pico hydropower in nepal - engineering for change · pico hydropower in nepal alastair ... this...

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:

EWB�UK Innovation Hub

Pico Hydro in Nepal Competition

Final Report

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,



Final Report

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)



Final Report

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)



Final Report

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



Final Report

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



Final Report

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


Power House




Roof 25 square metres 19,625

Labour 24 man� days 14,400

Distribution System

Cable 605 metres 13,310

Poles 16 number 48,000


Electricity Hub




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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Pico-Hydro in Nepal Design Competition

Notes :- All dimensions are approximate. Finaldimensions to be confirmed followinginformation from turbine manufacturer and sitesurvey.

Client: In Association With:

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Section 2

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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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