Preliminary Evaluation Tools for Wind-Pumped Storage Energy Generation System

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PLATFORM - A Journal of Engineering

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VOLUME 4 NUMBER 4 2020 e-ISSN: 26369877 PLATFORM

INTRODUCTION

Malaysia is a country heavily dependent on natural gas and coal, causing more concerns to the industry and its carbon dioxide gas emissions rate. Reflecting the more global trend, these energies are consumed by all sectors including, transportation [1]-[2], industrial- like manufacturing [3]-[4] and residential utility.

During 2018, the fuel mix for electricity generation in Malaysia was still dominated by a surprising portion of 96% for fossil fuels such as natural gas and coal.

Figure 1 below shows the details of shares for fuel mix in Malaysia [5].

This heavy dependence of electricity generation with fossil fuels has become a major concern to the industry as the reserve of fossil fuels are become less and less as the time goes, and as well as the worsening of carbon dioxide greenhouse gas emissions. From 2007 to 2017, Malaysia‘s electricity generation had scored a new high throughout the 10 years and it has shown a trend of increasing throughout the years. In 2017, the electricity

generation industry in Malaysia had produced over 107 megatons of carbon dioxide gas which is highest among the 10-years and 51% of all industry that produced carbon dioxide [6].

PRELIMINARY EVALUATION TOOLS FOR WIND-PUMPED STORAGE ENERGY GENERATION SYSTEM

C.J. Chang¹, M.A.H. Rasid², D.M.N.D. Idris²

1Faculty of Mechanical & Automotive Engineering Technology, Universiti Malaysia Pahang, Pahang, Malaysia

2Department of Mechanical Engineering, Engineering College, University Malaysia Pahang, Malaysia Email: [email protected]

ABSTRACT

Energy demand never ceases to increase with larger cities, urbanization and migration to the cities. However, supplying the remaining and important rural areas with electricity remains costly. Exploring the off-grid energy generation is therefore a promising solution. After an exhaustive qualitative evaluation on different energy generation system, this study has chosen the Wind-Pumped Storage Hybrid (WPSH) system to be evaluated. A simulation tool was built to take the wind energy and convert it into pumping power to store water in a reservoir that will supply a hydro-turbine, generating electricity to a domestic area. A preliminary evaluation was done in Kajang for a selected day of July 20 2020. The result shows that the wind fluctuations and energy demand fluctuations affect the WPSH system’s capability to deliver sufficient energy through 24 hours. During the day, the amount of water accumulated in the reservoir is insufficient to meet the energy demand. It is only after 7.00 p.m that the system will be able to meet the demand and reserve a surplus of water in the reservoir.

Keywords: renewable energy, wind-pumped storage, hybrid energy generation, wind power, evaluation tools

1

Preliminary Evaluation Tools for Wind-Pumped Storage Energy Generation System

C.J. Chang, M.A.H. Rasid, D.M.N.D. Idris

Faculty of Mechanical & Automotive Engineering Technology, Universiti Malaysia Pahang, Pahang, Malaysia

Email: [email protected]

ABSTRACT

Energy demand never ceases to increase with larger cities, urbanization and migration to the cities. However, supplying the remaining and important rural areas with electricity remains costly. Exploring the off-grid energy generation is therefore a promising solution. After an exhaustive qualitative evaluation on different energy generation system, this study has chosen the Wind-Pumped Storage Hybrid (WPSH) system to be evaluated.

A simulation tool was built to take the wind energy and convert it into pumping power to store water in a reservoir that will supply a hydro-turbine, generating electricity to a domestic area. A preliminary evaluation was done in Kajang for a selected day of July 20 2020. The result shows that the wind fluctuations and energy demand fluctuations affect the WPSH system's capability to deliver sufficient energy through 24 hours. During the day, the amount of water accumulated in the reservoir is insufficient to meet the energy demand. It is only after 19.00 p.m that the system will be able to meet the demand and reserve a surplus of water in the reservoir.

I NTRODUCTION

Malaysia is a country heavily dependent on natural gas and coal, causing more concerns to the industry and its carbon dioxide gas emissions rate. Reflecting the more global trend, these energies are consumed by all sectors including, transportation [1], [2], industrial-like manufacturing [3], [4]

and residential utility. During 2018, the fuel mix for electricity generation in Malaysia was still dominated by a surprising portion of 96% for fossil fuels such as natural gas and coal.

Figure 1 below shows the details of shares for fuel mix in Malaysia [5].

Figure 1 Fuel mix of electricity generation in Malaysia for 2018

This heavy dependence of electricity generation with fossil fuels has become a major concern to the industry as the reserve

of fossil fuels are become less and less as the time goes, and as well as the worsening of carbon dioxide greenhouse gas emissions. From 2007 to 2017, Malaysia‘s electricity generation had scored a new high throughout the 10 years and it has shown a trend of increasing throughout the years. In 2017, the electricity generation industry in Malaysia had produced over 107 megatons of carbon dioxide gas which is highest among the 10-years and 51% of all industry that produced carbon dioxide [6].

Potential Solution

Harnessing renewable energy in Malaysia wasn’t a new topic to be discussed. Despite that, the potential of harnessing renewable energy in Malaysia are still having uncharted area awaiting to be explored. For example, today's renewable energy in Malaysia is only available for solar photovoltaic, hydropower, and biomass. There is still plenty of other renewable energy to be discussed for being the choice for generating energy in Malaysia. But plenty of choices comes with plenty of factors that must be discussed in order to be chosen as one of the suitable solutions for Malaysia tropical weather. As most renewable energies are heavily dependent on weather condition for a specific area such as wind energy that relies on wind velocity which may fluctuate in different places. A brief overview of the advantages and inconvenient of each energy generation systems by sources can be summarized as in Table 1.

All the RE sources mentioned have their advantages and disadvantages. The fluctuation of energy supply becomes a major problem for sources such as wind, tidal and solar even if their implementation does not require a lot of space and cost.

Others like geothermal, biomass and hydro require a lot of space, construction, thus cost. In order to be implemented in a small area and assure the sustainability of the supply, Hybrid Renewable Energy System, HRES may become the solution.

It is a combination of two or more stand-alone renewable energies system. Such a hybrid system provides a solution to overcome some limitation of stand-alone system operating characteristics, as most of the time all the renewable energies had its limitation on operating parameters. In addition to that, a hybrid system could increase in term of combined efficiency, supply reliability, economics and much more. These hybrid systems make use their features and eliminate the limitations of a stand-alone system, in order to obtain higher efficiency and cost-effectiveness. Until today, hybrid renewable energy systems had been used throughout the world, these systems

Figure 1 Fuel mix of electricity generation in Malaysia for 2018

UTP-Platform - PAJE v4n4 2020 (005).indd 35 12/30/20 11:31 AM

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Potential Solution

Harnessing renewable energy in Malaysia wasn’t a new topic to be discussed. Despite that, the potential of harnessing renewable energy in Malaysia are still

having uncharted area awaiting to be explored. For example, today’s renewable energy in Malaysia is only available for solar photovoltaic, hydropower, and biomass. There is still plenty of other renewable energy to be discussed for being the choice for

Table 1 Advantages and disadvantages of renewable energies by sources Type of

renewable

energy Advantage Disadvantage References

Hydropower 1. High installed capacity for high demand 2. Natural energy storage

3. Multipurpose of impoundment

4. Low carbon footprint in building it and operating it

5. Longevity of equipment

1. High environmental impact for natural habitats

2. Large space consumption 3. High investment cost 4. Inflexibility for off-grid

[7]

Tidal 1. Zero carbon footprint in operation 2. Predictable and stable

3. Longevity of equipment 4. Natural energy storage

1. High construction cost

2. Relatively new technology and more justification for its performance are required

3. High environmental impact due to EMF produced

4. Inflexibility to store energy

[8]

Wind 1. Lowest carbon footprint in renewable energy

2. Low financial cost

3. Flexible to build in any favourable place 4. Low environmental impact

5. Energy sources are highly accessible 6. Modular and scalable

1. The fluctuation on wind speed and direction

2. Ecosystem threat as turbine hit species.

3. Profitably unfavored 4. Inflexibility to store energy

[9]

Solar 1. Lowest carbon footprint in renewable energy

2. Low financial cost

3. Flexible to build in any favourable place 4. Low environmental impact

5. Energy sources are highly accessible 6. Modular and scalable

1. The fluctuation on wind speed and direction

2. Ecosystem threat as turbine hit species.

3. Profitably unfavored 4. Inflexibility to store energy

[10]

Geothermal 1. Inexhaustible, predictable and stable source

2. Simplicity 3. Low running cost

1. Geographical limitation 2. Inflexibility for grid

3. High environmental impact 4. High installation cost

[11]

Biomass 1. Widely available 2. Carbon neutral

3. Reduces wastes in landfills

1. Less efficient than fossil fuel 2. Usage of human and animal waste

increases the methane gasses 3. Require a lot of space

4. Can lead to deforestation

[12]

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generating energy in Malaysia. But plenty of choices comes with plenty of factors that must be discussed in order to be chosen as one of the suitable solutions for Malaysia tropical weather. As most renewable energies are heavily dependent on weather condition for a specific area such as wind energy that relies on wind velocity which may fluctuate in different places.

A brief overview of the advantages and inconvenient of each energy generation systems by sources can be summarized as in Table 1.

All the RE sources mentioned have their advantages and disadvantages. The fluctuation of energy supply becomes a major problem for sources such as wind, tidal and solar even if their implementation does not require a lot of space and cost. Others like geothermal, biomass and hydro require a lot of space, construction, thus cost. In order to be implemented in a small area and assure the sustainability of the supply, Hybrid Renewable Energy System, HRES may become the solution. It is a combination of two or more stand-alone renewable energies system. Such a hybrid system provides a solution to overcome some limitation of stand-alone system operating characteristics, as most of the time all the renewable energies had its limitation on operating parameters.

In addition to that, a hybrid system could increase in term of combined efficiency, supply reliability, economics and much more. These hybrid systems

make use their features and eliminate the limitations of a stand-alone system, in order to obtain higher efficiency and cost-effectiveness. Until today, hybrid renewable energy systems had been used throughout the world, these systems often come without the energy storage or battery for the system, they tend to use the combination of different system to obtain the ability of storing energy in natural form [13].

Pumped Storage-Wind Hybrid

Figure 2 shows the schematic diagram of a Pumped Storage- Wind Hybrid System. It is built from the combination of a pumped storage system and wind energy system. The power regulation capacity of pumped storage enables the hybrid system to control over output according to demand and combining this with wind energy, it could compensate the fluctuation and reliability of the wind farm. This integration improves the overall efficiency by storing the surplus energy from wind energy into natural form in the reservoir [14], [15], [16]. A pumped storage stand-alone system may not enough for continuously supply to the grid because the amount of precipitation or input of water may vary due to climate condition.

While the installed capacity of the wind energy is hard to achieve the peak-load demand of the consumption., but with the aid of pumped storage, the installed

Figure 2 Schematic diagram of Pumped Storage-Wind Hybrid System

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38 PLATFORM VOLUME 4 NUMBER 4 2020 e-ISSN: 26369877

capacity can be easily compensated with the huge reservoir that stores the energy within. Not only pumped storage compensates wind energy operating limits, but wind energy able to achieve a high cost- efficiency which cover the high installation cost of pumped storage system [13].

From literature reviews in the introduction, we have concluded that the onshore wind energy is a more cost- efficient solution. Wind energy provides a continuous energy supply to the grid while its surplus energy can be stored by pumping water to the reservoir of the pumped-storage system. While this hybrid system compensates the fluctuation on wind energy supply by controlling the output of pumped storage according to the demand. A Wind-Pumped Storage Hybrid (WPSH) energy system is therefore proposed in this study and will be stimulated to make a preliminary evaluation of its potential in a selected location. In the following section, the construction of the model, its governing equation and the definition of input parameters will be presented.

METHODOLOGY

The proposed WPSH system can be seen in Figure 3. The system uses a wind turbine to capture the fluctuating wind energy. The Wind turbine is connected to a gear train to adapt the speed to enable a suction pump to pull up water from a flowing river to a reservoir built at a determined height.

The reservoir will store the water in potential energy form and only released it according to the power demand. The pressure losses in inlet and outlet pipes are also taken into account in this simulation.

The governing equation used in the model for all components of the system is as listed in Table 2.

The model was built in Matlab-Simulink. A standalone Matlab application was built to allow easier future utilization, where users can modify the input parameters to evaluate the potential energy that can be generated in another location with another dimension of components. Figure 4 shows the application where the input parameters can be key-in and the results of different parameters observable are directly displayed.

The interface is divided into tabs representing each stage of energy conversion in the WPSH system. In each tab, (wind turbine, gear train, pump, inlet pipe, reservoir, outlet pipe, hydro turbine and generator) their parameters of dimension or efficiency can be modified following the components chosen to be integrated into the system. These values depend therefore on the manufacturers of the components. For our first evaluation, the parameters used to simulate the model is presented in Table 3.

For the first evaluation of the tool constructed and its potential, a simulation was executed. The choice of the wind velocity profile of Kajang was done based

Figure 3 Schematic diagram of the proposed WPSH system

4

A µ

inlet

�

Generator − Power required from

generator,

ı

\

Table 2 Physical components of the designed system and its corresponding governing equations

Components Equations References

Wind Turbines - Power of wind turbine produced, P turbine = 1 C p ρ air A turbine V 3 [17]

Gear Train - Power transmitted by gear train, 2

P out _gear = η gear . P wind

Mechanical Pump - Flowrate of pump to reservoir

P

_{out_gear}

ρ

water

. g . H

wind

[17] with H is head of elevation of water tank

Inlet pipe (Outlet pipe) - Velocity of water inlet, V avg = Q

^pump

- Reynolds number, Re = ρ. V

^avg

. D

^inlet

- Major losses in pressure for inlet,

[18]

L V

²

∆ P

^L

= f

^inlet

.

^inlet

D .

_inlet^avg

with Haaland modified Colebrook equation, 2

l �

� l

ε 1 . 11 �

� \

− 2

f

inlet

= ı−1.8 log 10 � 6 . 9 + ı D inlet \

ıı �ı with ε the roughness ratio of the pipe

Re

_inlet

�

3 . 7

\ l �� ı

l

D

_inlet

- Power losses due to pipe friction, W l o ˙ s ses = Q pu m p . ∆ P L

- Power output after friction, W ˙ = W pu ˙ m p − W l o ˙ s ses - Velocity √ of water at outlet,

V avg = 2g H

Pumped-Storage - Volume of water stored in the reservoir, 2

V = Q

pum p

. t

- Potential energy of water stored in the reservoir, E = V ρ

water

g H

- Power required from reservoir, W r ˙ eq = W ˙ + W l o ˙ s ses

- Flowrate of reservoir required,

[18]

Q req

W

_r

˙

_eq

ρ

water

g H

Hydro Turbine Power required from hydro turbine,

W hy dr o ˙ t ur bi ne = η hy dr o −t ur bi ne W gene ˙ r at or [18]

[18]

W gene ˙ r at or = η gener at or W dea ˙ mnd

Figure 3 Schematic diagram of the proposed WPSH system

The reservoir will store the water in potential energy form and only released it according to the power demand. The pressure losses in inlet and outlet pipes are also taken into account in this simulation. The governing equation used in the model for all components of the system is as listed in Table 2.

The model was built in Matlab-Simulink. A standalone Matlab application was built to allow easier future utilization, where users can modify the input parameters to evaluate the potential energy that can be generated in another location with another

Figure 4 The Matlab application serving as interface for the Simulink simulation allowing users to modify input parameters and observe output

parameters - Part Wind Turbine

The interface is divided into tabs representing each stage of energy conversion in the WPSH system. In each tab, (wind turbine, gear train, pump, inlet pipe, reservoir, outlet pipe, hydro turbine and generator) their parameters of dimension or efficiency can be modified following the components chosen

Q pump =

=

Wind

House Turbine-Generator

Reservoir

River Flow Turbine Blades

Gear Train

Pump

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VOLUME 4 NUMBER 4 2020 e-ISSN: 26369877 PLATFORM Table 2 Physical components of the designed system and its corresponding governing equations

Components Equations References

Wind Turbines - Power of wind turbine produced, P_turbine = ^1–₂C_p ρ_air A_turbine V _wind³

[17]

Gear Train - Power transmitted by gear train, P_{out_gear} = η_gear .P_wind

Mechanical

Pump - Flowrate of pump to reservoir Q_pump = P_{out_gear}

––––––––

ρ_water·g·h

with H is head of elevation of water tank

[17]

Inlet pipe

(Outlet pipe) - Velocity of water inlet, V_avg = Q_pump

–––––

A_inlet - Reynolds number,

Re = ρ·V_avg·D_inlet –––––––––––

μ

Major losses in pressure for inlet, ∆P_L = f_inlet · L_inlet

––––D_inlet^· V _avg²

–––2 with Haaland modified Colebrook equation,

f_inlet =

(

^{–1.8 log}¹⁰

[

^Re^––––^6.9inlet

+

(

^––––^––––^D^3.7^inlet^ε

)

^1.11

])

^–2^with^––––^Dinlet^ε the roughness ratio of the pipe - Power losses due to pipe friction,

W.

losses = Q_pump ·∆P_L - Power output after friction,

W. = W.

pump − W.

losses

- Velocity of water at outlet, V_avg =

√

_––––^2gH

2

[18]

Pumped-

Storage - Volume of water stored in the reservoir, V = Q_pump·t

- Potential energy of water stored in the reservoir, E = V ρ_water g H

- Power required from reservoir, W.

req = W. + W.

losses

- Flowrate of reservoir required, Q_req = W.

––––––––req

V ρ_water g H

[18]

Hydro Turbine Power required from hydro turbine, W.

hydro–turbine = ηhydro–turbineW.

generator

[18]

Generator Power required from W.

generator = η_generatorW.

demand

[18]

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Figure 4 The Matlab application serving as interface for the Simulink simulation allowing users to modify input parameters and observe output parameters - Part Wind Turbine

4

A µ inlet

�

Generator

⁻

Power required from

generator,

ı

\

Table 2 Physical components of the designed system and its corresponding governing equations

Components Equations References

Wind Turbines - Power of wind turbine produced, P

turbine

=

¹

C

p

ρ

_air

A

turbine

V

³

[17]

Gear Train - Power transmitted by gear train,

2

P

out _gear

= η

_gear

. P

wind

Mechanical Pump - Flowrate of pump to reservoir

P_{out_gear} ρ water . g . H

wind

[17]

with H is head of elevation of water tank Inlet pipe (Outlet pipe) - Velocity of water inlet,

V

avg

=

^Q^pump

- Reynolds number, Re =

^ρ.^V^avg^.^D^inlet

- Major losses in pressure for inlet,

[18]

L V ²

∆ P

L

= f

inlet

.

^inlet_D

.

_inlet^avg

with Haaland modified Colebrook equation,

₂

l �

� l

ε

¹.11

�

� \

−2

f

inlet

= ı−1.8 log

₁₀

�

⁶.9

+ ı D

inlet

\

ıı �ı with

^ε

the roughness ratio of the pipe

Re_inlet

�

3.7

\ l �� ı

l

D_inlet

- Power losses due to pipe friction, W

l o

˙

_{s ses}

= Q

pu m p

.∆ P

L

- Power output after friction, W ˙ = W

pu

˙

_{m p}

− W

l o

˙

_{s ses}

- Velocity √ of water at outlet,

V

avg

=

2g H 2

Pumped-Storage - Volume of water stored in the reservoir, V = Q

pump

. t

- Potential energy of water stored in the reservoir, E = V ρ

_water

g H

- Power required from reservoir, W

r

˙

_eq

= W ˙ + W

l o

˙

_{s ses}

- Flowrate of reservoir required,

[18]

Q

req

W_r˙_eq ρ water g H

Hydro Turbine Power required from hydro turbine,

W

hy dr o

˙

t ur bi ne

= η

hy dr o−t ur bi ne

W

gene

˙

_{r at or}

[18]

W

gene

˙

_{r at or}

= η

gener at or

W

dea

˙

_mnd

Figure 3 Schematic diagram of the proposed WPSH system

The reservoir will store the water in potential energy form and only released it according to the power demand. The pressure losses in inlet and outlet pipes are also taken into account in this simulation. The governing equation used in the model for all components of the system is as listed in Table 2.

The model was built in Matlab-Simulink. A standalone Matlab application was built to allow easier future utilization, where users can modify the input parameters to evaluate the potential energy that can be generated in another location with another dimension of components. Figure 4 shows the application where the input parameters can be key-in and the results of different parameters observable are directly displayed.

Figure 4 The Matlab application serving as interface for the Simulink simulation allowing users to modify input parameters and observe output

parameters - Part Wind Turbine

The interface is divided into tabs representing each stage of energy conversion in the WPSH system. In each tab, (wind turbine, gear train, pump, inlet pipe, reservoir, outlet pipe, hydro turbine and generator) their parameters of dimension or efficiency can be modified following the components chosen to be integrated into the system. These values depend therefore on the manufacturers of the components.

Q

pump

=

Figure 5 The Matlab application serving as an interface for the Simulink simulation allowing users to modify input parameters and observe output parameters - Part Pump

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VOLUME 4 NUMBER 4 2020 e-ISSN: 26369877 PLATFORM Figure 6 The Matlab application serving as an interface for the Simulink simulation allowing users to modify input

parameters and observe output parameters - Part Reservoir

Table 3 Input parameters used to preliminarily evaluate the potential of a PSWH system.

Input parameters Values / Dataset

Wind Velocity Profile Weather data at Kajang on 20^th July [19]

Power Demand Profile Power consumption at Kajang on 20^th July 2020 [20]

Air Density 1.225 kg/m³

Swept Area of Wind Turbines 34.60 m²

Coefficient Performance of Wind 0.45

Gear Train Efficiency 96%

Water Density 997 kg/m³

Head of Elevation 14.5 m

Inlet Pipe Radius 0.06445 m

Length of Inlet Pipe 14.5 m

Reservoir Surface Area 100 m²

Intended Reservoir Height 10 m

Outlet Pipe Radius 0.06445 m

Length of Outlet Pipe 14.5 m

Hydro Turbine Efficiency 96%

Generator Efficiency 90%

5

For our first evaluation, the parameters used to simulate the model is presented in Table3.

For the first evaluation of the tool constructed and its potential, a simulation was executed. The choice of the wind velocity profile of Kajang was done based on the available and reliable reference existence to make a preliminary evaluation.

The evaluation can also be done on a different location, provided that the wind velocity data is available and reliable, as well as the availability of a water source such as river stream which can be sourced to our reservoir.

Figure 5 The Matlab application serving as an interface for the Simulink simulation allowing users to modify input parameters and observe output

parameters - Part Pump

Figure 6 The Matlab application serving as an interface for the Simulink simulation allowing users to modify input parameters and observe output

parameters - Part Reservoir

TABLE 3 I nput parameters used to preliminarily evaluate the potential of a PSWH system .

Input parameters Values / Dataset

Wind Velocity Profile Weather data at Kajang on 20th July [19]

Power Demand Profile Power consumption at Kajang on 20

^th

July 2020 [20]

Air Density 1.225kg/m

³

Swept Area of Wind Turbines 34.60m

²

Coefficient Performance of

Wind 0.45

Gear Train Efficiency 96%

Water Density 997kg/m

³

Head of Elevation 14.5m

Inlet Pipe Radius 0.06445m

Length of Inlet Pipe 14.5m Reservoir Surface Area 100m

²

Intended Reservoir Height 10m Outlet Pipe Radius 0.06445m Length of Outlet Pipe 14.5m Hydro Turbine Efficiency 96%

Generator Efficiency 90%

RESULTS AND DISCUSSION

In this first preliminary evaluation, we will only discuss up to the potential energy that can be stored in the reservoir using the WPSH system in a day. The scenario case simulated here was based on the input parameters and data at Kajang on 20th July 2020. Therefore, every result simulated here are based on the input of weather and power demand that obtained at the location of Kajang on the date of 20th July 2020.

Figure 7 shows the wind velocity at the chosen location on the selected day. It can be observed that the wind is fluctuating with a higher intensity towards the evening and night peaking at 5m/s from 17.00 pm to 20.00 pm. The power that can be extracted by the wind turbine is therefore reflected on the bottom graph with a maximum power of 2400 Watt extracted from 17.00 pm to 20.00 pm.

Figure 7 The wind velocity plot (top) and the corresponding power extracted from the wind turbine (bottom)

On the other end, in terms of consumption, Figure 8 shows the power required from the hydro turbine also fluctuates with a more constant demand in the midnight and early morning. The peak energy demand is identified at 17.00 pm at 2.3kW.

This can be reflected in the flow rate necessary at our outlet pipe that will rotate the wind turbine, presented in the bottom

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on the available and reliable reference existence to make a preliminary evaluation. The evaluation can also be done on a different location, provided that the wind velocity data is available and reliable, as well as the availability of a water source such as river stream which can be sourced to our reservoir.

RESULTS AND DISCUSSION

In this first preliminary evaluation, we will only discuss up to the potential energy that can be stored in the reservoir using the WPSH system in a day. The scenario case simulated here was based on the input parameters and data at Kajang on 20th July 2020. Therefore, every result simulated here are based on the input of weather and power demand that obtained at the location of Kajang on the date of 20th July 2020.

Figure 7 shows the wind velocity at the chosen location on the selected day. It can be observed that the wind is fluctuating with a higher intensity towards the evening and night peaking at 5m/s from 5.00 pm to 8.00 pm.

The power that can be extracted by the wind turbine is therefore reflected on the bottom graph with a maximum power of 2400 Watt extracted from 5.00 pm to 8.00 pm.

On the other end, in terms of consumption, Figure 8 shows the power required from the hydro turbine also fluctuates with a more constant demand in the midnight and early morning. The peak energy demand is identified at 5.00 pm at 2.3 kW.

This can be reflected in the flow rate necessary at our outlet pipe that will rotate the wind turbine, presented in the bottom graph.

Finally, the supply and demand of energy were put into comparison by means of comparing the total volume of water accumulated through the day, and the volume of water required to satisfy the energy demand. Figure 9 shows that the demand is higher than the supply from the system during daytime which means that the system was unable to supply the demand from 12.00 a.m. until 6.00 p.m. Despite that, since the wind velocity during evening and nighttime were much higher than the daytime, it shows the supply from the reservoir could deliver an adequate amount of water to generating electricity for the user. The space between both line in the top figure represents the surplus volume of water would be taken as a reserve to store in the reservoir. By the end of the day, the system was able to preserve a certain amount of surplus energy

Figure 8 The required amount of energy from the Hydro turbine (top) and the computed required flow rate from

the outlet pipe of the storage reservoir (bottom) Figure 7 The wind velocity plot (top) and the

corresponding power extracted from the wind turbine (bottom)

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with the form of water storage in the reservoir. But for the insufficient supply during the daytime, it shows that by solely relying on the system to provide energy to the user, the user would be suffering power shortage.

The bottom of Figure 9 shows the maximum capacity of water could be store in the reservoir. The fact that the graph shows a value below 0 during daytime indicates that the system was having an insufficient reserve for providing the energy and it still required an additional amount of water to match with the demand. But by end of the day, the water stored in the reservoir could be reaching around 2 m height. An indication from both results was if the users solely relying on the system to deliver the power, it would be insufficient and power shortage would occur.

CONCLUSION

With the simulation tool and its result, users able to easily identify the feasibility of having this hybrid system with all technical specifications they desired at a specific location. As the scenario was a showcase for the simulation software, it justifies that having this hybrid system for the scenario is impracticable as the system was not able to fulfil the demand solely by

itself. Thus, suggestions to users for having this hybrid system in real-life are to make changes in the technical specification of the system or input parameters of the system. For the scenario case, the results show the size of the reservoir was enough as water only utilized less than half of the maximum capacity of the system. In terms of addressing the issue of supply and demand gap, changing technical specification of components such as pipe inlet, generator, hydro turbine, and others would be insignificant, as their performance was already in quite a good form. But there may be significant changes in the overall performance of the system if the technical specification of outlet pipe could be changed as from the results, it shown the power losses due to friction in outlet pipe was significantly affecting the performance of the system, therefore users can make an adjustment either in the length of outlet pipe and diameter of outlet pipe to see which sets of the specification would deliver a better overall performance. A conclusion for this simulated scenario, the simulation results representing the performance of the actual hybrid system that build in Kajang, and from that it has shown the system was impractical in the aspect of supply and demand if the demand solely depends on this system.

Figure 9 The total amount of water accumulated in the reservoir storage across 24 hours on 20th of July 2020 (top), and the corresponding height of water in the reservoir (bottom)

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For the moment the study is in preliminary stages to identify how much energy can be stored, therefore potentially supplied. The cost study will be the next phase when the energy supply and energy demand matching for a potential location are identified.

In perspectives, a control strategy on the reserve retainment and release can be planned to better supply the energy. This will be studied in the near future with several other configurations of equipment and location.

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