CHAPTER -2
ARCHITECTURE OF PROPOSED SYSTEM, INTRODUCTION OF SOLAR POWER SYSTEM & SOLAR POWERED PUMPS
This chapter deals with the architecture of the proposed system, photovoltaic power generation and the pumps used for water flow. Architecture is the process of planning, designing of the system to understand how components fit into a system.
lefttopFIG. 2.1: Block diagram of proposed system
Let us know the following key terms in the architecture of the system:
1. Photo voltaic power generation.
Best services for writing your paper according to Trustpilot
2. DC-DC Converter.
3. Three phase inverter.
4. Three phase induction motor.
5. Centrifugal pumps.
2.1 SOLAR POWER GENERATION
Solar power is the conversion of energy from sunlight into electricity, either directly using photovoltaic (PV), indirectly using concentrated solar power or a combination. Concentrated solar power systems use lenses or mirrors and tracking systems to focus a large area of sunlight into a small beam. Photovoltaic cells convert light into an electric current using the photovoltaic effect.
Photovoltaic were initially solely used as a source of electricity for small and medium-sized applications, from the calculator powered by a single solar cell to remote homes powered by an off-grid rooftop PV system. Commercial concentrated solar power plants were first developed in the 1980s. The 392 MW HYPERLINK “https://en.wikipedia.org/wiki/Ivanpah_Solar_Power_Facility” o “Ivanpah Solar Power Facility” Ivanpah installation is the largest concentrating solar power plant in the world, located in the Mojave Desert of California.
As the cost of solar electricity has fallen, the number of grid-connected solar PV systems has grown into the millions and utility-scale solar power stations with hundreds of megawatts are being built. Solar PV is rapidly becoming an inexpensive, low-carbon technology to harness renewable energy from the Sun. The current largest photovoltaic power station in the world is the 850 MW HYPERLINK “https://en.wikipedia.org/wiki/Longyangxia_Dam” o “Longyangxia Dam” Longyangxia Dam Solar Park, in Qinghai, China.
The International Energy Agency projected in 2014 that under its “high renewables” scenario, by 2050, solar photovoltaic and concentrated solar power would contribute about 16 and 11 per cent, respectively, of the worldwide electricity consumption, and solar would be the world’s largest source of electricity. Most solar installations would be in China and India. As of 2016, solar power provided just 1% of total worldwide electricity production but was growing at 33% per annum.
FIG 2.2: A solar photovoltaic system array on a rooftop
2.1.1 Photovoltaic power system:
A photovoltaic system, also PV system or solar power system is a power system designed to supply usable solar power by means of photovoltaic. It consists of an arrangement of several components, including solar panels to absorb and convert sunlight into electricity, a solar inverter to change the electric current from DC to AC, as well as mounting, cabling, and other electrical accessories to set up a working system. It may also use a solar tracking system to improve the system’s overall performance and include an integrated battery solution, as prices for storage devices are expected to decline. Strictly speaking, a solar array only encompasses the ensemble of solar panels, the visible part of the PV system, and does not include all the other hardware, often summarized as balance of system (BOS). Moreover, PV systems convert light directly into electricity and shouldn’t be confused with other technologies, such as concentrated solar power or solar thermal, used for heating and cooling.
PV systems range from small, rooftop-mounted or building-integrated systems with capacities from a few to several tens of kilowatts, to large utility-scale power stations of hundreds of megawatts. Nowadays, most PV systems are grid-connected, while off-grid or stand-alone systems only account for a small portion of the market. Operating silently and without any moving parts or environmental emissions, PV systems have developed from being niche market applications into a mature technology used for mainstream electricity generation. A rooftop system recoups the invested energy for its manufacturing and installation within 0.7 to 2 years and produces about 95 percent of net clean renewable energy over a 30-year service lifetime.
Due to the exponential growth of photovoltaic, prices for PV systems have rapidly declined in recent years. However, they vary by market and the size of the system. In 2014, prices for residential 5-kilowatt systems in the United States were around $3.29 per watt, while in the highly penetrated German market, prices for rooftop systems of up to 100 kW declined to €1.24 per watt. Nowadays, solar PV modules account for less than half of the system’s overall cost, leaving the rest to the remaining BOS-components and to soft costs, which include customer acquisition, permitting, inspection and interconnection, installation labour and financing costs.
2.1.2 SOLAR CELL:
FIG 2.3: Solar cell
The photovoltaic effect was first reported by Edmund Becquerel in 1839 when he observed that the action of light on a silver coated platinum electrode immersed in electrolyte produced an electric current. Forty years later the first solid state photovoltaic devices were constructed by workers investigating the recently discovered photoconductivity of selenium. In1876 William Adams and Richard Day found that a photocurrent could be produced in a sample of selenium when contacted by two heated platinum contacts. The photovoltaic action of the selenium differed from its photo conductive action in that a current was produced spontaneously by the action of light.
No external power supply was needed. In this early photovoltaic device, a rectifying junction had been formed between the semiconductor and the metal contact. In 1894, Charles Fritts prepared what was probably the first large area solar cell by pressing a layer of selenium between gold and another metal.
In the following years photovoltaic effects were observed in copper {copper oxide thin _lm structures, in lead supplied and thallium supplied. These early cells were thin film Schottky barrier devices, where a semi-transparent layer of metal deposited on top of the semiconductor provided both the asymmetric electronic junction, which is necessary for photovoltaic action and access to the junction for the incident light. The photovoltaic effect of structures like this was related to the existence of a barrier to current flow at one of the semiconductor.
However, it was not the photovoltaic properties of materials like selenium which excited researchers, but the photoconductivity. The fact that the current produced was proportional to the intensity of the incident light, and related to the wavelength in a definite way meant that photo conductive materials were ideal for photographic light meters. The photovoltaic effect in barrier structures was an added benefit, meaning that the light meter could operate without a power supply. It was not until the 1950s, with the development of good quality silicon wafers for applications in the new solid state electronics, that potentially useful quantities of power were produced by photovoltaic devices in crystalline silicon.
During the 1990s, interest in photovoltaic expanded, along with growing awareness of the need to secure sources of electricity alternative to fossil fuels. The trend coincides with the widespread deregulation of the electricity markets and growing recognition of the viability of decentralized power. During this period, the economics of photovoltaic improved primarily through economies of scale. In the late 1990s the photovoltaic production expanded at a rate of 25% per annum, driving a reduction in cost. Photovoltaic first became competitive in contexts where conventional electricity supply is most expensive, for instance, for remote low power applications such as navigation, telecommunications, and rural electrification and for enhancement of supply in grid-connected loads at peak use. As prices fall, new markets are opened up. An important example is building integrated photovoltaic applications, where the cost of the photovoltaic system is offset by the savings in building materials.
There are several types of solar cells. However, more than 90% of the solar cells currently made worldwide consist of wafer-based silicon cells. They are either cut from a single crystal rod or from a block composed of many crystals and are correspondingly called mono-crystalline or multi-crystalline silicon solar cells. Wafer-based silicon solar cells are approximately 200 ?m thick. Another important family of solar cells is based on thin-films, which are approximately 1-2 ?m thick and therefore require significantly less active, semiconducting material. Thin-film solar cells can be manufactured at lower cost in large production quantities; hence their market share will likely increase in the future. However, they indicate lower efficiencies than wafer-based silicon solar cells, which mean that more exposure surface and material for the installation is required for a similar performance.
A number of solar cells electrically connected to each other and mounted in a single support structure or frame is called a ‘photovoltaic module’. Modules are designed to supply electricity at a certain voltage, such as a common 12 volt system. The current produced is directly dependent on the intensity of light reaching the module. Several modules can be wired together to form an array. Photovoltaic modules and arrays produce direct-current electricity. They can be connected in both series and parallel electrical arrangements to produce any required voltage and current combination.
FIG 2.4: Solar array
2.1.3 Overview:
A photovoltaic system converts the sun’s radiation into usable electricity. It comprises the solar array and the balance of system components. PV systems can be categorized by various aspects, such as, grid-connected vs. stand-alone systems, building-integrated vs. rack-mounted systems, residential vs. utility systems, distributed vs. centralized systems, rooftop vs. ground-mounted systems, tracking vs. fixed-tilt systems, and new constructed vs. retrofitted systems. Other distinctions may include, systems with micro inverters vs. central inverter, systems using crystalline silicon vs. thin-film technology, and systems with modules from Chinese vs. European and U.S.-manufacturers.
About 99 percent of all European and 90 percent of all U.S. solar power systems are connected to the electrical grid, while off-grid systems are somewhat more common in Australia and South Korea. PV systems rarely use battery storage. This may change soon, as government incentives for distributed energy storage are being implemented and investments in storage solutions are gradually becoming economically viable for small systems. A solar array of a typical residential PV system is rack-mounted on the roof, rather than integrated into the roof or facade of the building, as this is significantly more expensive. Utility-scale solar power stations are ground-mounted, with fixed tilted solar panels rather than using expensive tracking devices. Crystalline silicon is the predominant material used in 90 percent of worldwide produced solar modules, while rival thin-film has lost market-share in recent years. About 70 percent of all solar cells and modules are produced in China and Taiwan, leaving only 5 percent to European and US-manufacturers. The installed capacity for both, small rooftop systems and large solar power stations is growing rapidly and in equal parts, although there is a notable trend towards utility-scale systems, as the focus on new installations is shifting away from Europe to sunnier regions, such as the Sunbelt in the U.S., which are less opposed to ground-mounted solar farms and cost-effectiveness is more emphasized by investors.
Driven by advances in technology and increases in manufacturing scale and sophistication, the cost of photovoltaic is declining continuously There are several million PV systems distributed all over the world, mostly in Europe, with 1.4 million systems in Germany alone– as well as North America with 440,000 systems in the United States, The energy conversion efficiency of a conventional solar module increased from 15 to 20 percent over the last 10 years and a PV system recoups the energy needed for its manufacture in about 2 years. In exceptionally irradiated locations, or when thin-film technology is used, the so-called energy payback time decreases to one year or less. Net metering and financial incentives, such as preferential feed-in tariffs for solar-generated electricity; have also greatly supported installations of PV systems in many countries. The HYPERLINK “https://en.wikipedia.org/wiki/Levelised_cost_of_electricity” o “Levelised cost of electricity” levelised cost of electricity from large-scale PV systems has become competitive with conventional electricity sources in an expanding list of geographic regions, and grid parity has been achieved in about 30 different countries.
Photovoltaic is the field of technology and research related to the devices which directly convert sunlight into electricity using semiconductors that exhibit the photovoltaic effect. Photovoltaic effect involves the creation of voltage in a material upon exposure to electromagnetic radiation. The solar cell is the elementary building block of the photovoltaic technology. Solar cells are made of semiconductor materials, such as silicon. One of the properties of semiconductors that makes them most useful is that their conductivity may easily be modified by introducing impurities into their crystal lattice. For instance, in the fabrication of a photovoltaic solar cell, silicon, which has four valence electrons, is treated to increase its conductivity. On one side of the cell, the impurities, which are phosphorus atoms with five valence electrons (n-donor), donate weakly bound valence electrons to the silicon material, creating excess negative charge carriers.
On the other side atoms of boron with three valence electrons (p-donor) create a greater affinity than silicon to attract electrons. Because the p-type silicon is in intimate contact with the n-type silicon a p-n junction is established and a diffusion of electrons occurs from the region of high electron concentration (the n-type side) into the region of low electron concentration (p-type side). When the electrons diffuse across the p-n junction, they recombine with holes on the p-type side.
However, the diffusion of carriers does not occur indefinitely, because the imbalance of charge immediately on either sides of the junction originates an electric field. This electric field forms a diode that promotes current to flow in only one direction.
Ohmic metal-semiconductor contacts are made to both the n-type and p-type sides of the solar cell, and the electrodes are ready to be connected to an external load. When photons of light fall on the cell, they transfer their energy to the charge carriers. The electric field across the junction separates photo-generated positive charge carriers (holes) from their negative counterpart (electrons). In this way an electrical current is extracted once the circuit is closed on an external load.
2.1.4 SOLAR POWERED PUMPS:
A solar-powered pump is a pump running on electricity generated by photovoltaic panels or the radiated thermal energy available from collected sunlight as opposed to grid electricity or diesel run water pumps. The operation of solar powered pumps is more economical mainly due to the lower operation and maintenance costs and has less environmental impact than pumps powered by an internal combustion engine (ICE). Solar pumps are useful where grid electricity is unavailable and alternative sources (in particular wind) do not provide sufficient energy.
ComponentsA photovoltaic solar powered pump system has three parts:
Solar panels
The controller
The pump
The solar panels make up most (up to 80%) of the systems cost. The size of the PV-system is directly dependent on the size of the pump, the amount of water that is required (m³/d) and the solar irradiance available. The purpose of the controller is twofold. Firstly, it matches the output power that the pump receives with the input power available from the solar panels. Secondly, a controller usually provides a low voltage protection, whereby the system is switched off, if the voltage is too low or too high for the operating voltage range of the pump. This increases the lifetime of the pump thus reducing the need for maintenance. Other ancillary functions include automatically shutting down the system when water source level is low or when the storage tank is full, regulating water output pressure, blending power input between the solar panels and an alternate power source such as the grid or a petrol generator, and remotely monitoring and managing the system through an online portal offered as a cloud service by the manufacturer.
Voltage of the solar pump motors can be AC (alternating current) or DC (direct current). Direct current motors are used for small to medium applications up to about 4 kW rating, and are suitable for applications such as garden fountains, landscaping, drinking water for livestock, or small irrigation projects. Since DC systems tend to have overall higher efficiency levels than AC pumps of a similar size, the costs are reduced as smaller solar panels can be used. Finally, if an alternating current solar pump is used, an inverter is necessary that changes the direct current from the solar panels into alternating current for the pump. The supported power range of inverters extends from 0.15 to 55 kW and can be used for larger irrigation systems. However, the panel and inverters must be sized accordingly to accommodate the inrush characteristic of an AC motor. To aid in proper sizing, leading manufacturers provide proprietary sizing software tested by third party certifying companies. The sizing software may include the projected monthly water output which varies due to seasonal change in insolation.
2.2 DC TO DC CONVERTERS
There are mainly two types of DC to DC converters
1. DC to DC converters without isolation.
2. DC to DC converters with isolation.
1. DC to DC converters without isolation
This “isolation” refers to the existence of an electrical barrier between the input and output of the DC-DC converter. There is no isolation between the input and output. Some of the commonly used DC to DC converters with isolation are
Buck converter.
Boost converter.
Buck-Boost converter.
The Buck converter is step down converter (input voltage ; output voltage) whereas boost converter is a step up converter (input voltage ; output voltage). The buck boost converter is derived from step up and step down converters. The Buck-Boost converter can be operated in step up or step down mode base on duty cycle of switch (ton/Ts where ton is the duration for which switch is on and Ts is the switching period). The step down and step up converters are basic converter topologies based on which other converters are derived.
2. DC to DC converters with isolation
A transformer is provided in between to isolate the input and output stages. The electrical isolation is an additional feature and is mainly useful in cases where the input voltage level (Vin) and the output voltage level (Vout) differs significantly i.e. high or low values of Vout/Vin . The DC to DC converters with isolation is again divided into two types based on polarity of transformer core excitation. Unidirectional core excitation, core is excited with forward currents of only one direction. In these DC to DC converters the isolation transformer core is operated in only the positive part of B-H curve.
Bidirectional core excitation core is excited with currents in either direction. In these DC to DC converters the isolation transformer core is operated alternatively in positive and negative portions of B-H curve.
Some of the commonly used DC to DC converters with isolation are
Cuk converter (can be used in non-isolated mode also).
Fly back converter.
Forward converter.
Full bridge converter.
Half bridge converter.
Push-pull converter.
In this proposed system we using new DC to DC converter named two inductor boost converter. Brief explanation of TIBC is given in next chapter.
2.3 THREE PHASE INVERTER
A power inverter or inverter is an electronic device or circuitry that changes direct current (DC) to alternating current (AC).The input voltage, output voltage, frequency and overall power handling depends on the design of the specific device or circuitry. The inverter does not produce any power; the power is provided by the DC source. A power inverter can be entirely electronic or may be a combination of mechanical effects (such as a rotary apparatus) and electronic circuitry. Static inverters do not use moving parts in the conversion process. Circuitry that performs the opposite function converting AC to DC is called a rectifier.
Three phase inverters are used for variable-frequency drive applications and for high power applications such as HVDC power transmission. A basic three-phase inverter consists of three single-phase inverter switches each connected to one of the three load terminals. For the most basic control scheme, the operation of the three switches is coordinated so that one switch operates at each 60 degree point of the fundamental output waveform. This creates a line-to-line output waveform that has six steps. The six-step waveform has a zero-voltage step between the positive and negative sections of the square-wave such that the harmonics that are multiples of three are eliminated as described above. When carrier-based PWM techniques are applied to six-step waveforms, the basic overall shape, or envelope, of the waveform is retained so that the 3rd harmonic and its multiples are cancelled.
To construct inverters with higher power ratings, two six-step three-phase inverters can be connected in parallel for a higher current rating or in series for a higher voltage rating. In either case, the output waveforms are phase shifted to obtain a 12-step waveform. If additional inverters are combined, an 18-step inverter is obtained with three inverters etc. Although inverters are usually combined for the purpose of achieving increased voltage or current ratings, the quality of the waveform is improved as well. Some of the applications of three phase inverters are:
DC power source usage.
Uninterrupted power supplies.
Electric motor speed.
In refrigeration compressors.
Power grid.
Solar.
Induction heating.
HVDC power transmission.
Electroshock weapons.
2.4 THREE PHASE INDUCTION MOTOR:
An electric motor converts electrical energy into a mechanical energy which is then supplied to different types of loads. A.C. motors operate on an A.C. supply and they are classified into synchronous, single phase and 3 phase induction and special purpose motors. Out of all types three phase induction motors are most widely used for industrial applications mainly because they do not require a starting device.
A three phase induction motor derives its name from the fact that the rotor current is induced by the magnetic field, instead of electrical connections. The operating principle of a three phase induction motor is based on the production of r.m.f. There are so many types of three phase induction motor. They are
Slip ring motor.
Polyphase cage rotor.
Polyphase wound rotor.
Two-phase servo motor.
Single-phase induction motor.
Polyphase synchronous motor.
Single-phase synchronous motor.
Hysteresis synchronous motor.
These motors are self-starting and use no capacitor, start winding, centrifugal switch or other starting device. Three-phase AC induction motors are widely used in industrial and commercial applications. These are of two types, squirrel cage and slip ring motors. Squirrel cage motors are widely used due to their rugged construction and simple design. Slip ring motors require external resistors to have high starting torque. Induction motors are used in industry and domestic appliances because these are rugged in construction requiring hardly any maintenance, that they are comparatively cheap, and require supply only to the stator.
2.4.1 Applications of Three Phase Induction Motor
Lifts
Cranes
Hoists
Large capacity exhaust fans
Driving lathe machines
Crushers
Oil extracting mills
Textile and etc.
2.4.2 Advantages of Induction Motor
The motor construction and the way electric power is supplied all give the induction motor several advantages is shown in figure below. And let’s see of them in brief.
Low cost: Induction machines are very cheap when compared to synchronous and DC motors. This is due to the modest design of induction motor. Therefore, these motors are overwhelmingly preferred for fixed speed applications in industrial applications and for commercial and domestic applications where AC line power can be easily attached.
Low maintenance cost: Induction motors are maintenance free motors unlike dc motors and synchronous motors. The construction of induction motor is very simple and hence maintenance is also easy, resulting in low maintenance cost.
Ease of operation: Operation of induction motor is very simple because there is no electrical connector to the rotor that supply power and current is induced by the movement of the transformer performs on the rotor due to the low resistance of the rotating coils. Induction motors are self-start motors. This can result in reducing the effort needed for maintenance.
Speed Variation: The speed variation of induction motor is nearly constant. The speed typically varies only by a few percent going from no load to rated load.
High starting torque: The staring torque of induction motor is very high which makes motor useful for operations where load is applied before the starting of the motor.3 phase induction motors will have self-starting torque unlike synchronous motors. However, single-phase induction motors does not have self-starting torque and are made to rotate using some auxiliaries.
Durability: Another major advantage an induction motor is that it is durability. This makes it the ideal machine for many uses. This results the motor to run for many years with no cost and maintenance.
All these advantages make induction motor to use in many applications such as industrial, domestic and in many applications.
2.5 CENTRIFUGAL PUMPS
Centrifugal pumps are a sub-class of dynamic axisymmetric work-absorbing turbo machinery. Centrifugal pumps are used to transport fluids by the conversion of rotational kinetic energy to the hydrodynamic energy of the fluid flow. The rotational energy typically comes from an engine or electric motor. The fluid enters the pump impeller along or near to the rotating axis and is accelerated by the impeller, flowing radially outward into a diffuser or volute chamber (casing), from where it exits.
Common uses include water, sewage, petroleum and petrochemical pumping; a centrifugal fan is commonly used to implement a vacuum cleaner. The reverse function of the centrifugal pump is a water turbine converting potential energy of water pressure into mechanical rotational energy.
How it works
Like most pumps, a centrifugal pump converts rotational energy, often from a motor, to energy in a moving fluid. A portion of the energy goes into kinetic energy of the fluid. Fluid enters axially through eye of the casing, is caught up in the impeller blades, and is whirled tangentially and radially outward until it leaves through all circumferential parts of the impeller into the diffuser part of the casing. The fluid gains both velocity and pressure while passing through the impeller. The doughnut-shaped diffuser, or scroll, section of the casing decelerates the flow and further increases the pressure. It is important to note that the water is not pushed radially outward by centrifugal force (non-existent force), but rather by inertia, the natural tendency of an object to continue in a straight line (tangent to the radius) when traveling around circle. This can be compared to the way a spin-cycle works in a washing machine.
