optimizing : Hydroelectricity in uttara kannada

Hydroiogîcal Sciences~Joiirnal-des Sciences Hydrologiques, 45(2) April 2000 299
Optimal design of hydroelectric projects in Uttara
Kannada, India
T. V. RAMACHANDRA, D. K. SUBRAMANIAN & N. V. JOSHI
Centre for Ecological Sciences, Indian Institute of Science, Bangalore 560 012, India
Abstract The planning of water resources depends on the type and size of projects,
the ecological factors involved, etc. Emphasis is placed on presenting an overview of
water resources through meteorological, hydrological, ecological and economic data.
Economic data include all costs and benefits, specifically those hitherto under
estimated, environmental social costs and benefits. This study was carried out on the
Bedthi and Aghnashini rivers in the Uttara Kannada district of the Western Ghats
region, Karnataka State, India. It is estimated that 720 and 510 million kWh of
electricity can be generated in Bedthi and Aghnashini River basins, respectively, if all
the streams are harnessed. Focusing on land submergence impact, a model is proposed
to minimize submergence and maximize net energy in a region with seasonal power
generation, reservoir storage capacity (to meet the region's demand during all seasons)
and installed generation capacity as the decision variables. Net energy analyses
incorporating biomass energy lost in submergence show that maximization in net
energy at a site is possible if the hydroelectric generation capacity is adjusted
according to the seasonal variations in the river's water discharge. A Decision Support
System (DSS) used for optimal design of hydroelectric projects in Uttara Kannada
district is discussed.
Un système d'aide à la décision pour la conception optimale de
projets hydroélectriques en Uttara Kannada
Résumé La planification des ressources en eau dépend de la nature et de la taille des
projets, du cadre écologique, etc. Nous avons surtout voulu présenter ici un panorama
concernant les ressources en eau à travers des données météorologiques, hydrologiques,
écologiques et économiques. Les données économiques incluent tous les
coûts et bénéfices, en particulier ceux qui ont jusqu'ici été négligés, de même que les
coûts et bénéfices environnementaux et sociaux. Cette étude a été entreprise sur les
rivières Bedthi et Aghnashini du district Uttara Kannada de la région Ghats
occidentaux (Etat de Karnataka, Inde). On estime à respectivement 720 et 510
millions de kWh les quantités d'électricité pouvant être produites par les rivières
Bedthi et Aghnashini si elles étaient totalement aménagées. En nous intéressant
particulièrement à la submersion des terres, nous proposons un modèle minimisant les
submersions et maximisant la production énergétique, les variables de décision étant
la production saisonnière d'énergie, la capacité de stockage des réservoirs (devant
satisfaire la demande en eau quelle que soit la saison) et la puissance installée. Un
bilan énergétique incluant les pertes de production de biomasse résultant des
submersions montre que la maximisation de l'énergie nette produite est possible si la
puissance installée est adaptée au régime des débits. On examinera enfin un système
d'aide à la décision utilisé pour la conception optimale des projets hydroélectriques de
l'Uttara Kannada.
INTRODUCTION
Kamataka state has the unique distinction of having set up the first hydropower plant
in India at Shivanasamudram in 1942. Since then, hydroelectric plants have contributed
significantly to both the State's and national demand for electricity. Most of
Karnataka's hydroelectric plants are located in Uttara Kannada district. Construction of
Open for discussion until 1 October 2000
300 T. V. Ramachandra et al.
large reservoirs is restricted due to environmental constraints, necessitating the
development of ecologically sound alternatives.
Hydroelectric power development—present status and approaches in design
At present hydroelectric power development is undertaken on an ad hoc, project-byproject
basis with capacity based on 90% availability of water annually, estimated on
the basis of a 10-day period. Since seasonal and yearly fluctuations of rainfall/
streamflow are high, planners tend to opt for large reservoirs to achieve their goal.
There is a need to consider integrated systems planning of supply and demand for
optimal development of the potential considering 90% reliability of the system in the
region. Demands of appropriate benefit-cost ratio (e.g. greater than 1.5), or least cost
of generation for clearance, ignore the energy/economic costs of submergence and
alternative designs involving seasonal variation in generation. Optimization
(programming) and descriptive (predictive) model approaches are usually adopted to
accomplish this complicated task (Falkenmark, 1989). Decision Support Systems
(DSS) focus more on providing flexible tools for policy analysis than on providing
models to answer structured problems (Parker & Ul-Ataibi, 1986). This paper focuses
on the design of a hydroelectric project using DSS, emphasizing economic efficiency
and engineering soundness, subject to social, environmental, ecological, cultural,
institutional and legal constraints.
OBJECTIVE
The objective is to design a hydroelectric plant utilizing optimal energy in the water,
with minimum submergence and economic costs, considering seasonal variation in
power generation to meet the region's demand during all seasons.
STUDY AREA
Uttara Kannada district lies between 74°9'-75°10'E longitude and 13°55'-15°31'N
latitude with 67% of its area under forest, 27% under habitation and reservoirs, and the
rest under various cultivation covering 10 291 km2 (Fig. 1). The large reservoirs for
hydroelectricity generation of Kali and Sharavathi have submerged vast tracts of
natural forest and dislocated a large number of people. Therefore, an attempt is made
to explore ecologically sound means of harnessing the hydroenergy of the Bedthi and
Aghnashini rivers.
STREAMFLOW MEASUREMENT AND COMPUTATION OF POWER
Streamflow depends on drainage efficiency of hill slopes, moisture content of the soil,
subsurface geology and vegetation cover (Gordon et al., 1992). Streamgauging using a
current meter indicates that streams in these catchments are seasonal. The relationship
between runoff at gauged sites and rainfall was determined by regression analysis. This
relationship was used to assess the potential of ungauged streams. It was estimated that
Optimal design of hydroelectric projects in Uttara Kannada, India 301
Fig. 1 Geographical location of Uttara Kannada district.
about 720 and 510 million kWh of electricity could be generated in Bedthi and
Aghnashini River basins, respectively.
The potential assessment shows that most of the streams would cater to the needs of
local people in a decentralized way during the monsoon, ensuring continuous power
supply, which would otherwise be disrupted by dislocation of electric poles/pylons or
falling of trees/branches on transmission lines due to heavy winds. A detailed household
survey of villages in hilly areas shows that people have to spend at least 60-65% of the
season without electricity when depending on a centralized supply. In view of this, an
ecologically sound alternative is proposed, which would generate maximum electricity
during the monsoon season and sufficient electricity during the "lean" season.
DESIGN OF A RESERVOIR WITH ENERGY AND ECOLOGICAL
CONSTRAINTS
The environmental impacts associated with large reservoirs necessitate the design of
reservoirs of appropriate sizes to meet the target demand of a region (Mutreja, 1976).
302 T. V. Ramachandra et al.
Because of the negative aspects of hydroelectric projects in ecologically fragile hilly
terrain; the submergence area should be minimized; the project should be subject to
reasonable cost, minimum or no wastage of water and seasonal constraints (the region
receives maximum rainfall during southwest monsoon). Based on 90 years' precipitation
data and 18 months of river runoff data, a methodology is proposed to design a
storage reservoir at Magod to meet the region's demand during all seasons.
Hydroelectric energy operation module
A decision support system for optimal design and operation of a large network of small
reservoirs for agriculture is described elsewhere (Labadie, et al., 1988; Albuquerque,
1993). The operation module is designed based on predetermined hydrological flow
(database, environmental and socio-economic modules), a GIS module, technical data,
economic data and a certain user selected reliability level. It also generates adaptive
operation policies based on this reliability level. An adaptive optimum control module
decides the quantity of water to be drawn from the reservoir considering seasonal
constraints, volume of water stored for particular height of dam, seepage loss, evaporation
loss, dead storage capacity of dam and rate of sedimentation, to ensure there is no
wastage of water. It also decides the storage capacity during the non-monsoon season.
The net energy available in the region is also presented in this module. Figure 2 shows
the components of the planning operation module.
Design assumptions and parameters
Assumptions Detailed geological and topographical investigations carried out by
the Department of Mines and Geology (KPCL, 1993) to determine the best site for the
dam, pressure shaft alignment, power house location, etc., can be used for
implementing this design.
Parameters Input data consist of site specific data (discharge, water yield, generation
head, evaporation rate, seepage rate etc.), technical data (efficiency of turbine and
generator, and dependability norm for storage capacity, load factor, etc.) and economic
Adaptive Optimum Control
Module
Storage Reservoir Module
_. Forecasting Module
Environmental, Technical and
Socio Economic Module
Fig. 2 Design of hydroelectric power station with optimal storage option: detailed
operation module.
DATABASE
Module
GIS Module
Watershed Module
Unsteady Flow Routing
Module
USER
INTERFACE
MANAGER
MODULE
Optimal design of hydroelectric projects in Uttara Kannada, India 303
data (civil construction costs for various types and heights of dam, cost of electrical
machinery of various capacities, environmental costs, rehabilitation costs, etc.).
Decision variables The decision variables determine the optimum storage capacity,
installed generation capacity and seasonal power drafts; net energy availability in
the region (objective function) needs to be maximized subject to seasonal hydrological
constraints, and costs and submergence area are to be minimized.
NET ENERGY MODEL—PARAMETRIC OPTIMIZATION
The broad outline of an optimization model for exploiting a river for hydropower and
irrigation, incorporating energy cost and net increase in yield due to irrigation, with
constraints on arable area and crop water requirement and seasonal variation in precipitation,
has been formulated by Subramanian (1985). On the same lines, with
detailed engineering design and quantification of data, the parametric optimization
approach is used with an objective to maximize the net energy subject to ecological
constraints, given by:
Enei = Eh - Ehio (1)
where Zsnet is net energy, Eh is hydroenergy and i?bio is bioenergy. This model is solved
for various scenarios for optimal utilization of hydropower and thermal energy in the
region. This includes an equation which computes monthly hydropower production as
a function of volume of water discharged (Q), gross head of this water (H) and
efficiency of the couple turbine generator (r\, between 0.7 and 0.85).
Hydropower (kW) is given by:
P = 9.8l-Q-H (2)
The corresponding approximate electricity produced Eh = P-t-r\, where Eh is electricity
(kWh) and t is operating time. The monthly hydroelectricity generated in million kWh
is given by:
Eht = Y,9S,\Dt-H-x\ (3)
where t = 1, ..., 12 and D, is the power draft from the reservoir during a month (million
cubic meters, Mm3). Replacing 9.8l-H-r\ as constant k\.
Eh, = 'LkvDl
This is decomposed for seasonal drafts:
£A, = E*i •/>,« +2*i-A* (4)
where Dtm and Dtd are water drawn during monsoon (tm = 1, ...,4) and dry period
{td= 5,..., 12), respectively.
Energy loss due to submergence is given by:
Eblo=Asub-GriCV)-nc (5)
where Asab is the submerged area classified on the basis of land use, Gr is the annual
304 T. V. Ramachandra et al.
rate of growth or productivity, r\c is energy conversion efficiency and CV is the energy
equivalence factor in terms of primary energy content (e.g. a ton of dry fuelwood with
a calorific value of 4400 kcal kg"1 has a thermal content of 5112.8 kWh).
This model is subject to the following constraints:
Hydrological constraints These operate on a monthly basis and consist mainly of
the following continuity equation (Maass et al, 1962):
V^ = Vl + It-S,-El-Dt (6)
where Vt is the volume of the reservoir at the beginning of month t, It is inflow to the
reservoir, St is seepage loss, Et is evaporation loss, and Dt is discharge from the
reservoir during the month t. Equation (6) is solved using inputs such as the functional
relationship between surface area, seepage, evaporation vs volume, sequence of
monthly inflows into the reservoir and policy for determining the discharges from the
reservoir. A certain amount of "dead" storage capacity was added to account for
sedimentation.
Dependability The storage capacity (V) of any reservoir is the function of both
targeted draft (D) and reliability (R), given by:
V= f(D,R) (7)
It is seen that the required reliability of targeted draft has a direct relation to
effective storage capacity, which has to be provided. For a given draft, particularly the
one approaching a mean flow, the required storage is extremely sensitive to reliability.
Similarly for a given level of reliability, increase in targeted draft would result in large
storage. Thus, for a given draft, storage would increase substantially with increased
reliability levels. For hydropower planning, in the case of power generation schemes, a
dependability criterion of 90% on a yearly basis is normally adopted.
Constraint on seasonal variation in generation capacity If no variation is
allowed:
Ptm=Ptd (8)
Allowing seasonal variation:
Pt,n>P,d (9)
If variation of "r" is allowed:
Pt,„>rPtd (10)
The variables Ptm and Ptd, are hydroelectric generation capacity during monsoon and
dry months, respectively, written in terms of power draft as:
Pm = kyDJLFm (11)
and
Ptd = kvDld/LFtd (12)
where LFtm and LFtd are average load factors during monsoon and dry months,
respectively. Therefore:
Optimal design of hydroelectric projects in Uttara Kannada, India 305
DJLFm=DtdILFtd (13)
DJLFtm>r-DtdILFtd (14)
Assuming
LFtm = LFtd (as 0.5) (15)
Equations (13) and (14) would become
Dtm=Dtd (16)
and
Dtm>r-Dtd r= 1,2, ..., oo (17)
Constraint on minimum storage
Ka>V,îort=l,2,...,\2 (18)
where Ka is the active storage capacity.
Operating policy of the reservoir The feasible operating policy, considering
seasonal variation in water inflow, would be: {(S\-Ptm + 0 f o r a l l f = l , 2 , . . . , 1 2 (22)
and
F,>0forallf=l,2,...,12 (23)
Therefore
Ka > 0 (24)
306 T. V. Ramachandra et al.
CASE STUDY
This design is implemented for the hydroelectric scheme at Magod.
River discharge
The average annual yield at Magod is 1105 Mm3 measured by empirical method. The
90% dependable water yield is estimated as 995 Mm3. Water yield computed with
90 years precipitation data, shows that water quantity varies from 0.25 ± 1.25 during
January to 364 ± 136 during July.
Evaporation, seepage loss and silting capacity
Evaporation and seepage losses for the region are estimated as 99 Mm3 year"1 for
100 km2. The silt rate per annum is given by S = C(Â)314 = 4.25 (where C is the
catchment coefficient and A is the catchment area (in m2)) assumed for a basin with
plain and forested tracts. With the silt rate of 0.83 Mm3 year"1, the life of the reservoir
at FRL 450-455 m is about 50 years.
Dam site
The site proposed 0.91 km upstream of Magod Falls, at longitude 74°45'28"E and
latitude 14°5r41"N commands a basin area of 2084 km2 and has exposed rocky bed at
either side. The river bed level here is 373 m and it is 36 m wide.
Dam height and submergence area
When the water head is very high and given the reservoir profile—a deep valley with
steep walls, hydroelectric energy becomes very competitive compared to bio-energy.
When the water head is lower and the terrain has a slope less than 25°, the smaller
reservoir depths and smaller submergence area make firewood an attractive option. A
dam at this site would submerge areas having bioresources such as firewood, that are
used for domestic, commercial and other purposes.
The volume of water stored for a particular dam height, computed by assuming the
volume between two consecutive contours to be trapezoidal, is:
Vn = (al+a2)-0.5-hi2 (25)
where Vu is the volume between contours 1 and 2, ci\ and a2 are the area of contours 1
and 2 respectively, and h\2 is the height difference between contours 1 and 2. The
generalized form could be written as:
Vv=f/kMX i = l,j = i + l,i + 2,... (26)
Optimal design of hydroelectric projects in Uttara Kannada, India 307
200-
180-
160-
140-
120-
100-
80-
60-
40-
20-
0.
0J
15
~9~ Actuai area
—1— Yestimate=A*e~ (B*X)
0,86 1.84 z-êë-~===d%K
""" i 1 1
2&M
.... j
95JD8
1
195,85
1
Fit
0 20 40 60 80 100
Height in meters
. 3 Submergence area for various heights of dam at Magod.
The submergence area, ^sub, and corresponding volume computed for different
dam heights at Magod are depicted in Fig. 3. This shows that when the dam height,
//dam is 67 m, the submergence area is 5.7 km2 and the volume is 106.35 Mm3. Beyond
87 m, there is a steep increase in submergence area, as is evident from submergence
area of 95.03 km2 for dam height of 107 m. The relationship between submergence
area and height of the dam is exponential (Asub = 0.38-e0048'™3"1) with r=0.99 and
percentage error = 0.45. Similarly, the probable relationship between volume of water,
Vdam, and height of the dam is exponential (Vd3m = 5.03-e0054//dam) with r = 0.99 and
percentage error =0.22. This relationship between volume and height (actual and
predicted), for Magod, is shown in Fig. 4.
NET ENERGY ANALYSIS
Hydropower at each site has been computed before maximizing the net energy
function. Energy from water is computed based on parametric optimization techniques,
listed in Table 1. If variation is allowed between P,m and Ptd (equations (8)—(12)), it
reduces the storage capacity requirements. Figure 5 shows a graph of submerged area
(in km") vs hydroelectricity generated, Eh. Regression analysis of these variables gives
a hyperbolic relationship. More hydroelectric energy is harnessed by drawing the water
during monsoon on a ran-of-river basis and sufficient quantity is stored to meet the
non monsoon requirement. By allowing a P,m to P,d ratio of 3, the submergence area
saved is about 69.97% with an increase in electrical energy. This is because, for
smaller heights of the dam, the submergence area is smaller and therefore evaporation
and seepage losses are also lower. This saved area would also meet the bio-resource
requirement of the region.
308 T. V. Ramachandra et al.
E
o 3000-
g 2500-
'Ê
~ 2000
E
O
> 1500
11.14 24.64 J2£l
0 12.Sl21.54 406 3 ' 2 5 60 80 100
Height in meters
Fig. 4 Storage volume for various heights of dam at Magod.
Table 1 Power (MW) and energy (in million kWh) at Magod.
Height
(m)
107
97
87
87
87
82
82
82
77
77
77
72
70
67
Contour
(m)
480
470
460
460
460
455
455
455
450
450
450
445
443
440
Sub-area
(km2)
95.03
63.23
28.59
28.59
28.59
20.77
20.77
20.77
16.27
16.27
16.27
12.74
9.98
5.70
Volume
(million Mm3)
1736.35
1134.53
545.36
545.36
545.36
416.61
416.61
416.61
416.61
416.61
416.61
243.12
185.72
106.35
Note: for dam heights of 72, 70 and 67 m, multiple
Hydropower:
P1/P2
1.00
1.00
3.00
4.00
6.00
6.00
4.00
3.00
6.00
4.00
3.00
10.00
8
16.00
8
32.00
16
P1/P2 ratios
PI
(MW)
85.00
90.00
157.51
138.04
199.82
203.98
180.00
163.37
210.00
184.63
166.15
250.03
200.02
319.95
159.98
320.00
160.00
are possibl
P2
(MW)
85.00
90.00
52.50
34.51
33.30
34.00
45.00
54.46
35.00
46.16
55.38
25.00
20.00
10.00
e
Energy
(million kWh)
746.66
790.55
768.62
768.65
780.08
796.36
790.55
796.27
819.87
810.90
810.82
806.48
823.55
823.55
Biomass energy from lands to be submerged
The land-use pattern for various heights of dam shows area under natural forest as the
major constituent, consisting of evergreen, semi-evergreen and deciduous forests. The
primary production- of biomass is estimated to range between 6.5-27.5 t ha"1 year"1
Optimal design of hydroelectric projects in Uttara Kannada, India 309
830-
820-
810-
800-
790-
LU
780-
770-
760-
750
740
0 10 20 30 40 50 60 70 80 90 100
Area (sq.Kms.)
Fig. 5 Energy generated vs submergence area.
(Ramachandra, in press). Areca and coconut residues from gardens are in the range of
3-4.5 t ha" year"1. Considering the lower productivity of 6.5 t ha" year" , the dam at
Magod with a height of 107 m submerges about 95.03 km2, of which 88.53 km2 is
under evergreen and semi-evergreen forests, rich in biodiversity and worth 34.21 MW
in biomass (thermal) energy. A reduction in dam height to 67 m brings this value down
to 1.93 MW, due to the decrease in the submergence area.
The net energy computed (Table 2), considering thermal value of bioresidues,
indicates that, with decrease in dam height, the net available energy increases. At
Magod, the net energy increases from 416.89 (dam height of 107 m) to 803.14 million
kWh (dam height of 67 m). Considering the efficiency of the couple turbine generator
as 70%, the net energy function becomes:
Enel = Eh' -Ehi0 (27)
Table 2 Hydroenergy, thermal and net energy (million kWh) available from submerged area at Magod.
Bioenergy, Ebio
(@6.5tha"' year"1,
329.77
219.42
100.36
72.91
58.25
45.62
35.74
20.41
Net energy
Eh - Ehi0
416.89
541.13
679.72
723.36
752.57
770.86
787.81
803.14
(million kWh):
Eh' - Ebi0
407.24
455.59
510.93
531.87
547.19
555.57
563.97
569.34
Damheight
107
97
87
82
77
72
70
67
Hydroe
746.66
760.55
780.08
796.27
810.82
816.48
823.55
823.55
y = 733.86+ (1566.288/x) - 6024.64/(x*x)
r = 0.99
Std error of Y est: 3.36
• Actual Energy • Energy (estimated)
Note: Eh' = 0.7 Eh.
310 T. V. Ramachandra et al.
where Eh' is 0.7-Eh. To account for only the final amount of electricity, the thermal
energy content of source is discounted by the conversion efficiency of 35%, Thus:
Enet = Eh'-0.35-Ebm (28)
The result of this computation is given in the last column of Table 2. It shows that
variation in net available energy at Magod ranges from 407.24 to 569.34 million kWh.
The domestic fuelwood consumption survey revealed that 82-90% of households
still depend on fuelwood and agricultural residues, estimated to be 312 million kWh, to
meet their domestic requirements annually. Considerations of system efficiency, peak
power and socio-economic factors, all rale out the possibility of electricity entirely
substituting fuelwood as a source of domestic energy. This necessitates ecologically
friendly options to reduce the submergence of valuable forests.
The model and subsequent quantitative analyses demonstrate that much of the land
could be saved from submergence if the hydroelectric power generation capacity is
adjusted according to seasonal variations in the river's runoff. The viability of a mixed
hydroelectric power and biomass generation system is shown in energy terms, which
leads to a significant reduction in the total area used for power generation. Apart from
this, there is scope to generate hydroelectric energy from streams in a decentralized way.
ECONOMIC ANALYSIS
Computation of costs: net loss due to forest submersion
Forests play a role, not only in the social and economic well being of the society, but also
in maintaining the ecological balance. The direct costs of the submerged area are assessed
by considering standing biomass in the area, which is based on species diversity studies
carried out in sample plots at Sonda, Kallabe, etc. The cost of timber, fuelwood and minor
forest produce works out to be in the range of 2.25-4.55 million Rs (Indian Rupees: Rs
42 = US$1) per hectare depending on vegetation cover. In this computation, the price of
forest land is taken as Rs 111 200 ha~ . Some attempts have been made to quantify the
environmental cost of the loss of a forest arriving at 14.13 million Rs ha4 for tropical
forest and 12.87 million Rs ha"1 sub-tropical forest (Maudgal & Kakkar, 1992).
Loss due to submersion of agricultural and horticultural land
The details of villages submerged and number of households affected are obtained
from government agencies such as the Village Accountant's office. Displacement and
rehabilitation costs were based on data from earlier hydroelectric projects. Economic
valuation of submerged lands is done using the market value per hectare of arecanut
garden: Rs 890 000, of paddy: Rs 99 000 and of coconut plantation: Rs 218 000.
Annual charges on capital costs
The capital cost depends on: (a) civil construction costs (size and type of dam) and
(b) cost of the generating unit, which depends on the capacity (calculated using normal
Optimal design of hydroelectric projects in Uttara Kannada, India 311
load factor of 0.5). The schedule of rates approved recently by the government has
been used in computing civil and electrical costs. This calculation, carried out for
different heights, is listed in Table 3. The annual capital recovery factor (annuity
factor) is calculated for the total cost (civil + electrical + environmental + rehabilitation)
at 12% interest for 50 years of satisfactory functioning of the power station.
Table 3 Civil, electrical, environmental, rehabilitation costs (million Rupees) at Magod, for various
heights of dam.
Dam
height (m)
107
97
87
82
77
72
67
Civil + El
3902.75
3318.21
3497.07
3592.17
3718.18
3872.65
4029.24
Env (land)
1282.99
583.64
427.76
339.01
287.29
225.15
218.60
Rehabilitation
173.25
138.60
23.85
1.12
0.09
0.02
0.02
Env cost
20.00
9.10
3.03
0.80
0.18
0.03
0.02
Total cost
5378.99
4040.45
3948.68
3931.19
4005.74
4097.85
4247.88
Annual
expenditure
798.67
599.93
586.30
583.70
594.73
608.44
630.72
Civil + El: civil and electrical construction costs;
Env (land): land cost due to submersion;
Env cost: cost due to loss of environmental benefits.
Operation and maintenance (O & M) charges
Annual O & M charges are taken as 1% of the total cost of the project. The
depreciation works out to be 1.80%, taking into account the life of the dam as 70 years;
that of surge shafts, penstock, power house equipment, power house building and
substation equipment as 50 years, and of roads, etc. as 35 years. Hence, the annual
cost, C, is computed as:
C = (Annuity factor x Total cost) + O & M charges + Depreciation cost (29)
With this annual cost and energy information, the cost per kWh of energy, has
been computed in Fig. 6. It shows 40.5% reduction in cost (Rs 1.53 kWh"1 to Rs 0.92
kWlf1) for a dam height reduction of 32.75%o. If one considers electricity from water
resources only, then the cost reduction is from Rs 1.53 kWh"1 to Rs 1.09 kWh"1.
Benefits
Benefit would be the revenue accrued as a result of electricity consumption in various
sectors. The percentage share of each sector, calculated considering the annual
consumption pattern in Uttara Kannada district, shows that the industrial sector, with a
share of 86.38%, is a major consumer, followed by the domestic sector, with a share of
10.20%. Based on tariff information provided by Karnataka Electricity Board, sectorwise
revenue has been computed. The benefit, B, from the power project is given as:
B = fjertJ (30)
where j = 1,..., 6 (representing various sectors) and e, and tj are electricity consumption
and tariff, respectively, in Rs kWh"1 for sector "/'.
312 T. V. Ramachandra et al.
O)
ai
o
O
- * - Cost/Eh'
—•— Eh' + Ebio(@6.5)
-•*•• Eh'+0.35 Ebio(@6.5)
62 67 72 77 82 87 92 97 102 107 112
Dam heights (various designs)
Fig. 6 Cost per kWh of electricity generated for various heights of dam.
2.5
a
»
o o
c
a
m
1.5
0.5
2.30
2.24 2- 2 7 2.25
Dam heights (various designs),meters
- » - Case I —¥- Case II -••*--• Case III
- e - Case IV - K - Case V - ± - Case VI
Fig. 7 Benefit-cost ratio for various environmental costs.
Optimal design of hydroelectric projects in Uttara Kannada, India 313
The benefit-cost ratio, BIC, for various dam heights, considering the following
cases, is depicted in Fig. 7.
The value of forest land for Cases I, II and III is Rs 37 065, Rs 111 200 and
Rs 111 200 (+ Rs 12 000, minor forest produce + fuelwood) per hectare, respectively.
However, for cases IV, V and VI, the value of a hectare of forest land with standing
biomass is Rs 2.25 million, 4.55 million and 2.25 million (+ environmental value as
Rs 14.13 million), respectively.
The value BIC is greater than 1.5 for dam heights less than 97 m in Case I, 87 m in
Case II and 82 m in Case III, while for Cases IV, V and VI, BIC is less than 1.5 for all
heights of dam. This means that, by assigning environmental values, taking all components
into consideration, the hydroelectric generation through storage (for minimum
submergence also) becomes a less attractive option.
SUMMARY
The hydroelectricity potential of streams in the Bedthi and Aghnashini river basins is
estimated to be about 720 and 510 million kWh respectively. In order to reduce the
submergence of prime forests, it is necessary to look for an optimal range of reservoir
size and installed generation capacity, based on certain site specific factors. Quantification
of the energy cost of land submergence reveals that net energy in the region
(hydropower and thermal energy in the potential biomass increment), could be
maximized by optimal project dimensions.
This analysis explains the upper limit on the height of the dam and therefore the
area of the reservoir for the project to yield a positive net energy. Also, it is noticed
that savings in land submergence could be achieved by adjusting hydroelectric generation
capacity according to seasonal variation in the river runoff. By parametric
optimization technique, allowing a seasonal generation ratio of 3, the submergence
area saved is about 69.97% with subsequent increase in electricity generated. This is
mainly due to less evaporation and seepage loss due to reduced submergence area for
smaller dam heights.
Net energy analyses carried out by incorporating bioenergy lost in submergence at
Magod show a gain of 63.9% for a reduction of 37.3% in dam height. Apart from the
distinct reduction in submergence area, the overall reliability of a combined hydropower
and thermal energy system is much higher than that of pure hydropower
systems (which are very sensitive to fluctuations in rainfall).
Net energy computed for various dam heights shows that a reservoir with dam of
height 67 m stores enough water to meet the region's lean season electricity requirement
and the area saved has a bio-resource potential of 319 million kWh that can cater
to the domestic thermal energy demand of 312 million kWh.
The calculation of cost per kWh for various designs of the dam shows a 40.5%
reduction in cost for a dam height reduction of 32.75%. The benefit to cost ratio,
computed considering forest land value as Rs 111 200 ha"1 is greater than 1.5 for dam
height less than 87 m.
Acknowledgements This work was supported by grants from the Ministry of Environment
and Forests, Government of India and Indian Institute of Science. The authors are
314 T. V. Ramachandra et al.
grateful to Mr Joshua David for assisting in editing the manuscript. Climatological
data were provided by the India Meteorological Department, Government of India.
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Received 8 January 1997; accepted 2 November 1999