chapt-5 cost effective analysis of small hydropwer

8/6/2019 Chapt-5 Cost Effective Analysis of Small Hydropwer

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CHAPTER-5

COST EFFECTIVENESS OF SMALL HYDROPOWER

5.1 INTRODUCTION

Cost effectiveness in small hydro power depends largely on proper selection of site, good

planning of the layout of the scheme on optimization basis, hydrological and optimum power

potential studies, careful and correct designs of structures, proper estimates with realistic rates

and use of construction techniques appropriate to small hydro and efficient execution. This

requires an interdisciplinary approach at different stages of the work. Careful monitoring and

adherence to the construction schedule is essential to prevent cost and time overruns.

The procedure for cost-effectiveness analysis is a systematic comparison of alternatives of

selects the one that minimizes cost while reliably satisfying technical limitations and

preferences over the expected time for operation .The total cost of the project is related to size

and effectiveness.

The optimization process consists of three main steps: (1) find the maximum yearly energy;

(2) maximize the yearly benefits of all the maximized sets of power plants; and (3) select the

most beneficial of the feasible sets of run-of-river power plants on the basis of a combination

of the cited criteria

The design of reliable and cost effective small hydropower plants capable of large-scale

electrical energy production is a prerequisite for the effective use of hydropower as an

alternative resource. In this sense, the design of a small hydroelectric plant or equivalently the

determination of type and energy load of the particular hydro turbines should maximize the

energy output together with the life-time of the machines. In all cases, the design objective is

closely related to the total annual output of the overall hydro turbine operation in power terms.

5.2 THE IMPORTANCE OF MINIMIZING CAPITAL COST

In conventional large-scale hydropower, attention is given to maximizing the energy that

will be produced from the site over the life of the scheme, which may be a century or more.

The efficiency of energy recovery tends to dominate over considerations of initial capital cost.

On the other hand small hydro installations typically service small communities with limited

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resources, and the initial capital cost becomes the overriding issue, so it is more important to

maximize power per unit cost than to maximize power alone.

5.3 PLANNING FOR OPTIMUM DESIGN

Cost effective small hydro would depend largely on proper selection of site, good planning of

the layout of the scheme on optimization basis, competent hydrological and power potential

studies, careful and correct designs of structures, proper estimates with realistic rates and use

of construction techniques appropriate to small hydro and efficient execution. The procedure

for cost-effectiveness analysis is a systematic comparison of alternatives of selects the one

that minimizes cost while reliably satisfying technical limitations and preferences over the

expected time for operation .The total cost of the project is related to size and effectiveness.

Any SHP scheme should aim at maximising the power output as efficiently and

economically as possible at the selected site. This requires proper planning in selection of

site and equipment, techno-economically attractive design and configuration, economy in

construction of civil works and equipment and maximising the load factor etc. These

planning aspects are discussed in brief in the following paragraphs.

The data on flow discharge and head is normally sufficient to plan a SHP scheme and

simple methods can be used to generate these data. The larger and costlier the scheme, more

critical and accurate data is needed. For a SHP in a remote area, some amount of dependable

and year round power is required which can be determined based on the minimum usable

flow in the stream.

5.3.1 Site selection

The selection of appropriate site for the installation of SHP requires consideration of several

factors.

The site must be accessible or can be made accessible to facilitate construction,

operation and maintenance of the installation and transportation of equipment and material

etc.

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The available energy is optimally utilised and future needs of power are considered

while fixing the capacity of the SHP.

Net head, flow and power output have significant effect on site selection because a low

head installation requires larger flow of water whereas a high head site needs relatively

smaller flow for similar output. It is advisable to make use of higher head available because

most of the civil works and turbo-machinery get reduced in size resulting in reduction of cost.

Powerhouse to be situated at a reasonable distance from the consumers or existing grid

to avoid as far as possible high voltage lines and other costly step up equipment.

The site should have social benefit potential and also multi sector integration potential.

5.3.2 Civil works

The principal components of civil works are specific site, if necessary components are

excluded or unnecessary components are included, problems may arise in implementation,

operation and maintenance of the plant and can result in increase in the cost of SHP.

An intake is a component found in every SHP. An intake provides a controlled flow of

water from a river or stream into a conduit to convey water into the turbine to generate

power. In addition to this, major function of intake is to minimise the amount of debris and

sediment carried by the water. Therefore, the design of intake mainly depends upon the

quality and quantity of water to be fed into the power conduit and also whether a dam or a

weir is included in the layout. An important parameter in case of intake is its orientation

with reference to the stream. Best orientation is in the direction perpendicular to the stream

which can prevent sediment, debris etc. entering the power conduit. Intake can be

advantageously located behind or under big boulders which can deflect flood flows and

river borne debris and can also limit water flow into the intake.

Power conduit is required to carry the water flow from the stream to the inlet of penstock

with minimum loss of head and at the same time at minimum cost possible. Velocity in the

canal is inversely proportional to its cross section and also cost of construction, i.e. higher

the velocity, smaller is the cross section and volume of excavation. A power conduit is

generally a canal excavated in soil and it can be lined or unlined depending on velocity of

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flow, ease in maintenance and cost of construction. Common lining materials are brick,

stone masonry, LDPE etc. Hume pipes are suitable as power conduit but at higher cost.

There can be a trade off in the combination of power canal and penstock to obtain the same

head and power potential depending on the nature of terrain, allowable loss of head: ease of

maintenance and cost. The options available are:

Larger diameter and longer penstock pipe direct from the intake to the turbine

without a canal.

A power canal for longer distance and a smaller diameter and smaller length

penstock from end of the canal to the turbine.

A significant point to be considered here is that for a given length, the cost of power canal

using local material may be cheaper than steel penstock. The forebay is a basin located just

before the entrance to penstock to serve as a settling basin or for storage of water to cope up

with demand of water due to sudden increase in the turbine load. It can be a simple

excavated area. The size of particle to be removed depending on head is as follows. Bead

size of silt particle to be removed Medium High

The cost of power house can be minimised by restricting its configuration. For example the

powerhouse building can accommodate turbo-generating equipment only as a cost saving

measure. The volume flow rate of water will directly influence the cost of powerhouse, since

the leading dimensions of turbine and the powerhouse are related to the quantity of water.Impulse turbines are used for high heads and low flows which require smaller space whereas

reaction turbines are for low heads and higher flows and require larger space.

5.3.3 Cost effective penstock

The penstock cost is typically 1/3 of the overall installation costs; it is one of the most

expensive items and has to be carefully chosen. There are two components to achieving the

best power per unit cost, first finding the maximum power per unit length of penstock and

second, making a realistic choice ofpenstock. . Cost of penstock is high if it is buried, but itmay become unavoidable if topography warrants it. The cost towards supports and anchor for

penstock is a considerable amount and need to be reduced if possible. Different materials

which can be used for penstock in addition to steel are cast iron, ductile iron, PVC,

polyethylene, concrete and asbestos cement, ERW pipes and Indian Hume Pipes.

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There is a well-known analysis for finding the optimum discharge for a given diameter from

available piping, optimum is a compromise between

Small diameter ,cheaper piping with very high flow rates and high head losses due to

friction, and

Large diameter, more expensive pipe with low friction head losses.

This analysis shows that at the optimum discharge the friction head loss is one third of the

gross head. Mild steel and HDPE pipes are the most common penstock materials used in

small hydro power schemes. HDPE pipes are usually economical at low head and flows and

are also easy to join and repair

5.3.4 Determination of optimum installed capacity

The sizing of a small hydropower plant of the run-of-river type is very critical for the cost

effectiveness of the investment .To determines the optimal installation capacity of small hydro

plant all technical, economic and reliability indices are considered in a trade-off relation.

Using this approach, the amount of annual energy is determined by using categorized statistics

of the flow duration curve in different months. Then, after specifying the income and costs of

the plant, the economic indices of different alternatives are extracted. The reliability indices

are then calculated and ultimately, through comparison of the technical, economic andreliability indices, a superior alternative can be selected, determining the optimal installation

capacity. This method of calculating the technical, economic and reliability indices and the

subsequent processes used in the planning of an small hydro plant will be further discussed

and described

5.4 OPTIMIZATION

Optimization in general, is the search for a feasible operational policy that maximizes or

minimizes the value of the objective function or optimization criteria. Hydropower is non-

linear function though the operation problems in hydropower are non-linear problems. The

best solution to non-linear problems can be obtained by application of non-linear optimization

techniques.

In the hydropower industry, this optimization criterion may vary and usually is one of thefollowing:

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Maximization of energy production

Maximization of benefits or revenues

Minimization of squared differences between power profiles

Maximization of benefits in energy export-import

In the first single-objective optimization study, the target is to find the proper plant

configuration that minimizes or maximizes the value of some operation or economic

parameters. The economic indices NPV and BCR and an additional load coefficient Lf that

gives the ratio of the mean produced power to the installed capacity has been calculated .the

maximum value of NPV and BCR will gives maximum energy production, about 80% of the

water stream potential .the remaining 20% is lost due to hydraulic and other losses. How ever

low load coefficient values indicate, the installed power is too high, and this increases the

investment capital cost.

5.4.1 Basic components of an optimization problem

An objective functionexpresses the main aim of the model which is either to be minimized or

maximized. For example, in a manufacturing process, the aim may be to maximize the profit

or minimize the cost. In comparing the data prescribed by a user-defined model with the

observed data, the aim is minimizingthe total deviationof the predictions based on the model

from the observed data. In designing a bridge pier, the goal is to maximize the strengthand

minimize size.

A set of unknowns or variables control the value of the objective function. In the

manufacturing problem, the variables may include the amounts of different resourcesused or

the time spent on each activity. A set of constraintsare those which allow the unknowns to

take on certain values but exclude others. In the manufacturing problem, one cannot spend

negative amount of time on any activity, so one constraint is that the "time" variables are to be

non-negative.

The optimization problem is then to find values of the variables that minimize or maximizethe objective function while satisfying the constraints.

The optimization process consists of three main steps: (1) find the maximum yearly energy;

(2) maximize the yearly benefits of all the maximized sets of power plants; and (3) select the

most beneficial of the feasible sets of run-of-river power plants on the basis of a combination

of the cited criteria

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5.4.2 Linear programming problem

If the objective function and all the constraints are linear functions of the design variables,

the optimization problem is called a linear programming problem(LPP).

A linear programming problem is often stated in the standard form

Find X=

nx

x

x

.

.

2

1

(5)

Which minimizesf(X) = i

n

i

ixc

=1

(6)

Subject to the constraints

ji

n

i

ij bxa ==1

, j = 1, 2, . . . , m

xi 0 , j = 1, 2, . . . , m

Where ci, aij, andbj are constants.

5.6 CASE STUDY OF A SMALL HYDRO POWER PROJECT

For illustration purposes a typical small hydro plant which is located Arunachal Pradesh, India

and 100% dependability flow is 4.49 cumecs, 75% flow dependability is 5.55 cumecs. Based

on the discharge data collected from Arunachal Pradesh development agency, estimation for

mean monthly values of flow, over a period of 10 years is made and a flow duration curve is

calculated as shown in Fig.5.1 and cost of various components of civil works and electro-

mechanical works are estimated and shown in table 5.1. And estimation of generation cost and

load factor at a head of 60 m as shown in table 5.2. The graph between the generation cost and

installed capacity shown in fig 5.2

The economical analysis has been carried out considering costs and obtained incomes,

according to the given algorithm. The economic indices B/C Ratio, NPV Value has been

calculated and shown in table 5.3.The interest rate has been settled as 8 % and 11% in order to

attract foreign investment in developing countries.

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Fig 5.1 Flow Duration curve

Table 5.1 cost of small hydropower plant at 60m Head

S.no Components

Installed Capacity(kW)

2000 30000

4000

0 5000 6000 7000 8000 9000

1000

0 11000 12000

1 CIVIL WORKS

Weir and Intake 860.5 955.33 1050 1100 1150 1200 1250 1400 1450 1500 1550

Power channel 530 575 620 630 640 650 660 750 800 900 950

Desilting tank 155 172 190 200 210 220 230 260 300 320 350

Forebay &Spillway 115 119 124 128 132 136 140 155 160 165 170

Penstock 119 139 160 179 198 218 230 250 260 270 280

Power house 270 315 360 382 404 427 450 480 500 520 535

tail race channel 69 75 80 84 88 93 98 110 120 125 130

Total cost of civil

works 2118.5

2350.3

3 2584 2703 2822 2944 3058 3405 3590 3800 3965

2

Cost of E & M

Works 1271.1 1410.2 1550 1622 1693 1766 1835 2043 2154 2280 2379

Other Costs 211.85

235.03

3 258.4

270.

3

282.

2

294.

4

305.

8

340.

5 359 380 396.5

TOTAL COST

3601.4

5

3995.5

6 4393 4595 4797 5005 5199 5789 6103 6460 6740.5

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The main design parameters can be selected in order to produce a cost effective generation

that gives a high NPV with maximum energy generation. The economic indices are calculated

by using MATLAB coding.

Table 5.2 Estimation of generation cost of SHP at 60m Head

S.no Installed

capacity(kW)

Head(m) Annual

energy(MU

)

Generation

cost(Rs/kWH)

Load

factor

1 2000 60 17.52 1.23 1

2 3000 60 24.38 0.98 0.92

3 4000 60 29.82 0.88 0.854 5000 60 35.12 0.78 0.8

5 6000 60 39.94 0.72 0.76

6 7000 60 44.51 0.67 0.72

7 8000 60 48.88 0.64 0.69

8 9000 60 49.27 0.7 0.65

9 10000 60 49.77 0.73 0.55

10 11000 60 50.02 0.77 0.49

11 12000 60 50.51 0.8 0.47

The curve drawn between the installed capacity and cost per unit shows give below in Fig 5.2

Fig 5.2 Selection of optimum installed capacity

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The optimum point we can found by this graph. The economic indices of different alternatives

of Small Hydro Power are calculated and those are shown in Table 5.3

Table 5.3 Economic indices of different alternatives for SHP

S.no Installed

capacity(kW)

Cost Per

Unit

interest rate

8 % B/C

ratio

NPV

value(million)

interest rate

11% B/C ratio

NPV

value(million)

1 2000 1.23 2.20 24.11 2.25 24.65

2 3000 0.98 2.76 40.19 2.82 41.08

3 4000 0.88 3.07 52.28 3.14 53.54

4 5000 0.78 3.46 65.45 3.53 66.92

5 6000 0.72 3.77 77.23 3.85 78.96

6 7000 0.67 4.02 88.30 4.11 90.27

7 8000 0.64 4.24 98.80 4.33 101

8 9000 0.7 3.85 96.13 3.94 98.27

9 10000 0.73 3.69 95.44 3.77 97.5610 11000 0.77 3.50 93.79 3.58 95.87

11 12000 0.8 3.39 93.29 3.46 95.36

5.7 COST OPTIMIZATION OF SHP DEVELOPMENT

The methodology as discussed earlier and estimation of effective cost per unit capacity of

small hydropower projects at different capacities and at different heads. Costs data of SHP

plants given below in table4.1, table 4.2 and table 4. 3

The model which has been used to optimize the cost of SHP is given as follows

Total cost of project= 263.6*Capacity^.3587*Head^-.0399.. (7)

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Log (total cost) - 2.42 = .3587 Log (Capacity) - .0399 (Head).. (9)

Take

Log (total cost)-2.42 = Z

Log (capacity) = X1

Log (Head) = X2

The new objective function becomes

Z = 0.3587*X1 0.0399*X2 (10)

And new constraints after taking log of the older constraints are

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The optimum installed capacity has been found as 8000 kW and min cost of the project is

5370 lacs.

The similar methodology applied to two typical flow duration curves Objective function is

same and the constraints are given below

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In this case the optimum installed capacity has been found as 24000 kW, minimum cost of the

project has been worked out as 8709 lacs.

For another flow duration curve of small hydro project the constraints are given below

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In this case the optimum installed capacity has been found as 5000 kW, minimum cost of the

project has been worked out as 4466 lacs

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chapt-5 cost effective analysis of small hydropwer

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