pico hydropower in nepal - engineering for change
TRANSCRIPT
Pico Hydropower in Nepal Alastair Laurenson, Andy Waugh, Kit Stormont, Owen Emmington�Thomas, Tomos Howells
Buro Happold
29 March 2013
In association with:
With thanks to:
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I. INTRODUCTION
The village of Balmitar is located in the Gorkha district of
Nepal and is currently connected to the national electricity
grid system, however the supply is unreliable and during peak
times the village is subject to brownouts and the voltage of
the supply fluctuates.
A potential source of Pico Hydro�power has been identified
500m to the east of the village where two small streams run
nearby and merge. These can be used to generate power for
the new Balmitar nursery school and the village’s 27
dwellings. Both streams have existing dams which could be
utilised as intake sites.
The rate of flow in both streams is similar and varies
greatly between the low flows of the dry season
(approximately 1.6l/s) and the high flows of the monsoon
season (39.9l/s). The potential head, relative to the proposed
power house location, at intake A and B are 71m and 30m
respectively.
This report details a proposed scheme for providing the
village of Balmitar with a Pico Hydropower system. The
proposed scheme generates 8362kWh of electricity per
annum with at a peak of 1031W. To distribute the electricity
the school has been cabled directly, with an additional
electricity ‘hub’ to provide electricity for the rest of the
village.
II. OVERALL DESIGN
Following the initial design stage of the competition the
design was reviewed. It was decided that the most important
factor was to provide the required 500W in the most reliable
form with a system that could be truly fit�and�forget.
The original design combined the two flows at the pelton
wheel in a multi jet combination (see Fig. 2.1). However due
to the different pressures and the difficulty in combining the
sources the design required refining.
FIGURE 2.1 –INITIAL DESIGN CONCEPT
Combining the two sources mechanically was investigated
using separate pelton wheels (see Fig. 2.2). The difficulties
with this method are the complexity of the mechanical
components; the difficulty in balancing the different speeds
on the shaft; and the extra mechanical equipment cost.
Although this was considered a valid potential system layout
the potential power gain is minimal compared to the
increased cost.
FIGURE 2.2 –COMBINING TWO PELTON WHEELS VIA MECHANICAL
TRANSMISSION
Initial calculations for the design flow rate were based
solely on the worst case dry season flow. However
considering the flow profile throughout the year (see Table
2.1), it was decided that the design flow rate should be based
on 3 l/s. For the two months where there is low flow, a
different nozzle could be used based on a 1.6 l/s flow rate.
TABLE 2.1 –DESIGN FLOWRATES
Month River
Flowrate (l/s)
Penstock Design
Flowrate (l/s)
January 4.3 3.0
February 3.0 3.0
March 2.2 1.6
April 1.6 1.6
May 3.0 3.0
June 5.0 3.0
July 21.6 3.0
August 39.9 3.0
September 33.2 3.0
October 16.6 3.0
November 8.0 3.0
December 6.0 3.0
Assuming an approximate system efficiency, η, of 50%, a
flow, Q, of 3 l/s and a head of 71m, the potential Power, P,
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from intake A alone can be determined from the following
formula:
� � � � � � � � � …eq(1)
� � 71 � 3 � 9.81 � 0.5 � � 1044�
Therefore it is possible to provide the required power just
from intake A. This simplifies the system and allows a tried
and tested model to be implemented.
However, currently near intake A the village also sources
their potable water and irrigation. Therefore the proposal is to
move the village pipes to intake B so that the full flow can be
utilised at A. This is because the amount of head is not
critical for the potable and irrigation water system. Fig. 2.3
details the layout of the proposed final system.
FIGURE 2.3 – PROPOSED SYSTEM LAYOUT
III. INTAKE
In order to maintain a constant depth of water above the
penstock intake throughout the year, a long crested diagonal
weir is proposed to replace the existing intake A. A long
crested weir allows the width of the weir to be greater than
the width of the river, thus allowing the excess flow in the
river to discharge without having a great effect on the river
depth. Table 3.1 shows the initial sizing of the weir for the
highest flowrate in the river.
TABLE 3.1 –WEIR SIZING CALCULATIONS
River Flowrate (l/s) 39.9
Penstock Flowrate
(l/s) 3.0
Required Overflow
(l/s) 36.9
Width of Weir (m) 3
Height of Water over
weir (mm) 49.3
The height of water through a rectangular weir was found
using the following equation:�
Williams et al (1993) [1] suggests that a suitable value for
the discharge coefficient of a diagonal long crested weir is
0.38.
The intake is to be constructed out of local stone and
concrete in line with the river due to the site topology. A
trashrack will be installed so that any large floating debris
will not damage or block the penstock intake. A filter, made
by drilling holes into the pipe and capping the end, will also
be fitted to the penstock inlet to prevent any large objects
entering the pipe. It is important that the diameter of the holes
is less than the diameter of both the nozzles at the pelton
wheel to prevent particles large enough to block the system
from entering the penstock. The proposed upgrade of the
intake dam can be found in Appendix A.
IV. PENSTOCK PIPE
A High Density PolyEthylene (HDPE) pipe was chosen to
deliver the water from the intake to the powerhouse. This is
because the material is resistant to sunlight whereas PVC
would degrade. HDPE is also cheaper than PVC and also is
flexible therefore suitable to the terrain.
To reduce the cost of the pipe, the higher pressure rating
pipe was used only where required. Bernoulli’s equation was
used to determine the pressure at each point along the pipe
and Table 4.1 overleaf shows the breakdown of the pipe
lengths of each pressure rating required. These are
approximations based on the length and change in height of
the penstock, and will need to be measured on site to confirm
the exact lengths.
�� � ����
��2���� …eq(2)
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TABLE 4.1 –REQUIRED LENGTH OF PIPE SECTIONS
Length of Section
Pressure
Rating
(kgf/cm²)
136 2.5
130 4
130 6
72 10
To determine the optimum size of the penstock, a Net
Present Value analysis was used.
The head loss for each pipe size was calculated using the
Darcy�Weisbach equation for each pipe size and the available
electricity for both dry and wet season flows calculated. This
was then used to calculate the available income over 10 years
assuming a typical electricity cost of 7 NPR/kWh, and an
interest rate of 6.4%. The costs of the scheme over the 10
year period were then calculated, assuming a maintenance
cost of 18270 NPR/yr, an installation cost of 13000 NPR and
an interest rate of 6.4%. The outcome of the Net Present
Value (NPV) Analysis is shown in Figure 4.1.
FIGURE 4.1 – NPV ANALYSIS FOR DIFFERENT AVAILABLE PIPE SIZES
A 75mm pipe was chosen as using a larger pipe, therefore
reducing head loss, had no cost benefit to the system. The
headloss for the 75mm pipe was 3.36m for wet season
flowrate and 1.12m for dry season.
V. POWERHOUSE
The powerhouse will be positioned at the intersection of
the two rivers. It will be constructed from concrete and
locally sourced stone. The building will be raised so that the
outgoing water from the turbine can pass underneath the
building in a concrete channel back to the river. The
powerhouse will enable the equipment to be protected and
allow storage for maintenance tools and additional
equipment. A slanted corrugated iron roof will be installed so
that the water will run off the building. Appendix B shows a
plan layout for the powerhouse.
VI. TURBINE
From the original design a pelton wheel was selected as our
turbine. The pelton wheel was sized following the theory
explained by Bansal (1983) [2] and Apsley (2012) [3].
Table 6.1 shows the calculations to size the wheel and
bucket size. At the time of writing manufacturer quotes were
in abeyance therefore all sizing is based on ideal calculations.
TABLE 6.1 � PELTON WHEEL DESIGN CALCULATIONS
Wet
Season Dry Season
Design Flowrate (l/s) 3.0 1.6
Effective Head (m) 67.64 69.88
Nozzle Discharge Velocity (m/s) 32.79 33.33
Ideal Nozzle Diameter (mm) 10.79 7.82
Wheel Speed Ratio 0.45 0.45
Bucket Tangential Velocity (m/s) 14.75 15.0
Bucket Angle of Deflection (deg) 160 160
Power Transmitted to Bucket (W) 1473 812
Target RPM (see section VII) 1565 1565
Ideal Pelton Wheel P.C.D (mm) 180 183
From these calculations it can be seen that by using an
11mm and 8mm interchangeable nozzle and a pelton wheel
of 180mm pitch circle diameter we can provide the required
performance for both design conditions.
VII. GENERATOR
Due to the cost of a generator, it was decided that 3 phase
induction motor operating above its synchronous speed would
be used to act as a single phase generator. The 4 pole motor
was selected to operate at 50Hz. This provided an operating
shaft speed of 1500rpm using the formula:
�150000
�100000
�50000
0
50000
100000
0.05 0.063 0.075 0.09 0.11 0.125
10
yr
Pro
fit
/ L
oss
(N
PR
)
Pipe Diameter (m)
��� ! �"#$%� &: �( � )(*�
�+, …eq(3)
�-./012 � 3�45678891 : ;<=;<41 : 4> ?$4@== …eq(4)
Where: k is the fluid discharge coefficient (assumed 0.9)
@ is the bucket angle of deflection (assumed 160deg)
A�B � <�C�)
D7. 7) E791F …eq(5)
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Assuming a slip of 4.33% in the motor, the motor is
required to run at 1565 RPM to operate as a generator.
A 1.5kW motor was selected. This is because when
running motors as generators they produce excess heat.
According to Smith and Ranjitkar (2000) [4] a de�rating of
20% needs to be applied. 32 MicroFarad capacitors in a C�2C
configuration are required for the motor to act as a generator.
This was calculated following the design process outline in
Smith (1994) [5] however this will be confirmed and adjusted
on site. The motor being run as a generator should include an
induction generator controller (IGC) to maintain a constant
frequency and manage any excessive power. Portegijs (2000)
[6] recommends a suitable available product, the
“Hummingbird ELC/IGC” which has been developed for use
in micro and pico hydro schemes, and is manufactured using
inexpensive and widely available parts. Any excessive power
produced will be discharged through 2 cooking rings,
mounted on the wall of the power house.
TABLE 7.1 – ANNUAL ENERGY PRODUCTION
Month
Total
Generated
Electricity
(kWh)
Electricity
Required for
School
(kWh)
Excess
Electricity
for Village
(kWh)
January 767 124 643
February 699 113 586
March 423 124 299
April 409 120 289
May 767 124 643
June 742 120 622
July 767 124 643
August 767 124 643
September 742 120 622
October 767 124 643
November 742 120 622
December 767 124 643
Annual Total 8362 1461 6901
Table 7.1 shows the predicted annual electricity
distribution per year produced by the generator. A generator
efficiency of 70% has been assumed at this stage prior to
confirmation of the actual performance of the motor. It has
also been assumed that the pico hydro system is running for
24 hours a day, with the school requiring 500W of power
between 8am and 4pm.
VIII. ELECTRICITY DISTRIBUTION
As described in Section VII, control will be required to
dissipate any excessive power produced. A volt drop
calculation shows that all three cable types would be suitable
and have a volt drop of less than 6%. Therefore the squirrel
cable has been selected as its cost provides a saving over the
other two with little difference in volt drop.
TABLE 8.1 – CABLE VOLTAGE LOSS
Type Resistance
(ohm/km)
Resistance
(ohm/m)
NPR/m Total
Cost
Volt
Drop
%
Volt
Drop
Squirrel 1.37 0.00137 22 11066 4.70 2.14%
Gopher 1.01 0.00101 28 14084 3.46 1.57%
Weasel 0.91 0.00091 31 15593 3.12 1.42%
An MCB circuit breaker with an RCD will be provided
within the power house on the supply cable. The cable will be
installed on 3m high poles spaces at 35m between the power
house and the school, with an allowance of 250mm sag
between each set of poles. The cable will terminate in a
suitable location within the school to a small distribution
board. A second MCB circuit breaker with an RCD will be
used on the supply cable within the distribution board, then
two lighting circuits and two power circuits have been
allowed for all MCB with RCD devices. One of the power
circuits will supply the electricity hub (see section IX) where
2 single socket outlets will be provided.
IX. IMPLEMENTATION PLAN
The remaining power is proposed to be distributed to the
rest of the village via an Electricity Hub, creating a focal
point for the use of electricity, rather than connecting cables
to each individual house where issues of fair use, metering
and connecting the system into the existing grid bring about
complications. The Hub will provide facilities for villagers to
charge renewable battery packs for LED lanterns, providing a
portable light source for use in their homes and outside in the
evenings. One lantern will be provided to each house for a
subsidised fee along with two rechargeable battery packs (see
Figure 9.1), which they can take to the Hub to charge for a
small pay�as�you�go fee as and when required so that they
always have one working battery pack. The cost for battery
recharging will be based around what the villagers currently
pay for using grid electricity (~100 NPR per month) with the
intention that they will not
need to rely on the grid at all
and will only use it as a
back�up, meaning their total
household energy
expenditure will not increase
as a result of introducing
this system.
The Electricity Hub will
consist of a storage room
FIGURE 9.1 – LED LANTERN, D�
BATTERY PACK AND D�BATTERY
CHARGING UNIT
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for the system’s charging equipment and sockets as well as a
kiosk for serving customers. This is proposed to be
constructed using stone from the nearby mine and other
locally sourced materials – similar to that of the powerhouse
– to house the equipment and kiosk securely. Estimated costs
for this have been included in the costing plan. Alternatively,
the Hub could potentially be incorporated into part of the
school building or a village community hall if one already
exists which would save on capital costs and make the kiosk
more secure.
The Hub scheme is self�sufficient and will operate so that
the income generated will be fed back into the system by
covering all operation and maintenance costs. Assuming there
is currently no privately�owned lighting business in the
village and the villagers’ electricity bills are paid to a
centralised governing body, the hub system will operate as
conveyed in Figure 9.2. The Hub will be managed and
operated by a democratically elected Energy Committee
made up of four to five members who represent a broad range
of social classes in the community. The Balmitar Energy
Committee (BEC) will be in charge of any changes to the
system, as well as controlling profit flows from the electricity
hub and reinvesting it back into the system or community.
FIGURE 9.2 – ELECTRICITY HUB & BALMITAR ENERGY COMMITTEE (BEC)
To help ensure there is always a readily available supply of
charged D�batteries for all 27 houses, the BEC will be trained
on the impact of battery charging on the system’s overall
power output and a strategy for what time of day is best to
charge the batteries. Maximum power will be available
overnight when the school is not in use, so all the system’s
generated power can be used for battery charging at this time.
However a cap should be put on how many batteries can be
charged at one time during the day whilst the school requires
500W of power. The Coleman CPX 6 LED lantern and
5000mAh D�batteries shown in Figure 9.1 can run for a
minimum of 40 hours [8], meaning that each household will
need a new set of batteries every 5 days assuming they use
the lantern 8 hours a day. The battery packs use 4 D batteries,
so 108 D batteries would need to be charged over 5 days for
27 households. The 1000mA battery charger shown in Figure
9.1 can charge 4 batteries at one time with a charge duration
of 8 hours. Six chargers will therefore be used at night (8
hour period) when all the generated power is available, and
two chargers used during the day (16 hour period) when
500W is needed by the school. A total of 40 batteries can then
be charged per 24 hours, sufficing the 27 household’s energy
demand without affecting the school’s power usage.
The proposed scheme promotes fair distribution and usage
of the power generated from the pico�hydro system, and also
provides an income generation scheme and facilities that can
foster potential business activity and growth in the village.
The hub offers potential scope for villagers to run their own
micro�businesses, such as mobile phone charging, by leasing
out sockets from the BEC.
X. COST ANALYSIS
The capital costs of the proposed construction have been
estimated allowing for: the construction of the proposed
upgrade to intake A; the purchase and installation of the
penstock from intake A to the power house; the construction
of the power house and electricity hub; and the electrical
distribution system from the power house to the hub and the
school.
The cost of the pelton wheel, generator and associated
components will be provided by the manufacturer to match
our specification and currently to be confirmed. A nominal
sum of 130,000 NPR has been provided in the cost plan to
allow for the purchase and installation of the turbine system
with actual costs to be confirmed by the manufacturer. All
capital costs for the whole system are listed in Table 10.1
overleaf.
The operating costs of the system are expected to be in the
region of 40,500 NPR per annum based upon a case study for
similar scheme in Nepal [7]. The expected revenue from the
sale of electricity is estimated as 48,000 NPR per annum on
the basis that surplus electricity will be sold at a rate of
7NPR/kWh. On this basis, the NPV of the system, assuming a
30 year design life and an interest rate of 6.5%, has been
estimated at 672,532 NPR as detailed below:
Capital Costs: 785,010 NPR (£6,039)
Annual Operating Costs: 40,500 NPR
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Total NPV of Operating Costs over 30 years:
455,747 NPR (£3,506)
Annual Revenue 48,000 NPR
Total NPV of Revenue over 30 years:
540,144 NPR (£4,155)
Hence, NPV: 700,613 NPR (£5,390)
TABLE 10.1 – CAPITAL COSTS
Item Quantity Cost (NPR)
Reservoir
Stone 1 x 2 cubic metres 3,000
Cement 4 x 50kg bags 3,160
Sand 1 x 2 cubic metres 3,000
Bars 30 number 4,500
Labour 10 man�days 6,000
Penstock
Penstock 460metres 114,000
Labour 30 man�days 18,000
Power House
Stone 10 x 2 cubic metres 30,000
Cement 50 x 50kg bags 39,500
Sand 3 x 2 cubic metres 9,000
Roof 25 square metres 19,625
Labour 24 man� days 14,400
Distribution System
Cable 605 metres 13,310
Poles 16 number 48,000
Labour 10 man�days 6,000
Electricity Hub
Stone 10 x 2 cubic metres 30,000
Cement 50 x 50kg bags 39,500
Sand 3 x 2 cubic metres 9,000
Roof 25 square metres 19,625
Labour 24 man �days 14,400
Equipment
Generator and Turbine 1 number 130,000
Lanterns 27 number 87,750
Batteries 162 number 84,240
RDC Boards 3 number 39,000
Total 785,010
XI. TRAINING PLAN
The training plan is a fundamental part of the whole
installation. It is critical that the system is understood by the
village and that selected individuals have a comprehensive
understanding to ensure it operates and is maintained
correctly. The system has been designed as fit�and�forget, but
some care and maintenance will be required. It is therefore
important that potential issues are identified and suitable
remedies are outlined for a quick and easy solution to rectify
any problems. Some of the areas that need to be considered
are as follows:
• Ensuring the filter system at the top of the penstock
does not become blocked; • Visual inspections of the power houses, a pictorial
explanation of items to check and solutions will be
included; • A fault finding explanation of the electrical installation
will be developed and remedies included; • Operational information on opening and closing the
isolating valve; • Safety on starting and stopping the pelton wheel and
generator; • How to measure the water flow rate and adjust the
nozzle to set the system up for dry season flow rate at
the right time. The training will be implemented following the
democratic election of the BEC, who will then be given an
overview of the system, with pictorial explanations of the
electrical faults and remedies. Practical examples will be used
as much as possible and some role play type scenarios
included. Details for a suitable local contractor will also be
found to both continue the training and to provide expert
assistance where required to resolve problems.
ACKNOWLEDGMENTS
The authors thank their colleagues at Buro Happold,
particularly Duncan Ker�Reid and Gordon Findlay, for their
assistance and advice.
REFERENCES
[1] M. L. Williams, J. M Reddy and V Hasfurther, “Calibration of Long Crested Weir
Discharge Coefficient”. Available online at http://library.wrds.uwyo.edu/wrp/93�
13/93�13.html, May 1993
[2] Dr. R. K. Bansal, “Fluid Mechanics and Hydraulic Machines”, Laxmi
Publications, New Delhi. pp851�870. September 1983
[3] D Apsley, “Pumps and Turbines”, Manchester University, available onlne at
http://personalpages.manchester.ac.uk/staff/david.d.apsley/lectures/hydraulics2/t
4.pdf 2012.
[4] N. Smith and G. Ranjitkar, “Nepal Case Study – Installation and Performance of
the Pico Power Pack”, Pico3Hydro March 2000, available online at
http://www.eee.nottingham.ac.uk/picohydro/docs/NepalCaseStudy_1.pdf
[5] N. Smith, “Motors as Generators for Micro�Hydro Power”, ITDG Publishing,
London. 1994
[6] J. Portegijs, “The hummingbird Electronic Load Controller/ Induction Generator
Controller”, Eneco, available online at
http://williamson.us.com/Information/Development/Hydro%20power/Manuals/Hu
mbird/Humbird%20ELC.pdf December 2000.
[7] B. Shrestha and N. Smith, “Nepal Case Study – Part 3 Lessons from project
implementation and 20 months of operation”, available online at
http://www.eee.nottingham.ac.uk/picohydro/docs/NepalCaseStudy_3.pdf
[8] Coleman CPX 6 Easy Hanging LED Lantern, Outdoor Kit.
http://www.outdoorkit.co.uk/product.php?product_id=11934&utm_source=froogl
e&utm_medium=organic&utm_campaign=froogle&gclid=CKWx3MXaorYCFcr
HtAod�AoAOg
Proposed Upgrade to Intake A
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Section 1
Section 2
Plan
250
Proposed Power House Layout
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Nozzle and Pelton Wheel
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Pelton Wheel and Motor asGenerator
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