efficiencyimprovement of pelton wheel andcross...

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International Journal Of Engineering And Computer Science ISSN:2319-7242

Volume 2 Issue 2 Feb 2013 Page No. 416-432

EFFICIENCYIMPROVEMENT OF PELTON WHEEL ANDCROSS-

FLOW TURBINES IN MICRO-HYDRO POWER PLANTS: CASE

STUDY Loice Gudukeya¹,Ignatio Madanhire

2

¹University of Zimbabwe, Department of Mechanical Engineering

P O Box MP169,Mount Pleasant, Harare, Zimbabwe

[email protected]

2University of Zimbabwe, Department of Mechanical Engineering

P O Box MP169,Mount Pleasant, Harare, Zimbabwe

[email protected]

Abstract:This research study investigated hydro power plant efficiency with view to improve on the power output while keeping the overall

project cost per kilowatt produced within acceptable range. It reviews the commonly used Pelton and Cross-flow turbines which are

employed in the region for such small plants. Turbine parameters such as surface texture, material used and fabrication processes are dealt with the view to increase the efficiency by 20 to 25 percent for the micro hydro-power plants.

Keywords:hydro, power plant, turbine, efficiency, manufacture, micro

1.Introduction

Micro-hydro power plants are an attractive option for

providing electricity in off grid areas of the country [2]. The

simple Pelton and Cross-flow turbines are predominantly

used for these projects as they are cheaper to construct for

this form of renewable energy. Current level of efficiency is

estimated to be 60%, thus allowing for improvements on the

overall efficiency of whole micro-hydro system.

At 60% turbine efficiency micro-hydro schemes seem to be

underutilising resources. Communities are benefitting by

having their business centres, clinics and schools powered.

However more electrical power can be attained without

increasing the resources but by only increasing the turbine

efficiencies [4]. This can ensure that more households in the

catchment area get more than just lighting, but are able to use

other devices such as refrigerators, stoves etc in their houses.

2. Justification

The improvement of turbine efficiencies will increase the

micro-hydro scheme power output while keeping the project

within the monetary budget. Therefore more electricity is

generated from the same resources head (H) and flowrate (Q)

The design of a micro hydro scheme should ensure better

environmental sustainability as the use of hydro energy

enables communities to rely less on non-renewable sources

such as firewood, paraffin and coal thus ensuring that less

CO2 is emitted into the atmosphere leading to less global

warming [3]. Renewable energy is also a cleaner and safer

form of energy.

3. Overview of micro-hydro power plant

Hydro power is the harnessing of energy from falling water,

such as water falling through steep mountain rivers. The

energy in flowing water is converted into useful mechanical

power by means of a water wheel or a turbine [5]. The

mechanical power from the turbine can be converted into

electricity using an alternator or a generator.

Hydro power systems are classified as micro has the power

generation capacity of less 100kW. They are relatively small

power sources that may be used to supply power to a small

group of users or communities, who are independent of the

general electricity supply grid [7].

A micro-hydropower system (MHS) has the following

components [8]:

A water turbine that converts the energy of flowing

or falling water into mechanical energy. This drives

an alternator, which then generates electrical power

A control mechanism in the form of electronic load

controller to provide stable electrical power.

Electrical distribution lines

To develop an MHS the following features are needed as

given in Figure 1 [9]:

an intake or weir to divert stream flow from the

water course;

a headrace, the canal or pipeline to carry the water

to the forebay from the intake;

a forebay tank and trash rack (gravel trap) to filter

debris and prevent it from being drawn into the

turbine at the penstock pipe intake;

a penstock (pipe) to transport the water to the

powerhouse. This may be set up above the ground

surface or underground depending on the

topography of the site. At rocky sites, penstocks are

supported above ground on concrete blocks called

Anchors or Saddle (Pier) supports. The saddle

supports are provided along the straight length at

regular intervals and anchors are provided at

horizontal and vertical bends along the alignment

of the penstock. These are designed to carry the

thickness and the diameter of the penstock

a powerhouse, being the building that

accommodates and protects the electro-mechanical

equipment, (turbine and generator), that convert the

power of the water into electricity;

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Loice Gudukeya International Journal Of Engineering And Computer Science 2:2 Feb 2013(416-432)

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a tailrace through which the water is released back

to the river or stream without causing erosion;

Figure 1:Components of a micro-hydro power system [8]

Figure 2:The inside of a power house[9]

3.1 Power generation

A hydro scheme requires water flow and a drop in height

(head) to produce useful power. It is a power conversion

system, absorbing power in the form of head and flow, and

delivering power in the form of electricity.

To measure the potential power and energy on a site the first

step is to determine the flow rate and the head through which

the water falls. These two parameters are defined thus:

Flow rate (Q) is the quantity of water flowing past

a point at a given time. Q is measured in cubic

metres per second (m3/s)

Head (H) is the vertical height from the level where

the water enters the penstock at forebay tank to the

level of turbine centerline. The typical unit of

measurement is metres (m).

Figure 3: Concept of the head[8]

The power available from a micro-hydro power system is

directly related to the flow rate, the head and the force of

gravity as expressed by the power equation as below:

𝑃𝑔𝑟𝑜𝑠𝑠 = 𝜌𝑤𝑎𝑡𝑒𝑟 × 𝑄 × 𝑔 × 𝑕𝑔𝑟𝑜𝑠𝑠

where

Pgross is the theoretical power produced

(kW)

ρwater is the density of water (kg/m3)

Q is the flow rate in the penstock pipe

(m3/s)

g is the acceleration due to gravity

(9.81m/s2)

hgross is the total vertical drop from intake

to turbine (m)

No power conversion system delivers 100% useful power as

some power is lost by the system itself in the form of

friction, heating, noise etc. The efficiency of the system

needs to be taken into account, since all the equipment used

to convert the power from one form to another do so at less

than 100% efficiency. Figure 4 shows the power losses and

efficiencies within a micro-hydro power system [7]:


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Figure 4: Power losses and efficiencies in a micro-hydro

system [7]

Typical system component efficiencies are shown in Table 1:

Table 1: Typical system component efficiencies [5]

System Component Efficiency

Canal 95%

Penstock 90%

Turbine 60 -80%

Generator 85%

Step-up and down transformers 96%

Transmission 90%

To determine the actual power output from the MHS the

theoretical power must be multiplied by the system

efficiency factor, ηtotal:

𝑃𝑎𝑐𝑡𝑢𝑎𝑙 = 𝜌𝑤𝑎𝑡𝑒𝑟 × 𝑄 × 𝑔 × 𝑕𝑔𝑟𝑜𝑠𝑠 × 𝜂𝑡𝑜𝑡𝑎𝑙

where Pactual is the actual power produced (kW)

ρwater is the density of water (kg/m3)

Q is the flow in the penstock pipe (m3/s)

g is the acceleration due to gravity (9.81m/s2)

hgross is the total vertical drop from intake to

turbine (m)

𝜂𝑡𝑜𝑡𝑎𝑙 = 𝜂𝑐𝑎𝑛𝑎𝑙 x 𝜂𝑝𝑒𝑛𝑠𝑡𝑜𝑐𝑘 x 𝜂𝑚𝑎𝑛𝑖𝑓𝑜𝑙𝑑 x 𝜂𝑡𝑢𝑟𝑏𝑖𝑛𝑒 x 𝜂𝑑𝑟𝑖𝑣𝑒 x

𝜂𝑔𝑒𝑛𝑒𝑟𝑎𝑡𝑜𝑟

It is common to assume an overall system efficiency of 50 –

60%. However, in practice actual power output may be as

low as 30% of gross input power for very small installations

and as high as 70% for larger schemes [3]. Therefore, during

the detailed design stage, it is important to recalculate the

power output based on the actual design and manufacturer’s

data for the proposed equipment.

The turbine efficiency is typically the lowest of the

component efficiencies [7]. Hence it has the highest chances

of being improved and once this has been done, the overall

system may be improved.

3.2 The turbine

The turbines convert energy in the form of falling water into

rotating shaft power. They basically consist of the following

components [2]:

intake shaft - a tube that connects to the piping or

penstock which brings the water into the turbine

water nozzle - a nozzle which shoots a jet of water

(Impulse type of turbines only)

runner - a wheel which catches the water as it

flows in causing the wheel to turn (spin)

generator shaft - a shaft that connects the runner to

the generator

generator - a unit that creates the electricity

exit valve - a tube or shute that returns the water to

the stream from where it came

powerhouse - a small shed or enclosure to protect

the water turbine and generator from the elements

Selection of the turbine depends on the site characteristics,

the main factors being the head available, the flow rate and

the power required as well as the speed at which the turbine

is desired to run the generator [6]. All turbines have a power-

speed characteristic and an efficiency-speed characteristic.

For a particular head they will tend to run most efficiently at

a particular speed, and require a particular flow rate.

Water turbines are often classified as being either Reaction

or Impulse turbines, depending on whether the runner is

fully immersed in water or whether it operates in air.


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3.2.1 Reaction turbine

In a reaction turbine, the runners are fully immersed in water

and are enclosed in a pressure casing. The runner blades are

angled so that pressure differences across them create lift

forces, like those on aircraft wings, and the lift forces cause

the runner to rotate [5]. The casing is scrolled to distribute

water around the entire perimeter of the runner hence the

runner and the casing are carefully engineered so that the

clearance between them is minimized. Examples of reaction

turbines are the Francis and Kaplan type of turbines.

In a Francis turbine shown in Figure 5, water enters around

the periphery of the runner, passes through the guide vanes

and runner blades before exiting axially from the centre of

the runner. The water imparts most of its ‘pressure’ energy to

the runner and leaves the turbine via a draught tube. A

Francis turbine is most effective on medium to high ‘head’ of

water.

Figure 5: Francis turbine [7]

A Kaplan turbine as shown in Figure 6 is a reaction turbine

that is a propeller type which consists of a propeller fitted

inside a continuation of the penstock tube, its shaft taken out

where the tube changes direction. Usually three to six blades

are used, three in the cases of very low head units. Water

flow is regulated by the use of swiveling gates upstream of

the propeller. Kaplan turbines are more sophisticated

versions of propeller turbines and are used in large-scale

hydro sites. Swiveling of the propeller blades simultaneously

with wicket gate adjustment has the effect of maintaining

high efficiency under part-flow conditions. Wicket gates are

carefully profiled to induce tangential velocity of ‘whirl’ in

the water.

Figure 6: Kaplan turbine

3.2.2 Impulse turbine [4]

In an impulse turbine, the runner operates in air and is turned

by one or more jets of water which make contact with the

blade. The water remains at atmospheric pressure before and

after making contact with the runner blades. In this case,

pressure energy is converted into the kinetic energy of a high

speed jet of water in the form of a nozzle. Then it is

converted to rotation energy in contact with the runner

blades by deflection of the water and change of momentum.

The nozzle is aligned so that it provides maximum force on

the blades. An impulse turbine needs a casing only to control

splashing and to protect against accidents.

3.2. 3 Advantages of impulse over reaction turbine

Impulse turbines are cheaper than Reaction turbines because

no specialist pressure casing and no carefully engineered

clearances are needed. These fabrication constraints make

impulse turbines more attractive for use in micro-hydro

systems. Other advantages of using impulse turbines over

reaction turbines in micro-hydro systems are that impulse

turbines are more tolerant to sand and other particles in the

water. They also allow better access to working parts and are

easier to fabricate and maintain [3].

They are also less subject to cavitations. They have flatter

efficiency curves if a flow control device is built in (e.g

nozzle area change, spear valve, change of number of jets,

guide vanes, partitioning of flow).

The major disadvantage of the Impulse turbines is that they

are mostly unsuitable for low head-to- power ratios.

However, the Cross-flow and multi-jet Pelton are impulse

turbines that are suitable for medium head-power ratios. An

impulse turbine can also operate on a low head, if the power

transmitted is also low and slow speed is acceptable.

It is apparent then that for micro-hydro projects, Impulse

turbines are more suitable than Reaction turbines. Table 4

shows groups of Impulse turbines and the head levels they

best function under.

Table 2: Types of impulse turbines and optimum operating

heads

Turbine

Runner

Head (Pressure)

High Medium Low

Impulse

Pelton

Turgo

Multi-jet Pelton

Cross-flow

Turgo

Multi-jet Pelton

Cross-flow

In this study the Pelton wheel and the Cross-flow turbine are

considered in detail

4. Pelton wheel turbine [6]

A Pelton turbine consists of a series of cups mounted around

the periphery of a circular disc. The shaft of the Pelton

turbine is mounted either horizontal or vertical. The turbine

is not immersed in water but operates in air with the wheel

driven by jets of high pressure water which hit the cups. The

kinetic energy of the water jets is transferred to the turbine as

the water jet is deflected back. The kinetic energy of a jet of

water is converted into angular rotation of the cups as the jet

strikes. The high-velocity jet of water emerging from a

nozzle impinges on the cups and sets the wheel into motion.

The speed of rotation is determined by the flow rate and the

velocity of water and these are controlled by the spear valve.


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The water must have just enough speed to move out from

between the cups and fall away under gravity from the

wheel.

Figure 7: Pelton turbine [6]

Figure 8: Pelton buckets

4.1 Characteristics of Pelton wheel cups/buckets [7]

The central part of each bucket has a splitter ridge. This is

the part that the water jet hits first. This splitter ridge should

be sharp and smooth, so that it cleanly splits the jet into two

halves. The force on the bucket comes from it catching the

water and taking out as much of the water’s momentum as it

can. The more the water’s momentum absorbed by each

bucket, the better the turbine efficiency. Getting a good

torque from this force requires the force to act at as large a

radius as possible. To achieve this, the position of the end

point of the splitter ridge is important. The optimum position

will have most of the water hitting the bucket when it is

nearly at right angles to the jet. The angle of the splitter ridge

is set so that it is approximately at right angles to the jet

when the full cross-section of the jet is hitting it. The rest of

the internal shape is designed to allow water to flow freely

round, and out at the edges. The water should emerge at a

favourable an angle to give maximum moment from the

momentum change. This is achieved by having the cup

surfaces smoothly curved, with a reasonably large radius.

The jet should always strike the surface between the splitter

ridge first and never at the edges of the bucket. The

surface between the splitter ridge and the outside end of the

bucket has to be shaped so that it directs all the water from

the ridge into bucket cups.

Ideally the bucket should take the water around a complete

‘U’, removing all the energy from the jet, and leaving the

water stationary in air and then have it fall under its own

weight into the tailrace. In reality this is not achievable

because the next bucket would hit the water left hanging in

mid-air. The edges of the bucket are consequently angled

outwards; just enough to make sure that the water clears the

next bucket.

Figure 9: Water jet being deflected back at an angle of 165

0.

For optimum efficiency the speed of the jet, vj, should be

about twice the speed of the bucket, vb. Because the runner

is moving away from it, the speed at which the jet enters the

bucket is given by 𝑣𝑗 − 𝑣𝑏 . The jet is split by the ridge and

flows round the two cups to emerge at the sides of the

bucket. The inside of the bucket should be as smooth as

possible and evenly curved so that the water does not loose

much speed as it goes round. Lack of smoothness reduces

efficiency. If there were no losses, the water jet would leave

at a velocity equal to𝑣𝑗 − 𝑣𝑏 . If the jet speed, vj, is twice the

bucket speed, vb, then the water, relative to the bucket, leaves

at a speed of: 𝑣𝑗 − 𝑣𝑏 = 2𝑣𝑏 − 𝑣𝑏 = 𝑣𝑏

So if the bucket is moving at a velocity of vb and the water is

coming out of the bucket at a speed of vb, in almost the

opposite direction, this would mean that the speed of the

water coming out relative to the housing is nearly zero; its

energy having been completely removed by the bucket [7].

The rotational speed of the buckets hence the runner is

determined by the jet velocity as illustrated in Figure 10.

Figure 10: Water jet hitting the bucket

The net head acting on the Pelton wheel

H = Hg - hf

where Hg = gross head

hf is the head loss due to friction,

which is given by the Darcy – Weisbach Equation

𝑕𝑓 =4𝑓𝐿𝑉2

2𝑔𝐷∗

where f = Darcy friction factor (dimensionless)

L = length of the penstock (m)

V = volumetric flow rate (m/s)


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g = acceleration due to gravity (m/s2)

D* = diameter of penstock (m)

then

velocity of the jet at inlet = √(2gH)

in figure 10 this is = Vω

v = v1 = πDN / 60

where N = speed of the wheel in rpm

D = diameter of the wheel

the velocity triangle at inlet will be a straight line where

Vr = Vω – v

α = 0 and θ = 0

from the velocity triangle at outlet

Vr1 = Vr

and Vω1 = Vr1 cos ф – v1

the force exerted by the jet of water in the direction of

motion is:

F = ρaVω [Vω + Vω1]

where ‘a’ is the area of the jet given as:

a = πd2 / 4

d = diameter of the jet

the angle β is an acute angle, therefore positive sign is taken

work done by the jet on the runner per second

= F x v = ρaVω[Vω + Vω1] x v (Nm/s)

power given to the runner by the jet

= ρaVω[Vω + Vω1] x v (W)

work done / s per unit weight of water striking/s

= ρaVω[Vω + Vω1] x v

weight of water striking/s

= ρaVω[Vω + Vω1] x v

ρaVω x g

= [Vω + Vω1] x v

g

the energy supplied to the jet at inlet is in the form of kinetic

energy and is equal to mV2 / 2

and kinetic energy of jet per second

= ρaVω x Vω2

2

Therefore the kinetic energy of the water jet is transferred to

the buckets and hence the runner. So the runner rotational

speed depends on the jet velocity.

4.3 Pelton wheel turbine efficiency [7]

The parameters of the runner that affect efficiency are:

diameter of runner, number of jets, number of buckets of a

runner and method used to attach buckets to a runner.

A small runner is cheaper to make than a larger one. It takes

less material and the housing and associated components can

be made smaller. To use smaller runners requires dividing

the flow of water among a large number of jets. Multiple-jet

Pelton turbines can have up to six jets before interference

effects between jets lead to too much inefficiency. Multiple-

jet machines have the following advantages over the single-

jet machines:

higher rotational speed

smaller runner and case

some flow control is possible without extra

equipment such as the spear valve

less chances of blockage in most designs due to

reduced surge pressures

In order to optimize efficiency, the number of buckets on the

turbine runner is generally between 18 and 22. For the Pelton

wheel turbine to function as expected, the buckets must be

attached securely onto the runner. This is to avoid buckets

flying off the runner during operation or buckets moving

from their original positions, hence compromising efficiency.

There are a number of ways of mounting buckets onto the

runner hub. The whole runner and buckets may be cast as

one piece or buckets may be cast separately and are then

bolted, clamped or welded onto the runner [4]. Casting of

buckets and mounting them to the runner is the process

widely used in the manufacturing of turbines. It is cheap,

reliable and can produce complex shapes easily.

4.4 Materials for Pelton wheel turbine buckets

The chief material requirements are high strength, abrasion

resistance, casting suitability and ability to withstand

extended use in water. Materials in common use are

Aluminium, Copper Alloys, Grey Cast Iron, Stainless Steel

and Plastic.

4.5 Flow control for Pelton wheel turbine efficiency

In order to maximise the efficiency of the turbine, it is

important to be able to control the flow rate. The need to

control this flow arises due to site conditions that include

change in water flow rate with changing seasons. There are

various options that are used to control the flow of the water

jet, and these include the varying of number of jets, the spear

valve and the replacement of nozzles [5].

Varying number of jets: If a multi-jet has shut off valves

fitted on each of its jets, it can be run at different flow rates

by simply altering the number of jets playing on the runner.

Figure 11 shows a four-jet turbine. If jets are of equal

diameter then the flow will simply vary in proportion to the

number of active jets. It may be economic to use unequal

diameter jets, and divide the year into more seasonal flows.


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Figure 11: A four-jet Pelton turbine [5]

It is possible to utilise the nozzle replacement approach in a

multi-jet turbine to provide greater variation in flow. This

will reduce the cost of adding further jets, but will require

increased input from an operator of the plant.

Spear Valve:The spear valve is a streamlined spear head

arranged to move within the nozzle allowing variation in

effective orifice cross-sectional area without introducing

energy loses. Hence the water flow rate is varied with a

constant jet velocity. Large turbines may include more

than one spear valve around the periphery of the rotor. The

spear is moved by a handle or automatically by a mechanical

speed governor as shown in Figure 12.

Figure 12: Spear valve and Jet Deflector plate on a single jet

turbine

Figure 13 shows the effect of the spear valve on the water

jet. When the spear valve is moved in the forward direction

more the water jet diameter is smaller, and vice versa is true.

Figure 13: Effect of spear valve position to the water jet

diameter

Spear valves are very effective where continuous flow

regulation is considered necessary and their use in such cases

may be cost effective. In addition they can stop a foreign

body which has fallen into the penstock from blocking the

nozzle.

However in some cases, multi-jet Pelton wheel turbines are

chosen over single-jet with a spear valve because the spear

valve is expensive. It can also present the danger of

instantaneously blocking the nozzle should it become

detached while the turbine is operational.

Replacement of nozzles:One nozzle is removed and replaced

with a more appropriate one to suit the seasonal change.

Thus wet season flow would require a larger nozzle size than

dry season flow. It is possible to divide the yearly flow

variation into two, three or more parts and provide a suitable

nozzle for each flow. This is a low-cost method of

controlling flow. It is important to be certain that sufficient

operator skill and input is available and the plant has to be

stopped when nozzles are changed. The water jet may be

diverted by a jet deflector plate, by breaking the jet and by

shut-off valves.

Jet deflector plate

The water jet may be deflected away from the buckets of the

runner when the plate is rotated into the jet’s path as shown

in Figure 12. This is very useful in stopping the turbine

without shutting off the flow in the penstock hence avoiding

the dangers of pressure surges. The process of stopping the

turbine is then completed by diverting the flow at the forebay

tank.

Breaking jet

The turbine may be stopped by moving the spear valve in the

forward direction until the water striking the runner is

reduced to zero or by use of the Jet Deflector Plate. However

when the water has been completely stopped from reaching

the runner, due to inertia the runner goes on revolving for

some time. To stop the runner in a short time, a small nozzle

maybe provided which directs the jet of water on the back of

the buckets. This jet is called the Breaking Jet and is shown

in Figure 14.

Figure 14: The breaking jet

Shut-off Valves

A gate valve or butterfly valve may be placed in the turbine

manifold. Pelton wheels are driven by long penstocks in

which surge pressure effects, due to valve closure, can be

very dangerous and lead to damage caused by bursting of the

penstock. If these valves are fitted, they must always be

closed slowly, particularly during the last phase just before

shut off.


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4.6 Friction

Turbine efficiency can be considered separately as hydraulic

efficiency, mechanical efficiency, volumetric efficiency and

overall efficiency [7].

i. Hydraulic efficiency

Hydraulic efficiency is defined at the ratio of power

given by water to the runner of a turbine to the

power supplied by the water at the inlet of the

turbine. The power at the inlet of the turbine is the

highest and this power goes on decreasing as the

water flows over the buckets of the turbine due to

hydraulic losses as the buckets are not as smooth.

Hence the power delivered to the runner of the

turbine will be less than the power available at the

inlet of the turbine. From Figure 10, mathematically

the hydraulic efficiency of a turbine is:

ηh = power delivered to runner

power supplied at inlet

= work done per second

K.E. of jet per second

=ρaVω[Vω + Vω1] x v

(ρaVω) x (Vω)2 / 2

= 2 [Vω + Vω1] x v

(Vω)2

ii. Mechanical efficiency

The power delivered by water to the runner of a

turbine is transmitted to the shaft of the turbine. Due

to mechanical losses, the power available at the

shaft of the turbine is less than the power delivered

to the runner of a turbine. The ratio of the power

available at the shaft of the turbine to the power

delivered to the runner is defined as mechanical

efficiency. Hence, it is written as:

ηm = power at the shaft of the turbine

power delivered by water to the runner

iii. Volumetric efficiency

The volume of the water striking the runner of a

turbine is slightly less than the volume of water

supplied to the turbine. Some of the volume of the

water is discharged to the tail race without striking

the runner of the turbine. Thus the ratio of the

volume of the water actually striking the runner to

the volume of water supplied to the turbine is

defined as volumetric efficiency. It is written as:

ηv = volume of water actually striking the runner

volume of water supplied to the turbine

iv. Overall efficiency

Overall efficiency is the ratio of power available at

the shaft of the turbine to the power supplied by the

water at the inlet of the turbine. It is written as:

ηo = volume available at the shaft of the turbine

power supplied at the inlet of the turbine

= ηm x ηh

Friction has the greatest impact on hydraulic efficiency and

in turn hydraulic efficiency is one of the factors affecting the

overall efficiency. This makes friction an important factor in

overall turbine efficiency. For example in the analysis of

flow friction of Pelton turbine hydraulics it is indicated that

the flow friction in the Pelton buckets has a substantial

impact on the system efficiency.

The direct influence is determined by the friction, which

directly retards the bucket motion and thus determines the

power output. The indirect way is determined by the changes

of relative flow and the pressure distribution in the bucket.

The flow friction theorem points out that the total reduction

of the system efficiency is equal to the total efficiency

reductions by two different ways. In the total efficiency

reduction, the effect from the indirect way dominates. In

addition, frictions in the bucket, whether at the bucket

entrance or at the exit, always cause a reduction in system

efficiency. The efficiency drop resulting from the flow

frictions represents the greatest part in the total loss in the

system efficiency of a Pelton turbine.

4.7 Water jet and Pelton wheel buckets

Of great importance is the interaction of the water jet with

the Pelton buckets. The jet discharged from the nozzle of a

Pelton turbine is a key item of hydropower systems and its

precise shape and position are highly relevant to the

optimum design of the turbine buckets to match the

incoming flow.

In the first configuration, the interaction between the runner

and an axial-symmetric jet characterized by a given velocity

jet profile were investigated, whereas in the second

configuration the runner was coupled with the needle nozzle

and the final part of the penstock and the interaction between

the jet and the bucket were analyzed. The results confirmed

that the turbine efficiency is affected by the water jet

interaction with the turbine was shown.

5 Cross-flow turbines The turbines comprise of a drum shaped runner consisting of

two parallel discs connected together near their rims by a

series of curved blades. It has its runner shaft horizontal to

the ground in all cases [8].

Figure 15: Cross-flow turbine

The Cross-flow turbine consists of a cylindrical water wheel

or runner with a horizontal shaft, composed of 18 up to 37

blades, arranged radially and tangentially. The blade's edges


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4

are sharpened to reduce resistance to the flow of water. A

blade is made in a part-circular cross-section. The ends of the

blades are welded to disks to form a cage, instead of the bars,

the turbine has trough-shaped blades.

In operation, the water jet of rectangular cross-section passes

twice through the rotor blades, arranged at the periphery of

the cylindrical runner. The water strikes the blading first

from the periphery towards the centre, imparting most of its

kinetic energy, and then crosses the runner from inside

outwards striking the blades on exit and imparting a smaller

amount of energy on leaving the turbine as shown in Figure

16.

Figure 16: Flow of water across the turbine

Going through the runner twice provides

additional efficiency. When the water leaves the runner, it

also helps clean the runner of small debris. The Cross-flow

turbine is a low-speed machine that is well suited for

locations with a low head but high flow.

The effective head driving the Cross-flow runner can be

increased by the inducement of a partial vacuum inside the

casing. This is done by fitting a draught tube below the

runner which remains full of tail water at all times. Any

decrease in the level induces a greater vacuum which is

limited by the use of an air bleed valve in the casing. Careful

design of the valve and casing is necessary to avoid

conditions where water might back up and submerge the

runner. This has the additional advantage of reducing spray

damage on the bearings since the internal vacuum causes air

to be sucked in through the bearing seals, so impeding the

movement of water out of the seals.

The efficiency of Cross-flow turbine depends on the

sophistication of its design. For example a feature such as

vacuum enhancement is expensive because it requires the use

of air seals around the runner shaft as it passes through the

casing, and airtight casing. Sophisticated machines attain

efficiencies of 85%. Simpler ones range typically between

60% and 75%.

Two major attractions of the Cross-flow turbine are that it is

a design suitable for a wide range of heads and power ratings

and it lends itself easily to simple fabrication techniques.

This is a feature that is of interest in developing countries,

e.g. the runner blades can be fabricated by cutting a pipe

lengthwise in strips.

The turbine housing may be entirely made of mild steel

plates. Mild steel is tougher than grey cast iron and is good

on impact and frost resistance and is rigid enough to

withstand high operational stress and enable smooth

operation. The design and hydraulic layout result in

minimized vibrations and noise level. Special care should be

taken in the layout of the main bearings for the runner and

the guide vane. The casing is designed in such a way that

different options for the bearing system are available to cope

with the specific site requirements, flywheel or belt drive. A

sealing system is included in the side covers. The guide vane

unit can easily be taken out through a side cover for

inspection, cleaning or replacement. To obtain the

guaranteed efficiency, the cylindrical runner is fabricated

with high precision.

5.1 Flow control in Cross-flow turbine

Flow control is done by a guide vane. The shaft of the guide

vane is parallel to the rotor shaft, it fits neatly inside the

nozzle to keep leaks at the side in the closed condition within

limits. It guides water to the runner and controls the amount

of water entering the runner. The device is operated by a

screw and nut which is connected to a hand wheel. It can

also be coupled to automatic operation, to the hydraulic

cylinder of a speed governor. In addition, rubber gaskets are

used to seal up the turbine housing.

The correct design speed of a turbine depends on the power

rating of turbine, the site head and the type of turbine [9].

Small turbines designed for micro-hydro applications may at

times have techniques for altering the flow rate of water. On

larger machines a method of altering flow is different. Cross-

flow has guide vanes which alter the water flow rate.

Different turbine types respond differently to changed flow

at constant head. Typical efficiency characteristics of three

turbines are given in Figure 17. The curves shown assume

pressure turbines which have facilities for varying water flow

rate at constant head, for example, spear valves or multiple

jets on Pelton turbines, partition devices of flow control

vanes on Cross-flow turbines.

Figure 17: Part-flow efficiency of various turbines

6 Micro-hydro plants overview The turbines for this study are for micro-hydro power plants

at sites located in Malawi, Mozambique and Zimbabwe as

shown in Table 3.

0

50

100

0 0.5 1

Effi

cien

cy (

%)

Flow (as a fraction of maximum flow)

Part-flow efficiency of different turbines

Pelton & Turgo

Cross-flow

Francis

http://en.wikipedia.org/wiki/Welding

http://en.wikipedia.org/wiki/Efficient_energy_use


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5

Table 3: Micro-hydro power plant by site

SITE NAME GROSS

HEAD

(m)

DESIGNED

FLOW

RATE

(m3/s)

TURB

INE

TYPE

DESIGNED

EFFICIEN

CY (%)

A BONDO,

MALAWI

51 0.325 Pelton 60%

B DAZI, NYANGA 138 0.035 Pelton 60%

C NYAMWANGA,

HONDE

VALLEY

26 0.277 Cross-

flow

60%

D CHITUNGA,

MOZAMBIQUE

35 0.180 Cross-

flow

60%

SITE A: Bondo

The Bondo MHS has a gross head of 51m and a design

flowrate of 0.325m3/s. A special characteristic at this site is

the high flowrate. This is due to the vast amount of water

that flow in Bondo River. Figures 18 to 20 show the weir,

part of the canal at Bondo project and the Pelton turbine in

use at this site.

Figure 18: Weir at Bondo MHS

Figure 19: Part of the canal at Bondo MHS

Figure 20: The Pelton wheel turbine at Bondo MHS

The Bondo project benefits two schools in the area; a

primary and a secondary schools and teachers’ houses, one

clinic including the waiting mothers’ home and staff houses

and one business centre. The business centre has some

grocery shops, a battery charging centre, hair salon and an

electric grinding mill. There are seven villages in the Bondo

catchment area with a total of 3084 households. However,

evidence shows that if more power could be produced further

developments would be possible.

SITE B: Dazi micro-hydro project

At the site the head is 138m, the design flowrate is

0.035m3/s. A pelton turbine is in used. A special

characteristic of this site is the very high head that

compensates for the low flows. The project benefits a school

in Figure 21, a clinic and lighting for about 1000 people in

nine villages. More power would allow the 1000 people to

use electrical gadgets such as refrigerators and stoves.

Figure 21: A classroom lit by power from the Dazi MHS

SITE C: Nyamwanga project

The Nyamwanga MHS is located 27km North East of Hauna

Township in Chief Zindi’s area in Mutasa District . The

gross head is 26m, the flowrate is 0.277m3/s. A Cross-flow

turbine is in use at this project as shown in Figure 22. The

project benefits one school, and one shopping centre with

fifteen shops. The plan for the shopping centre is shown in

Figure 23:


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6

Figure 22: The Cross-flow turbine for Nyamwanga project

Figure 23: Plan for Nyamwanga business centre that is

benefitting from the project.

SITE D: Chitunga project

The rainfall pattern is shown in Figure 24.

Figure 24: Average rainfall graph for Chitunga

At the site, the gross head is 35.12m, the designed flowrate

is 0.180m3/s. The project benefits one school, one clinic, an

energy centre, local authority offices, four grinding mills and

366 households. A cross-flow turbine is in place at this

project site.

7. Research design process

Visits were done to the workshops where turbines are

fabricated were. There the study of the factory

manufacturing of turbines was done by following through the

fabrication process. Visits were also made to the project sites

to physically test turbine efficiencies.

7.1 Physical testing of turbine efficiency

Physical testing of the turbine rotational speed was done

using a tachometer. A tachometeris an instrument that

measures the rotational speed of a shaft or disk. Tachometers

may either be manual or digital. A digital one is shown in

Figure 25 [8].

Figure 25: Digital Tachometer

The digital gadget displays the RPM on the screen. The

rotation of the turbine was measured using a digital

tachometer model by placing the tip of the tachometer on a

point on the centre of the runner at site C. The rotation of the

turbine was then used to calculate the efficiency of the

turbine as follows:

𝑷 = 𝝆𝒖𝑸(𝒗𝒋 − 𝒖)(𝟏 + 𝒌𝒄𝒐𝒔𝜽)

and 𝑢 = 𝜔𝑅

and 𝜔 = 2𝜋𝑁

60

where P = turbine power output (W)

ρ = density of water (kg/m3)

u = bucket rotational velocity (m/s)

vj = jet velocity

Q = flowrate (m3/s)

R = runner radius (m)

N = runner speed (rpm)

k = constant of friction

Also efficiency could be assessed by checking the

performance of the turbine. A load (e.g. an industrial welding

machine) is carried to site. A typical example is one which

operates at 25amps and about 35Amps when striking an arc.

The community is then disconnected and the load is

connected. The operating current is measured and multiplied

by the system voltage. This gives the power output which is


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7

then compared to the designed power output. From this, one

can tell if the turbine is still performing as designed.

It is important to make certain the correct number of buckets

on a runner. This guarantees that the outgoing bucket does

not interfere with water jet now hitting the next bucket. To

ensure the correct number of buckets on a runner, a

simulation program called Autodesk Inventor was used to

simulate the turbine rotation. This is a 3D mechanical solid

modelling design software for creating 3D digital prototypes

used in the design, visualisation and simulation of products.

8. Results analysis

8.1 Design and manufacture of turbines

The friction within the Pelton buckets, the interaction of the

water jet with the buckets, the accuracy in the cutting of

Cross-flow blades and the method of welding of the blades to

the runner all have major roles in the efficiency of a turbine.

8.1.2 Pelton turbine manufacture

The head and flowrates were collected from each of the four

study sites. This data was used to calculate the gross power

output hence the size of the runner, number of buckets,

number and size of water jets. The efficiency of the turbine is

designed at 60%. Two of the four sites that were analysed

have Pelton wheel turbine working on them. Data from the

sites is given in Table 4.

Table 4: The two MHS sites that have the Pelton wheel

turbine installed on them SITE GROSS

HEAD

(m)

FLOW

RATE

(m3/s)

CAPACITY

(kW)

TURBINE

TYPE

EFFICIENCY

(%)

A 51 0.325 88 Pelton 60%

B 138 0.035 20 Pelton 60%

The capacity for each site is the actual power output .

Buckets are sand cast individually and bolted to a runner.

Figures 25 to 30 show this process. The pattern is used to

produce the mould, the hollow section in the sand box where

the molten metal is poured in to produce the required Pelton

buckets.

Figure 26: Pelton bucket that has been sand cast.

Figure 26 is showing a single bucket that has been sand cast.

The feeder and the riser are still attached to the bucket. The

feeder is the entrance through which the molten metal is

poured into the mould and the riser is the way excess metal

goes through.

Figure 27: Pelton bucket that has been machined

In Figure 27 the bucket has been machined to remove the

feeder and riser. It has 2 holes drilled through it for bolting to

the runner. It is important to have the holes expertly drilled

otherwise the buckets will not sit on the runner perfectly and

the turbine is misaligned. This reduces the efficiency of the

turbine as some energy is lost to heavy vibrations and noise

since the water jet will not be hitting on the correct spot

anymore.

Figure 28: Alignment of buckets on the runner

Figure 28 shows how individual buckets are aligned on the

runner. They sit at an angle to each other. This allows for the

full force of the jet to be applied on each bucket one after

another without hindrance from the previous bucket. This

ensures maximum efficiency of the turbine.


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8

Figure 29: A complete turbine

A finished turbine is shown is Figure 29. Seventeen buckets

are bolted onto the runner. The number of buckets per runner

is important in making sure there is enough space between

the buckets to allow the water jet to hit individual buckets

with the same force.

Figure 30 shows the turbine housing being welded together.

Figure 30: Turbine housing being welded together

The individual parts of the turbine housing were cut using a

cutting torch. The inside of the turbine housing is shown in

Figure 31. The nozzle through which the water jet goes

through to the turbine is seen in the picture. The sizing of the

nozzle is important in having the correct size water jet, hence

the right amount of force on the turbine that ensures

maximum efficiency.

Figure 31: The inside of the turbine showing the

nozzle

8.1.3 Cross-flow turbine manufacturing

Cutting and welding are basically the two procedures carried

out in the fabrication of Cross-flow turbines. The site head

and flow rate are collected from the site as the critical

parameters. These are used to calculate the expected power

output hence the size of the runner, number, length and width

of blades the turbine. The overall efficiency of the turbine is

also designed at 60%. Two of the four sites that were studied

are using the Cross-flow turbine as shown in Table 7.

Table 5: The two MHS sites that have the Cross-flow

turbine installed on them

The capacity for each site is the actual power output.

The blades are then cut using a cutting torch and welded to

the runner. Figures 31 to 33 show the Cross-flow turbine

ready for mounting.

Figure 32: Finished Cross-flow turbine

Figure 32 is shows a Cross-flow turbine that is ready for

connection. The cuttings on the runner where the blades are

welded into are the ones that give the blades the required

curve.

Figure 33: Blades welded to the runner

SITE GROSS

HEAD

(m)

FLOW

RATE

(mᶟ/s)

CAPAC

ITY

(KW)

TURBIN

E

TYPE

EFFICIE

NCY

(%)

C

26

0.277

30

Cross-flow

60%

D

35

0.180

34

Cross-flow

60%


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9

Figure 33 shows closely the blades welded into the runner.

The curving of the blades guides the flowing water as it

flows from one end of the turbine to the other.

Figure 34: The turbine casing.

The turbine casing is shown in Figure 34. The cutting torch

is used to cut the different parts which are then welded

together.

8.2 Effect of roughness due to manufacturing

The processes used to manufacture turbines are sand casting,

oxyacetylene welding and flame cutting. Different

manufacturers of turbines provided quotations that included

the turbine efficiencies and methods used to manufacture the

turbines.

Each manufacturing process has a different roughness. This

combined with material roughness determines the friction of

a turbine and it will then translate to turbine efficiency, in

particular hydraulic efficiency. The hydraulic efficiency

affects overall turbine efficiency directly [6].

Table 6 compares different manufacturing processes against

the overall turbine efficiency associated with each process.

Table 6: The turbine efficiencies associated with roughness

of different manufacturing processes

Manufacturing

Process

Turbine

Efficiency Roughness

Pressure die casting A 85.0 1.6

Investment casting B 85.0 3.2

Milling C 85.0 6.3

Laser D 80.0 6.3

Electron beam E 80.0 6.3

Oxyacetylene welding F 60.0 25.0

Sand casting G 60.0 25.0

Flame cutting H 60.0 50.0

Figure 35 shows a graph that was drawn to relate this

roughness to the turbine efficiencies

Figure 35: Turbine efficiency & roughness for different

manufacturing processes

The graph indicates that as the manufacturing process

roughness increases the overall efficiency of the turbine

produced decreases. This emphasizes the need to use

manufacturing processes with minimal roughness.

This diagnosis of roughness affecting the overall efficiency

of turbines tallies with the findings that the flow friction in

the Pelton buckets has a substantial impact on the system

efficiency of the turbine. The efficiency drop resulting from

the flow frictions represents the greatest part in the total loss

in the system efficiency of a Pelton turbine.

Mechanical efficiency is the other determining factor of the

overall efficiency. One way to improve this efficiency in

casting procedures is to cast segments comprising of a

number of buckets or whole runners, comprising the runner

and all the buckets.

8.3 Effect of the water jet movement

Of great importance in the mounting of the Pelton turbine is

its interaction with the water jet. To maximize efficiency the

jet must hit precisely the centre of each Pelton bucket. That

way the jet gives the maximum drive to each bucket as noted

earlier in the design of the buckets that the rotation of the

turbine depends on the water jet velocity. This fact matches

with the experimental studies of the jet of a Pelton turbine.It

was concluded that the jetdischarged from the nozzle of a

Pelton turbine is a key item of hydropower systems and its

precise shape and position are highly relevant to the

optimum design of the turbine buckets to match the

incoming flow.

8.4 Turbine material

The type of material used to fabricate a turbine affects its

efficiency. Good materials are hard and must be able to resist

erosion and corrosion. This ensures that the turbines will

function at their best efficiency for the expected life span on

the micro hydro power plant. Stainless steel is mainly used

for Pelton and Cross-flow turbines and mild steel is used for

casings.

This study revealed that other materials that maybe used for

turbines are Aluminium, Cast Iron, Copper based alloys such

as Brass and Bronze, and Sheet steel. The properties of these

materials and their prices per kg are given in Table 7.

0.0

20.0

40.0

60.0

80.0

100.0

A B C D E F G HManufacturing process

Turbine efficiency & roughness for different manufacting processes

RoughnessTurbine Eff


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0

Table 7: Properties of different materials and their prices per

kg

MATERIAL MATERIAL ROUGHNESS

(x100-2)

BRINELL

HARDNESS

(x100)

PRICE/

KG

(US$/kg

)

A Aluminium 0.2 1.2 1.32

B Grey cast

iron

25 3.02 0.83

C Brass 1 3.6 5.54

D Bronze 1 3.6 5.54

E Stainless

steel

3 4.15 1.47

F Sheet Steel 15 4.5 0.29

Figures 36 and 37 show the relationships between roughness

and price per kg of material and hardness and price per kg of

material respectively.

Figure 36: Material roughness compared to material price

Figure 37: Material hardness compared to material price

The two graphs shows why Stainless steel is the most

commonly used material in the manufacturing of turbines for

MHS. It has a high hardness, a very low roughness and price

is close to the lowest. Sheet Steel maybe the cheapest and its

hardness is slightly higher than that of stainless steel but its

roughness is much higher than Stainless Steel. Such a

roughness means that it has a much higher friction than

Stainless Steel and this is not good for the hydraulic

efficiency of the turbine and hence the overall efficiency.

Brass and Bronze are too expensive for MHS. This is

because they are alloys of Copper which is a very expensive

metal. Its price is about $8 per kg.

Aluminium has a price close to Stainless Steel and the lowest

roughness, but is susceptible to damage if debris such as

stones and sand find their way to the turbine. This is because

it has the lowest hardness. The roughness of Grey Cast Iron

is too high. This compromises the turbine efficiency despite

having a low price and a fairly high hardness.

8.5 Effect of increasing turbine efficiency on MHS power

out put

The resultant change in actual power output due to increase

in turbine efficiency of the four MHS that were studied is

shown in the Table 8.

Table 8: Differences in power output due to increase in

turbine efficiency

SITE TURBIN

E TYPE

CURRENT

TUBINE

EFICIENCY

CURRENT

POWER

OUTPUT

(kW)

NEW

TURBINE

EFFICIENC

Y

POSSIBLE

POWER

OUTPUT

(kW)

Bondo (A) PELTON 0.60 88.00 0.85 124.67

Dazi (B) PELTON 0.60 20.00 0.85 28.33

Nyamwanga

(C)

CROSSF

LOW

0.60 34.00 0.80 45.33

Chitunga (D) CROSSF

LOW

0.60 30.00 0.80 40.00

Figure 38: Difference in MHS power output for the four

sites analysed

In all the four cases there is a remarkable increase in power

output coming from the same resources. Therefore using the

materials and manufacturing processes that give the highest

possible yield from each site and resources is most ideal.

0

5

10

15

20

25

30

A B C D E F

Mat

eria

l ro

ugh

nes

s

Material

Material roughness compared to price of material

ROUGHNESS (x100^-2)

PRICE/KG

0

1

2

3

4

5

6

A B C D E F

Mat

eria

l har

dn

ess

Material

Material Hardness compared to material price

BRINELL HARDNESS (x100)

0.00

20.00

40.00

60.00

80.00

100.00

120.00

140.00

A B C D

PO

WER

OU

TP

UT

SITE

DIFERENCE IN POWER OUTPUTS

CURRENT POWER OUTPUT (kW)POSSIBLE POWER OUTPUT (kW)


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1

8.6 Performance measurements

After the turbine has been set up and the micro hydro is just

starting to run, it is of utmost importance to measure the

efficiency of the turbine in order to verify if it is meeting the

expected efficiency. This is done using a tachometer. This is

done at the initiation of a project and after it has run for six

months to check if all is performing as expected. During the

period of study the tachometer was used to check the

performance of the turbine at Site C as shown in Table 9.

Table 9: Tachometer readings at Site C TACHOMETER

READINGS

1 2 3 4 5

495 rpm 515 rpm 511 rpm 492 prm 498 rpm

The average of these numbers was used to calculate turbine

power output.

The designed power output for this site is 34kW and turbine

efficiency is designed at 60%. The calculated power output

from these readings was 33.3kW. The two power outputs are

comparable to each other, therefore it was concluded that the

turbine was still operating at 60%.

The need for performance measurement is invaluable. When

done on regular intervals problems are identified and

rectified before the MHS needs to be shut down.

9.Financial analysis There is a limit on the project cost per kilowatt for each

MHS. It entails that total project cost of each site depends on

its capacity. A project is considered financially viable if the

budget does not exceed $6000 per kW. Table 10 shows the

costs that were involved in the selected projects.

Table 10: Costs involved in the selected four projects

SITE TURBINE

TYPE

TURBINE

EFFICIENC

Y

MHS

CAPA

CITY

TURBINE

COST (US$)

TOTAL

PROJEC

T

COST(U

S$)

PROJ

ECT

COST

PER

kW

A Pelton 60% 88kW 5000.00 509

444.00

5

789.14

B Pelton 60% 20kW 5000.00 81 775.20 4

088.76

C Cross-

flow

60% 30kW 7000.00 174

719.00

5

823.97

D Cross-

flow

60% 34kW 7000.00 158

340.00

4

166.84

Using quotations from suppliers new MHS capacity were

calculated, total project cost and project cost per kW as

shown in Table 11.

Table 11: Costs involved with better efficiency turbines

SITE TURB

INE

TYPE

TURBIN

E

EFFICIE

NCY

NEW

CAPACITY

TURBINE

COST (US$)

TOTAL

PROJECT

COST(US$)

PROJEC

T COST

PER kW

A Pelton 85% 125kW 6500.00 510 944.00 4 087.55

B Pelton 85% 28kW 6500.00 83 275.20 2 974.12

C Cross-

flow

80% 40kW 8200.00 175 919.00 4 397.98

D Cross-

flow

80% 45kW 8200.00 159 540.00 3 545.33

New turbines have a better efficiency; therefore the capacity

of a MHS is improved. These turbines are more expensive

than the current turbines in use and this translates to higher

total project costs. However, because a turbine with better

efficiency also improves the MHS capacity the projects are

made even more viable because in the end the project cost

per kW is reduced. The change in project cost per kW for

each site is shown in Table 12.

Table 12: The difference in project costs per kw

SITE CURRENT PROJECT

COST PER kW

EXPECTED PROJECT

COST PER kW

A 5 789.14 4 087.55

B 4 088.76 2 974.12

C 5 823.97 4 397.98

D 4 166.84 3 545.33

This reduction is shown graphically in Figure 39.

Figure 39: The reduction in project cost per kW on each site

The graph is showing that even though turbines of higher

efficiencies are more expensive the overall project cost per

kW actually decreases.

I. 10. RESEARCH RECOMMENDATIONS

It is highly recommended to consider investing in processes

that produce turbines with higher efficiencies such as:

Pressure die casting of turbines. They may be

cast as whole turbines or as segments made up

of a number of buckets.

Investment casting of whole turbines.

CNC milling of Pelton buckets.

Cutting of Pelton runner and Cross-flow runner

and blades using CNC laser, CNC plasma.

Electron beam and laser welding of blades to

runners.

0

1000

2000

3000

4000

5000

6000

7000

A B C D

$ /

kW

SITE

REDUCTION IN PROJECT COST PER kW

CURRENT PROJECT COST PER kW

POSSIBLE PROJECT COST PER kW


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2

These processes offer far less roughness compared to current

methods that include sand casting, flame cutting and

oxyacetylene welding. That reduction in roughness lessens

friction and the overall efficiency of a turbine is increased.

11. Conclusion

This study has revealed that turbines of better efficiencies

can be manufactured, made available for MHS and the

projects remain financially viable. This was achieved

through the comparison of current fabrication methods used

locally to methods used by different suppliers of turbines.

Even though the better efficiency turbines are more

expensive than the ones being used currently the overall

benefit is clear. More electricity is generated hence the cost

per unit kW actually decreases making the projects even

more viable. The financial viability of a project was

determined by the project cost per kilowatt produced. Use of

better efficiency turbines will make it possible to harness

more electrical power from the same resources.

12 Further research

Further studies may be carried out on need forexperimental

investigations with respect to the flow friction effects on the

hydraulic efficiency of a Pelton turbine as well as

considering materials which can be locally sourced for

fabrication of the MHS in the country. As the MHS has

potential for renewable energy resource, meaning less

pollution to the environment which is encouraged by the

dictates of Cleaner Production for sustainable development.

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<http://www.balino.com/ingles/turbinas/pelton.htm

> viewed on 6 October 2012

[2] BETP ( 2012), Hydraulic Turbines

<http://www.betp.net/2012/01/pelton-wheel-

turbine/> viewed on 6 October 2012

[3] Bright hub (2012), Hydraulic Turbines: Francis

Turbine

<http://www.brighthub.com/engineering/mechanica

l/articles/27407.aspx> viewed on 15 September

2012

[4] Development book shop( 2012), Micro-hydro Pelton

Turbine Manual

<http://developmentbookshop.com/product_info.ph

p?products_id=441> viewed on 13 sept 2012

[5] Greenstone (2012), Community Development

Library, Pelton Turbine

<http://www.greenstone.org/greenstone3/nzdl%3Bj

sessionid=0f.9.pp&sib=1&p.s=ClassifierBrowse&p.

sa=&p.a=b> viewed on 6 October 2012

[6] HARC (2012), Turbines

<http://files.harc.edu/Documents/EBS/CEDP/Hydro

powerPart2.pdf>viewed on 1 November 2012

[7] Hydropower( 2012),Axco Generators for hydropower

applications

<http://www.axcomotors.com/hydropower_generat

or.html> viewed on 16 September 2012

[8] John F Douglas, Janus M Gasiorek, John A

Swaffied, Lynn B Jack ( 2005). Fifth edition. Fluid

Mechanics

[9] R.K. Bansal ( 2005). A textbook of fluid mechanics

and hydraulic machines: (in S.I. units)

Authors’ Profiles

MrsLoiceGudukeya,graduated with a Honor’s Degree

in Industrial and Manufacturing Engineering in 2004 from

the National University of Science and Technology,

Bulawayo, Zimbabwe and Masters Degree in Renewable

Energy in 2012 from the University of Zimbabwe, Harare,

Zimbabwe. She has been an Assistant Lecturer at the Harare

Institute of Technology and University of Zimbabwe. She

has also understudied micro-hydro projects at Practical

Action. Currently she is a Lecturer in the Mechanical

Engineering Department at the University of Zimbabwe and

working on preparatory work for her Phd in Climate Change.

MrIgnatioMadanhire, graduated with a BSc Mechanical(Hon) Engineering and

MSc in Manufacturing Systems and Operations Management

in 1993 and 2010 respectively from the University of

Zimbabwe. He has been a mechanical engineer with

Department of Water – Large Dam Designs, and also worked

as a Senior Lubrication Engineer with Mobil Oil Zimbabwe

as well as Castrol International dealing with blending plants

and lubricants end users. Currently, he is a lecturer with the

University of Zimbabwe in the Mechanical Department

lecturing in Engineering Drawing and Design. He has

published a number of research papers on cleaner

production.

http://www.balino.com/ingles/turbinas/pelton.htm



http://www.betp.net/2012/01/pelton-wheel-turbine/

http://www.betp.net/2012/01/pelton-wheel-turbine/

http://www.brighthub.com/engineering/mechanical/articles/27407.aspx



http://developmentbookshop.com/product_info.php?products_id=441

http://developmentbookshop.com/product_info.php?products_id=441

http://www.greenstone.org/greenstone3/nzdl%3Bjsessionid=0f.9.pp&sib=1&p.s=ClassifierBrowse&p.sa=&p.a=b




http://files.harc.edu/Documents/EBS/CEDP/HydropowerPart2.pdf

http://files.harc.edu/Documents/EBS/CEDP/HydropowerPart2.pdf

http://www.axcomotors.com/hydropower_generator.html

