Master of Science Thesis
KTH School of Industrial Engineering and Management Energy Technology EGI-2016-020MSC EKV1132
Division of Heat & Power SE-100 44 STOCKHOLM
Renewable Energy System Model
for Water Purification and
Lighting for a Remote Village
in Sri Lanka
Master of Science Thesis EGI-2016-020MSC EKV1132
Renewable Energy System Model for Water Purification and Lighting
for a Remote Village in Sri Lanka
Gayan Rantharu Attanayake Mudiyensalage
Approved
2019-05-15
Examiner
Miroslav Petrov - KTH/ITM/EGI
Supervisors at KTH
Amir Vadiee
Commissioner
Open University of Sri Lanka
Local Supervisor
Dr. K.A.C. Udayakumar
Abstract
Today, there are 3 billion people around the world not having access to drinking water. 1.76 billion people are living in the areas having water stress. It has been forecasted that 1.8 billion people will face an absolute water scarcity and two third of the world population will be living under water stressed condition by 2025. Mainly the water scarcity happens due to lack of technological development to convert water resources in to drinkable condition. As a result of scarcity of drinkable water people are facing health risks.
In some areas of Sri Lanka, the high risk of water related diseases has been found to be very serious. Chronic Kidney Disease (CKD) is one of many aggressive diseases, which spreads in the North Central region of Sri Lanka. Scarcity of potable water is directly connected with the lack of availability of energy resources, as energy is need to purify water that is being supplied from natural resources such as rivers and lakes.
In this study, the techno-economic viability of utilizing local renewable sources of energy to generate electricity and purify water for drinking purposes was explored. For the case study, a remote village situated in Sri Lanka was selected.
It was estimated that energy demand in the village for supply of electricity and water purification would be around 100 kWh/day. Based on this amount of energy, a system was designed that utilizes solar and wind energy. The system needed 3.6 kWh to pump water having four water tanks each with 10m3 capacity. Electricity storage is to be composed of 21 Lead-Acid batteries of 200Ah, 24V.
To power the intergraded systems for water pumping and electricity supply, a 5 kW wind turbine and 25 kW solar panels were used. This whole system would cost roughly 46,620 USD which is approximately 6 million Sri Lanka Rupees (as of 2016).
1
SAMMANFATTNING
Idag finns det 3 miljarder människor runt om i världen som inte har tillgång till dricksvatten. 1,76 miljarder människor lever i de områden som har vattenstress. Det har förutspåtts att 1,8 miljarder människor kommer att möta en absolut vattenbrist och två tredjedelar av världens befolkning kommer att bo under vattenbelastat tillstånd år 2025. Huvudvis sker vattenbristen på grund av brist på teknisk utveckling för att omvandla vattenresurser till drickbart tillstånd. Som ett resultat av bristen på kranvatten står människor inför ett stort antal hälsorisker.
I vissa områden på Sri Lanka har den höga risken för vattenrelaterade sjukdomar visat sig vara mycket allvarlig. Kronisk njursjukdom (CKD) är en av många aggressiva sjukdomar som sprider sig i norra centralregionen av Sri Lanka. Bristen på drinkvatten är direkt kopplat till bristen på tillgång till energiresurser, eftersom energi behövs för att rena vattnet som utvinns ur naturresurser som floder och sjöar.
I det här examensarbetet undersöktes den teknoekonomiska lönsamheten för att utnyttja lokala förnybara
energikällor för att generera el och rena vatten för dricksändamål. För fallstudien valdes en avlägsen by i Sri Lanka. Det uppskattades att energibehovet i byn för tillförsel av el och vattenrening skulle vara omkring 100 kWh / dag. Baserat på denna mängd energi har ett system utformats som utnyttjar solenergi och vindkraft. Systemet behövde 3,6 kWh för att pumpa vatten med fyra vattentankar vardera med 10m3 kapacitet. Ellagring skall utnyttjas som består av 21 blybatterier av 200Ah, 24V.
För att driva de intergraderade systemen för vattenpumpning och elförsörjning användes en 5 kW vindkraftverk och 25 kW solpaneler. Hela systemet skulle kosta ungefär 46 620 USD vilket är cirka 6 miljoner Sri Lanka Rupees (priser och växelkurser enligt år 2016).
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ACKNOWLEDGEMENT
I would like to take this opportunity to express my sincere gratitude to Dr. N.S. Senanayake who has given fullest support to make success this research report. He guided me to achieve the research objectives on regularly. At the start of this project, I had no idea on the project. He helped me step by step from data collection to final report writing.
Throughout my MSc study period, Mr. Ruchira Abeyweera helped me to complete my course modules and related assignment. Instead of guiding me, he made me drive to complete my studies. I am much grateful to him for supporting me and encouraging my studies.
On the other hand, Mr. Jeevan Jayasuriya and Ms. Chamindie Senaratne helped me to coordinate my study modules and giving me theoretical knowledge. Whenever I had a problem on my studies, they immediately respond me and supported me on their best.
This MSc program was a great opportunity to sharpen my theoretical knowledge and practical aspect on renewable energy technology concept. As this was a distance based study, I found lot of literature through the books and internet. This was benefited me, because, I did most of the studies myself. So I could be able to understand of the subject more than the on campus study. I would thank full to the KTH staff who introduced this course. And also the lecturers and the supervisors who conduct lectures and practical sessions.
I also thankful my colleagues and senior batches who provide me literature and examples to carry out my studies and my project team members who collaboratively done the teamwork on my modules.
I greatly remind my parents who made me a good person to the society and the world. They honestly helped me and encourage me to achieve my life time goals. Also my younger brother who encourage me and be with me throughout my ups and downs.
3 TABLE OF CONTENTS 1 BACKGROUND ... 8 2 INTRODUCTION ... 9 2.1 PROBLEM IDENTIFICATION ... 10 2.2 RESEARCH OBJECTIVE ... 10 3 METHODOLOGY ... 11 3.1 FLOW CHART ... 12
4 LITERATURE SURVEY AND BACKGROUND INFORMATION ... 13
4.1 ANALYZING THE QUALITY OF WATER WITHIN THE REGION ... 13
4.2 SOLAR AND WIND ENERGY POTENTIAL WITHIN THE REGION ... 13
4.3 WATER PURIFICATION SYSTEMS ... 14
4.3.1 Osmosis process ... 14
4.3.2 Reverse osmosis process ... 14
4.3.3 Semipermeable membrane ... 15
4.4 WIND POWER SYSTEM ... 16
4.5 SOLAR PV SYSTEM ... 17
4.5.1 Solar power... 17
4.5.2 Photovoltaics system ... 18
4.5.3 Operational characteristics of pv systems ... 18
4.5.4 Pv module parameters ... 19
4.5.5 solar irradiance ... 25
4.5.6 solar irradiation ... 28
4.5.7 Maximum power point tracking ... 28
5 DATA ANALYSIS AND CALCULATIONS ... 30
5.1 THE WATER REQUIREMENT OF THE VILLAGE ... 30
5.2 APPROXIMATE ESTIMATION OF THE ELECTRICITY REQUIREMENT FOR THE VILLAGE ... 30
5.3 ESTIMATION OF THE ENERGY REQUIREMENT FOR WATER PURIFICATION ... 31
5.4 CALCULATION OF REQUIRED PUMP CAPACITY ... 33
5.5 CALCULATION OF THE AVAILABLE WIND POWER ... 39
5.6 CALCULATION OF THE AVAILABLE SOLAR POWER FOR THE PV PANEL ... 41
5.6.1 Assumptions ... 41
5.6.2 PV calculation ... 42
5.7 ENERGY STORAGE BATTERY BANK ... 43
5.7.1 Estimation of battery capacity ... 43
6 SOLAR + WIND HYBRID WATER PURIFICATION SYSTEM DESIGN AND COST ANALYSIS ... 44
7 ECONOMIC, ENVIRONMENTAL AND SOCIAL BENEFITS ... 47
7.1 ECONOMICAL BENEFITS ... 47 7.2 ENVIRONMENTAL BENEFITS ... 47 7.3 SOCIAL BENEFITS ... 47 8 DISCUSSION ... 48 9 CONCLUSION ... 49 10 REFERENCES ... 50 11 ANNEX ... 52
4
LIST OF FIGURES
FIGURE 1.1.0: MASLOW’S HIERARCHY OF NEEDS ... 8
FIGURE 2.0.0:LOCATION OF KAMMALAKKULAMA ... 9
FIGURE 4.3.1:OSMOSIS PROCESS ... 14
FIGURE 4.3.2:REVERSE OSMOSIS PROCESS ... 14
FIGURE 4.3.3:SEMI PERMEABLE MEMBRANE ... 15
FIGURE 4.3.4:TYPICAL ROSYSTEM ... 15
FIGURE 4.4.0:WIND POWER SYSTEM ... 16
FIGURE 4.5.1: INCOMING SOLAR ENERGY ... 18
FIGURE 4.5.3: PV ELECTRICITY GENERATION PROCESS ... 19
FIGURE 4.5.4.1:IV CURVE FOR SOLAR CELL FOR OPEN CIRCUIT VOLTAGE... 20
FIGURE 4.5.4.2:IV CURVE FOR SOLAR CELL FOR SHORT CIRCUIT CURRENT ... 21
FIGURE 4.5.4.3:IV VARIATION OF FILL FACTOR WITH DIFFERENT SHORT CIRCUIT CURRENT AND OPEN CIRCUIT VOLTAGE ... 22
FIGURE 4.5.5.1:SOLAR ANGLES ... 25
FIGURE 4.5.5.2:ZENITH ANGLE ... 26
FIGURE 4.5.6: AZIMUTH ANGLE ... 27
FIGURE 4.5.7:SURFACE AZIMUTH ANGLE ... 27
FIGURE 4.5.8:TYPICAL MPPT ... 29
FIGURE 4.5.9:MPPT CIRCUIT DIAGRAM ... 29
FIGURE 5.3.0:SCHEMATIC OF DOUBLE STAGE RO SYSTEM ... 31
FIGURE 5.4.0:PROPOSED WATER PUMPING SYSTEM ... 37
FIGURE 5.4.1:DYNAMIC VISCOSITY OF WATER AT DIFFERENT TEMPERATURES ... 38
FIGURE 5.4.2:MOODY DIAGRAM ... 38
5
LIST OF TABLES
TABLE 4.1.0:ELEMENT COMPOSITION OF UNDERGROUND WATER ... 13
TABLE 4.2.0:MONTHLY CLIMATIC CONDITION AT ANURADHAPURA ... 13
TABLE 4.3.3:TYPICAL REJECTION CHARACTERISTICS OF RO MEMBRANE [12] ... 15
TABLE 4.5.0:YEARLY SOLAR FLUXES AND HUMAN ENERGY CONSUMPTION ... 17
TABLE 4.5.4:MAXIMUM POWER DENSITIES ... 24
TABLE 4.5.5:CONVERSION EFFICIENCIES AT 300K... 24
TABLE 4.5.5:SOLAR HOUR ANGLE OF THE DAY ... 26
TABLE 5.4.0:ROUGHNESS OF MATERIAL ... 36
TABLE 5.5.0:MONTHLY WIND SPEED ... 39
TABLE 5.6.1:MONTHLY SOLAR IRRADIATION... 41
6
NOMENCLATURE
𝑃𝑤𝑛 : Power consumed by feed pump, booster pump, chemical water treatment pump and Low/High pressure pump (kW)
𝑄𝑛 : Rate of feed water
𝑃𝑟𝑛 : Feed pressure(Pr1), boosted pressure (Pr3), rejection pressure (Pr2 &Pr4)
𝐸𝑛 : Net Efficiency of feed pump
𝐸𝑝 Pump efficiency
𝐸𝑛 Motor efficiency for booster pump and energy recovery turbine
Q : Water flow rate (m3/s)
V : Water velocity through pipe (m/s)
A : Cross sectional area of the pipe (m2)
D : Diameter of the pipe (m)
𝑘 : Conversion factor ( k = 0.849)
𝐶 : Roughness coefficient
𝑅 : Hydraulic radius
𝑠 : Head loss per length of pipe
ℎ𝑓 : Head loss in meters
𝐿 : Length of the pipe in meters
𝑑 : Inside pipe diameter
𝜌 : Density of water (1000 Kg/m3)
𝜇 : Dynamic viscosity (N.s/m2 )
ε : Roughness (m)
f : Friction Factor
𝑁𝑅 : Reynolds Number
P : Required pump power
𝜌 : Air density (Kg/m3)
𝐴 : Interception area
𝑉 : Wind speed (m/s)
𝐶𝑝 : Betz coefficient
𝑘 : Conversion factor ( k = 0.849)
𝜌(𝑧) : Air density as a function of altitude (Kg/m3 )
𝑃
0 : Standard sea level atmospheric density (1:225 kgm-3);𝑅
: Specific gas constant for air (287:05 J kg-1K-1); T : Temperature (K)7
𝑧
: Altitude above sea level (m)𝐼𝑠𝑐 : Short circuit current at an irradiance G
𝐼𝑠𝑐0 : Short circuit current at standard solar irradiances G0 (1000 W/m2)
𝐺 : Solar irradiances
𝐺0 : Standard solar irradiances
∝ : Exponent factor
𝑣𝑜𝑐 : Normalized value of open circuit voltage to the thermal voltage
𝑉𝑜𝑐 : Open circuit voltage
𝑘 : Boltzmann Constant (1.38X1023 J/K) 𝑇 : PV module temperature (K) 𝑛 : Identity factor (1<n<2) 𝑞 : Charge on an electron (1.6X1019C) 𝑅𝑠ℎ Shunt resistance 𝑟𝑠 Normalized resistance
𝛽𝑐 : Surface tilt angle (rad) 𝛾𝑠 : Solar azimuth angle(rad) 𝛾𝑐 : Surface azimuth angle(rad) 𝜃𝑧 : Solar zenith angle(rad)
𝐼𝑡 : Total irradiation on PV panel (w/m2)
𝐼𝑏 : Beam irradiation (w/m2)
𝐼𝑑 : Diffused irradiation (w/m2)
8
1 BACKGROUND
Every human being has the important right to live with comfort. As per the Maslow’s hierarchy of needs (see Fig. 1.1), water, food, breathing, etc. are the basic needs of all human beings. Today, although we have come up to the edge of the development of technology, many people still struggle on satisfying their basic needs. Most importantly, scarcity of clean water has been a major problem in many parts of the world, especially in developing nations.
The water problem comes in several ways such as accessibility to water resources, contaminated drinking water, etc. Even though the water resources are available, often there is a lack of technology to harness and produce clean water. Global statistics show that more than 1.1 billion people in developing countries are suffering from inadequate access to water and 2.6 billion people are failing to satisfy their basic sanitation needs [2]. Furthermore, about 80% of developing countries are having poor water and sanitation facilities [3].
Water scarcity is directly proportional to the accessibility to electricity. Although sufficient water resources exist, the lack of electricity prevents the supply of water in useable form for human consumption. Remote villages without access to the main grid face difficulties in getting electricity for lighting in addition to the water supply problems. Under these conditions, stand-alone electricity generation would be much appropriate for meeting the basic needs of both clean water and electricity for lighting and to power home appliances for uplifting of the living standards of the villagers.
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2 INTRODUCTION
Sri Lanka is an island in the Indian Ocean, which has over 3000 years of recorded history. Nowadays it is a developing country with 21 million of population. The urban population is 15.1% from the total population and the urbanization rate is 1.36% [4]. Sri Lanka has a distribution occupation as: 31.8% agriculture, 25.8% production industry and 42.2% service sector industry [5].
As an island, Sri Lanka has around 1500 km of seashore boundary and 65,000 km2 of land area. Sri Lanka receives
on average 2500 mm of rainfall in wet areas and 1000 mm in dry areas. The country exceeds 5,120 watt hours per square meter per day of average solar insolation. Average wind speed was recorded as 12 km/hour [6].
North Central province is one of the largest agricultural areas where the most of the food requirement of the nation is supplied. Rice is the main crop which is cultivated in two seasons of the year. Most of the remote villages in the province do not have access to utilities due to various reasons. Although 96% of Sri Lanka is electrified, these villages have not benefitted from accessibility to grid electricity. It is due to the very high cost of expanding power transmission lines to these areas where the investment recovery is low due to the low income of the population. In this study, a village called Kammalakkulama was selected which is among several remote villages where no infrastructural facilities have been implemented. The geographical coordinates of the village are 8° 31' 0" North, 80° 28' 0" East [7], it is situated in the Mihinthale region of North Central Province. The village is comprised of 55 families with a total of 280 people, and 90% of the villagers are full time farmers who engage in cultivation of crops and in animal husbandry. Paddy, coconut, banana, peanut and vegetables are the main crops which they cultivate. Each family possesses approximately 5 acre of land. Agricultural water is obtained from the water reservoirs via water tunnels. Also, the villagers have water wells for drinking and other domestic usages.
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2.1 PROBLEM IDENTIFICATION
The main problem faced by villagers is the non-availability of electricity. They use kerosene lamps for night time lighting. They have created a village society for the welfare activities. One electricity generator is used only for special events like funerals, weddings or other social activities. Due to this, they are facing difficulties on caring their daily life. There is not much communication with the main cities and it creates a barrier for sharing the information with the outside residents. The villagers are at a low level in financial capabilities and the average monthly income is around Rs. 5000.00 per family.
The main problem faced by the villagers is obtaining purified water for drinking purpose. Although they use wells for water, the underground water table contains heavy metals that reportedly causes Chronic Kidney Disease (CKD). Especially in North Central province, this issue is very well-known. The region is categorized under dry ecological zones in Sri Lanka. The annual average precipitation is 960mm. Fluoride is one of the suspected chemical contaminants which causes CKD. It has been observed that there is a higher Fluoride level in the well water in the studied region (1.5 mg/l). The high concentration of calcium mixed with fluoride creates calcium fluorides (CaFl2).
This causes Kidney Tubular Damages, among other illnesses [8] triggered by the heavy metal contamination in the ground water such as the high levels of arsenic and cadmium. This problem is suspected to originate from the use of agrochemicals.
As an immediate solution it would not be possible to do away with agrochemicals, and therefore it is essential to implement a water purification system to produce clean drinkable water. In urban areas in the province, there are some programs in place for centralized production and distribution of purified water, however, remote villages are not supplied with even such short term solutions owing to the high cost of water transportation and poor accessibility to these locations.
2.2 RESEARCH OBJECTIVE
The objective of this study was to propose a concept design and to evaluate technically and economically a renewable energy based system that enables the local production of potable water and generates electricity for domestic lighting purpose, solely powered by local renewable energy sources.
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3 METHODOLOGY
A survey was carried out to obtain data on population, employment, production, energy consumption pattern, etc, in the selected village.
A feasibility study was carried out on promoting the utilization of renewable energy sources in the village. Mainly, Solar, Wind and Biomass were considered as promising local renewable energy (RE) sources. These are freely available but their intensity varies depending on the region. Site condition was tabularized for proper analysis, especially the variability of wind power and solar irradiation.
After the assessment of available potentials of renewable energies in the region, the required energy source capacity was decided for a system composed of wind turbines and PV panels. Similarly, the water purification equipment to be used was analyzed to match the demand and the energy availability. In this study, the Reverse Osmosis System (RO) was selected as the most applicable water purification method.
At the same time, biomass gasification system was studied which would be used as backup energy generation source in absence of solar and wind or in case of higher energy demand. In the proposed prototype, all the equipment shall be embedded in one unit container, which could be easily relocated.
The hybrid system was designed with water purification as the primary goal and potable water as the main product. An embedded water purification system would be most beneficial for uplifting the living standards of the villagers. Another critical part is controlling and synchronizing of all power generation sources in the combined system. The wind turbine generates an alternating current while the solar PV system generates direct current. This generated electricity shall be stored in batteries for nighttime lighting and other necessities. Therefore, a battery bank and a control system were added to the design.
The main components of the combined system have been selected and evaluated in this study. Namely, the water purification equipment, the wind turbine and solar panels have been taken into consideration.
After designing the system, the required total power needed to run the system was analyzed. Then, a simulation model was created for analyzing how this power could be generated with the available RE resources.
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13
4 LITERATURE SURVEY AND BACKGROUND INFORMATION 4.1 ANALYZING THE QUALITY OF WATER WITHIN THE REGION
Table 4.1 shows data on the quality of the available drinking water within the studied region.
4.2 SOLAR AND WIND ENERGY POTENTIAL WITHIN THE REGION
Solar irradiance in the selected area was evaluated for the design of PV system and analysis of the amount of electricity generation by solar power. Sample data was obtained from nearby regions. Also, the expected wind speed profile was tabulated in order to design the wind power system as given in Table 4.2. When obtaining the climatic condition data, available measurements from the neighboring Anuradhapura city were selected [11]. The focus of this study, Kammalakkulama village, is located within Anuradhapura region.
Item Unit Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec
Daily Irradiation kWh/m² 4.44 5.38 5.99 5.69 5.57 5.28 5.31 5.45 5.34 4.77 4.06 3.99 Clearness 0 - 1 0.49 0.55 0.58 0.55 0.54 0.52 0.53 0.53 0.52 0.49 0.44 0.45 Temperature °C 25.1 25.76 27.2 27.41 27.22 26.95 26.64 26.62 26.48 26.24 25.88 25.48 Wind speed m/s 5.35 4.58 3.8 3.68 5.61 7.1 6.16 6.4 5.49 4.3 4.05 4.91 Precipitation mm 89 55 75 167 92 18 38 41 72 259 260 224 Wet days d 4.9 4.1 5.1 9.3 6.8 5.3 5.1 4.8 7 13.2 14.7 13
Table 4.2.0: Monthly climatic condition at Anuradhapura
Element Concentration (g/L)
Min Max Mean
Li <0.10 13.52 4.56 B 26.6 101.4 45.5 Al 2.5 73.3 12.2 Mn 0.15 236.9 35.98 Co 0.053 0.47 0.129 Ni 0.81 1.57 1.13 Cu <0.80 1 0.53 Zn 0.6 2.8 1.5 As <0.15 0.48 0.25 Se 0.182 0.683 0.383 Rb 0.18 9.8 1.97 Sr 101 660 369 Mo 0.234 7.77 1.595 Cd <0.0027 0.024 0.0055 Pb <0.046 0.234 0.049 U 0.084 0.336 0.176
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4.3 WATER PURIFICATION SYSTEMS 4.3.1 OSMOSIS PROCESS
In osmosis process, the fluid is passing through a semipermeable membrane. The fluid contains impurities such as Sodium, Sulfate, Calcium, Arsenic etc. [12]. The theory behind this system is, the weaker concentration of solution will migrate to higher concentration solution.
4.3.2 REVERSE OSMOSIS PROCESS
In reverse osmosis process, external pressure is applied on the high concentration fluid side. Then the contaminant is obstructed from the semi permeable membrane and only fresh water will go through the membrane. In hear, additional pressure will be given in reverse side compared to natural osmosis proves.
Figure 4.3.1: Osmosis Process
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4.3.3 SEMIPERMEABLE MEMBRANE
This is a type of a biological membrane. It allows certain molecules or ions to pass through it and rest will be barricaded. The permeability will depend on the solute size. And the performance of the system will depend on the feed pressure, permeate pressure, concentrate pressure, feed conductivity, permeate conductivity, permeate flow, feed flow and temperature.
Countries like Singapore use this system in order to maximize the utilization of water. NEWater is a brand which use duel membrane system, micro filtration and reverse osmosis, for water purification along with ultraviolet
technology. Element % of removal Sodium 85 - 94 Sulfate 96 - 98 Calcium 94 - 98 Potassium 85 - 95 Nitrate 60 –75 Iron 94 – 98 Zinc 95 – 98 Mercury 95 – 98 Selenium 94 – 96 Phosphate 96 – 98 Lead 95 – 98 Arsenic 92 – 96 Magnesium 94 – 98 Nickel 96 – 98 Fluoride 85 - 92 Manganese 94 – 98 Cadmium 95 – 98 Barium 95 – 98 Cyanide 84 – 92 Chloride 85 – 92
Table 4.3.3: Typical rejection characteristics of RO membrane [12]
Figure 4.3.3: Semi permeable membrane
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4.4 WIND POWER SYSTEM
Wind power is a form of solar energy, which basically is caused by uneven heating of the Earth by the sun. The wind flows modified due to rotation of the Earth and the uneven geographical condition of the surface. This is one of the green renewable energy sources available anywhere in the world.
The usage of wind energy has the history over 3000 thousands years. In the early eras, wind energy conversion devices used to pump water for irrigation and to grind grains. Nowadays, wind energy is mostly used to generate electricity.
Wind turbine is the main tool for generation of wind electricity. Simply, wind turbine is opposite to the fan operation where, fan uses electricity to rotate the blades. But in wind turbines, the blades are rotated by the wind in order to generate electricity.
In this chapter, it will be discussed the calculation of the available wind energy in the region and the design of a wind power plant to maximize utilization of available wind power.
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4.5 SOLAR PV SYSTEM 4.5.1 SOLAR POWER
Solar power means the conversion of sun light into electricity. As an alternative renewable energy, solar power is becoming popular in the world. As per the “US Energy Information Administration”, it was estimated that annual solar energy which is absorbed by earth’s atmosphere ocean and land is approximately 3,850,000 exajoules (EJ) where only 539 EJ are used as primary energy by humans and 67 EJ used as electricity.
Solar 3,850,000 EJ
Wind 2,250 EJ
Biomass potential ~200 EJ
Primary energy use (2010) 539 EJ
Electricity (2010) ~67 EJ
Table 4.5.0 : Yearly solar fluxes and Human Energy Consumption Note : Exa-joule (EJ) = 1018 Joules = 278 billion kilowatt-hours (kW•h)
Solar energy can be directly converted in to electricity by photovoltaics (PV) method, or indirectly by Concentrated Solar Power (CSP) where sunlight is focused on to a single small beam with the extraction of solar heat. Installation of CSP systems for electricity production is costly and demands advanced maintenance, which are outside the scope of this study.
Solar water heating is one method to store energy of the sun. Normally, shallow water of a lake is warmer than the deep water due to heating by the sun. Same scenario can be used for heating systems in buildings. There are two main parts, Solar Collector and Storage Tank. The solar collector, the most common type is flat plate collector, will be mounted on the roof top. It contains thin tube where water is circulating and absorbs the heat from the solar. The heated water will be stored in the tank for later usages.
The solar heat can be used instead of fossil fuels in a similar way to the generate steam by concentrating solar beams in a single point. There are several solar concentrating techniques such as, Parabolic through, Spherical Dish and Solar Tower.
There are some other techniques like Passive Solar Heating / Day Lighting and Solar Process Space Heating / Cooling. These alternatives are used to maximize the utilization of solar power by simple methods in the build environment, whenever it is available.
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4.5.2 PHOTOVOLTAICS SYSTEM
PV system is the most effective way to convert solar irradiation in to electricity. The main advantage is that it can be used in isolated area or connected to the main grid. Remote areas where the accessibility to the main gird is difficult would benefit from this method. If used in large scales, solar PV has become the cheapest way of renewable electricity generation. Key features of this system are its maintenance-free character, low operational cost, long life span and nearly zero local pollution.
4.5.3 OPERATIONAL CHARACTERISTICS OF PV SYSTEMS
PV cells are made out of at least two layers of semi-conductors, where one layer contains positive charge and other contains negative charge. Sunlight can be regarded as small particles called photons which carry the solar energy. When the PV cells are exposed to sunlight, the negative layer of the PV cells absorbs the photons from the sun’s rays and delivers free electrons. These negative charges travel from negative layer to positive layer where they create a voltage difference. When these two layers have been interconnected to an external load, the circuit will create a flow of electricity. Although the generated electricity from a single cell is up to 1-2 watts, by increasing the number of cells higher capacities can be achieved.
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4.5.4 PV MODULE PARAMETERS
There are some important parameters, which determine the performance of the PV cells. These are mainly based on the internal characteristics of the PV module, the site condition and the accuracy of the installation;
1. Open Circuit Voltage (Voc)
2. Short Circuit Current ( Isc)
3. Fill Factor (FF) 4. Maximum Power
5. Maximum Power Point Voltage 6. Maximum Power Point Current 7. Efficiency
4.5.4.1 OPEN CIRCUIT VOLTAGE (VOC)
The maximum available output voltage performed by the solar cell where the total current through the device is zero. Solar cell consists of P-N junctions and when the temperature increase, the saturation current increases exponentially. So that the Voc has an exponential growth with respect to the temperature. This can be deviated by
various other factors such as shunt resistance, non-ideality of the diode and series resistance. It has been considered a temperature dependent model in this case.
𝑉𝑜𝑐 = 𝑉𝑜𝑐0 1 + 𝛽 (𝐺𝐺 )0 (𝑇0 𝑇) 𝛾 ………... ( 1 ) 𝑃𝑚𝑎𝑥 = 𝑉𝑜𝑐. 𝐼𝑆𝑐. 𝐹𝐹 ………... ( 2 )
20 𝑛 = 𝑉𝑜𝑐. 𝐼𝑆𝑐. 𝐹𝐹 𝑃𝑖𝑛 ………... ( 3 ) Where;
𝑉𝑜𝑐 : Open circuit voltage at an irradiance G
𝑉𝑜𝑐 : Open circuit voltage at standard solar irradiances G0
𝛽 : Dimensionless coefficient
𝛾 : Exponent to make up for all the nonlinear temperature voltage effect
4.5.4.2 SHORT CIRCUIT CURRENT ( ISC)
It is the current through solar cell where the voltage across solar cell is zero. This occurs due to the generation and accumulation of light generated charge carriers. In ideal case, the short circuited current and the light generated current will be identical. Hence the largest current which could be drawn from the solar cell is short circuit current. There are several factors affecting the short circuit current. The area of the solar cell in terms of short circuit current density, the number of photons which is depend on the intensity of light, the spectrum of the incident light, the optical properties of the solar cell and the collection probability which depend on the surface passivation and the carrier life time [21].
21 𝐼𝑠𝑐 = 𝐼𝑠𝑐0 (𝐺 𝐺0 ) ∝ ………... ( 4 ) Where;
𝐼𝑠𝑐 : Short circuit current at an irradiance G
𝐼𝑠𝑐0 : Short circuit current at standard solar irradiances G0 (1000 W/m2)
𝐺 : Solar irradiances
𝐺0 : Standard solar irradiances
∝ : Exponent factor
4.5.4.3 FILL FACTOR (FF)
As explained above, the Short Circuit Current and Open Circuit Voltage are the maximum current and voltage that could be obtained in the PV system. But, at these extremes, the delivered power is zero. Hence, the Fill Factor has been introduced where the maximum power could be obtained as the product of the values for Short Circuit Current and Open Circuit Voltage.
Normally the Fill Factor determines the squares of the IV curve. The maximum FF can be determined by 𝐹𝐹𝑚𝑎𝑥 = 𝑑(𝐼𝑉)
𝑑𝑉 ………... ( 5)
22 𝐹𝐹0 = 𝑣𝑜𝑐 − ln (𝑣𝑜𝑐+ 0.72) 1 + 𝑣𝑜𝑐 ………... ( 6 ) 𝐹𝐹 = 𝐹𝐹0(1 − 𝑟𝑠) ………... ( 7 ) 𝑟𝑠 = 𝑅𝑠 𝑅𝑠ℎ ………... ( 8 ) 𝑅𝑠ℎ = 𝑉𝑜𝑐 𝐼𝑠𝑐 ………... ( 9 ) 𝑟𝑠 = 𝑅𝑠 𝑉𝑜𝑐 𝐼𝑠𝑐 ⁄ 𝐹𝐹 = 𝐹𝐹0(− 𝑅𝑠 𝑉𝑜𝑐 𝐼𝑠𝑐 ⁄ ) ………... ( 10 ) 𝑣𝑜𝑐 = 𝑉𝑜𝑐 𝑛𝑘𝑇 𝑞 ⁄ ………... ( 11 ) Where;
𝑣𝑜𝑐 : Normalized value of open circuit voltage to the thermal voltage
𝑉𝑜𝑐 : Open circuit voltage
𝑘 : Boltzmann Constant (1.38X1023 J/K) 𝑇 : PV module temperature (K) 𝑛 : Identity factor (1<n<2) 𝑞 : Charge on an electron (1.6X1019C) 𝑅𝑠ℎ : Shunt resistance 𝑟𝑠 : Normalized resistance
Figure 4.5.4.3: IV variation of Fill Factor with different Short Circuit Current and Open Circuit Voltage
23
4.5.4.4 MAXIMUM POWER
Maximum power output will be expressed in terms of Fill Factor. The multiplication of Short Circuit Current, Open Circuit Voltage and Fill Factor will give the maximum power output, as follows;
𝑃𝑚𝑎𝑥 = 𝑉𝑜𝑐. 𝐼𝑆𝑐. 𝐹𝐹 ………... ( 12 ) 𝑉𝑜𝑐 = 𝑉𝑜𝑐0 1 + 𝛽 (𝐺𝐺 )0 (𝑇0 𝑇) 𝛾 ………... ( 13 ) 𝐼𝑠𝑐 = 𝐼𝑠𝑐0 (𝐺 𝐺0) ∝ ………... ( 14 ) 𝐹𝐹0 = 𝑣𝑜𝑐 − ln (𝑣𝑜𝑐+ 0.72) 1 + 𝑣𝑜𝑐 ………... ( 15 ) 𝐹𝐹 = 𝐹𝐹0(1 − 𝑅𝑠 𝑉𝑜𝑐 𝐼𝑠𝑐 ⁄ ) ………... ( 16 ) Hence ; 𝑃𝑚𝑎𝑥 = 𝑣𝑜𝑐 − ln (𝑣𝑜𝑐+ 0.72) 1 + 𝑣𝑜𝑐 . (1 − 𝑅𝑆 (𝑉𝑜𝑐 𝐼𝑠𝑐 ⁄ ) ) . ( 𝑉𝑜𝑐0 1 + 𝛽 (𝐺𝐺 )0 . (𝑇0 𝑇) 𝛾 ) . 𝐼𝑠𝑐0 (𝐺 𝐺0) ∝ ( 17 ) 4.5.4.5 EFFICIENCY
This is the most commonly used parameter to measure the performance of the solar cell. It is the ratio between energy outputs from the solar cell in to energy input to the solar cell
𝑃𝑚𝑎𝑥 = 𝑉𝑜𝑐. 𝐼𝑆𝑐. 𝐹𝐹 ………... ( 18 ) 𝑛 = 𝑃𝑚𝑎𝑥 𝑃𝑖𝑛 ………... ( 19 ) 𝑛 = 𝑣𝑜𝑐 – ln (𝑣𝑜𝑐+ 0.72) 1 + 𝑣𝑜𝑐 . (1 − 𝑅𝑆 (𝑉𝑜𝑐 𝐼𝑠𝑐 ⁄ )) . ( 𝑉𝑜𝑐0 1 + 𝛽 (𝐺𝐺 )0 . (𝑇𝑇0) 𝛾 ) . 𝐼𝑠𝑐0 (𝐺𝐺 0) ∝ 𝑃𝑖𝑛 ( 20) Where;
24
Solar module conversion efficiency can be derived as a function of Open Circuit Voltage, Short Circuit Current and Fill Factor [22].
The maximum output power densities can be represented as follows [23];
Jsc (W/cm2) Voc (V) FF = 0.7 FF = 0.8
0.025 1.01 0.0177 0.0202
0.030 1.07 0.0229 0.0257
0.035 1.13 0.0277 0.0316
Table 4.5.4 : Maximum power densities
Sun Factor ( Fsun)
Voc
(V)
Isc = 0.025 A Isc = 0.030 A Isc = 0.035 A
FF: 0.7 / 0.8 0.7 / 0.8 0.7 / 0.8
1 1.01 13.14 / 14.46 15.71 / 17.95 18.33 / 20.95
10 1.07 13.87 / 15.85 16.64 / 19.02 19.42 / 22.19
100 1.13 14.65 / 16.74 17.58 / 20.09 20.51 / 2.44
25
4.5.5 SOLAR IRRADIANCE
In this section, the parameters related to calculating the solar irradiance will be discussed.
4.5.5.1 DECLINATION ANGLE (𝜹)
The angular position of the sun at solar noon with respect to the plane of equator. As there is a tilt of the earth in 23.450, the declination angle varies with season to season with maximum and minimum angle of±23.450. Where
on January 21st, δ is +23.450and on December 21st, δ is−23.450. The δ is zero on March 22nd and September
22nd.
sin δ = {0.39795. cos [2. 𝜋.
(𝑛 − 173)
365 ]} ………... ( 21 )
Where;
𝑛 : Day of the year with starting January 1st , d =1
For an accurate expression
δ = sin−1{0.39795. cso [2. 𝜋.(𝑛 − 173)
365 ]} ………... ( 22 )
4.5.5.2 SOLAR HOUR ANGLE (𝝎)
The sun’s angular displacement, east or west, with respect to the local meridian. At noon, the solar hour angle becomes zero because the position of the sun and the local meridian lay on the same line. In the morning, the solar angle is negative and in the afternoon it is positive. The solar hour angle varies with the resolution of 150 per hour.
26
sin 𝜔 = sin 𝛼 − sin 𝛿. sin Ψcos 𝛿 . cos Ψ ………... ( 23 )
𝜔 = sin−1{sin 𝛼 − sin 𝛿. sin Ψ
cos 𝛿 . cos Ψ } ………... ( 24 )
Where;
𝛹 : Latitude
𝛿 : Declination angle
𝛼 : Solar altitude
Hour 6 a.m 7 a.m 8 a.m 9 a.m a.m 10 a.m 11 p.m 12 1 p.m 2 p.m 3 p.m 4 p.m 5 p.m 6 p.m
Angle (0) -90 -75 -60 -45 -30 -15 0 15 30 45 60 75 90
Table 4.5.5 : Solar hour angle of the day
4.5.5.3 ZENITH ANGLE (𝜽𝒛) AND SOLAR ALTITUDE (𝜶)
The angle between the horizontal line of the earth center and the intersect line of sun and earth centers. The solar attitude is 900-𝜃
𝑧
𝜃𝑧
= cos−1(cos 𝜑 . cos 𝛿 . cos 𝜔 + sin 𝜑 . sin 𝛿) ………... ( 25 )
𝛼𝑧 = 90 − 𝜃𝑧 ………... ( 26 )
27
4.5.5.4 SOLAR AZIMUTH ANGLE ( 𝜸𝒔 )
The deviation of the projection on horizontal plane and of the normal to the surface from the local meridian.
𝜸𝑠 = 𝑠𝑔𝑛(𝜔).
|
cos−1{
𝑐𝑜𝑠 𝜃𝑧.𝑠𝑖𝑛 𝜑−𝑠𝑖𝑛 𝛿𝑠𝑖𝑛 𝜃𝑧.𝑐𝑜𝑠 𝜑
}|
………... ( 27)
4.5.5.5 SURFACE AZIMUTH ANGLE ( 𝜸𝒄)
Surface azimuth angle is the angle between south and the horizontal projection of the surface normal.
Solar panels will be placed perpendicular to South. So the surface azimuth angle(𝛾𝑐) will become zero [25];
𝜸𝒄 = 0 degrees ………... ( 28 )
Figure 4.5.6: Azimuth Angle
28
4.5.5.6 SURFACE TILT ANGEL ( ∑ = 𝜷𝒄 )
Surface tilt angle is the angle between the surface vertical and surface normal. In the Table 7.5.5 it is shown as ∑ . In these calculations, the surface tilt angle is assumed at 450 (0.78 rad).
4.5.5.7 SURFACE INCIDENCE ANGLE (𝜽)
This will be calculated from the following equation 450
𝜽 = cos−1(cos 𝛽𝑐 . cos 𝜃𝑧 + sin 𝛽𝑐 . sin 𝜃𝑧 . cos(𝛾𝑠− 𝛾𝑐) ……… ( 29 )
Where;
𝛽𝑐 : Surface tilt angle (rad) 𝛾𝑠 : Solar azimuth angle(rad)
𝛾𝑐 : Surface azimuth angle(rad)
𝜃𝑧 : Solar zenith angle(rad)
4.5.6 SOLAR IRRADIATION
𝐼𝑡 = 𝐼𝑏. cos 𝜃 + 𝐼𝑑 ………... ( 30 )
Where;
𝐼𝑡 : Total irradiation on PV panel (w/m2)
𝐼𝑏 : Beam irradiation (w/m2)
𝐼𝑑 : Diffused irradiation (w/m2)
𝜃 : Surface incidence angle(rad)
4.5.7 MAXIMUM POWER POINT TRACKING
Maximum Power Point Tracking (MPPT) is an algorithm which is used in charge controllers to obtain maximum energy from the available PV module. To obtain the MPPT, the parameters such as Open Circuit Voltage, Short Circuit Voltage, FF, Maximum power and Efficiency.
Separate controller circuit is needed with an embedded algorithm to obtain the MPPT strategy. It’s like a closed loop circuit which monitors the input and output. [24]
29
DC-DC power converter is used in order to operate the MPPT. [25]
Figure 4.5.8: Typical MPPT
30
5 DATA ANALYSIS AND CALCULATIONS
5.1 THE WATER REQUIREMENT OF THE VILLAGE Water Purification System Design
No. of Families in the area = 55 Nos.
Population = 280 Nos.
Average purified water requirement per day = 25 Liters/pp [9] This include only drinking and cooking.
Total water requirement per day = 7,000 Liters
Total water requirement per day with 1.5 safety factor = 10,500 Liters
For keeping 2 days water storage (Feed water) = 21,000 Liters
For keeping 2 days water storage (Feed water) = 21.0 m3
For keeping 2 days water storage (Product water) = 21.0 m3
Required No. of water tanks ( if 10,000 L each) = 4 Nos. [10]
30,000 L capacity of water storage will be considered for the calculation
5.2 APPROXIMATE ESTIMATION OF THE ELECTRICITY REQUIREMENT FOR THE VILLAGE Estimation of the electricity requirement
Considering one family with basic electricity needs
10 W LED Bulbs - 6 nos. per house = 60 Watt
Other Electrical needs (TV, Radio, Cooking) = 40 Watt
Operating time per day = 6 Hours
Total Electricity requirement per family = 0.60 kWh
Allow safety factor of 1.5 = 0.90 kWh
Electricity requirement for the village per day = 49.50 kWh
Required electricity to purify water (RO System) = 4 kWh/m3
Additional electricity for water purification = 35.00 kWh
Energy requirement for pumping water from well = 3.6 kWh
Total Electricity requirement = 88.10 kWh
We will assume village daily electricity requirement = 100.00 kWh
The target of the proposed renewable energy generation system is to produce 100 kWh per day. This includes the water purification process and basic electricity requirement for lighting, etc.
1.5 safety factor was added to avoid unforeseen impact to the system. Although the water requirement per day is 10,500 Liters, we kept water storage for 2 days of feed-water and 2 days of product-water to avoid water shortage in the village. Keeping 2 days storage will help for emergency situation and also cater for future requirement due to population growth. The purified water is stored in a central point in the village. The villagers are allowed to fetch water on daily basis or weekly basis. Altogether 4 storage tanks, 10,000 L each, will be kept at the village.
31
5.3 ESTIMATION OF THE ENERGY REQUIREMENT FOR WATER PURIFICATION
As per the literature review, it was noted that the daily water consumption of the village to be kept as 30 m3/day.
Based on the daily water requirement, RO system was selected. The proposed design was two stage with three membrane elements in each stage as per the above figure. This selection was done to increase the water productivity by applying boost pump. This will recover significant amount of energy. SW30HRLLE-400 membrane was used on this analysis [13]
𝑃𝑤𝑛 = 𝑄𝑛. 𝑃𝑟𝑛 𝐸𝑛
………... ( 31 )
𝐸𝑛 = 𝐸𝑝. 𝐸𝑛 ………... ( 32 )
Where;
𝑃𝑤𝑛 : Power consumed by feed pump, booster pump, chemical water treatment pump and Low/High pressure pump (kW)
𝑄𝑛 : Rate of feed water (𝑄1), boosted water (𝑄3) and fresh water production(𝑄5+ 𝑄6) (m3/s)
𝑃𝑟𝑛 : Feed pressure(Pr1), boosted pressure (Pr3), rejection pressure (Pr2 &Pr4)
𝐸𝑛 : Net Efficiency of feed pump
𝐸𝑝 Pump efficiency
𝐸𝑛 Motor efficiency for booster pump and energy recovery turbine
32
The low-pressure pump (𝑃𝑤𝑛) consumes the highest energy. Others pumps consume 20% of the low-pressure
pump’s energy. From the literature review, following data was calculated;
ITEM AMOUNT UNIT
Total water requirement per day with 1.5 safety factor = 10,500 Liters
For keeping 2 days water storage = 21,000 Liters
Daily water requirement = 10.5 m3
Required feed water flow rate (Say) = 10 m3/hour
Assumed the pressure of water in first stage RO = 45 bar
Assume pump efficiency = 0.85
From equation (1) 𝑃𝑤1 = 𝑄𝑛.𝑃𝑟𝑛 𝐸𝑛 = ( 10 3600).(45.10 5) 0.85 .1000 = 14.71 kW
Power requirement for other pumps, including booster (20% of 𝑃𝑤1 ) = 2.94 kW
Total power requirement for RO system = 17.65 kW
Average production of portable water = 4.4 m3/hour
The work done by the system = 4.01 kWh/m3
No. of hours needed to run the system (10.5/4.4) = 2.38 hours
Required electricity per day for water purification (2.38x17.65) = 42 kWh Without energy recovery
For Energy recovery turbine;
Assume efficiency of energy recovery turbine 𝐸𝑡 = 0.85
Concentrate pressure 𝑃𝑟𝑛 = 50 bar
Concentrate water flow 𝑄𝑛 = 6 m3/hour
𝑃𝑤𝑛 = 𝑄𝑛. 𝑃𝑟𝑛. 𝐸𝑡 [14] ………... ( 33 )
Where;
𝑃𝑤𝑛 : Energy recovery (kW)
𝑄𝑛 : Rate of feed brine(m3/s)
𝑃𝑟𝑛 : Feed pressure
𝐸𝑡 : Turbine efficiency
From equation (33) Energy recovery potential (6x50x0.85x105/3600*1000) = 7.08 kW
Required power for water purification with energy recovery (17.65-7.08) = 10.57 kW
33
5.4 CALCULATION OF REQUIRED PUMP CAPACITY
In this study, only the requirement of potable water is considered. The village has a dedicated water canal for agricultural purpose, which is fed by a water tank located nearby. But they are not using this water for drinking purposes. There is a separate well for drinking. As per the above calculation, it was noted that the daily drinking water requirement is 10,500 Liters with the safety factor included.
Total water requirement per day = 10,500 Liters
Water flow rate for the chosen pump = 120 Liters/minute
Operating period of the pump = 87.5 minutes
Operating period of the pump (say) = 1.5 hours
Required water flow rate (Q) (120/(60x103) = 0.002 m3/s
Depth of the Well = 6 m
Inside diameter of the well = 6 m
Depth of the static water level at critical condition = 5.2 m
Length of the pipe (L) = 110 m
Height of the tanks = 7 m
No. of gate valves = 3 Nos.
No. of elbows = 5 Nos.
Q = A.V = 0.002 m3/s
A = 𝜋𝐷2
4
⁄
D D ( Selected pipe diameter) = 50 mm
A = 𝜋. (50𝑥10−3)2
4
⁄ = 0.00196 m2
V = Q/A
V = 1.0204 m/s
From Hazen – William’s modified formula for friction head loss
V = 𝑘. 𝐶. 𝑅0.63. 𝑆0.54 [13] ………. ( 34 )
(Assume Asbestos – cement material used in pipe) 𝐶 = 140
Given that 𝑘 = 0.849 𝑠 = ℎ𝑓 𝐿 = 10.67. 𝑄1.85 1401.85. 𝐷4.87 ………. ( 35 ) 𝑅 = 𝐷 4⁄ ………. ( 36 ) 𝑅 = 0.0125 mm 𝑠 = 10.67. 0.002 1.85 1401.85. 0.054.87 = 0.025
34 V = 𝑘. 𝐶. 𝑅0.63. 𝑆0.54 𝑆 = √(𝑉⁄𝑘. 𝐶. 𝑅0.63 0.54 ) [ From equation() ] 𝑆 √(1.0204 0.849.140. 0.01250.63 ⁄ 0.54 ) = 0.024 𝑆 = ℎ𝑓 𝐿 ℎ𝑓 = 𝑆.𝐿 = 0.024 x 110 ℎ𝑓 = 2.64 m 𝑅𝑒 = 𝜌. 𝑣. 𝐷/𝜇
From the figure (6.1.2) 𝜇 = 0.8x10-3 N.s/m2
𝑅𝑒 = 1000x1.0204x0.05x1000⁄0.8 = 63,775
𝑅𝑒 63,775
𝑅𝑒 >4000 ; Flow is turbulent [14]
Hence the head losses of bends and valves are given by HLcomp
HLcomp = Kv2/2g [15]
But the flow is turbulent. Friction factor is governed by the relative roughness and Reynolds number. Hence, the friction factor can be computed based on the pipes inside roughness and Reynolds number. Generally, relative roughness is expressed as𝐷 𝜀⁄ . The Moody Diagram is used to find the friction factor of the turbulent flow. Table 6.1 shows the typical roughness values for some materials.
Referring to the Figure 6.1.2, the friction factor will be found.
Considering steel material 𝜀 = 4.6 x 10-5 m
D = 0.05 m
𝐷⁄𝜀 = 1086.956
𝑅𝑒 = 63,775
Swamee and Jain converted the Moody diagram in an equation for the turbulent portion [15]
f = 0.25 [log 1 (3.7. (𝐷 𝜀⁄ ))+ 5.74 𝑁𝑅0.9 ] 2 ………..……….. ( 37 ) 0.25 [log 1 (3.7. (1086.956))+ 5.74 637750.9] 2 f = 0.01927
35
From Darcy’s Equation, head loss in pipe is given by
ℎ𝐿 = 𝑓. (𝐿 𝐷⁄ ). 𝑉2
2. 𝑔
⁄ ………..……….. ( 38 )
0.01927x(110 0.05⁄ )x 1.02042⁄2x9.81
ℎ𝐿 = 2.24 m
From Bernoulli’s equations 𝑃𝐴 𝜌. 𝑔 ⁄ +𝑉𝐴2 2. 𝑔 ⁄ + 𝑍𝐴+ 𝑃𝑢𝑚𝑝𝑖𝑛𝑔 𝐻𝑒𝑎𝑑 =𝑃𝐵⁄𝜌. 𝑔+𝑉𝐵 2 2. 𝑔 ⁄ + 𝑍𝐵+ ℎ𝑓+ ℎ𝐿 ( 39 )
As the well Diameter and Height is considerably larger than the pipe diameter 𝑉𝑎 is zero
𝑉𝑎= 0 𝑃𝐴=𝑃𝐵= 𝑃𝑎𝑡𝑚 Hence; H = 𝑃𝑢𝑚𝑝𝑖𝑛𝑔 𝐻𝑒𝑎𝑑 = 𝑉𝐵2 2. 𝑔 ⁄ + 𝑍𝐵+ 𝐻𝑓+ 𝐻𝐿− 𝑍𝐴
𝑍𝐵 = Total head of the tank
= 6+7 𝑍𝐵 = 13 m 𝑍𝐴 = 0 m 𝑉𝐵 = 𝑉 𝐻 = ( 𝑉𝐵2 2. 𝑔 ⁄ ) + 𝑍𝐵+ ℎ𝑓+ ℎ𝐿− 𝑍𝐴 = ( 1.0204 2x9.81⁄ ) + 13 + 2.64 + 2.24 − 0 𝐻 = 17.93 m
Assume the efficiency of the required water pump (𝜂) = 0.3
Power requirement to operate the water pump
P = 𝜌. 𝑄. 𝑔. 𝐻/ 𝜂 = 1000x0.002x9.81x17.93 0.3 P = 1172.662 W P (Say) = 1.2 kW
The calculation was done for 1.5 hours per day. But for safety margin, assume, pump operation for 3 hours per day.
36
Where;
Q : Water flow rate (m3/s)
V : Water velocity through pipe (m/s)
A : Cross sectional area of the pipe (m2) D : Diameter of the pipe (m)
𝑘 : Conversion factor ( k = 0.849)
𝐶 : Roughness coefficient
𝑅 : Hydraulic radius
𝑠 : Head loss per length of pipe
ℎ𝑓 : Head loss in meters
𝐿 : Length of the pipe in meters
𝑑 : Inside pipe diameter
𝜌 : Density of water (1000 Kg/m3)
𝜇 : Dynamic viscosity (N.s/m2 ) ε : Roughness (m)
f : Friction Factor
𝑁𝑅 : Reynolds Number
P : Required pump power
Material Roughness ε (m)
Plastic 3.0 x 10-7
Steel 4.6 x 10-5
Galvanized iron 1.5 x 10-4
Concrete 1.2 x 10-4
37
38
Figure 5.4.1: Dynamic viscosity of water at different temperatures
39
5.5 CALCULATION OF THE AVAILABLE WIND POWER
Daily average wind speed was tabulated for the nearest location available, and the critical wind speed was selected for the calculation. The required data was obtained from the literature survey in chapter 4. The lowest recorded average wind speed is observed in April, namely 3.68 m/s.
Consider the month of April for calculation of wind turbine output:
Power of the air mass
𝑃𝑤 = 1 2. 𝜌. 𝐴. 𝑉 3 ……… (40) 𝑃𝑤 𝐴 ⁄ = 1 2. 𝜌. 𝑉 3
Power in the wind cannot be extracted 100% because of the air mass shall go through turbine blades to rotate the wind mill. Hence, Betz coefficient will be applied in order to obtain the optimum utilization of energy from the wind. This was discovered in 1926 by Betz [18]. It is assumed a constant linear velocity of the wind. The rotational forces such as turbulence, wake rotation will reduce the maximum efficiency [19]
𝑃𝑤 = 1 2. 𝜌. 𝐴. 𝑉 3. 𝐶 𝑝 ……… (41) 𝑃𝑤 𝐴 ⁄ = 1 2. 𝜌. 𝑉 3. 𝐶 𝑝
It was found that the maximum and optimal possible energy extraction 𝐶𝑝 = 59%. In practice, the practical performance of a small wind turbine could be assumed as 𝐶𝑝 = ~30%..
The specific wind turbine power output is proportional to the air density and the rotor intercept area A
40 𝜌(𝑧) = 𝑃0 𝑅𝑇
exp (
−𝑔𝑧 𝑅𝑇)
……… (42) Where; 𝜌 : Air density (Kg/m3) 𝐴 : Interception area 𝑉 : Wind speed (m/s)𝐶𝑝 : Betz coefficient or actual aerodynamic efficiency coefficient
𝑘 : Conversion factor ( k = 0.849)
𝜌(𝑧) : Air density as a function of altitude (Kg/m3 )
𝑃
0 : Standard sea level atmospheric density (1.225 kg*m-3);𝑅
: Specific gas constant for air (287.05 J kg-1K-1);T : Temperature (K)
𝑔
: Gravity constant (9:81ms-2);𝑧
: Altitude above sea level (m)However, in this calculation the air density is assumed constant at;
𝜌 = 1.225 Kg/m3
Hence, the specific average wind power output for April would be;
(𝑃𝑤 𝐴 ⁄ ) 𝑚𝑖𝑛 = 1 2. 𝜌. 𝑉 3. 𝐶 𝑝 = 1 2x 1.225 x 3.68 3 x 0.3 = 9.2 W/m2
For the safety reason let’s confer with the highest specific wind power output by considering the month of June when the highest wind speeds occur;
(𝑃𝑤 𝐴 ⁄ ) 𝑚𝑎𝑥 = 1 2x 1.225 x 7.1 3 x 0.3 = 65.8 W/m2
Therefore, suitable wind turbine to be selected for given range of specific performance per unit of rotor area between 9 W/m2 and 66 W/m2.
As per the wind statistics, the cut in wind speed shall be 3 m/s to generate electricity.
Let us assume that the wind turbine operates for 15 hours per day at the April-average wind speed; Daily electricity need for the village = 100 kWh
Windmill operating time period (Assumed) = 15 Hours/day
The required capacity of the wind turbine (100/15) = 7 kW
To generate the electricity requirement for the village entirely by wind power, a minimum 7 kW rated wind turbine ought to be selected. However, a portion of the requirement will be satisfied by the integrated PV system. Therefore, the optimum combination of wind turbines and PV panels should be decided [20].
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5.6 CALCULATION OF THE AVAILABLE SOLAR POWER FOR THE PV PANELS
In this section, the availability of solar power at the chosen location and the necessary size of the devised PV system will be evaluated.
5.6.1 ASSUMPTIONS
Table 4.4 was considered when performing the calculations
A critical month was selected with the lowest solar energy occurrence within the year and random day was considered within the selected month
As per the Table 5.6.1, noon time selected for solar hour angle. This is the time for maximum solar irradiation happen during the day
It is considered diffused horizontal irradiation instead of diffused irradiation. (in the calculation, this was considered as zero)
The month when the minimum solar irradiation occurs should be taken for the calculation. During December, solar irradiation is measured at 3.99 kWh/m2 average per day. 15th of December 2013 (n = 349) was selected.
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5.6.2 PV CALCULATION
Day considered in the calculation : 15th December 2013
Day number ( n) : 349 City : Anuradhapura Longitude : 80° 28' 0" Latitude (𝜑) : 8° 31' 0" δ = sin−1{0.39795. cos [2. 𝜋.(𝑛−173) 365 ]} [equation ()] sin−1{0.39795. cos [2. 𝜋.(349 − 173) 365 ]} = 23.415 degrees δ = 0.409 rad
As per the table 7.5.2 , in the noon time hour angle 𝜔 is = 0 rad
Latitude (𝜑) = 8° 31' 0" degrees
𝜑 = 0.1396 rad
𝜃𝑧 = cos
−1(cos 𝜑 . cos 𝛿 . cos 𝜔 + sin 𝜑 . sin 𝛿) [equation ()]
cos−1(cos 0.1396 . cos 0.409 . cos 0 + sin 0.1396 . sin 0.409)
𝜃𝑧 = 0.2694 rad 𝛾𝑠 = 𝑠𝑔𝑛(𝜔).
|
cos−1{
𝑐𝑜𝑠 𝜃𝑧.𝑠𝑖𝑛 𝜑−𝑠𝑖𝑛 𝛿 𝑠𝑖𝑛 𝜃𝑧.𝑐𝑜𝑠 𝜑}|
[equation ()] = +.|
cos−1{
𝑐𝑜𝑠 0.2694.𝑠𝑖𝑛 0.1396−𝑠𝑖𝑛 0.409 𝑠𝑖𝑛 0.2694.𝑐𝑜𝑠 0.1394}|
𝛾𝑠 = 3.141 rad 𝛽𝑐 = 0.785 rad 𝛾𝑐 = 0 rad 𝜃 = cos−1(cos 𝛽𝑐 . cos 𝜃𝑧 + sin 𝛽𝑐 . sin 𝜃𝑧 . cos(𝛾𝑠− 𝛾𝑐) [equation ()]
cos−1(cos 0.785. cos 0.2694𝑧 + sin 0.785. sin 0.2694. cos(3.141 − 0)
𝜃 = 1.0544 rad
𝐼𝑡 = 𝐼𝑏. cos 𝜃 + 𝐼𝑑 [From Equation()] (Assumed 𝐼𝑑 = 0)
= 3.99. cos(1.0544)
𝐼𝑡 = 1.97 kWh/m2
Considering 1 hour time, 𝐼𝑡 = 1.97 kWh/m2
Assume 6 hours of effective solar irradiation per day
Hence, approximate solar irradiation (1.97/6) = 0.328 kW/m2
Available solar power to generate electricity = 328 W/m2
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5.7 ENERGY STORAGE BATTERY BANK
Storage of energy is a main necessity for the system, especially considering the remote location of the rural village. If the electricity consumption is only to satisfy the basic needs, during the daytime only the water purification system will be operated. That is the only energy load that will be in operation, moreover exactly when the PV output is certainly available. Additional energy consumption is for lighting during night time. Therefore, the energy storage system shall be evaluated for supporting the night time lighting load.
Normally the capacity of a battery is given by Ah, from which the stored energy can be deducted once knowing the voltage level of the battery bank.
5.7.1 ESTIMATION OF BATTERY CAPACITY
Referring to the considerations exposed above, the necessary battery capacity can be estimated as follows; [26]
Required daily electricity = 100 kWh
Nominal battery unit voltage = 12 V
Nominal capacity of each battery unit = 200 Ah
Energy stored in the each battery unit (12 x 200 / 1000) = 2.4 kWh
Assumed battery cycle efficiency = 0.8
No of batteries needed (100/2.4/0.8) ≅ 52 Nos.
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6 SOLAR + WIND HYBRID WATER PURIFICATION SYSTEM DESIGN AND COST ANALYSIS
Already it is calculated the available energy which could be generated by Solar irradiation and wind power. In this section, it will be discussed the possibility of combination both two energy resources to maximize the utilization of available power and determine the best combination of both sources.
Energy requirement for water purification 35.00 kWh
Energy requirement for water pumping 3.60 kWh
Energy requirement for lighting 49.50 kWh
Total Energy Requirement 88.10 kWh
Total Energy Requirement (Say) 100.00 kWh
Available Wind energy 129.30 W/m2
Available Solar energy 328.00 W/m2
No. of battery needed 21.00
Table 6.0.0: Energy Storage
In the total cost calculation, five options were set up to obtain the optimal and economical combination of the power sources.
In the below table, it can be seen that Option 1 and Option 4 are economical that other combinations. But considering those two options, Option 1 is the most suitable combination because, setting up one 5kW wind plant is economical than setting up five numbers of 1 kW wind plants.
Increasing no. of wind plant and reduce the solar panels will reduce the cost of investment. But when we increasing more wind power plants will increase the energy dependence towards wind power only. So that optimal utilization of both power sources can’t be obtained. Also in case of wind unavailability, the whole system will get down.
In here, setting up a gasification system was not considered. It can be used rice husk to generate electricity by gasification process. But considering this small village, it will be hard to implement a gasification system. A dedicative person shall be there to operate the system and required regular maintenance. It will be hard to put a dedicative person from the village because, they all are struggling to find day-today income. Therefore, setting up a gasification process is not economical in the long run.
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OPTION 1 OPTION 2 OPTION 3 OPTION 4 OPTION 5
Total energy (electricity) requirement 100 kWh 100 kWh 100 kWh 100 kWh 100 kWh
Selected wind turbine rated capacity 5 kW 3 kW 2 kW 1 kW 1 kW
No. of wind turbines 1 nos 1 nos 2 nos 5 nos 3 nos
Total wind power capacity 5 kW 3 kW 4 kW 5 kW 3 kW
Operation time per day per wind turbine 15 hours 15 hours 15 hours 15 hours 15 hours
Generated electricity by wind turbines 75 kWh 45 kWh 60 kWh 75 kWh 45 kWh
Balance electricity requirement 25 kWh 55 kWh 40 kWh 25 kWh 55 kWh
Operation time of solar panels 6 hours 6 hours 6 hours 6 hours 6 hours
Required capacity of the PV 4 kW 9 kW 7 kW 4 kW 9 kW
Cost of wind turbines 10,000 USD 6,000 USD 8,000 USD 10,000 USD 6,000 USD
Cost of solar system 12,000 USD 26,400 USD 19,200 USD 12,000 USD 26,400 USD
Inverter 2,000 USD 4,400 USD 3,200 USD 2,000 USD 4,400 USD
Battery bank (52 units of Lead acid batteries) 4,200 USD 4,200 USD 4,200 USD 4,200 USD 4,200 USD Other electrical control systems (Allow) 1,000 USD 1,000 USD 1,000 USD 1,000 USD 1,000 USD
Water Pump 500 USD 500 USD 500 USD 500 USD 500 USD
Water storage tank (10,000 L, 4 nos.) 3,200 USD 3,200 USD 3,200 USD 3,200 USD 3,200 USD Shed for battery bank storage 2,000 USD 2,000 USD 2,000 USD 2,000 USD 2,000 USD
Reverse Osmosis system 4000 USD 4000 USD 4000 USD 4000 USD 4000 USD
Water Pipes ( assumed) 1,500 USD 1,500 USD 1,500 USD 1,500 USD 1,500 USD
Transport the material to site (Allow) 1,000 USD 1,000 USD 1,000 USD 1,000 USD 1,000 USD
Installation charges 2,000 USD 2,000 USD 2,000 USD 2,000 USD 2,000 USD
Technical consultancy 1,000 USD 1,000 USD 1,000 USD 1,000 USD 1,000 USD
Contingencies (allow 5%) 2,220 USD 2,860 USD 2,540 USD 2,200 USD 2,860 USD
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7 ECONOMIC, ENVIRONMENTAL AND SOCIAL BENEFITS 7.1 ECONOMICAL BENEFITS
As this project is based on enhancing the living condition of a rural village, the payback period shall not be considered. This will be a social service to the country. The fund raising could be done by governmental or non-government organization. It was finally estimated that the total incurred cost on this project is approximately USD 46,000. It’s in Sri Lankan Rupees, 6 million. But when the cost incurred on extend the main grid in to this area, it will be expensive than the setting up standalone system at the village itself.
However, to cover up the maintenance cost and operational cost, the welfare society to be executed and each family shall contribute a monthly fee for the plant. So that the villagers will have a responsibility on properly maintaining the plant. This will be a starting point on implementing self-sustained village concept which will be independent from the external factor.
By considering the social welfare to the society, the investment cost will be more economical in term of opportunity cost to the village.
7.2 ENVIRONMENTAL BENEFITS
Both energy sources are freely available in the area. Also both has zero emission of CO2 at operating
stage. This system is environmental friendly and minimize the pollution occurrences to the environment. As the plant can be located nearby village in an empty land, the environmental issue happen wile construction can be minimized.
However, at the construction stage, noise pollution, air pollution could be happening. But it can be minimized using proper tools and standards. The visual impacts happen due to wind turbines and solar panels. But considering a small village, this effect is negligible and not o major issue.
7.3 SOCIAL BENEFITS
The villagers are indeed of having electricity to their village. So there is positive feedback on implementing standalone energy system to this region. Some issue will happen when maintenance and sudden breakdown. The villagers have no knowledge in electrical system and repairs. So young people in the village shall be educated for repair and maintenance. Spare part storage shall be kept for emergency requirement. The nearest city is Anuradhapura. So dealers who involve with solar, wind energy and water purification shall be updated for immediate access and repairing. Workshop can be conducted to the people for proper energy usage in a home. Educational campaign can be conducted for safe drinking water.
