Energy crisis is an important issue in today’s world. Availability of Power supply is an important factor for a country’s socio-economic development. Bangladesh is a third-world country where only 47 percent of the entire population has access to power supply and the per capita power consumption is only 220 kWh . From Table 1.1, it is seen that compared to per capita electricity consumption of BRICS countries (Brazil, Russia, India, China, and South Africa) and SAARC (South Asian Association for Regional Cooperation countries such as Pakistan, Srilanka) the per capita consumption of Bangladesh is very low.
Table 1.1: Per Capita Electricity Consumption of Bangladesh in 2009 (KWh) 
In Bangladesh most of the power plants run by conventional energy resources like natural gas, coal and other fuels. These Conventional energy resources are not only limited but also the prime cause for environmental pollution. The consumption of fossil fuels has an environmental impact, in particular the release of carbon dioxide (CO2) into the atmosphere. CO2 emissions can be greatly reduced through the use of renewable energy technologies.
Use of Renewable energy gained popularity among the people in Bangladesh from the late 1990s. Solar, Wind, Biomass and Hydro energy are some of the Renewable Energy resources used in the country. Among all these, solar energy is a promising one for Bangladesh due to its location. Bangladesh is situated between 20.30 -26.38 degrees north latitude and 88.04- 92.44 degrees east with abundant solar radiation in a clear day. Solar energy is rapidly gaining the focus as the location of Bangladesh is ideal to harness the Sun’s energy. The daily average solar radiation in Bangladesh is 4 to 6.5KWh/m2 which is better compared to many European nations working on solar energy in a large scale . Solar panel is the basic part of Solar Energy system, which is mainly made from semiconductor materials to generate electricity from the radiation of Sun. The major component of solar panels is Silicon, which has maximum 24.5% efficiency .
Energy, water and agriculture together form a formidable synergy, which when appropriately utilized and managed, can drive a nation way forward. Despite having fertile soil for agriculture, Bangladesh’s food and agricultural production is low due to the gaps between demand and supply of energy. Especially for diesel fuel and electric power, irrigation suffers drastically in the rural areas. Applying solar photovoltaic panels for irrigation can change the energy scenario of the country. Integration with the conventional electric pumps can be made to convert those pumps into solar water pumps.
In this thesis, a simple but efficient photovoltaic water pumping system is presented. It provides the operation of a DC solar water pump in direct-coupled method and pump-controller connected method. The solar water pumping system is built in the Laboratory of Bangladesh University of Engineering and Technology (BUET), Dhaka, Bangladesh. A pump-controller in Buck topology is designed and implemented to increase the overall efficiency of pumping system.
Agricultural productivity holds the key to any country’s overall economic growth. Bangladesh has fertile agricultural land, abundant water in wet season but limited water in dry season (January to May). Due to limitation of water in dry season, irrigation plays the vital role to expand cultivable area and improve agricultural production in Bangladesh. Water is pumped from ground and surface water level for irrigation in Bangladesh. LLPs (Low Lift Pumps) are used to lift water from surface water level and STWs (Shallow Tube-wells), DTWs (Deep Tube-wells), HTWs (Hand Tube-wells) are used to lift water from ground water level. LLP, STW and DTW are operated by electrical or mechanical power. Electricity and diesel are the sources of electrical and mechanical power respectively .
Approximately 0.15 million LLPs were in operation in the year 2008-09 Boro season to irrigate 1 million hectare of land in Bangladesh. 7% of the LLPs were electric and remaining 93% were diesel pumps. Fig 1.1 shows the distribution of power source uses for LLPs in 2008-09 Boro seasons .
Figure1.1: Power source wise LLPs used in Bangladesh in 2008-09
Approximately 1.4 million STWs were in operation in the year 2008-09 in the Boro season to irrigate 3.5 million hectare of lands in Bangladesh. 15% of the STWs were run by electricity and remaining 85% were run by diesel. Fig 1.2 shows the distribution of STW power sources in 2008-09 in the Boro season .
Approximately 32000 DTWs were in operation in the year 2008-09 in the Boro season to irrigate 0.8 million hectare of lands in Bangladesh in which ~10% of the DTWs were run by diesel and remaining 90% were run by electric supply. Fig 1.3 shows DTW distribution of power source in 2008-09 Boro seasons .
Figure1.3: Power source wise DTWs used in Bangladesh in 2008-09
The use of renewable energy has risen considerably in the recent times in developed and developing countries. In Asia, India and China have achieved considerable success in innovating and using the technology of renewable energy. Although the initial installation cost of renewable energy is higher now, in near future it will gradually decline and will come down within the purchasing capacity of the people. The long-term economics will make PV pumps suitable over other watering options, except where gravity feed is available. One study completed by the Bureau of Land Management (USA) compared solar water pumping systems to generator systems. For one 3.8 gpm system with a 275 foot design head, the PV system cost only 64% as much over 20 years as the generator system did over only 10 years. This remote solar site also used only 14% as many labor hours. Inexpensive diesel or gas generators have low initial costs but require consistent maintenance and have a design life of approximately 1500 hours. Small to medium sized solar pumping systems often cost less initially than a durable slow speed engine driven generator.
As in other Renewable Energy systems, initial installation cost is the main disadvantage of Solar Water Pumping system. History of solar water pumping technology dates back to four hundred years (when Solomon de Caux of France raised water from a mountain by the expansion of solar-heated air). Presently, approximately 50,000 solar pumps are in operation worldwide .
Bangladesh already achieved limited success to harness solar energy to provide electricity especially to remote area people in rural areas. Now it is time to introduce solar energy into irrigation system which demands major electricity supply during the BORO season. Bangladesh has 1.55 millions units of mechanized (diesel and electric) irrigation pumps . Among these pumps, 16.30% of pumps are electric and 83.70% of pumps are diesel pump .
1.3 million Diesel pumps consume 10 billion litres of high speed diesel fuel annually. Government has to give subsidy on diesel price every year, which is around BDT 55 billion yearly . Diesel has to be imported from that makes the diesel price and its availability highly vulnerable. 0.25 Million electric pumps require 1100 megawatts of electric supply daily during the irrigation season. Power companies have to load-shed in a large scale during irrigation season to provide continuous electricity to the farmers. Natural gas reserve of our country is decreasing every year and it hinders the electricity generation.
This thesis presents a means to mitigate energy crisis through solar water pumping system. A solar water pumping system has been designed and built to comprehend the irrigation with solar photovoltaic panels and locally available electric pumps. All components in the system design have been procured locally except solar panels. A DC-DC Buck converter is built to integrate with the solar water pumping system to operate it efficiently. Automatic solar tracking system has also been designed and constructed to apply in the water pumping system in future.
The history of PV dates back to 1839 when a French physicist, Edmund Becquerel, discovered the first photovoltaic effect when he illuminated a metal electrode in an electrolytic solution. Thirty-seven years later British physicist, William Adams, with his student, Richard Day, discovered a photovoltaic material, selenium, and made solid cells with 1~2% efficiency . In 1954 the first generation of semiconductor silicon-based PV cells was fabricated with efficiency of 6%. Then these were used in space applications. Presently the production of PV cells is following an exponential growth curve since technological advancement of late ‘80s. The development has started improvement of efficiency and reduces cost. Today’s PV cells convert only about 10 to 20 percent of the radiant energy into electrical energy. Fossil fuel plants, on the other hand, convert 30 to 40 percent of their fuel’s chemical energy into electrical energy. Research to increase the efficiency will continue to achieve a good conversion rate compared with the conventional energy resources.
The most abundant and convenient source of renewable energy is solar energy, which can be harnessed by photovoltaic cells. Photovoltaic cells are the basis of a solar system. The word photovoltaic comes from “photo” means light and “voltaic” means producing electricity. Therefore, the photovoltaic process is “producing electricity directly from sunlight”. The output power of a photovoltaic cell depends on the amount of light projected on the cell. Time of the day, season, panel position and orientation are the factors behind the output power. Photovoltaic cells are also called PV cells or solar cells. Solar-powered calculators, toys, and telephone call boxes use solar cells to convert light into electricity.
Photons of light with energy higher than the band-gap energy of PV material can make electrons in the material break free from atoms that hold them and create hole-electron pairs, as shown in Figure 2.1 . These electrons fall back into holes causing charge carriers to disappear. If a nearby electric field is provided, those in the conduction band can be continuously swept away from holes toward a metallic contact where they emerge as electric current. The electric field within the semiconductor itself at the junction between two regions of crystals of different type, called a p-n junction.
The PV cell has electrical contacts on its top and bottom to capture the electrons, as shown in Figure 2.2 . When the PV cell delivers power to the load, the electrons flow out of the n-side into the connecting wire, through the load, and back to the p-side where they recombine with holes. Conventional current flows are in the opposite direction from electrons.
The electrical equivalent circuit of a solar cell is shown in Fig. 2.3 . It has a current source Iph, a diode and two resistors (Rs and Rsh). Upon incidence of light on the solar cell, current Iph is generated and part of the current can be delivered to load.
The Current of the solar cell is given by the following equation:
I = output current (amperes)
Iph = photo-generated current (amperes)
Id = diode current (amperes)
V = voltage across the output terminals (volts)
RS = series resistance (?)
I0 = reverse saturation current of diode (amperes)
n = diode ideality factor (1 for ideal diode)
q = elementary charge
k = Boltzmann’s constant
T = absolute temperature
Rsh= shunt resistance (?)
The current-voltage and power-voltage characteristics of a photovoltaic cell are shown in Fig. 2.4 .
2.3 Present Applications of Solar Energy in Bangladesh
In the last decade, solar PV as an alternative source of energy has gained popularity and has been used to generate energy in different forms. Grid connected solar PV and Solar Home System (SHS) are the two most popular models used throughout the world. In remote areas of the developing world, SHS has become very popular as the over all system is relatively simple, easy to handle and reliable. During the last 5 years, Bangladesh has seen a significant growth in SHS. Bangladesh Infrastructure Development Company Limited (IDCOL) has established 454,000 SHS installation up to January 2010 . IDCOL has a revised target of 1million SHS within the year 2012. IDCOL has also financed other solar programs in Bangladesh .
2.4 Future Applications
Solar Power Station is mini power station with solar power, battery backup, diesel or natural gas generator as a secondary power generation source. The system consists of high quality photovoltaic (PV) modules, mounting structures to secure modules on the roof, warranties and instructions. These systems are suitable for schools, government offices, hospitals, military check post points and other important installations where the electrical load is light. This type of system can mitigate energy crisis of Bangladesh by making smaller load systems capable to maintain their own power supply.
2.4.2 Grid Tied Solar System
Most commonly used systems in the industrialized world are grid tied solar systems. These systems produce electricity and sell it to the grid when there is excess electricity. Battery is not required for this system and hence the overall system cost reduces. This system will only operate when the sun light is available. Daytime electricity usage from the grid can be reduced dependency on conventional generators by this system. In Bangladesh this type of system can be integrated in the industrial area where heavy electrical loads are operated during the peak day hour.
Grid-tie with battery backup system is the costliest system among the various types of solar power systems. Specialized grid interactive inverters and other system components are required to be imported for these kinds of system. Integration of net metering with this system can sell excess energy to the Grid.
2.4.3 DC Solar irrigation Pump
Given the energy crisis and rising price of petroleum products, it is important to explore alternative energy sources for irrigation to ensure both food and energy security. It is appropriate time that Bangladesh should concentrate to diversify the applications of solar energy to areas of agriculture. One of the choices is to introduce solar photovoltaic pumping for irrigation. Solar photovoltaic pumping can be introduced in Bangladesh in two ways. Existing pumps can be retrofitted or replaced by solar pumps directly. STW diesel pumps should be replaced by DC solar pumps. The DTW electric pumps should be retrofitted into AC solar pumps at initial stage.
Solar cells internal characteristics along with P-V and I-V curves are described in this chapter. Then the prospects of solar energy in Bangladesh have been discussed. Also various types of Solar PV based application are briefed in this chapter.
SOLAR WATER PUMP
Water pumping is one of the attractive and appropriate usages of solar energy. From crop irrigation to stock watering to domestic uses, water pumps are used extensively throughout the world. Operation of water pumps requires electricity supply or diesel. Solar energy can mitigate electricity demand or diesel requirement to run water pumps by using Solar Water Pumping System.
Solar-powered pumping systems meet a broad range of water needs. In principle they may be used virtually anywhere, but the most compelling needs and opportunities are found in the fuel-poor but sun-rich rural areas of the third world country like Bangladesh. Solar pumps may be of any size. Small farms, villages, and animal herds in developing countries require hydraulic output power of less than a kilowatt. Many of these potential users are too far from an electrical grid to economically tap that source of power, and engine-driven pumping tends to be prohibitively expensive as well as unreliable due to the high cost of purchased fuel and insufficient maintenance and repair capabilities. Usually electric water pumps that are plugged into an outlet using alternating current (AC) are generally not built to operate very efficiently because there is no limitation to the amount of power available. A solar-powered pumping system generally costs more initially than a gas, diesel, or propane-powered generator but requires far less maintenance and labor. Comparing installation costs (including labor), fuel costs and maintenance costs over 10 years, it is observed that solar is an alternate choice. These systems have the added advantage of storing water for use when the sun is not shining, eliminating the need for batteries, enhancing simplicity and reducing overall system costs. Solar water pumps are designed to use the direct current (DC) provided by a PV array, although some newer versions use a variable frequency AC motor and a three-phase AC pump controller that enables them to be powered directly by the solar modules. Because PV is expensive and its power production can be variable, solar pumps need to be as efficient as possible i.e. they need to maximize the gallons of water pumped per watt of electricity used.
The key to PV’s choice is the low labor and maintenance costs relative to the other options. The long-term economics make PV pumps comparable to most other remote watering options in the rural areas. The lifetime of solar water pump is usually 20 years, which ultimately is lower than the life span period cost compared to the conventional pumps. Bangladesh is a potential place for implementing solar water pumping due to lack of electricity supply in the rural areas needing irrigation. By using photovoltaic pumps, load on the grid system can be reduced and the subsidy on the diesel can be lowered .The advantages of solar water pumping system over the conventional pumping are tabulated in the Table 3.1.
Table 3.1: Comparison between Solar water pump and Conventional Water Pump
|Attributes||Solar Water Pump||Conventional water Pump|
|Grid Electricity Needed?||No||Yes|
|Maintenance||Low Maintenance and unattended operation.
Simple and reliable
|Need maintenance and replacement|
|Fuel||No fuel cost or Spill||Fuel often expensive and supply intermittent|
|Upfront Cost||Upfront cost higher but last longer||Moderate capital cost|
|20 years total cost||Lower||Higher|
3.3 Types of Solar Water Pumps
Solar Water pumping System can be divided into two basic types.
1. According to the storage system.
2. According to the types of the motor used.
Again, there are two types of solar-powered water pumping systems according to the storage system.
3.3.1 Battery- coupled Solar Water Pump
Battery-coupled water pumping systems consist of photovoltaic (PV) panels, charge control regulator, batteries, pump controller, pressure switch and tank and DC water pump (Figure 3.1 ). The electric current produced by PV panels during daylight hours charges the batteries, and the batteries in turn supply power to the pump anytime water is needed. The use of batteries spreads the pumping over a longer period of time by providing a steady operating voltage to the DC motor of the pump .
In direct-coupled pumping systems, electricity from the PV modules is sent directly to the pump, which in turn pumps water through a pipe to where it is needed (Figure 3.2 ). This system is designed to pump water only during the day time. The amount of water pumped is totally dependent on the amount of sunlight hitting the PV panels and the type of pump. Because the intensity of the sun and the angle at which it strikes the PV panel changes throughout the day, the amount of water pumped by this system also changes throughout the day. Direct-coupled pumping systems are sized to store extra water on sunny days so it is available on cloudy days and for the night. Water can be stored in a larger-than-needed watering tank or in a separate storage tank and then gravity-fed to smaller watering tanks .
Figure 3.2: Direct coupled solar water pumping system 
Solar water pumps can be segmented into two categories according to the motor used.
1. AC Solar Pump
2. DC Solar Pump
AC solar pump is the modification of existing electric pumps by retrofitting some components. Usually, the electric pumps are driven by AC supply but the power output from the solar panel is DC. To use the DC power to run the AC system, an inverter is required additionally. Figure3.3  represents the basic diagram of AC solar pump (ACSP).
|Power Conditioning Unit|
DC solar pump is widely used throughout the world today. DCSP operates in a very simple mechanism. Figure3.4  shows the basic connection diagram of a DCSP.
|Power Conditioning Unit|
Figure3.4: DC solar water pump 
Solar photovoltaic pumping can be introduced in Bangladesh in two ways. Existing pumps can be retrofitted or replaced by solar pumps directly. STW diesel pumps should be replaced by DC solar pump where as the DTW electric pumps should be retrofitted into AC solar pumps at initial stage. AC solar pumps require sine wave inverter to convert solar panel’s DC supply to AC supply. On the other hand, DC solar pump operates in very simple mechanism. A DC pump is easy to be maintained and operated by non-technical people of the rural areas. Considering the aspects of Bangladesh, a DC direct-coupled solar water pump is designed and then the performance of the designed system is studied to complete the thesis.
DESIGN AND CONSTRUCTION OF DC SOLAR WATER PUMP SYSTEM
Designing of a photovoltaic water pumping system has two important aspects:
1. Selection of the suitable system components requiring low maintenance, long life system and reliability of operation.
2. Matching of system components responsible for efficient operation of the system .
4.2 Construction of a DC solar Pump system
In the proposed photovoltaic water pumping system, the solar panels are directly connected to a DC motor that drives the water pump. For such simplified systems, DC motors and centrifugal pumps are required, because of their ability to be matched to the output of the solar panels. Volumetricpumps, often referred to as (positive) displacement pumps, have completely different torque-speed characteristics and are not well suited to being directly coupled to solar panels.
Similarly, a range of motor types is used for water pumping systems, including DC series motors, DC permanent magnet motors, DC permanent magnet brushless motors, AC asynchronous induction motors and AC synchronous motors. For AC motors, an inverter is to be included between the solar panels and the motor.
A DC motor and a centrifugal pump is used in developing this system. Initially this system is implemented without Power Conditioning Unit (PCU) to observe the performance of the pumping system. Later a Buck converter is designed to supply initial high current to the motor for starting. Components are sized accordingly and then connected directly with the panels to examine the converter design.
4.3 Solar panel
There are different sizes of PV modules commercially available (Appendix A); SIEMENS SP-75WP Solar panels are used in the proposed system . The specifications of the solar panels are provided below:
Rated Current : 4.4 A.
Rated Voltage : 17 V
Short Circuit (SC) Current : 4.8 A
Open Circuit (OC) Voltage : 21.7 V
Temperature Co-efficient (SC) : 2.06mA / ºC
Temperature Co-efficient (OC) : .0777V / ºC
Twelve (12) 75wp solar panels have been used to provide DC power supply for the water pumping system. The ambient condition to have the highest output power from this type of solar panel is 25?C and 1000watt/m2. Such 12 solar panels supply 900Wp power during the ambient condition. Unfortunately the ambient condition is not always found in the environment. The highest irradiance level was found 400watt/m2 during a typical winter day when the test results were taken. It was found that average 400 to 450 watts of power from these 12 solar panels at an irradiance level of 400 watt/m2.
Available solar panels have been connected in three arrays. The first and second array, 5 panels are put together and at the top array other 2 panels are kept. All twelve panels are connected in parallel to provide power supply to the pumping system.
4.3.2 Solar Panel Sizing and Wiring
Parallel connections from all the panels are brought to a combiner point, named as combiner box. Combiner box is designed with a simple terminology. Two bus bar conductors of current carrying capacity of 100amps are used to construct the combiner box’s main frame. Each bus bar has 13 holes to screw 12 input strings from solar panel and 1 output string to provide power at the circuit breaker. The combiner box is attached with the pillar at the roof with the help of ceramic bars. Single string of a solar panel meets at the combiner box with the string of the other panels. Each positive string of the panel enters at the combiner box through a power diode. The forward bias voltage drop of the power diode is 0.6 volt. All the strings are bolted with screw at the combiner box’s hole. Total short circuit current that gathers at the bus bars is 57.6 amps and open circuit voltage is 21 volts.
An output string is drawn from the bus bars to the circuit breaker to provide the power supply. The circuit breaker is a single phase breaker where a auto cutoff switch is provided. Turning on the breaker ON, supply solar panel’s power into the input of the motor-pump set.
Figure 4.2: Combiner Box connection from Solar Array
A centrifugal AC pump is selected to be used in the water pumping system. The configuration of the pump is:
Shallow tube well pump, TOYO; Model: TJ-10M;
Power: 0.50 hp; Voltage: 220V; Frequency: 50 Hz;
Suction lift: 5 m; Maxm head: 7 m; Single impeller; Made in China.
The centrifugal pump has an AC induction motor connected with the pump. To construct a DC pump set from the AC pump, the AC motor is detached from the pump. Then a Permanent Magnet DC motor (PMDC) is coupled with the pump to make a DC pump set from the conventional AC pump. The specification of the DC motor is:
Power: 0.9 hp; Type: Permanent Magnet;
Operating Voltage : 12 volts; SAWAFUJI
Made in Japan
The features of the constructed DC pumps are:
1. Direct DC power supply from solar panel runs the system.
2. No inverter is required to convert solar panel’s DC supply into AC supply.
3. The coupling of the DC motor with the pump is done with an iron ring.
4. The alignment of the system is not perfect and there exists considerable friction losses.
5. The characteristics of the constructed DC pump set do not match perfectly with the given data of the AC pump’s specifications.
6. The pumping system can be operated without any operator.
7. There is no maintenance or dependence on Grid electricity for the system.
8. It is useful to operate in the household water supply.
9. Small Scale irrigation can be done throughout the day time when the sun light available.
10. No storage material (e.g. Battery) is required.
Power supply from the combiner box passes to the DC pump set through a circuit breaker. At the beginning, this simple mechanism is connected to observe the performance of the system. After observing the performance of the system, power electronics device is integrated into the system to increase the overall efficiency of the system. The block diagram of the direct system is given in the Figure 4.4.
Figure 4.4: Direct Coupled Solar Water Pump
The observed performance with the direct coupled system has been analyzed and the
ways of improving the overall system performance are tabulated in the Table 4.1.
|Attributes||Directly Connected Solar Water Pump||Ways of Improvement|
|System Voltage||4 to 6 volts||Increasing the supply current will build up the system operating voltage|
|RPM||900-1100 RPM||Increasing armature current will raise the speed of the DC pump system gradually.|
|Discharge Capacity||35-45 Lit/min||Depends on the RPM of the system.|
|Armature Current||20-28 amps.||Conversion of input voltage to increase current.|
The efficiency of the direct coupled solar pump can be increased in various ways. Some of those ways are described briefly in the following section.
MPPT technology deals with the operating curve of the solar system. Maximum power point tracking (MPPT) is the process to maximize the output power from solar panel by keeping the solar panel’s operation on the knee point of P-V characteristics (Fig. 4.5 ). A number of MPPT algorithms have been developed and employed around the world. MPPT technology only offers the maximum power that can be received from a stationary array of solar panels at a particular time; it cannot, however, increase the power generation when the sun is not aligned with the system .
Maximum Power Point tracking technology can improve the overall efficiency of solar water pumping system, by matching the load line of the pump with the characteristic curve at different irradiance level. MPPT technology has not been tried in the proposed system to increase the efficiency.
Battery coupled system can be integrated with water pumping to stabilize the power supply to DC motor. Battery provides constant voltage supply to the load until the deep-discharging point. The system operates at the highest efficiency in the battery coupled system sacrificing some other obstacles. The main disadvantage of a battery coupled system will be the additional cost and the maintenance of battery. The system will be costly as well as the battery needs to be replaced after every 3 to 5 years. Integration of battery in the system will also require some other power electronics equipment to be introduced. Charge controller will be required to protect the battery from over charging and deep discharging. The voltage output from the solar panel also varies with the temperature and to stabilize the voltage charge controller is required too. A typical battery coupled system’s configuration is given below.
Figure4.6: Battery Coupled System 
4.6.3 Thin Film Solar Panel
Thin film amorphous solar panels gained popularity for solar water pumping system recently. Thin film solar panel is effective when low sun hour and variation of sun energy is inevitable. This type of solar panel can generate power from the panel even in the dark light condition that assures to run the pump in bad light too. By increasing the effective operating time of solar panel, the power supply to the motor increases and the overall efficiency improves. The specification of a 50Wp thin film solar panel is given below:-
· Open circuit voltage (Voc) =78.5 volts
· Short circuit current (I sc) =1.16 amp
· Power output from a single panel = 50 watts
· Rated voltage = 60.2 volts
· Rated current = .83 amp
It is observed clearly that the rated current of the thin film solar panel is lower than the mono-crystalline panel that have been used in the proposed system. So when the irradiance level of sunlight decreases, it has less impact on the power generation of thin film solar panel than the crystalline panels. The current of a solar panel solely depends on the irradiance level and voltage level depends on the temperature of the atmosphere. Two 50Wp thin film solar panels’ picture is given in the Figure 4.7 .
Figure 4.7: Two 50Wp thin film Solar panel 
Automatic solar tracker increases the efficiency of the solar panel by keeping the solar panel aligned with the suns position change. Solar tracking is a mechanized system to track the sun’s position that increases power output of solar panel by 30% to 60% than the stationary system . Many methodology of solar tracking system have been proposed in recent days. From the literatures it is evident that sensing of sun light, providing initial position of the solar panel and power consumption of the motor for the tracker are the major challenges of the solar tracking system . Solar tracking system can be used in two ways, Dual-axis tracking and Single-Axis Tracking. A small scale solar tracker has been designed and constructed to find out the feasibility of the designing process of the solar tracker . To integrate solar tracking system with the existing fixed mounted solar panels could not be done, but a small scale solar tracker has been built as a part of the thesis.
A DC-to-DC converter is a device that accepts a DC input voltage and produces a DC output voltage. Typically the output produced is at a different voltage level than the input. In addition, DC-to-DC converters are used to provide noise isolation, power bus regulation, etc. Switching DC-DC power supplies are compact, lightweight and more efficient than ordinary linear regulated power supplies. Besides there are SMPS configurations which can step up, step down voltages with precise voltage regulation. DC-DC converters those are operated under high frequency can be classified into four categories .
i. Buck Converter
ii. Boost Converter
iii. Buck-Boost Converter
iv. ?uk Converter
In this thesis the Buck topology is adopted for current boost (by voltage step down) required for the DC motor. Hence a simplistic analysis of the Buck converter is provided only with next subsection.
In this circuit the transistor turning ON will put voltage Vin on one end of the inductor. This voltage will tend to cause the inductor current to rise. When the transistor is OFF, the current will continue flowing through the inductor but now through the diode. We initially assume that the current through the inductor does not reach zero, thus the voltage at Vx will now be only the voltage across the conducting diode during the full OFF time. The average voltage at Vx will depend on the average ON time of the transistor provided the inductor current is continuous.
To analyze the voltages of this circuit let us consider the changes in the inductor current over one cycle. From the relation
The change of current satisfies
For steady state operation the current at the start and end of a period T will not change. To get a simple relation between voltages we assume no voltage drop across transistor or diode while ON and a perfect switch change. Thus during the ON time Vx=Vin and in the OFF Vx=0. Thus
This simplifies to,
Defining “duty ratio” as-
The voltage relationship becomes Vo =D*Vin Since the circuit is assumed lossless and the input and output powers must match on the average Vo* Io = Vin* Iin. Thus the average input and output current must satisfy Iin =D*Io. These relations are based on the assumption that the inductor current does not reach zero.
Development of solar panel tracking system has been ongoing for many years. As the sun’s position changes across the sky during the day, it is advantageous to have the solar panels track the location of the sun, such that the panels are always perpendicular with the position of the sun. Available solar trackers in the market are costly to integrate with solar panel system . In the developing countries where cost is one of the major issues to integrate technologies and solar tracking prototype presented at this section can provide a solution. The major components are used in the prototype are given below:-
· Photo resistor
· Stepper motor
Cadmium sulphide (CdS) photo resistor is used in the designed prototype. The CdS photo resistor is a passive element that has a resistance inversely proportional to the amount of light incident on it. To utilize the photo resistor, it is placed in series with another resistor. A voltage divider is thus formed at the junction between photo resistor and another resistor; the output is taken at the junction point to pass the measured voltage as input to microcontroller. In the solar tracker prototype, it is desired that output voltage at junction point will increase as the light intensity increases and so the photo resistor is placed at the top position in series connection with resistor.
The ATMEGA32 microcontroller has been used in the prototype . Microcontroller is the heart of overall system. ATMEGA32 microcontroller requires a 5 volt regulated voltage supply. ‘7805’ voltage regulator IC is used to provide fixed 5 volts supply to the microcontroller . ATMEGA32 has features such as analog comparator (AC), analog to digital converter (ADC), universal synchronous asynchronous receiver transmitter (USART), times etc (Appendix B). Utilization procedure of these features is given below in the following section.
4.7.2 Analog comparator
There are two pins which are known as analog input 0 (AIN0) and analog input 1 (AIN1). Two analog voltage signals coming from two junctions of photo resistor circuit are fed to these pins. There is a bit called analog comparator output (ACO) which is set to either ‘1’ or ‘0’ and can be defined as:-
4.7.3 Analog to digital converter
Among 8 analog to digital converter input pins ADC0 and ADC1 have been used; where is expected. Differential input is converted into digital value and the most 8 significant bits are defined as ADC_result to compare with threshold.
ADC_result = [VADC0 – VADC1] digital (4.17)
This threshold value, set according to the photo resistor response against the solar radiation intensity, is provided, since ADC_result alone might be insufficient for rotation of motor.
And if ADC_result > Threshold; motor rotates one step.
The built-in timer of ATMEGA32 is utilized to create delay. The Earth rotates on its own axis, with respect to the Sun 360? in a day and so it rotates, (360?/24=) 15? an hour or 3.75? in 15 minutes. Delay for 1.5 minutes and 15 minutes are required. These delays are mentioned as short delay and moderate delay respectively.
In the proposed algorithm two variables I and Count have been used. I represent total number of rotation the motor must make to track the sun from dawn to dusk. First hour after the sunrise and last hour before the sunset is not considered for the tracking, as in the first hour after sunrise the west sensor does not have sufficient light than the east one; the tracker remains off. The last hour before sunset will provide additional energy to rotate the panel in the initial position and so the tracker no more rotates to the west rather it will rotate reversely. As 2 hours in day time are not considered for tracking, (2?15?=) 30? of rotation is not required to be done by the solar tracker. Half stepping of stepper motor is considered which gives 3.75? rotation in each stepping; approximately ((180?-30?)/3.75?=) 40 rotations are required in each day to track the Sun at daylight. Count is used for counting the number of ‘wait’ states when weather is cloudy and ADC does not permit to rotate the motor.
A small scale prototype of the solar tracker has been made to check feasibility of the design methodology. At initial stage a small plastic board, considered as the solar panel, is mounted on an aluminium shaft. Figure 4.10  illustrates the dummy panel along with other circuitry of the prototype.
Figure 4.10: Prototype of Solar tracker 
Solar tracker provides three ways of operation and control mechanism through the programme written in microcontroller (Appendix D).
Two photo resistors are used in the solar tracker to compare the output voltages from two junctions. As the sun’s position changes from east to west in the day time, AIN0 needs to provide higher voltage than AIN1 to sense the rotation of the sun. This condition is considered as normal day light condition and tracker rotates the panel 3.75? after every 15 minutes.
188.8.131.52 Bad weather condition
When the sky gets cloudy, there will be less striking of light on both the photo resistors and so sufficient voltages might not be available at junction point. The difference of voltage at junction point will not be greater than the threshold value to rotate the tracker. At the mean time, sun continues change position in the western direction. To solve this problem, a short delay is provided which will check for voltage input from junction point in every 1.5 minutes. Microcontroller will use the variable Count to check for consecutively 10 times to make the ‘wait’ state equal to 15 minutes (moderate delay) to rotate the stepper motor one step.
184.108.40.206 Bidirectional rotation
At day time, the solar tracker will rotate in only one direction from east to west. Variable I will count the total rotation in day time and that is approximately calculated as 40 rotations considering 150? rotation in a single day. When the sun sets, no more rotation is needed in western direction. For the next day, the solar panel needs to go to the initial position in the morning to track the sun’s position again. To do so, the variable I that counts the number of rotation in the day time will work out.
When the variable (I) shows value greater than 40, the tracker stops rotating in the western direction and rotates reversely in the eastern direction to set the tracker to the initial position for the next day. When it goes to initial position, power supply to the tracker will be turned off and the tracker will be in stand by till sunlight in the next morning.
The most challenging and difficult part of the system are to design & construct the DC-DC Buck converter. Designing process of the converter requires extensive knowledge on Power Electronics. The following steps have been followed to construct the Buck converter.
1. Calculation of the required inductor
2. Calculation of the capacitor
3. Selection of the diode
4. Selection of the MOSFET
Input and output voltage values as well as the switching frequency needs to be fixed at the very first of the designing process. Assumptions are:
VIn = 17 volts
VOut = 12 volts
Fswitching = 30 KHz
Duty Cycle, D= 12/17= 0.705
4.8.1 Calculation of the required inductor
Starting with the basic equation for current flow through an inductor:
V = L di/dt (4.18)
Rearranging the terms to calculate “L” and the equation changes to:
L = V dt/di (4.19)
Rearrange and substitute:
L = (Vin – Vout) · (D / Fsw ) / Iripple (4.20)
L = 5 V · (0.705 / 30 KHz) / 0.117A
L = 1.004 mh.
4.8.2 Calculation of the capacitor
The peak-to-peak ripple voltage of the capacitor is defined as:
dVc= di/ (8* Fsw * Cout) (4.21)
Rearranging the terms to calculate “Cout” and the equation changes to:
Cout= di/ (8* Fsw *dVc ) (4.22)
Assuming dVc = 2.3 mV, the value of Cout is obtained as:
Cout= .117 / (8* 30 KHz * 2.3 mV)
Cout= 211 µF
Figure 4.13: One of the Capacitor Banks
Maximum Diode Current needs to be analyzed first:
Id = (1-D) · ILOAD
Id = (1.0- 0.705) · 51.42 = 15.1689 A
Five (5) amps, 12 volts ten (10) diodes are connected in parallel to provide the required Id for the designed DC-DC converter.
Figure 4.14: Diode Paralleled Bus bars
Traditional Power MOSFETs are chosen to provide the Gate pulse from SMPS circuit. 6 power MOSFETs are connected in Parallel to operate under a high current. The MOSFETs are switched synchronously from the pulse of SMPS.
Figure 4.15: MOSFET gate
4.8.5 SMPS circuit
In a Switch Mode Power Supply (SMPS), pulse is provided at the MOSFET gate to turn on/off to control voltage regulation of the DC-DC converter. SG3524 IC is used as to make SMPS. This IC can be used for switching regulators of polarity, transformer-coupled DC-to-DC converters, transformer less voltage doublers and polarity converters, as well as for other power control applications. The system frequency of the SMPS is kept at 30 KHz. High frequency switching is expected in the converter design to make the system audible noise free as well as to provide better sensitivity to the system. The SG3524 is designed for commercial applications of 0°C to +70°C (Appendix C). The test circuit diagram of the SMPS IC is given in the Figure 4.21.
4.9 Solar water PUMP with DC-DC buck converter
Following assessments were made on the Direct coupled Solar water pump before
connecting the DC-DC buck converter:
1. The system works well and can lift water from a tank of 10 to 50 feet height when the sun light is sufficient for the system.
2. The DC motor operating voltage is 12 volts but it requires a high current of 40 t