Low Speed Vertical Axis Current Turbine for Electrification of Remote

Areas in Malaysia

ATEF SALEM MEFTAH SOUF ALJEN and ADI MAIMUN

Marine Technology Centre, Faculty of Mechanical Engineering

Universiti Teknologi Malaysia

81310 Johor Bahru, Johor

MALAYSIA

adi@fkm.utm.my

Abstract: For Malaysia, rivers and ocean energy can be the best source of environment friendly water/marine

renewable energy. Generation of the electricity by burning of fossil fuels produces undesired greenhouse gases

and on the other hand the reserves of fossil fuels are being depleted and there is no accurate way to determine

how much remains. Fossil fuels are also known to have harmful effects on the environment. This paper

presents the development of an advanced novel small current turbine electric system for low speed flow stream

which is suitable for deployment in remote areas (rural areas and islands) in Malaysia. In this paper, analytical

computation based on a system of two current turbines of 2 kW output capacities at 1 m/s average current speed

is shown. Each turbine will produce daily energy of about 2.5 KWh which can supply electrical power for a

household with autonomy time of 2 days (battery storage) based on the national average. Higher electrical

power supply is possible with increase in number of turbines or increase in current speeds. This gives the

possibility of an optimised novel electrical power system consisting of small current turbines to be developed in

future. The specifications of the system components and its performance parameters can be estimated by using

a developed computer program.

Keywords: Renewable energy, LS-VACT, Electrification, Remote area, Computer program.

1 Introduction In parallel with Malaysia’s rapid economic

development and growing energy demand, more

alternative energy sources are needed to fulfil its

demand for energy [1, 2]. Due to, the rapid growth

of gas emissions which causes to the climate

change will make the country suffer from the

floods and other effects. Moreover, the Malaysian

fossil fuels reserve will be depleted soon [15] and

there is no accurate way to determine how much

remains [14]. In 2009, Malaysia formulated the

National Green Technology Policy [3] to promote

green technology usage for economic growth as

stated in [1]. Malaysia’s rivers and ocean can be the

best resource of green marine renewable energy. As

known the forms of these resources of marine

energy especially the ocean energy can be

categorized into tidal, wave, current, thermal

gradient and salinity gradient [4, 5]. Among them,

the marine currents present a relatively new and

almost unexploited source with a worldwide

diffusion of potentially highly-productive sites. So

in this area, there are two kinds of hydro-turbines;

vertical-axis and horizontal-axis turbines that can

be used as power generation devices as stated in

[6]. Horizontal-axis turbines are complex system

and suitable only for large size plants where high

installation and maintenance costs are balanced by

large energy produced. On the other hand, vertical-

axis turbines are relatively simple and represent a

promising technology to exploit marine currents

due to their small plants with reduced installation

and maintenance costs [7] and they are suitable for

deployment in remote areas[8, 9]. Current speed

and water depth are the important factors which the

marine current turbine more depending on [3].

From the literatures, at least 2 m/s (4 knots) is the

ideal marine current speed to make the turbine

work. In Malaysia’s sea and river areas, the average

current speed is about 1m/s (2.0 knots) as reported

by the Royal Malaysian Navy [3, 10]. The range of

current speeds is between 0.5 to 2.5 m/s. Due to the

low current speed, a big system of turbine is

required to harness the current energy. The problem

lies in that the blade length is limited to the

available water depth [3]. Previously, a Savonius

vertical-axis turbine has been proposed to harness

current energy [11]. But this type of turbine has

two main drawbacks which are low efficiency and

low tip speed ratio TSR (λ) which makes this rotor

Recent Advances in Renewable Energy Sources

ISBN: 978-1-61804-303-0 75

difficult to be integrated with a generator. So, a

Low Speed Vertical Axis Current Turbine (LS-

VACT) based on Savonius rotor (which can extract

the energy from low current speed [6, 12]) with the

novel modifications in having an arm to increase

the torque and self-adjusting blades to reduce the

drag [13], appears to be the suitable technology to

harness marine energy from the low speed current.

Therefore, this turbine will be used in the small

electric system to harness the energy from low

velocity stream. These small marine current electric

systems can make a significant contribution to our

nation’s energy needs. In rural areas and islands,

for consumers wanting to generate their own green

power, installing a small low speed marine current

turbine electric system can be an option to avoid

the high costs of extending utility power lines to

remote locations. Small LS-VACT electric system

is an electric generator that uses the energy of the

flow current to produce clean, emissions-free

power for individual homes in islands, fishing

farms, and small businesses near coastal areas.

With this simple and compact technology,

individuals can generate their own power and cut

their expenses on fuel to produce energy while

helping to protect the environment. Moreover,

these Off-grid (systems not connected to the utility

grid) stand-alone small turbine electric systems can

store power in batteries for on-demand use.

2 Small Electric System Components

2.1 System Overview The LS-VACT current energy converter is mounted

to the floating buoy which is moored to the seabed.

The buoyant is equipped with permanent magnet

synchronous generator (PMSG) and gearbox

(speed-up gear). The small electric system also

contains; batteries, controller and invertor. A

functional principal sketch of LS-VACT electric

system is shown in Figures 1 and 9.

In this stand-alone system as shown in Figure 2, the

LS-VACT converts the current flow energy to the

mechanical power. After that, the generator

converts the mechanical power to electrical power

for battery charge and for feeding the off grid

inverter. Inverter or a power conditioning unit

converts the power from direct current (DC)

to alternating current (AC). Both, generator and

battery as DC power sources must be capable of

supplying enough current for the intended power

demands of the load system.

The current turbine electric system is a

configuration involving multiple turbines. The

arrangement of the floating system is shown in

Figure 3.

Fig 3: Small Current Turbine- Floating System

In this paper, a small compact system consists of

two buoys, with a set of current turbine mounted on

AC

Load

LS-

VACT

Synchronous

Generator

Controller Inverter

Current

Energy

Mechanical

Power

Electric

Power

Battery DC

Load

Fig 2: A Diagram of Standalone Low Speed Vertical

Axis Marine Current Turbine Electric System

Fig 1: A Functional Principal Sketch of LS-VACT Electric

system

Charge

Controller

Battery

Bank

DC LOAD

AC LOAD

Inverter

Small

Low

Speed

Current

Turbine

Electric

System

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each buoy is considered. Inside each buoy is

asynchronous generator fitted with speed-up

gearing. These buoys are attached to each other

together using frames and moored to the seabed

using either flexible or rigid moorings. This will

allow the study on how each turbine will interact

with the wake from adjacent turbine.

2.2 System Advantages and Electrification

Benefits The proposed current turbine–generator system is

an efficient and environmental friendly small low

speed vertical axis current turbine which can

extract the energy from low velocity stream. In

addition the turbine has novel modifications which

are arms to increase the torque to match it with

suitable generator and self-adjusting buckets

(blades) to reduce the drag to enhance the generator

output and hence the efficiency. Moreover, the

small system has a variable speed generator and

variable voltage charge controller to make the

system operate automatically and sufficiently and

to keep the batteries from overcharging.

Using such systems for electrification of remote

areas will have big benefits due to the impact of

rural electrification; such as quantified benefits in

cost saving and increased productivity [16]:

1. Electricity is used by the industrial and small

business

2. Electricity is used by the Household in Lighting,

cooking etc.

3. Electricity is used by the Agricultural in Water

pumping

Other benefits of the electrification of rural

areas which cannot be directly quantified are

improvements in; social equity, modernization,

dynamism, attitude changes, quality of life,

community services, participation and finally job

creations.

2.3 Marine Current Flow Marine Currents are generally driven by the effects

of the tides and to some extent by oceanic

circulations. The tides are driven by the interaction

of the gravity fields of the moon, the earth and the

sun whereas oceanic circulation is caused partly by

the earth’s rotation and partly by temperature

variations and salinity variations in the seas. Tidal

currents, being based on the motion of the earth,

moon and sun, are predictable far into the future,

unlike the weather dependent renewables such as

wind, wave or solar energy. There are several

characteristics of marine currents that make them

attractive as an energy source. Marine currents,

especially tidal currents, are largely predictable. As

an energy source they also offer a potentially high

degree of utilization, something which could have a

strong impact on the economic viability of any

renewable energy project [17]. Limited rated

velocity of each device gives smaller difference in

power production between spring and neap and

thus also a higher degree of utilization [18]. Hence

the predictable nature of the resource combined

with a limited power of each device could be

beneficial for management of power delivery in the

case of a large scale marine current turbine farm. In

some places the tide is phase shifted along the

coastline, which means that several marine current

turbine farms could be geographically located to

even out the aggregated output over the tidal cycle.

This has for instance been shown to be the case

around the British Isles [18, 19].

Malaysia sea areas have an average current

speed of only 1m/s (2.0 knots) [3, 10]. This is about

half of the speeds for turbines that have been

designed and developed in other countries. Current

speed and water depth are the important factors to

be considered for application of marine current

turbines. The study on ocean based energy sources

in Malaysia is still in the beginning stages and in

the literature only few researches and studies were

found and most of them are limited studies and

assessment studies [3].

2.4 The Specifications of the Current

Turbine-generator System The main characteristics of the Low Speed Current

Turbine-Generator System are presented in the

following Table 1 below and a functional

dimensional principal sketch of the self-adjusting

and fixed blades or buckets of LS-VACT is shown

in Figure 4 and 5 respectively.

Fig 4: Schematic representations of self-adjusting blades

or buckets [13]

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Table 1: Specifications of the turbine-generator system Parameter Dimension Remarks

Turbine Principal Particulars

Turbine Diameter (DP) (m) 1

Bucket Diameter (d) (m) 0.35

Swept area (AS ) (m2) 0.525

Arm Length (Rotational

radius) (R) (m)

0.5 R = DP / 2

See fig 4.

Arm Length ( ) (m) 0.15 = R – d

Arm Length (lever) (r) (m) 0.325 r = R – d/2

Turbine Height 1.5

Number of Blades 4

Generator Specifications [21]

Rated Power Output (KW) 2

Rated Rotation (RPM) 180

Rated Voltage (V) DC 115

Rated Current (A) 17.4

Efficiency >85%

Required Torque 106.103

Starting Torque (Nm) 0.3

Weight (kg) 57

Fig 5: A functional and dimensional principal sketch of

the fiexed blades LS-VACT

3 Analytical Computation The turbine parameters and mechanical power were

computed using MATLAB M-File programming

using theory for primary turbine design and

estimations and by matching it with suitable

synchronous generator.

3.1 Determination of Turbine Dimensions

Determination of the LS-VACT dimensions is

based on the targeted generator size for private use

in remote areas with low speed current. However,

to feed a rural area which require a larger capacity

of electrical power, a group of generators of say, 2

KW each and attached to arrays of LS-VACT

turbines is a possible solution. As mentioned

earlier, one disadvantage of Vertical Axis Current

turbine type is that of having low TSR. Thus, it is

difficult to match it with the targeted generator due

to significant loss of torque after the gearbox (in

order to gain rotational speed). To solve this

problem an arm is added to the LS-VACT to

increase the torque and the following steps are used

to determine the arm length:

3.1.1 Input Data

1. Electrical generator:

PG = 2000 w, n2 = 180 rpm, TGreq. = 106.103 Nm,

Starting torque = 0.3 Nm

2. Environment:

U∞= 0.5 to 2.5 m/s, Water depth > 2.5 m and

ρ(Ocean) = 1025 kg/m3 and ρ(River) = 1000 kg/m

3

3. Gearing: speed-up gearing.

Gear ratio (K) = n2/n1 = 18.85 (max)

4. Turbine bucket diameter (d) = 0.35 m, bucket

height (H) = 1.5 m and total diameter (DP) = 1 m

3.1.2 Calculation procedure:

The arm of the turbine can be obtained by

following the steps below:

- Swept area of turbine, AS = d * H (1)

- Force acting on blade, F = Pressure*AS (2)

- Pressure = 0.5 * ρ * U2∞ (3)

- Gear ratio K = (nG / nT) or (n2 / n1) (4)

- The required torque of the turbine can be

obtained from the gear ratio relationship,

Treq. = K*TGreq. (5)

- The Arm is equal to: r = Treq./ F (6)

- Hence, T = Treq.- turbine torque (7)

- From the angular velocity, the turbine RPM is,

n1 = 30* ω / π (8)

From ω = 2 * π * n1 / 60 (9)

- The turbine power (P) = T * ω (10)

- Assuming that the Blade tip speed (u) = current

speed (Speed of incoming flow (U∞)) → u = R* ω

and u = U∞ so, R = U∞ / ω (11)

3.2 Matching the Turbine with the

Generator

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The arm and geometry of the LS-VACT turbine is

calculated based on the data of conventional

Savonius design modified by adding arms that

connect the two blades/buckets with rotor for

increasing the torque which leads to enhancing the

required generator torque after gearing

(transmission) and so improving the possibility to

produce power from the generator even with low

current speed. A Speed-up gearbox specification

used in this paper is shown in Table 2.

Table 2: Speed-up gearbox specification [22]

Type GK37

Input power (KW) 0.18 - 3

Transmission ratio 5.36 -106.38

Allowable torque (N.m) 200

Weight (kg) 11

4 Results and Discussion

4.1 Computation of Analytical Results The results of the turbine analytical design are

shown in the Table 3 below and Figure 6 shows the

mechanical power curve of the turbine. The torque

produced after gearing and generator outputs are

presented in Table 4 below:

Table 3: Analytical computation results for LS-VACT:

U∞

(m/s) r (m) RPM

T

(Nm) P (w)

Daily average

mechanical

energy (KWh)

0.5 0.325 9.549 21.86 21.86 524.64

1 0.325 19.099 87.45 174.89 4197.36

1.5 0.325 28.648 196.75 590.26 14166.24

2 0.325 38.197 349.78 1399.1 33578.4

2.5 0.325 47.746 546.53 2732.7 65584.8

Table 4: The 2KW -180 RPM generator output

Turbine

Torque

(N.m)

Gear

ratio

Torque

after

gearing

(N.m)

Output

(Watt)

Daily

average

energy

(Wh)

21.86 18.85 0.812 13.01 312.15

87.45 9.43 6.495 104.07 2497.63

196.75 6.28 21.920 351.20 8428.80

349.78 5.36 45.680 731.89 17565.46

546.53 5.36 71.375 1143.58 27445.97

Fig 6: Output curve of the turbine

4.2 System Output Energy The consumption of the loads and nominal power

are very important factors that play a major role in

stand-alone power system. The estimated

consumption of electricity for the Malaysian

household is approximately 2,200 kWh of energy

annually. In comparison with USA, a typical home

uses approximately 10,000 KWh of electricity per

year (about 830 KWh per month). Home energy

usage based on averages in two areas of the capital

of Malaysia is shown in Figure 7. As an

assumption, a rural household will consume about

75% of the estimated consumption of electricity for

the typical Malaysian household. A typical power

consumption reference for rural household and a

fish farm are shown in Table 5:

0

500

1000

1500

2000

2500

3000

3500

0 1 2 3

Tu

rbin

e M

ech

anic

al P

ow

er (

Wat

t)

Current Speed (m/s)

Power as function of current speed

Power (W)

Fig 7: Household energy consumption breakdown % [20]

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Table 5:Power Consumption Reference

Appliance

Load

power

(W)

Quantity

(pcs)

Daily

Working

Time (h)

Daily Energy Consumption

(Wh)

Power Consumption Reference for one Fish Farm

LED

Lamps 7 4 12 350

Laptop 90 1 12 1100

Fan 50 1 24 1300

Satellite

Receiver 25 1 18 500

LCD TV 70 1 18 1400

Rice

Cooker 500 1 0.5 250

Water

pump and

vacuum

1500 1 10 15000

Other 10 1 10 100

Total 1500 14 20000

Power Consumption Reference for one rural household

Led Lamp 7 4 12 350

Laptop 90 1 6 450

Desktop 120 1 6 750

Fan 50 2 12 1200

Satellite

Receiver 25 1 8 500

LCD TV 70 1 8 600

Rice

Cooker 500 1 1 500

Other 10 1 10 100

Total 775 10 4450

4.2.1 The Energy Produced by the System

The system energy is estimated based on:

Input Power:

P = 0.5 * ρ* AS* U3∞ (Watt) (11)

Operational Calculation:

Pm = T * ω (Watt) (12)

Output or Electrical Power:

Pe = T * ω * η (η=85%) (13)

Considering an average of 1 m/s current speed,

the daily average energy for one turbine is 2.5

KWh and the daily average energy for two turbines

is 5 KWh. The summary of energy produced by the

system is shown in Table 6 below:

Table 6: Average energy produced by the system

Description One

turbine

Two

turbines

Daily Average Output (W) = 104 208

Daily average output (KWh) = 2.5 5

Monthly average output (KWh) = 74.88 149.76

Annual average output (KWh) = 911.04 1822.08

At 1m/s of average current speed and working with

2 turbines would be sufficient to provide 5 KWh of

power for a rural house-hold. However, for a fish

farm that requires 20 KWh per day would need 8

turbines or a higher average current speed of 1.65

m/s.

Since current speeds vary, the use of batteries for

storing electrical energy is necessary. Based on the

power consumption from Table 6, the following

calculation for battery capacity required for

autonomy can be estimated;

Example 1: The small electric system of 8 current

turbines can supply daily 1 fish farm with energy of

20 KWh. The capacity (KWh) of a system with 8

batteries is;

Battery capacity = 8*250*12 (14)

= 24000 Wh → 24 KWh

This will give an autonomy time of 1.2 day.

Example 2: The small electric system of two

current turbines can supply energy daily for a

household for 5 KWh. The capacity (KWh) of a

system with 4 batteries is:

Battery capacity = 4*250*12 (15)

= 12000 Wh → 12 KWh

This will give an autonomy time of 2.4 days.

A set of 2, 2 kW current turbine electric system

(see Figure 8) will meet the needs of a house-hold

requiring 100 - 150 KWh per month in a location

with a 1 m/s annual average current speed.

Fig 8: LS-VACT Electric System Diagram

• Current speed

• 0.5 - 2.5 m/s

• RPM 10 - 48

• T= 25 - 550

• P = 21-2733

LS-VACT

• KG (η=70%)

• G. Ratio 5.36 -106.38

• T orque after gearing - 0.8 -75

Gear • 2 sets @ 2 KW

• P 15 - 1350 KW

• Daily Energy 0.5-65 KWh

Generator

•1 household (4

batteries)@ 1m/s

•1 Fish farm (8

batteries)@ 1.65

m/s

Load/

Battery

LS-VACT

Gear

Generator

Load

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ISBN: 978-1-61804-303-0 80

5 Conclusion The paper presents the development of a small-

current electric hydropower system which extracts

the energy from the kinetic energy of freely moving

low speed marine current and potentially can be

used for electrification of rural areas of Malaysia.

A system of a set of two current turbines of 2 kW

output capacities at 1 m/s average current speed is

proposed. Each turbine will produce daily energy

of about 2.5 KWh which can supply electrical

power for a household with autonomy time of 2

days (4 batteries storage). Higher electrical power

supply is possible with increase in number of

turbines or increase in current speeds. For a fish

farm, this would require either 8 turbines or

operating in an average current speed of 1.65 m/s

instead of 1 m/s.

In future, a simulation program will be

developed for predicting the performance of the

turbine and the system output. The simulated

results will be validated using laboratory and field

tests of a configuration involving arrays of turbines.

This will allow for possible increase in electrical

power supply and also investigating how each

turbine will interact with the wake from adjacent

turbines. The prediction tool will be developed

using Matlab-Simulink and will combine the

parameters of the low speed vertical current turbine

(LS-VACT), transmission system and generator in

order to determine the quality and the quantity of

the power output.

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_alternator_permanent_magnetic_generator.html

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Fig 9: A Functional Principal Sketch of Off-Grid Marine Current Turbine Electric system

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ISBN: 978-1-61804-303-0 82