Vadiee, Miroslav Petrov

Commissioner

Open University of Sri Lanka

Local Supervisor

Dr. K.A.C. Udayakumar

Abstract

The main focus of this thesis work is to perform a preliminary evaluation for the introduction of a

pumped energy storage system to an existing hydropower plant located on the Randenigala water

reservoir in Sri Lanka. The selected power plant is located in an area where farming is done

extensively, therefore electrical power generation and release of water for downstream irrigation

purposes is to be properly coordinated with relevant authorities. The solution to this situation is to

introduce a wind powered pumped energy storage power plant to the Mahaweli hydro cascade for

the purpose of saving peak power for around half an hour. A feasibility study was carried out on

the utilization of wind energy and excess power to drive the motors of the pumped storage system.

Three versions with different numbers of pump motors and wind turbines have been considered

to meet the half hour peak demand of the energy storage system. The optimum number of turbines

and motor capacities and their number and brand have been selected with view of both energy and

water management system.

Finally, the selected system case has been compared with the function of pumped hydro storage

using excess power from the national electricity grid, in view of the expected expansion of new

coal-fired power plants in Sri Lanka in the near future, where the existing hydropower will need to

take the role of a system balancing factor.

The annual savings to the Ceylon Electricity Board using the optimum pumped hydro

configuration were found to be Rs. 55 million per year (euro ~300’000 as of 2018).

SAMMANFATTNING

Detta examensarbete fokuserar på den preliminära utvärderingen av en möjlig omvandling av det

existerande vattenkraftverket vid fördämningen Randenigala i centrala Sri Lanka till en

energilagringsanläggning genom att pumpa upp vatten från sjön nedströms och använda det till

att lindra toppbelastningen i landets elenergisystem under de vardagliga kvällstopparna.

En rak utvidgning av vattenkraften är omöjlig eftersom områdets vattenavrinning inte räcker till

ny kraftkapacitet, samtidigt som nästan allt vatten används nedströms till storskalig bevattning av

lantbruket som i sin tur styr mängden vatten som kan släppas ut från alla sjöarna i hela Mahaweli

vattensystemet.

De föreslagna lösningarna inkluderar en vindkraftpark som kopplas direkt till pumpanläggningen;

samt ett annat alternativ där överskottsel från den framtida expanderingen av nya kolkraftverk i

Sri Lanka matas in så att vattenkraften får en fullvärdig balansrol i landets elkraftsystem.

Storleken och anordningen av den föreslagna pumpanläggningen inklusive alla huvudsakliga

komponenter och själva vindturbinerna med kopplingar emellan har beräknats och valts.

Flera möjliga anordningar för pumpanläggningen och kraftinmatningen har utvärderats och

jämförts tekniskt och ekonomiskt, där en halvtimme av elsystemets toppbelastning på kvällen kan

kapas och levereras av vattenkraften istället för de nuvarande diesel-eldade gasturbiner och

kolvmotorer som används som toppkraftaggregat i landet. Den ekonomiska effekten beräknades

till en årlig besparing på upp till 55 miljoner Rs (Sri Lankan rupee) för det mest optimala

konfigurationen, som är lika med ca 3 miljoner svenska kronor om året (referensår 2018).

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Table of Contents

Abstract

List of figures

List of tables

Nomenclature

Acknowledgement 8

1 Introduction 9

2 Problem Formulation and Objective 12

3 Methodology 13

4 Literature Review 15

4.1 15

4.2 18

4.3 18

4.4 22

4.5

Application of pumped hydro storage power plant

Wind Powered Pumped Storage System

Power Generation Expansion Planning of Sri Lanka

Power Station and Reservoirs of Mahaweli complex

Wind Data in Sri Lanka 23

5 Analysing and Calculation 25

5.1 25

5.2 27

5.3 29

5.4 34

5.5 39

5.6 41

5.7

Analysis Peak Saving Methods

Analysis and Selection of Centrifugal Pumps

Analysis of Wind Turbine data Characteristic

Different Options to Wind Turbine with the Pumped Storage Plant

Designing Water Flow Distribution System

Use Excess Power to Drive Water Pump

Economic Feasibility Analysis of Pump Storage System 44

6 Results and Discussion 49

7 Conclusion 55

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List of Figures

Figure 1, Arrangement of Mahaweli Scheme River Basing

Figure 2, Geographical Area of Ransenigala & Rantambe Reservoir

Figure 3, Typical Arrangement of Pumped Storage with Wind Turbine

Figure 4, Pumped Storage System

Figure 5, Sea Water Pumped Storage System

Figure 6, Compositions of the Capacity Additions in Next 15 Years

Figure 7, Starts-up Duration of Plants

Figure 8, Power System Load Profile of Sri Lanka

Figure 9, Map of Central Province which is Ambewela and Randenigala Site

Figure 10, Monthly Wind Pattern in Ambewela Area

Figure 11, Randenigala Reservoir Area

Figure 12, Vertical Profile of Wind Profile by Web Based Software

Figure 13, Weibull Wind Speed Distribution for Randenigala Area

Figure 14, Result from power Calculator with 3MW Vestas V112 at Randenigala Site

Figure 15, Single Wind Turbine with Single Water Pump

Figure 16, Two Wind Turbines with Water Pump

Figure 17, Three Wind Turbines with Two Water Pumps

Figure 18, Change Load Profile over Years of Sri Lanka

Figure 19, Energy Mix over Next Years in Sri Lanka

Figure 20, Wind Speed & Rainfall Profile of Randenigala Area

Figure 21, Design Arrangement of Pumped Storage System

Figure 22, Cumulative Capacity by Plant type with Peak Power Variation

Figure 23, Normal Daily Load Curve of Sri Lanka Power System 50

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List of Tables

Table 1, Required Capacity Plant Type 19

Table 2, Capacity Additions by Plant Type 20

Table 3, Wind Speed and Rainfall in Randenigala Area - Year 2013 24

Table 4, Matching Wind Turbines 33

Table 5, Summary of Wind Turbines Data 38

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Nomenclature

Appellation Sign Unit

Acceleration due to gravity g m/s2

Head of pumped water H m

Pressure drop of Pipe Hf m

Length of a pipe L m

Efficiency η %

Efficiency of the pump ηpump %

Density of water ρ kg/m3

The hydraulic power needed to pump water Phdy kW

The power needed to pump water Ppump kW

The power at the shaft connected to the pump Pshaft kW

The average power which one wind turbine can produce Pave.turbine kW

Wind speed V m/s

Dynamic viscosity of the fluid µ kg/s m

Diameter of a pipe D m2

Velocity of water in pipe U m/s

Flow rate of a water Q m3/s

The area swept by the blades of a three bladed wind turbine A m2

Weibull Shape Factor, part of the Weibull equation k

Friction factor f

Reynolds number Re

Revelation per Minute RPM

Ceylon Electricity Board CEB

Long Term Generation Expansion Plan LTGEP

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Acknowledgements

I take this opportunity to thank all colleagues who gave their helping hands for the success

of this thesis. Without such cooperation I would not have achieved this goal.

Furthermore, my special thanks go to the project supervisors Mr. Miroslav Petrov and Dr.

KAC Udayakumar who guided me from the beginning to the end for the successfully

completion of this thesis.

Further, I would like to give my thanks to Eng. Ruchira Abeyweera who did the co-

supervision and giving me various instructions while carrying out this project.

Let me take this opportunity to thank all staff in the transmission and generation planning

branch of Ceylon Electricity Board, Department of Meteorology in climate change studies

and Sustainable Energy Authority of Sri Lanka.

HHD Nalin

January, 2016

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1. Introduction

One of the main problems of the load curve of the developing countries like Sri Lanka is that

it has a poor load factor. The reason for this is that mainly the domestic consumers dominate

the load curve. This means the country needs to generate electrical power which is utilized

fully only for very few hours. As a result cost per unit of generation is high. One of the ways

o solving this problem is “peak saving method” use of pump storage power plant is one of

the options to solve this problem. The pump storage plant develop the power during the peak

demand by release water from upper reservoir to the lower. During off peak time water is

pump back to the upper reservoir by consuming power from the grid.

In Sri Lanka pumped storage plants do not exist at present. The present project is to

investigate the possibility of utilizing one of the hydropower plants as pumped storage plant.

What is new in this work is to use pumped storage system with energy produced by the wind

turbines is use to drive the pump in the water from lower reservoir to upper reservoir.

The main source of electricity in Sri Lanka is based on hydro power generation. As at today

the hydro power alone cannot meet the electricity demand of the country. It is

required to find alternative technologies of electricity in Sri Lanka.

In this study, a power plant operated under the Mahaweli river project was selected. Water

in the Mahaweli complex is meant for two purposes: irrigation and electricity

generation. Today, the Mahaweli complex water utilization system gives maximum

benefits to Sri Lanka, that is mainly with respect to irrigation and ecological system, socially

& economically and electricity power generation.

The primary objective was Mahaweli complex to provide water for irrigation purposes. The

use of water to produce electricity is the second priority. Mahaweli Authority and Ceylon

Electricity Board jointly decide the water utilization of this reservoir’s in manner that both

parties benefit ultimate giving the maximum benefit to Sri Lanka.

In considering Mahaweli scheme that is first reservoir Kotmale. It has three turbines and

generation capacity of each unit 67MW. Output water release after power generation water

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flow along the river to a small pond of Polgolla. Polgolla barrage water is divided to North

Central Province for irrigation purposes. Remain water flow is carryout long tunnel to use to

operate two 20MW drive the turbine in Ukuwela power station. Then releasing water use to

operating two turbine units of Bowatenna power station. It is generation capacity 40MW and

output water release to Anuradapura district for use to irrigation system.

In rainy seasons Polgolla pond over spill and water flow divert along the Mahaweli River to

Victoria reservoir. Victoria power station has 3x70MW turbine unit at operation water use

from Victoria reservoir. Then water release after operation at Victoria power station, water

flow divert to Randenigala reservoir. It is largest reservoir in Mahaweli scheme. Randenigala

power station capacity is 2x62MW and Radenigala power station output water release to

Rantambe reservoir. The Rantambe reservoir is small pond and can be regulated. Rantambe

pond water is use to operate 25MW capacity, two turbine at Rantambe power station. Output

water from Rantambe power station is divert to Minipe annicut. This water is distribute to

through right bank and left bank of Minipe canals to be use for irrigation system.

The water management system of the Mahaweli scheme is given in Appendix A.

Cascade system of the Mahaweli scheme is given in figures 1 & 2 .

Source: CEB website

Figure 1 – Arrangement of Mahaweli Scheme River Basin

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Source: Google website

Figure 2 – Geographical Area of Randenigala & Rantambe Reservoir

Pumped storage power plant is storing energy at electricity demand of off peak time and

energy release quickly at electricity demand of peak time. Country electricity demand

changes throughout the day. Generally, peak demand of the system load curve occurs

between 7:00pm and 8.30pm.

Therefore, the peak load is usually met by the hydro power plants. There can be instances in

which the hydro power plants are not capable of meeting the total demand during peak

periods. This is significant especially during the dry seasons in such instances to keep the

power balance there can be load shading. The coal power electricity generation plant not

suitable use to meet peak demand because it can’t be start up and pick up loads quickly. This

plant most suitable use to base load operation.

The pumped storage power plant gives opportunity to produce electricity without releasing

water to the downstream. This is important during the period when is not required for the

irrigation purposes.

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2. Problem Formulation and Objective

Aim;

Introduce a wind powered pumped power plant to the Mahaweli scheme for the purpose of

peak saving. If coal is used as base load then no excess power during off peak.

Objective;

The main objective of this thesis was to do a feasibility analysis and design of a pumped

storage system to be located at a Randenigala hydropower plant in Mahaweli complex area of

Sri Lanka.

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3. Methodology

Analysis of wind turbine parameters, water pump parameters and observe existing hydro

plant data then applying different mathematical solution to propose the best system. The

optimum pump storage system will be selected out of two options as of below:

Option - 1

To use pumped storage system which electrical energy produced by the wind turbines and

produced energy use to drive the water pumps in the pumping station as shown in given

below figure 3.

Figure 3 – Typical Arrangement of Pumped Storage with Wind Turbine

Option – 2

To use the excess grid power to pump the water in pumped storage power plants. In near

future large capacity coal power plant will cover the base load and intermediate load in

Sri Lanka. Hence, in the off-peak time, the associated coal power plant can provide energy

for water pumping which will store water from lower reservoir at Rantambe to

Randenigala upper reservoir.

For this purpose use the application software package of Microsoft Excel for create graph and

calculation part, software package of Windenergie – Datender Schweiz.htm for selection of

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wind turbine and software package of ITT industries or Goulds pump selection system for

selection of centrifugal water pump.

Methodology graphically can be illustrated as,

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4. Literature Review

4.1 Application of pumped hydro storage power plant

Pumped storage power plant is storing energy at electricity demand of off peak time and

energy release quickly at electricity demand of peak time. This type of plant used by some

power plants for load balancing. Method of energy storage system is water pumped from a

lower level reservoir to higher level reservoir. It use low cost off peak electricity power for

drive water pumps. So, during period of high electricity demand, upper reservoir storage

water release through turbines and generation electricity. Low electricity demand time use

excess power generation capacity to pump water in to higher level reservoir.

Globally, use reversible turbine for pure pump storage power plant which is water between

reservoirs combined pump storage plant generate their own electricity power like

conventional hydroelectric plant through natural water flow.

Evaporation losses of expose water surface and conversion losses is approximately 70% -

85% of electricity energy use to pump the water in to the elevated reservoir. This technique is

currently most cost wise effective of storing large amount of electricity energy on operation

basis. But capital cost and appropriate geography are critical decision factors.

Relatively low energy density of pump storage system is required either very large body of

water and large variation in height. Example 1,000kilograms of water or one cubic meter of

water at the top of 100meter tower has potential energy of about 272Wh.

Pump storage system is most be economical because it flattens out load variation on the

electricity power grid. Thermal power plant such as coal power plant, combine cycle power

plant and nuclear power plant and some of suitable renewable energy power plant can be

provide base load electricity demand to continue operating at peak time. At the movement, in

electricity system use for peaking time power plant that unit cost very high. But pumped

storage power plant capital cost is high.

When considered energy management system, pump storage pant system help to load flow

control in electricity network frequency and provide reserve power generation.

Load flow system of electricity generation and transmission system, thermal plant are much

less able to response to sudden changes of electricity demand because causing frequency

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and voltage instability. Considering of hydroelectric power plant and pump storage plant cab

be quick respond with power system load changes within few seconds.

The working principle of pump storage plant is shown given below in figure 4 and currently

operated Okinawa sea water pump storage power plant in shown given below in figure 5.


Figure 4 – Pumped Storage System


Figure 5 – Sea Water Pumped Storage System

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Number of countries of the world utilizes pumped storage plants. One of the biggest stations

is power station at Dinorwig UK with the capacity of 1,800MW. The plant can supply about

1,320MW in twelve seconds. A small pumped storage plant can also be useful and one of the

smallest one is in Germany with a capacity of about 0.5MW.

Globally interest in building pump storage power plant is to reach the peak electricity demand

become more popular. This will probably be more important in the future when countries

need to balance and guarantee the reliability of electricity production because of increasing

installation of unpredictable or irregular energy resources that wind power plant and solar

power generation plant. Pump storage power stations supply high value electricity power

during peak hours to the electricity grid.

Pumped storage stations use low price electricity when the grid power demand is low in

pump the water from low level reservoir to high level reservoir. As in pump hydropower

plant energy use to store the water during full time. Power is the excess only use this energy

during power is required. These types of power plants can be considered under energy

storage devices. This method of energy storage is in fact to store electricity as

potential energy.

A pumped storage station is needed for a hydropower plants station where water shortage can

occur or generation and consumption of not absolutely synchronous. In all electricity

networks there is a surplus or lack of electricity. A pumped storage power station can control

and guarantee a safe operation in the electricity grid.

In a classical pumped storage power station design the turbines and the pumps are separate

units. This has many advantages like better efficiency of the pumps when operated at full

capacity using low cost surplus power.

Several advantages can be achieved that wind power park combined with pump storage plant

system. The majority of wind parks combined with pumped storage systems are both

connected to the electricity grid and generated electricity use to water pump to high level

reservoir.

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Electricity generated by wind turbine and use to during low consumption time to pump water

to high level reservoir. It is water release again when there is the need to produce energy at

peak times in the electricity network. At high electricity demand time and wind power not

available time can be use storage water in upper level reservoir is utilized. At locations where

variable tariff is applied there is the possibility to achieve significant economic benefits by

design on optimum turbine and centrifugal pump.

4.2 Wind Powered Pumped Storage System

Mechanism of wind turbine is convert kinetic energy of wind to mechanical energy then

converts to electrical energy. Today, wind turbines have highest efficiency, and they are

reliable. More reliable supply of electricity can be achieved by combining one or more wind

turbines with pumped storage power station.

At locations selection is pump storage station in place where, wind strength is sufficient for a

wind farm installation. The wind farms electricity generations is used for both the pumped

and the electricity grid. Example of wind power pump storage system installation is Gran

Canaria Island. The installation in wind power pump hydro storage system is increase

reliability of the electricity produced and utilization of wind power energy is connected to

national electricity grid. In that system is promote clean energy, green energy and renewable

energy.

The wind turbines are installed to generate the power for the pumps in a pumped storage

power station. One possibility of connection is a direct connection of shaft with the rotor of

the motor. This is called a wind-pump. This technology is mostly used today to pump water

from underground wells in rural areas for agricultures purpose and multi-bladed wind

turbines are used in this method.

4.3 Power Generation Expansion Planning of Sri Lanka

According to the Ceylon Electricity Board, electricity power generation and transmission

design plan estimate required capacity according to base case are given below table 1.

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Year

Hydro

Addition

Thermal

Addition

Thermal

Retirements

2009 -

2×90MW GT part Kerawalapitiya CCY

plant -

2010 -

20×10MW Midium Diesel 2×135MW

kerawalapitiya CCY plant

2×90 MW GT part

Kerawalapitiya CCY

plant

2011

150MW

Upper

Kothmale

2×75MW Gas Turbine

1× 35 MW Gas turbine

5×17MW Gas turbine

Kalanitissa

2012 - 1×285MW Puttalam Coal (Stage 1)

20MW ACE pwer

Matara

2013 -

1×285MW Puttalam Coal (Stage 2)

2×250MW Trinco Coal (Stage 1)

22.5MW Lakdanawi

Plant 4×18MW,

Diesel Plant

20Mw ACE Power

2014 - 1×285 MW Puttalam Coal (Stage 3) -

2015 - 2x250MW trinco coal stage – 2 and

1x300MW coal steam at east coast 2

60MW Colombo,

100MW Diesel ,

100MW ACE

2016 - 1×300MW coal steam – east coast -2 -

2017 - 1×300MW coal steam – east coast -2 -

2018 - 1×300MW coal steam – east coast - 2 115 MW Gas Turbine

7 at KPS 49 MW

Asia Power plant

2019 - 1×300MW Coal Steam (West Coast 2) -

2020 - 1×300MW Coal Steam (West Coast )

2×10 MW Medium

Diesel

2021 - 1×500MW Interconnection -

Source: CEB, LTGEP Report

Table 1- Required Capacity Plant Type

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In the planning process, base case plan is identified and the sensitivity of the base case

parameters is evaluated subsequently. The required power capacity of additional, according to

base case are given above table 1.

Power capacity additional by plant type are summarized for 5 year period show in table 2.

Capacity show in graphically below in figure 6.

Type of Plant 2007-2011 2012-2016 2017-2021 Total additional capacity

MW MW MW MW %

Hydro 150 - - 150 3.1

Combined

Cycle

315 - - 315 6.6

Coal - 2,455 1,200 3,655 76

Gas Turbines 185 - 185 3.9

Interconnection 500 500 10.4

Total 650 2,455 1,700 4,805 100


Table 2 Capacity Additions by Plant Type


Figure 6 – Compositions of the Capacity Additions in Next 15 Years

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5 days

4 hours

1 hours

3 hours

3 - 5 minutes

0 1 2 3 4 5

Nuclear

C oal

G as C / C

Oil

Hydro

The majority of share from total new capacity (76%) is coal base power plants. Therefore,

coal power plant will play an important role in the supply of archive to future electricity of

country in Sri Lanka. At the movement, according to the CEB – LTGP, government is going

to introduce the huge coal power in to the Sri Lankan power system after year 2011. After

completion of coal power stations, studies to pumped storage power stations can play a key

role in generation perspectives. Cheap coal plants will be use to drive centrifugal pump

during off peak time and most of the used energy will be recovered during night peak hours.

At the moment, country electricity load curve is not flat curve that should be excess power

due to coal power plants. Country electricity power demand has change throughout the day.

Example, use day to day electricity demand for TV, Kitchen, lighting and other purpose on

case on sudden peak in demand. Currently, power station do not generate more electrical

power in immediately. Therefor there will be power load shedding around the country and all

sort of other trouble will occurs. Now, main problem in our country is most of electricity

power generation by fossil fuel power plant. That take half an hour or crank themselves up to

full power and also generally at high peak of load curve is worked out between 7.30pm and

8.30pm.

So, there is possible to install pump storage power plant due to availability of the excess

capacity than base load in Sri Lanka power system after year 2015 using excess coal power.

The daily load curve in Sri Lanka has two peaks. Day time peak at around 11.00am due to

industrial demand and night time peak at 7.30pm – 8.30pm caused mainly by using

household. Therefore, according to the electricity supply of Sri Lanka the way of supplying

electricity on night peak time based on thermal power plant. Available power sources in Sri

Lanka and it is starts up duration are summarized in graphically shown in figure 7.

Source: CEB system control

Figure 7 – Starts-up Duration of Plants

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4.4 Power Station and Reservoirs of Mahaweli complex

Mahaweli scheme have been six major hydropower station and total electricity capacity is

660MWs. Therefore, contribute around 13% electricity energy to Sri Lanka annually. So,

major hydropower station under Mahaweli scheme are Kothmale, Victoria, Randenigala,

Rantambe, Ukuwela, Bowatenna and Nilambe. Total area of covering in Mahaweli basin is

1,268sqkm. Capacity of each hydropower plant are Kothmale-67x3MW, Victoria -70x3MW,

Randenigala-61x2MW, Rantambe -24.5x2MW, Ukuwela-20x2MW. Bowatenna-40x1MW

and Nilambe-1.66x2MW.

Largest reservoirs in Sri Lanka are located in the Mahaweli River forming a cascade. Most

upstream reservoir is the Kothmale Reservoir. Downstream of this Polgolla diversion is

located. The Victoria reservoir is the next reservoir in the cascade and downstream of this,

Randenigala reservoir is located. A run-of-river generation Rantambe dam is the next and last

dam of the cascade.

Randenigala reservoir is the largest reservoir in Sri Lanka holding more than 860mcm. The

reservoir is centrally important to the country because of its storage for irrigation water, space

for flood control and power generation. The irrigation area extends to the Eastern plains of the

country. Just below the Randenigala dam a run of the river power plant called Rantambe is

situated. About 4km downstream of this Minipe diversion weir is located. This diversion

takes water to irrigate both left bank and right bank of the river. Further down the river is the

Mahiyangana Township which is the largest inland town in the Eastern part of the country.

The town is the social, economic and agricultural hub coordinating and providing for all

needs of the agriculture community of the irrigated lands.

Rantambe Reservoir is the last reservoir in Mahaweli cascade system. It has a low capacity of

less than 11.2mcm. Regulating the discharge is done by upstream Randenigala reservoir and

this dam serves as run-of-the river type power generation after picking up the discharge from

Uma-Oya River. The reservoir is centrally important to the country because of its power

generation and its location upstream of the Mahiyangana city that attracts pilgrims. About

4km downstream of this dam, Minipe diversion weir is located. This diversion takes water to

irrigate both left bank and right bank of the river. The irrigation area extends to the Eastern

plains of the country. Further down the river is the Mahiyangana Township which is the

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largest inland town in the eastern part of Sri Lanka. The town is the social, economic and

agricultural hub coordinating and providing for all needs of the agriculture community of the

irrigated lands.

4.5 Wind Data in Sri Lanka

CEB revealed that wind power is most promising one option from country available

renewable source for electric power generation. In CEB pre electrification unit curried out

resource asses management unit study of solar power and wind potential in year 1992. This

study has cover overall wind potential of 8MWper sqkm in open land area. Wind power has

overall potential in approximately 200MW in south eastern quarter of country.

CEB has been commission in pilot scale 3MW wind power plant located in southeast of

the country at Hambantota area in year 1999. That plant yearly operated at capacity factor

of 10.1% while in year 2010 capacity factor was 11.4%.

Also, through energy resource assessment unit of CEB has been studied in Puttalam area and

Central region area carried out by year 2002. It has produce encouraging result on wind

power energy potential in both areas.

By National Renewable Energy Laboratory of Sri Lanka has wind mapping study in year

2004. That is conform Sri Lanka has many area estimated have good wind resources. Most of

resource tend to be locate in North western coastal region from Kalpitiya area to Mannar

Island in Jaffna peninsula and central highlands areas. Also, NREL in Sri Lanka has estimate

suggest that nearly 5,000sqkm of wind power resource potential. It is recommended

additional study to assess practical resource by accounting for the transmission grid

accessibility.

Renewable energy resource development unit of Sri Lanka Sustainable Energy Authority is

identified district wise distribution of gross availability of different type renewable energy

resources in year 2012.

I study of wind energy resource assessment perform a feasibility study of potential wind

speed for an Abewela location.

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The given wind data base has been based on the average value from several years and given

per 10minut basis over the whole year. The required wind capacity is given in below table 3.

Month

Wind Speed Rainfall

Maximum wind speed

(m/s)

Average wind speed

(m/s)

Average

rainfall

Jan 9.87 3.94 117.9

Feb 11.25 4.09 167.6

Mar 9.09 3.74 30.0

Apr 7.68 3.03 127.9

May 18.19 8.42 1.5

Jun 23.05 14.69 0.0

Jul 23.54 11.31 38.5

Aug 22.55 12.33 4.9

Sep 25.51 9.04 31.7

Oct 24.09 7.92 263.8

Nov 17.71 4.41 193.0

Dec 18.68 4.35 569.3

Mean 17.60 7.27 128.84

Source: Weather Department of Sri Lanka

Table 3 - Wind Speed and Rainfall in Randenigala Area - Year 2013

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5. Analyzing and Calculation

5.1 Analysis Peak Saving Methods

Both industrial and commercial load in Sri Lanka still is low and electricity consume by

domestic is greater. Therefore, country electricity power system load profile has poor load

factor. It is not stable and flat curve. The reason for this is that mainly the domestic

consumers dominate the evening peak and industrial and commercial load effected day

time in the system load as shown in figure 8.

Source: CEB system control

Figure 8 - Power System Load Profile of Sri Lanka [1]

According to electricity power system load profile is electricity power demand variation

throughout the day. Sri Lanka is developing country. Therefore a requirement of electrical

power usage in industrial sector is lower than the domestics sector. In generally cat high peak

of load curve is worked out between 6.00pm and 8.30pm. This period huge number of

domestic people use electrical power to domestic appliances. That case of a system

demand is suddenly peak up and the power stations does not more electric power generate

in immediately. Therefore, sometimes electric power load shedding is applied around

the country in order to prevent blackout when demand exceeds generation.

26

Electricity generation by fossil fuel power plant like that gas turbine power plant and

diesel power plant which take a short time (minutes) to crank themselves up to full power.

This project is not targeting full peak power saving but rather peak power saving of around

half hour or until the thermal power stations catch up. According to appendix B, if consider

evening time in between 6.30pm to 7.00pm of peak power saving for around half an hour and

selected 100MW on system load side, then calculate required average energy of

between times 6.30pm to 7.00pm.

According to the above analysis to required time of peak demand saving power time ½ hours.

This short period time required energy to manage the time of peak demand as given below.

From system load details of figure 4 and Appendix B,

Required peak power saving energy = 100/2=50MWh =50,000kWh

From Randenigala hydro power plant load details of Appendix C,

Power plant capacity of one unit

Full loading power of one unit for ½ hours

Spinning reserve loading plant capacity

Power output of spinning reserve load

Both unit power output of 82% load

= 62MW

= 62x0.5 = 31MWh = 31,000Wh =

82%

= 31x0.82 = 25MWh = 25,000kWh

= 25x2 = 50,000kWh

Required peak power saving energy = Energy releasing for half an hour of unit-1&2

According to the above analysis to required water management for ½ hour time is given

below,

From Randenigala hydro power plant water released data of Appendix C,

= 90m3/s = 324,000m3/h

= 648,000m3/h

= 324,000m3/h

Capacity of output water in one unit at full load

Capacity of output water in two unit at full load

Output water capacity of both units at ½ hours

Output water capacity of two units at 82% load = 265,680m3/h

27

From water pump capacity data of Appendix D,

Maximum output water capacity of one pump = 1.83m3/s

Output water capacity of one pump at 24hours full load = 1.83m3/s = 158,112m3/h

Both pump output capacity at 24hours full load = 316,224m3/h

Pumping water capacity at 24 hours >Required water for peak power saving at ½ hour

5.2 Analysis and Selection of Centrifugal Pumps

Centrifugal pumps are most popular type of pumps due to durability, versatility and

simplicity. Pump efficiency is measured by how much of the power input to the shaft is

converted to useful water pumping by the pump. It is therefore not fixed for a centrifugal

pump because it is a function of the discharge and therefore also the operating head and the

frequency.

The pump will be connected with a shaft to gearbox and motor. One of many producers of

pumps is the Goulds pumps corporation. The Goulds model 3175 centrifugal pump is shown

in Appendix D. The ideal power used to pump water by a pump in watts often

called hydraulic power is as follows;

Phyd = ρ x g x H x Q (3.1)

In equation 3.1 [7], Phyd – hydraulic power, ρ – density of fluid (water – 1,000kg/m3), g –

gravitational constant (9.81m/s2), H – head of pump water (m) and Q – flow rate (m3/s).

In the market have Goulds pump, can pump maximum 1.83m3/s of water up to the height of

40m. This information is given in the total head and capacity graph and the Goulds software

in Appendix D. This pump was selected, because all necessary information about the pump

was available. The graph shows that a 20x24-28H Goulds pump at the height of 40m, can

pump about 29,000GPM. This is equal to 1.83m3/s. The power calculated to operate the

28

pump with a flow rate of 1.83m3/s and the head equal to 40m is now calculated with equation

3.1;

Phyd = 1000x9.81x40x1.83 = 718kW

To pump 1.83m3/s of water up to a height of 40m and a minimum power of 718kW is needed.

Because the pump is not an ideal machine and have loses. The pump power is divided by the

pumps efficiency and the shaft power is as follows;

P shaft= Ppump/ η pump (3.2)

In equation 3.2 [7] Pshaft is the power at the shaft where it connects to the pump, Ppump is the

power required to pump water and ηpump is the efficiency of the pump.

The pump manufacturers information and calculated from the Goulds software shown in

Appendix D. States that the pump power at 890RPM is 990kW and the efficiency is 73%.

The efficiency of the pump can also e calculated with the equation 3.2;

η pump = useful work output/power input

η pump = 718kW/990kW = 0.73 or 73%

The calculated pump efficiency is 0.73 or 73%.

Total hydraulic power required to drive the pump when pumping 1.83m3/s of water up to a

height of 40m and pump efficiency is 73%. Shaft power can be calculated with equation 3.2;

P shaft= Ppump/ η pump = (1000x9.81x40x1.83)/0.73 = 984kW

Analysis and selection of most suitable water pump depend on the according to electricity

system daily load profile, Randenigala dam and Rantabe reservoir water level data and

available market hydraulic pump data. Therefore In this thesis can be selected and uses

Goulds centrifugal pump type 3175XL water pump is total power at the shaft needed to pump

1.83m3/s of water up to height of 40m with pumps is about 1,000kW.

29

5.3 Analysis of Wind Turbine data Characteristic

Central Province was selected as the candidate area because of Randenigala dam site region

and the good wind potential and the measured availability wind data by wind energy resource

assessment in central regions of Sri Lanka which was conducted by sustainable energy

authority.

According to the Sustainable Energy Authority of Sri Lanka, collected and available wind

data has only Abewela area. Wind data in Randenigala has almost same in Abewela data due

to geographically small distance and same province as shown in figure 9.


Figure 9 – Map of Central Province which is Ambewela and Randenigala Site

Monitoring and available wind data has locations in the Central Province which is given by

the Ambewela area. So, the detailed is considered for analysis Ambewela area.

Available site wind data of Ambewela area and location in the elevation is about 1,800 above

MSL. According to study of wind data overall wind flow in generally monsoon climate tine

in Sri Lanka. That is characterized by south west monsoon period – May to September and

north east monsoon period – December to February. Mean monthly wind speed pattern in

Ambewela area as shown in figure 10 and Appendix G. Therefore, annual average wind flow

speed in Ambewela area is 7.27m/s. it is measuring height is 40m.

30

Figure 10 – Monthly Wind Pattern in Ambewela Area [6]

According to the wind turbine characteristics parameters with site characteristics such as

wind speed, frequency of wind patent, wind flow direction, site conditions, air temperature

and rainfall pattern... etc.

Used wind turbine parameter analysis by ‘the Swiss wind power data website’. The web site

is mandate by federal department of the environment, transport, energy and communications

Swiss federal office of energy in Switzerland. Above software consists of calculators to

obtain by wind flow profile, Weibull distribution condition, air density and wind power of

turbine.

The wind profile calculator estimate for vertical wind speed profile. So, increase of wind

speed with height above ground level, and ground level wind is strongly affected by obstacles

and surface roughness. The high above ground level in uniform air layers of the geotropic

wind as approximate 5km above ground level. The wind is no longer influenced by surface

between two extremes wind speed changes with height.

Randenigala Reservoir have 2,330sqkm of catchment area, 861MCM of gross storage

capacity, 558MCM of live storage capacity and 1,350Ha surface at retention level. It is

largest surface reservoir as shown in figure 11.

31


Figure 11 – Randenigala Reservoir Area

According to the Randenigala reservoir data, it is largest surface reservoir. Therefore in this

site practically has a very high wind speed in around the year. Can install the wind turbines in

the catchment area on top of the mountains.

Therefore, it is called vertical wind shear. So, suitable roughness length for the Randenigala

reservoir area is 0.0002 and wind turbine location is on the water surface of Randenigala

reservoir. When the height above ground level, wind speed and roughness length are define

the software calculate wind speed at different elevations. The output result obtained for the

Randenigala reservoir area given below figure 12 and Appendix E.

Figure 12 – Vertical Profile of Wind Profile by Web Based Software [3]

According to wind turbine design requirement is variation of wind speed to be visualized

accurately in order to optimize the design of turbine. The evaluation of field data on wind

speeds gives the probable wind energy availability at the site. For this purpose can be use

32

web base software tool to approx. wind speed distribution with Weibull function. So, obtain

Weibull parameters may subsequently use in power calculator to estimate the power

electricity power production by wind turbine. The result obtained by Randenigala site is

given in figure 13 and Appendix E.

Figure 13 – Weibull Wind Speed Distribution for Randenigala Area [3]

The following parameters of the Welibull distribution were used for web based software

power calculations.

= 7.2m/s

= 7.87

• Mean wind speed (V)

• Scale factor of Weibull

• Shape factor of Weibull (k) = 1.48

The Swiss wind power data website power calculator has been run different type of more

than 45 wind turbines. It is possible to estimate the energy output, plant factor and fill power

capacity for site for different turbine types.

Also, it can be produce power production distribution curve, wind speed distribution curve

and load profile of each wind turbine when it is subjected site parameters. That turbine

availability of 100% was assumed witch are no losses due to down time, park effects and

power transformer losses. The best optimum result of wind turbine obtained for the

Randenigala site is given in figure 14 and Appendix E.

33

Figure 14 – Result from power Calculator with 3MW Vestas V112 at Randenigala Site [3]

In Table 4 from Appendix E, shows the selected best wind turbine from more than the 45

different wind turbines.

Table 4 ; Best wind turbines from 45 different wind turbines of Swiss power calculator

Wind Turbine

Model

Max_ Power

Capacity

(kW)

Capacity

Factor

(%)

Power

Production

(kWh/year)

Average power

(kW)

D8/80Dewind 2,000 26.6 4,660,452 532

G87 Gamesa 2,000 29.1 5,103,301 583

90 Vensys 2,000 27.4 6,009,348 686

100 Vensys 2,500 29.5 6,459,581 737

V80 Vestas 2,000 27 4,726,102 540

V90 Vestas 3,000 24.5 6,439,750 735

V112 Vestas 3,000 31.1 8,190,553 935

V 112 Vestas 3,075 30.5 8,219,227 938

Table 4 - MatchingWind Turbines

34

5.4 Different Options to Wind Turbine with the Pumped Storage Plant

Currently modern wind turbine is based on aerodynamic lifting. The blades interact with the

wind and use both the drag force and lifting forces (Perpendicular). The lifting force are

mainly driving turbine power rotor because it is multiple of drag force. Lifting force of air

flow are intercepted by rotor blade and causes necessary driving torque for the wind turbine.

Modern horizontal axis wind turbines like Vestas V112 consist of tower, rotor, blades and

nacelle located on top of tower. Nacelle contain the gearbox and generator. In large wind

turbines, wind vane, anemometer and controller, control the yaw drive to point the rotor into

or out of the wind. The pitch controls the blades capture maximum power from wind.

As shown in power profile at Appendix E, for the wind speed interval 7m/s to 10m/s, an

average of 1,000kW are produced at 7.27m/s. The column, Mean wind speed used, shows

average wind speed where the mean wind power was collected from the power curve for the

Vestas112. Produced energy kWh/y is the energy produced at each interval. From output

energy of the Vestas112 wind turbine is 8,190,553kWh/y, converted to average power of the

year;

Pave.turbine= power production / hours per year

Pave.turbine= 8,190,553kWh / 8,760 = 935kW

Calculated power usage at the shaft for the Goulde pump from equation 3.2 was 984kW. One

Vestas112 wind turbine could be used to drive one pump up to a 40m height if no power was

lost in the gearbox and motor. The power lost by friction of the shafts is not included in these

calculations because the efficiency of the gearbox is estimated.

Therefore power loses in the turbine, motor, gearbox and a generator and pump to calculate

in this purpose. The wind turbine and pump selection case studies wise as follows,

Case Studies-1

In feasibility studies one wind turbine has an installed a gearbox, a motor and a generator and

is producing electricity power as shown in Figure 14 and power production information from

35

Table 4 is used. As shown in Figure 15, a 112m rotor diameter, 9,852m2 swept area per

turbine and 119m hub height wind turbine has an installed a gearbox, a motor and a generator

and is producing electricity. The expected efficiency of the wind turbine generator is about

95% [7]. The efficiency in the motor is estimated to be 90% [7]. The gearbox is expected to

have 95% efficiency and the estimated centrifugal pump efficiency is 73% (see calculation in

chapter 5.3).

The bus bar power 935x0.95=888kW, motor output power is 888x0.90=799kW, gearbox out

put power is 799x0.95=759kW and centrifugal pump out put power is 759x0.73=554kW. The

calculated pump out put power with the electricity motor is about 554kW.

Figure 15 –A Single Wind Turbine with Single Water Pump

The water flow rate can be calculated with formula 3.1,

Q = 554/ (1000x9.81x40) =1.41m3/s

36

Case Studies -2

If considered to feasibility studies two wind turbines, one turbine has a 112m rotor diameter,

9,852m2 swept area per turbine and 119m hub height with average power producing each

wind turbine 935kW as shown in figure 16. Power production information from table 4 is

used. Each wind turbine generators expected have 95% efficiency [7] and bus bar power is

935x0.95x2=1,776kW. The efficiency in the motor is 90% [7] and motor output power is

1,776x0.90=1,598kW.

The gearbox is having 95% and it is power is 1,598x0.95=1,518kW. The centrifugal pump

efficiency is 73% and it is output power is 1,598x0.73=1,108kW. The power calculated at the

shaft to the pump with the electricity motor is about 1,108kW. Two wind turbine with

installed a motor, gearbox and water pump total output power is 1,108kW.

Figure 16- Two Wind Turbines with Water Pump

In Case Studies - 2, pump output power is 1,108kW when the efficiency of a generator motor,

shaft and pump are taken into account. Also, calculated water flow rate is 1,108x1000/

(1000x9.81x40)=2.82m3/s and design water rate one water pump is 1.83m3/s. Therefore the

calculated water flow rate for one electrical motor connected to a centrifugal pump if

1,108kW is usable for pumping as figure 16 with the head at a 40m height.

37

But analysis to saving peak few hours for generate electrical power is required water to flow

is 1.83x2=3.66m3/s for one day cycle. Therefore cannot achieve to water flow is 3.66m3/s

which is one unit as shown in figure 16. Also, two units are technically usable but

economically unusable.

Case Studies - 3

If considered to feasibility as three wind turbines, one turbine has a 112m rotor diameter,

9,852m2 swept area per turbine and 119m hub height producing electricity as shown in figure

14 and power production information from table 4 is used. As shown in figure 16, wind

turbine has operation in parallel with bus bar an installed two separate gearbox, two separate

motor and three generator is producing electricity power is 2,664kW on bus bar. The each

wind turbine generator is expected have 95% efficiency [7]. The efficiency in the each motor

is 90% [7]. The each gearbox is having 95% efficiency and calculated centrifugal pump

efficiency is 73% (sec calculations in chapter 3.4). The power calculated at the shaft to the

pump with the electricity motor is about 720kW.

Figure 17- Three Wind Turbines with Two Water Pumps

38

In case studies - 3, this combination of one gearbox, one motor, one centrifugal pump, shaft

and steel pipes is called one unit. For one unit has calculated flow rate for one shaft driven

pump if 720kW is usable for pumping water to a 40m height is 1.83m3/s. Therefore most

suitable to uses two units for saving peak few hours for generate electrical power is required

water to flow is 3.66m3/s for one day cycle as shown in figure 17. Also, two pump units are

technically feasible and economically usable.

In Table 5, shows the summary of all case most suitable and selected wind turbines are

Veatas V112.

Table 2; Analysis and selection of wind turbine with pump

Parallel operation of 1 wind turbine with 1 pump

No. Type of Capacity WT Ave. WT BB power Motor power GB power Pump power 1 Pump uses Cal. Pump

Wind Turbine (MW) power (kW) @95% (kW) @90% (kW) @95% (kW) @73% (kW) power (kW) power (kW)1 D8/80 - Dewlnd 2 532 505 455 432 315 991 718

2 G87 - Gamesa 2 583 553 498 473 345 991 718

3 V80 - Vestas 2 540 513 461 438 320 991 718

4 90 - Vensys 2.5 686 652 587 557 407 991 718

5 100 - Vensys 2.5 737 701 630 599 437 991 718

6 90 - Vestas 3 735 698 629 597 436 991 718

7 112 - Vestas 3 935 888 799 759 554 991 718

8 112 - Vestas 3.075 938 891 802 762 556 991 718




2 G87 - Gamesa 2 1165 1107 996 946 691 991 718

3 V80 - Vestas 2 1079 1025 923 876 640 991 718

4 90 - Vensys 2.5 1372 1303 1173 1114 814 991 718

5 100 - Vensys 2.5 1475 1401 1261 1198 874 991 718

6 90 - Vestas 3 1470 1397 1257 1194 872 991 718

7 112 - Vestas 3 1870 1776 1599 1519 1109 991 718

8 112 - Vestas 3.075 1877 1783 1604 1524 1113 991 718




2 G87 - Gamesa 2 1748 1660 1494 1420 1036 1982 1436

3 V80 - Vestas 2 1619 1538 1384 1315 960 1982 1436

4 90 - Vensys 2.5 2058 1955 1760 1672 1220 1982 1436

5 100 - Vensys 2.5 2212 2102 1891 1797 1312 1982 1436

6 90 - Vestas 3 2205 2095 1886 1791 1308 1982 1436

7 112 - Vestas 3 2805 2665 2398 2278 1663 1982 1436

8 112 - Vestas 3.075 2815 2674 2407 2286 1669 1982 1436

Table 5 - Summary of Wind Turbines Data

39

5.5 Designing Water Flow Distribution System

When designing a water distribution system to determination the sizing of pipes, duct and the

pressure drop in the system. Calculate diameter of pipe, Reynolds number Re, friction factor f

and pressure drop Hf are calculate with equations 3.4, 3.5 and 3.6 and then simplified in

equation 3.7.

Re = 4*ρ*Q/ (π*μ*D) (3.4)

In equation 3.4, Re is the Reynolds number, ρ is the density of the water (water is

1,000kg/m3), Q is the volume of the flow rate (m3/s), π is equal to 3.1415, µ is the dynamic

viscosity of the water (1.5x10-3kg/s m) and D – diameter of pipe (m). To calculation friction

factor f which depend by Reynold number Re of pipe flow, equation 3.5.

f = 0.316(Re)-1/4 (3.5)

In equation 3.5, f – friction factor and Re – Reynold number from equation 3.4. The water

flow is laminar if the Reynolds number is lower than 2,000 in pipes, but if it is higher than

3,000, it is turbulent. To calculate a pressure drop, the equation 3.6 uses the friction factor f

and is,

Hf = 8fLQ2/ (π2gD5) (3.6)

In equation 3.6, Hf is the pressure drop, f – friction factor (equation 3.8), L - length of pipe

(m), Q - volume of flow rate (m3/s) and π is equal to 3.1415, g – gravitational constant

(9.81m/s2) and D - diameter of pipe (m). By simplifying equation 3.6, using Q=1.83m3/s and

L=40m, the diameter of the pipe calculated with equation 3.7;

D = (0.099/Hf) 1/4.75 (3.7)

In equation 3.7, D is the diameter of the pipe in meter and Hf is the pressure drop. The

pressure drop in equation 3.7 now is calculated with equation 3.8.

Hf = ηxP/Q (3.8)

40

In equation 3.8, Hf - pressure drop in a pipe. η – Efficiency (73%), P mean input horse power

at the shaft (1,109kW/0.746=1,486HP) and Q is the volume of the flow rate (1.83m3/s

=1,830l/s). The pressure drop in a pipe calculated with equation 3.8.

Hf = 0.73x1486/1830 = 0.593

The pressure drop is about 0.593. The diameter of the pipe calculated with equation 3.7.

D = (0.099/0.593)1/4.75 = 0.686m

The calculated diameter of the pipe is 0.686m. In the calculations, steel pipes that are about

0.686m in diameter are use because of higher pressure capacity. The velocity of the water in

the pipe can be calculated with equation 3.9;

V = 4Q/(π*D2) (3.9)

V = 4*1.83/(π*0.6862) = 4.95m/s

In equation 3.9, V is the velocity of the water in the pipe (m/s), Q is the volume of the flow

rate (m3/s), π is equal to 3.1415 and D is the diameter of the pipe (m). With a flow rate about

1.83m3/s and a pipe diameter of about 0.686m, the velocity of the water is about 4.95m/s.

According to the appendix C; Randenigala dam is given in statistics maximum head = 90m.

Also According to the appendix H; Randenigala plant has actual plant factor = 21.88%. So,

the actual head of Randenigala is very low. Also, energy production of Randenigala plant =

250GWhr and in CEB expected energy is 380GWhr.

Under my project scope, I have considered evening time in between 6.30pm to 7.00pm of

peak power saving for around half an hour and selected 100MW on system load side. For that

the pumping time is whole day.

Therefore, pump doesn’t have to pump up to the maximum head in Randenigala dam.

According to the analysis of above data, pump efficiency and most economical pump

available in market is 1,000kW, 40m height at flow rate 1.83m3/s.

41

5.6 Use Excess Power to Drive Water Pump

The objective in this section is how to utilize excess power which is produced during low

electricity demand in the future and to apply the excess power to drive the water pumps.

The method is again to store energy through water pumping from lower level reservoir to

upper level reservoir. Low cost off peak electric power is used to drive water pumps.

During high electricity demand, storage water is released through existing hydro turbines.

Although, loses of pump process make the plant a net consumer of energy in overall, it

provides revenue by selling more electricity during period of peak demand when electricity

price is highest. At that time low electricity demand use excess generation capacity to drive

water pump and water pump into the upper reservoir.

According to the CEB Long Team Generation Expansion Plan 2013 - 2032, the government

is going to introduce for power generation system, the huge coal power plant in Sri Lanka at

near future. Since, country power electricity load curve still is not flat. Curve there should

be excess power due to coal power plants. Daily load profile scenario over the years in in Sri

Lanka as shown in figure 18 and Appendix B.

Source: CEB LTGEP2013-2023

Figure 18- Change Load Profile over Years of Sri Lanka

42

There is a possibility to install the water pumps due available of excess coal power capacity

than base load of power generation system in Sri Lanka in near future. According to the CEB

– LTGEP report in duration year 2013 to 2032, energy mix over next years in Sri Lanka as

figure 19 and Appendix F.


Figure 19 – Energy Mix over Next Years in Sri Lanka

At that time coal power will be taking over the base load. Hence, off peak time, the

associated coal power plants provide energy for drive water pump and pumping water

from Rantambe reservoir to Randenigala upper reservoir. Hence, shown in figure 21 is

most suitable for use to pumped storage system which electric energy produce by wind

turbine use to drive pump in pumping station and also, to use the excess power to pump

the water in pumped storage power plants in the off peak time.

Rainfall system of Sri Lanka has multiple origin type such as monsoonal, convectional and

expressional. Annually rainfall system share above season and mean annual rainfall change

from under 900mm in driest part – southeastern and northwestern to over 5,000mm in wettest

part – western slopes of central highlands.

Country climate is dominate in topographical fractures and southwest and northeast

monsoons regional scale with wind regimes. In past experience of climate change has 12

months period characteristic data. According to past data, climate scenario can be divide by 4

43

seasons as first one is inter monsoon season – March to April, second one is southwest

monsoon season – May to September, third one is inter monsoon season – October to

November and finally northeast monsoon season – December to February.

Figure 20 – Wind Speed & Rainfall Profile of Randenigala Area

Southwest-monsoon Season (May-September) has amount of rainfall during season change

above 100mm to over 3,000mm is island. Amount of rainfall is rapidly decrease from

maximum region to ward higher elevation in Randenigala area in Central Province as shown

in figure 20 and Appendix G. but average wind speed from month of May to September very

high. Therefore this situation is considered for typical arrangement of pumped storage

system.

Final typical design arrangement is concerning use pumped storage system with electricity

energy produce by wind turbines and use to drive pump in pumping station system and to use

the excess power to pumps the water in pumped storage power plants. Also, consider

southwest - monsoon season (May - September) rainfall profile of design arrangement.

In above mention figure 17 of Case Studies - 3 is small modification with combination of one

gearbox, one mortar, one centrifugal pump, shaft and steel pipes is called one unit and two

pump units are technically feasible and economically usable. Also to required power

44

transformer, circuit’s breakers and power bus bar to connected national electricity network

for use excess power. Export power wind turbine can be used to national electricity network

due to during southwest –monsoon season or pump system maintenance time. Therefore most

suitable to uses two units for saving peak demand few hours for generate electrical power is

required water to flow is 3.66m3/s for one cycle as shown in figure 21.

Figure 21 – Design Arrangement of Pumped Storage System

5.7 Economic Feasibility Analysis of Pump Storage System

Assuming, not for calculation evaporation loses from exposed water surface, losses of

electrical transformer energy and zero maintenance and no expenses for installation or

repairs. Also, check of economic feasibility in generally. From Appendix F, according to the

CEB LTGEP – year 2013 to 2032 required capacity additions cumulative capacity by plant

type with require peak power energy shown in figure 22.

45


Figure 22- Cumulative Capacity by Plant type with Peak Power Variation

In this bar chart clearly seen that peak loading capacity is depend on the thermal power plants

for the near future. Also, at the movement use to cover of peak loading power fuel type is

auto diesel fuel. According to the data of the Ceylon Electricity Board there are existing

peak loading plants such as diesel engine power plant and gas turbine plant available at

Kalanitissa power station which is open cycle 105MW gas turbine is installed in 1997. Fuel

type of auto diesel is used in the gas turbines. The fuel is delivered from the local Ceylon

Petroleum Corporation refinery by pipelines.

Gas turbine power generation cost

From Appendix I, existing 105MW Kalanitissa gas turbine power plant generation unit cost is

around 32.00 Rs./kWh. Therefore at that time peak loading energy cost is 32.00 Rs./kWh.

From system load of figure 8 and Appendix B,

This thesis required peak loading energy per day = 50,000kWh

Gas turbine power generation cost = 32.00 Rs./kWh

Cost of peak loading energy for ½ hours per day = 32.00x50, 000

Rs.1, 600,000.00

46

Randenigala hydro power generation cost

From Appendix I, existing Randenigala hydro power plant generation unit cost is around 1.61

Rs./kWh. Therefore above plant all day energy generation cost is 1.61 Rs./kWh.

From system load details of figure 5 and Appendix B,

Required peak power saving energy = 50,000kWh

From Randenigla hydro power plant details and Appendix C,

Power plant capacity of one unit = 63MW

Full loading power of one unit for ½ hours = 31,000kWh

Spinning reserve loading plant capacity = 82%

Power output of 82% loading = 25,000kWh

Both unit power output of 82% loading = 50,000kWh

Randenigala hydro power generation cost = 1.61 Rs./kWh

Total cost of generation for ½ hours per day = 1.61x50,000

= Rs. 80,500.00

Wind turbine power generation cost

In this thesis did not calculate wind turbine cost in deeply due to this project duration is six

month. But Sri Lanka has wind turbine life cycle cost. According to data of Appendix I,

existing wind power generation unit cost was considered analyze the cost calculation.

From Appendix I, in year - 2013 existing wind power generation unit cost in Sri Lanka

around 11.96 Rs./kWh.

There no of wind turbines average capacity = 935x3 = 2,805kW

Wind turbines average energy production per day = 2,805x24 = 67,320kWh

Wind power generation cost = 11.96 Rs./kWh

Total cost of wind power generation per day = 11.96x67, 320

Rs. 805,147.00

47

Coal power generation cost

From Appendix I and CEB LTGEP year 2013 to 2032, at the movement base load or

intermediate load energy cost in about 10.20 Rs./kWh in Sri Lanka. Also, in near future

larger coal power plant will come into the base load or intermediate load in Sri Lanka, see

Appendix F. Hence, in the off peak time, associated coal power plants provide energy for

pump water from lower level Rantambe lower reservoir to upper level Randenigal.

Two no of water pump power capacity = 2,665kWh

Required water pump energy consumption per day = 2,665x24 = 63,960kWh

Total cost of water pump operating per day = 10.20x63, 960

Rs. 652,392.00

Option I;

In above chapter 3, concerning profitability of use a pumped storage system with electric

energy product by wind turbine and use to drive pumps in pumping station.

Cost of Gas turbine peak loading energy for ½ hours per day = Rs. 1,600,000.00

Cost of Randenigala hydro power energy for ½ hours per day = Rs. 80,500.00

Cost of wind power energy per day = Rs. 805,147.00

Hence, peak power energy saving profit per day = Rs.1, 600,000-(80,500+805,147)

Rs. 714,353.00

Peak power energy saving profit per year = Rs. 714,353.00x365

Rs. 260,738,845.00

Design is go through in option 1, Rs. 261 million per year is profitable of use this pumped

storage system.

48

Option 2;

In above chapter 3, concerning profitability of use the excess power to pump the water in

pumped storage plants.

Cost of Gas turbine peak loading energy for ½ hours per day = Rs. 1,600,000.00

Cost of Gas turbine peak loading energy for ½ hours per day = Rs. 80,500.00

Cost of use excess power for water pump operating per day = Rs.652, 392.00

Hence, peak power energy saving profit per day = Rs.1, 600,000-(80,500+652,392)

Rs. 867,108.00

Peak power energy saving profit per day = Rs. 867,108.00x365

Rs. 316,494,420.00

Design is go through in option 2, Rs. 316 million per year is profitable of use this pumped

storage system.

Hence, Rs.55 million per year is profitable design option 2 than design option 1.

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6. Results and Discussion

At this time and in future of the world, wind power energy will be important for electricity

power distribution. Future improvements in modern wind turbines has been cost reduction,

more electric power generation and fast growth global market. It will large wind power and

new system application.

Governments of Sri Lanka are more concerned about environments factors today and future

also, many rural areas like that Central Province are priceless from the tourist point of view

and some are seen as very good agricultural areas. Mahaweli scheme has two objective. That

are provide watwer to irrigation and agriculture of primary one. Electrical power generation

is second one. For this purpose, CEB and Mahaweli authority of Sri Lanka - MASL jointly

decide water utilization of Mahaweli reservoir base. Both parties deliver maximum

benefit to the country.

Largest reservoir in this complex is Randenigala, water is used to operate 2x62MW

capacity turbine units and output water release to Rantambe pond. Rantambe pond can be

regulated. Rantambe power station is operate 2x25MW capacity turbine unit and output

water discharge to Minipe anicut. This water distribute to right bank and left nank

Minipe canals to use downstream agriculture and irrigation purpose. But Rantambe power

station cannot operate in regulated mode because water is used for downstream irrigation

purposes. Therefore actual plant factor of Rantambe power station is 28% and

Randenigala power station is 21.88%. Running plant factors for Rantambe power station

75-77% and for Randenigala power station 72% are shown in Appendix H.

The water management system of Rantambe reservoir is difficult due to Rantambe reservoir

overflow dependent of Randenigala power generation and Uma-Oya river flow rate shown in

Appendix A.

One of the ways of solving above problem is “peak saving methods” and Pumped storage

power system is one of the options that Rantambe reservoir water can be utilized.

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The purpose of pumped storage power plant is storing energy at electricity cost cheaper

time and water release it quickly at peak hours. Demand for electrical changes throughout

the day. In generally Sri Lankan electrical power at high peak of load curve is worked

out between around 6.00pm 8.30pm as show in figure 23.

Source: CEB System Control

Figure 23- Normal Daily Load Curve of Sri Lanka Power System

According to the merit order generation method, generations are startup and run in minimum

unit cost to maximum cost respectively. In Sri Lanka normally base load is supplied by hydro

power, Intermediate load is supplied by part from hydro and low cost thermal, peak load is

supplied by high cost thermal. Sometimes this order becomes different due to reasons like

low water capacity of reservoirs etc. But basically this is correct.

In duration of 6.00pm and 8.30pm peak time power stations do not generate more power

immediately. Therefore, manage the peak power to need power cuts around the country it

can be all sort other trouble occur. Problem of in this situation is our country electricity

power generated by fossil fuel plant also, as high cost thermal.

Therefore this thesis is profitability assessment “peak time high cost thermal power

generations saving” and Rantambe reservoir water utilized. This purpose pumped storage

power plant can be use above situation.

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The aim of this project is to peak power generations sheaving with pumped hydro power

plant. Main objective this thesis use an economically analysis & design for a pumped storage

system located at a Randenigala hydropower plant in Mahaweli complex area of Sri Lanka.

The profitability analysis of a pumped storage system answered in two options:

Option – 1

In this case a wind pumped storage system uses wind turbines to produce electricity to drive

the pumps. This is most common in wind pumped storage systems today.

In this system is few hours in peak time electricity produced with a Randenigala hydro

turbine from the pumped water. In concerned above option had been selected 3MW Vestas

V112 wind turbine case studies wise;

In case studies – 1, if one wind turbine has 112m rotor diameter, 9,852m2 swept area per

turbine and 119m hub height producing electricity as calculated is 554kW power to pump

when expected efficiency of the wind generator is about 95%. The efficiency in the motor is

estimated centrifugal to be 90%. The gearbox is expected to have 95% efficiency and the

estimated centrifugal pump efficiency is 73%. Calculated water flow rates 1.41m3/s but

design water flow rate is 1.83m3/s. Therefore the calculated water flow rate for one electrical

motor connected to a centrifugal pump if 554kW is unusable for pumping as shown in figure

15 with the head at a 40m height.

In case studies – 2, if considered two wind turbines, one turbine has 112m rotor diameter,

9,852m2 swept area per turbine and 119m hub height and total producing electricity is

1,108kW power to pump when the efficiency of each wind turbine generator are expected

have 95% efficiency. The efficiency in the motor is 90%. The gearbox is having 95%

efficiency and calculated centrifugal pump efficiency is 73%. Also, calculated water flow rate

for 2.82m3/s and design water flow rate is 1.83m3/s. Therefore the calculated water flow rate

for one electrical motor connected to a centrifugal pump if 1,108kW is usable for pumping as

shown in figure 16 with the head at a 40m height. But analysis to power saving peak few

hours for generate electrical power is required water to flow is 3.66m3/s for one day cycle.

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Therefore cannot achieve to water flow is 3.66m3/s which is one unit as shown in figure 15.

Also, two units are technically usable but economically unusable.

In case studies – 3, one turbine has 112m rotor diameter, 9,852m2 swept area per turbine and

119m hub height with three wind turbines has operation in parallel with bus bar an installed

two separate gearbox and two separate motor is producing electricity power is 2,664kW on

bus bar. This combination one gearbox, one mortar, one centrifugal pump and shaft are called

one unit. The each wind turbine generator is expected have 95% efficiency. The efficiency in

the each motor is 90%. The each gearbox is having 95% efficiency and calculated centrifugal

pump efficiency is 73%. For one unit has calculated flow rate for one shaft driven pump if

720kW is usable for pumping water to a 40m height is 1.83m3/s. Therefore most suitable to

uses two units for saving power for peak few hours for generate electrical power is required

water to flow is 3.66m3/s. for one day cycle as shown in figure 17. Also, two pump units are

technically feasible and economically usable.

In this project, consider night time in between 6.30pm to 7.00pm if peak saving for around

half an hour and selected 100MW in system load side. Then calculate required average peak

power saving energy of between times 6.30pm to 7.00pm is 50,000kWh.

This project duration is six month, therefore project scopes is limited and not considered

wind turbine costs and pumped storage costs. Only considered existing life cycle cost of gas

turbine plant, coal power plant, Randenigala hydro power plant and wind power plant.

Therefore, assumptions,

Wind turbine capital cost in covered under unit cost, calculated based on life cycle cost.

Pump storage cost is neglected as comparing the option 1 and 2 where both will have the

same cost.

Pump and wind turbine construction, installation and commissioning cost are neglected

due to above two reasons.

If above cost considered, very difficult to calculation due to market price of manufacturing

and fuel, CIF values, and Tax etc., are change time to time. Therefore, the unit cost is was

taken from the actual data for existing wind, hydro, coal & gas power plant in the country. It

53

was assumed that this will cover the operational variations of the system. Sensitivity analysis

was not carried out as the actual unit cost data was used.

At the movement peak time high cost thermal power generation of Sri Lanka is exiting gas

turbine power plant generation unit cost is around 32.00 Rs./kWh. Therefore cost of peak

loading energy for ½ hours is around Rs.1, 600,000/=. Existing Randenigala hydro power

plant generation unit cost is around 1.61Rs./kWh and required ½ hours generation cost is

around Rs.80,500/=. In year - 2013, exiting wind power generation unit cost in Sri Lanka

around 11.96 Rs./kWh.

Therefore, this unit cost concerned for calculation and total cost of 3MW Vestas V112 three

wind turbine power generation all day Rs. 805,147/=. Therefore peak power energy saving

profit per year Rs. 260,738,845/= According to above cost analysis and design is go through

in option - 1, Rs. 261 million per year is profitable of use this pumped storage system.

Option – 2

In this case to use the excess electricity power from grid network to drive water pumps the

water in pumped storage power plants. In near future, huge coal power plant will come into

the base load or intermediate load in Sri Lanka. Hence, in the off peak time, the associated

coal power plants provide energy for pump water lower level Rantambe to upper level

Randenigala reservoir.

At the movement, off peak time associated base load or intermediate load with low cost

thermal energy cost is about 10.20 Rs./kWh in Sri Lanka. Hence, total cost of water pump

operating per day Rs. 652,392/=. Also, existing cost of peak loading energy for ½ hours is

around Rs. 1,600,000/=. Existing Randenigala hydro power plant required ½ hours generation

cost is around Rs. 80,500/=. So, Peak power energy saving profit per year Rs. 316,494,420/=.

According to above cost analysis and design is go through in option 2, Rs. 316 million per

year is profitable of this pumped storage system. Hence, Rs.55million per year is profitable to

design option – 2 than design option – 1. The profitable assessment calculations show that it

is profitable to build to build wind pump storage system for electricity production at existing

hydropower plants.

54

Wind pump storage system should be installed more security. Hence, rainfall data observed

fluctuation in Randenigala area in Central Province as shown in figure 20. But average wind

speed from month of May to September very high. Therefore this situation is considered for

typical arrangement of pumped storage system. Final typical design arrangement is

concerning use pumped storage system with electric energy production by wind turbine and

use to drive pump in pumping station system and to use the excess power to pump the water

in pumped storage power plants. Also, export power from wind turbine can be used to

connect national electricity network due to during southwest - monsoon season or pump

system maintenance time.

In design system is combination of one gearbox, one motor, one centrifugal pump and shaft is

called one unit and two pump units are technically feasible, economically usable and

environmental friendly. Also to required power for transformer, circuit’s breakers and power

bus bar to connected national electricity network for use excess power. Therefore most

suitable to uses two units for saving peak few hours for generate electrical power is required

water to flow is 3.66m3/s for one day cycle as figure 21.

According to the methodology only option 1 and option 2 is considered. In our country only

900MW coal power plant is available which is operated for the base load & day load which is

not sufficient to run through the day. The cost comparison was made on coal, unit cost is Rs.

10.20. It is required to import coal in our country, and not environmentally friendly, but the

wind was selected as it is sustainable & environmental friendly and government preference.

Therefore, this thesis was not considered as a redundancies.

This thesis, selected by best wind turbines from table - 4 as Appendix E, Vestas V112 - 3MW

and average output power 935kW. Also, in case study wise analysis most suitable wind plant

and finally, analysis and selected maximum power is 3MW wind plants. So, wind turbines

work at full capacity. This project is not expected to cover full peak, but keep peak power

saving for around half an hour. According to appendix B, if consider night time in between

6.30pm to 7.00pm of peak power saving is around 100MW on system load. If the wind power

is not available the system will run on grid power and if access power is generated by wind

turbine, they are feed back to the grid as per figure 21.

55

7. Conclusion

The main reasons for profitable use of a wind pumped storage system for peak time

electricity production in Sri Lanka are the high price of powerful thermal plant and the low

electricity sale price.

The next step is to design a wind pumped storage system described in this thesis where one

gearbox, one motor, one centrifugal pump and shaft is called one unit and two pump units

required. Other accesses are power transformer, circuit’s breakers and power bus bar to

connected national electricity network for possibility use excess power. Therefore most

suitable to uses two units for high thermal generation cost saving in peak few hours for

required water to flow is 3.66m3/s for one day cycle. Also, most important is to get a reliable

price for a motor with a gearbox and a generator because with the installation cost of the

equipment part in the profitability assessment. Other very important factors are the sale price

for the electricity & average wind speed.

If design go through in option - 1, peak power energy saving profit per year Rs. 261 million

per year is profitable of uses this pumped storage system. If design is go through in option –

2, peak power energy saving profit per year Rs. 316million per year is profitable of uses this

pumped storage system. Hence, Rs. 55million per year is peak power energy saving

profitable to design option – 2 than design option - 1 wind pumped storage systems.

So, conclusion is typical design arrangement for use pumped storage system with mainly

electric energy product by wind turbine then use to drive water pump in pumping station

system and possible tine use the excess power to drive water pump pumped storage power

plants. Also, export power from wind turbine can be use to connect national electricity

network due to during southwest - monsoon season or pump system maintenance time.

Producing energy with wind turbines is categorized renewable and a minimum impact on the

environment has nearly non CO2 emission. Renewable energy like wind power plant is most

suitable for connect to national grid in Sri Lanka. Therefore this pumped storage system is

essential most reliable, technically feasible, economically usable and environmental friendly

power generation system for our peak load operation.

56

References

[1] CEB, The web site is mandate by Ceylon Electricity Board - CEB, Sri Lanka.

http://www.ceb.lk

[2] CEB, The web site is mandate by Ceylon Electricity Board, Department of Generation

in Mahawali Complex, Sri Lanka. http://www.mahawelicomplex.lk/default.aspx

[3] ‘Swiss wind power data website’, this web site is mandate by federal department of

environment, transport, energy and communication Swiss federal office of energy,

Switzerland. http://wind-data.ch/index.php

[4] Kothari, D.P., Singal, K.C., Rakesh Ranjan, Book of Renewable Energy Sources and

Emerging Technologies.

[5] CEB, Book of “LTGEP - Long Term Generation Expansion Plan 2013-2032”

Prepared by CEB, Sri Lanka.

[6] SEASL, The web site is mandate by Sustainable Energy Authority of Sri Lanka.

http://www.energy.gov.lk/

[7] Nesbitt, B. (2006). Hand book of “Pumps and Pumping”. Elsevier Science.

[8] P. Samaraweera, Book of Mahaweli Water Management to Maximize Benefit,

Prepared by Mshaweli Authority of Sri Lanka.

pumped energy storage system for the randenigala...

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