SARHAD UNIVERSITY OF SCIENCE &INFORMATION TECHNOLOGY,

PESHAWARfaculty of under Graduate Studies

Techno Economic Modeling And simulation of Off-GridPhotovoltaic (PV) electricity generation system

Group Members :

Syed Bilal Ahmad Madni (SUIT-11-01-008-0008)

Muhammad Shoaib (SUIT-11-01-008-0005)

Mehran Khan (SUIT-11-01-008-0003)

Discipline: BS Electronics

Supervised by: Engineer. Danial Naeem

This report is submitted in partial fulfillment of the requirements of the degree ofBS in Electronics field.

Faculty of Under Graduate studies, at Sarhad University of science andinformation Technology, Peshawar 2015

Acknowledgement: We truly acknowledge the cooperation and help make by Mr Danial Naeem,and Waqas Ali Lecturer and supervisor at Comwave institute Haripur. They have been a constant source of guidance throughout the course of this project. We would also like to thank Mr sajid Ali from Comwave intitute Haripur for his help and guidance throughout thisProject.

We are also thankful to my friends and family whose silent support led me to complete myProject.

1- Name of friend 2- Name of friend ...

Dated:

TECHNO-ECONOMIC MODELLING &SIMULATION OF OFF-GRID PHOTOVOLTAIC

(PV) ELECTRICITYGENERATION SYSTEM

This report was successfully submitted toSarhad University Of Science And Information Technology

Peshawar

External supervisor Internal SupervisourName of external SUIT, Peshawar DesignationName of organization

Declaration:

This is certify that, Students Name:Syed Bilal Ahmad Madni Registration No: SUIT-11-01-008-000 Students Name: Mehran Khan Registration No:SUIT-11-01-008-0008 Students name: Mohammad Shoaib Registration No:SUIT-11-01-008-0008has successfully completed the final project named as TECHNO-ECONOMIC MODELLING & SIMULATION OF OFF-GRID PHOTOVOLTAIC (PV) ELECTRICITY GENERATION SYSTEM at the Sarhad University of Science & Information Technology, Peshawar, to fulfill the partial requirement of the degree of ___________________.

Abstract:

Photovoltaic that is an important topic which can be studied and researched in Pakistan because

of availability of solar energy potential at full day time. This report deals with simulations and

designs of off -grid photovoltaic system for an electrical home loads. It provides theoretical

studies of photovoltaic and modeling techniques using equivalent electric circuits .the report

includes maximum obtains of solar power in simulation software Power sim to verify the DC to

AC conversion with battery charge controller. The inverter model that would be chosen for

generating square wave as an output to hold the 500watt load of a house

In this report 7056 watt-hour /day energy load of a house. In this system Poly crystalline PV

modules are used each module has rated power of 150watt and inverter has rated output of

650watt, 1000KVA with 9kwh storage capacity of battery is included in this system

The economic feasibility design of OFF-Grid PV system is simulated by using RET screen

Based on economic evaluation grid tie system is as 22Rs/kwh and the cost of energy generated

by stand-alone PV power generation system is 16Rs/kwh.

Chapter 1 Introduction:

The basic idea of a solar cell is to convert light energy into electrical energy, the energy of light is transmitted by photons, small packets or quantum of lights, electrical energy is stored in electromagnetic fields, which in turn make a current of electrons flow, thus the solar cells converts light, a flow of photons, to electric current, a flow of electrons. The development of solar cell technology begins with the 1839 research of French physicist Antoine-Cesar Becquerel, he observed the photovoltaic effect while experimenting with the solidelectrode in an electrolyte solution, when he saw a voltage develop when light fell upon the

electrode. In 1941, the silicon solar cell was invented by Russell Ohl. In 1954, three American researchers Gerald Pearson, Calvin fuller and Daryl Chapin designed a silicon solar cell capable of a six percent energy conversion efficiency with direct sun light the three inventors created an array of several strips of silicon, (each about the size of a razor blade) Placed them in sunlight, captured the free electrons and turned them into electric current.

The world energy consumption and the resulting carbon dioxide emission is increasing simultaneously and this increase puts in danger the environmental stability of our earth, making this an important topic in a society, both in political and social aspects. The energy production has mainly been based on energy source like oil, gas and coal. Which until recently looked upon as close an inexhaustible. As World energy consumption is growing with a high rateand the fossil fuels reserves are decreasing need of renewable energy source is much important for research. The Sun is non-polluting resource responsible for the sustained life on earth and cangive us efficient renewable energy in Pakistan, because a potential is available.

In this master thesis a standalone PV system will be studied. A standalone PV system is used in the places where no electrical grid is available. The PV system will utilize the solar energy as thepower source and transfer the power into the battery through conditioning by power electronics, after that the energy is stored in battery then converted by another stage of power electronics to be used in a home load. The power electronics is an essential part of a PV system, and it is necessary to understand how to utilize and control this part for optimization of thepower generation. This issue will support teaching in control of power electronics, through learning many control strategies and know the suitable parameters to obtain more efficient performance for a standalone PV system by using PSIM and RET Screen program and simulate this system on real conditions. To achieve this objective the mathematical models were studied which characterize each part of system such as PV module, DC-AC converters,Charge controller,battery and inverter. After that the suitable rated value for all components in a standalone PV system was calculated according to the energy consumption in kWh for a home load. In addition, economical study wasmade to know the cost in Rs/ kWh for a standalone PV system and compare it with other PV system which is a grid tie PV system considering the feed in tariff. Photovoltaic offers to consumers the ability to generate electricity in clean, quiet and reliable way. Photovoltaic system is comprised of photovoltaic cells, devices that convert light energy directly into electricity because the source of light is usually the sun; they are often called solar cells. The word photo meaning light and Voltaic which refers to producing electricity, therefore the photovoltaic process is producing electricity directly from sunlight. Photovoltaic is also known as PV. In chapter one, the study begins with an introduction to this thesis, it gives information about objective, procedure and the main outline of the research.

The model of PV system is implemented Using PSIM (Power Simulation) software to study and simulate real Off-Grid PV system.

.1. Photovoltaic cells: The photovoltaic (PV) cell is basically a pn junction with a central depletion region. At theend of each zone an electrical contact is placed. The more heavily doped zone is called theemitter zone and the other is the base zone. This last region is also called the absorber regionbecause the great part of incident light is absorbed here. Differently from a diode, the PV cellis designed so to allow holeselectrons couples to be generated inside the junction due toincident light. The aim of this section is to define the law that ties voltage and current of a PV cellincluding the dependence on incident light. Solar cells are made from semiconductorMaterials (PN junction) usually silicon which are specially treated to from an electric field,Positive on one side (backside) and negative on the other (towards the sun). When solarenergy (photons) hits the solar cell, electrons are knocked loose from the atoms in thesemiconductor material, creating electron hole-pairs.if electrical conductors are then attached to the positive and negative sides, forming anelectrical circuit, the electrons are captured in the form of electric current (photo current)

Figure 1.1 Photovoltaic Cell

A typical PV cell made of crystalline silicon is 12 centimeters in diameter and 0.25 millimeter thick, in full sunlight it generates4 amperes of direct current at 0.5 volt or 2 wattsof electrical power

.2 Types of Photovoltaic cell: There are essentially two types of PV technology. Crystalline and thin-film. Crystalline can again be classified into two types.

1. Mono crystalline cells

2. Polycrystalline cells

Mono crystalline cells

These are made of cells cut from a signal cylindrical crystal of silicon. While mono crystalline cells offers the highest efficiency (approximately 18% conversion of incident sunlight), their complex manufacturing process makes them slightly more expensive

Polycrystalline cellsthese are made by cutting micro-fine wafers from ingot of molten re-crystallized silicon. Polies crystalline are cheaper to produce, but there is a slight compromise on efficiency (approximately14% conversion of incident sunlight) Thin film PV is made by depositing an ultrathin layer of photovoltaic material onto a substrate. The most common type of thin-film PV is made from the material a-Si (amorphous-Silicon), but numerous other materials such as CIGS (copper Indium/galliumselenide) CIS (copper indium selenide, CdTe (Cadmium Telluride) The efficiency of this types varies approximately in the range from 2% - 10% .

a) Mono-crystalline PV b) Poly-crystalline PV c) amorphous PV Figure 1.2 Mono crystalline PV

1.3 The Photovoltaic Array:

If an output voltage and a current from a single module is smaller than desired, the modules can

be connected into arrays, the connection methods depends on which variable that need to be

increased. For a higher output voltage the modules must be connected in series while connecting

them in parallel in turns gives higher currents, it is important to know the rating of each module

when creating an array, the highest efficiency of the system is achieved when the MPP

(maximum power point) of each of the modules occur at the same voltage level.

Figure 1.3 Cell, Module and Array

2.4 Physics of Photovoltaic Cells:

2.4.1 The Photoelectric Effect

The transformation of the radiated energy coming from the Sun into electrical energy implies thestudy of the interaction of electromagnetic waves with matter. This mechanism can beunderstood starting from the photoelectric effect in which electrons are emitted from a materialwhen it is exposed to electromagnetic radiation. In particular, it was observed that (using visiblelight for alkali metals, near ultraviolet for other metals, and extreme ultraviolet for non-metals)the energy of emitted electrons increased with the frequency and did not depend on the intensityof the radiation. This effect was first observed by Heinrich Hertz in 1887 and for several years itwas apparently in contrast with James Clerk Maxwells wave theory of light; according to thistheory, the electron energy would be proportional to the intensity of the radiation. The followingmain experimental results, for given material, were observed:

1. The rate at which photoelectrons are ejected is directly proportional to the intensity of the

incident light

2. A threshold frequency, below which no photoelectrons are emitted, exists

3. Above the threshold frequency, if the intensity of light is increased, the number of

emitted electrons is increased as well but their maximum energy does not vary; moreover

very low intensity of incident light, with frequency greater that the threshold, is able to

extract electrons;

4. Above the threshold frequency, if the frequency of incident light is increased, the

maximum energy of photoelectrons is also increased; Albert Einstein theorized, in 1905,

that light is composed of discrete quanta, now called photons, and that the energy of a

quantum of light is given by the product of the frequency of the corresponding wave

multiplied by a constant, later called Plancks constant.

2.4.2 Conductors, Semiconductors, Insulators:

In a single isolated atom, energy levels of electrons are discrete. For hydrogen atom, the Bohrs

model gives:

(1.1)

Where mo is the free electron mass and q its charge, e2o is the free space permittivity and n is a

positive integer known as principal quantum number. The fundamental level corresponds to n=1

and the related energy is

If N atoms interact (for example in a crystal), N outer levels have energy only slightly different

and thermal energy allows electrons to pass from one level to another (the energy corresponding

to T = 300 K is kT & 0.026 eV). Resulting energy levels are grouped in bands. Two main bands

are recognizable: conduction band and valence band. These two bands are separated by a

forbidden region that is characterized by an energy value Eg. This value makes the difference

among insulators, conductors, and semiconductors. In an insulator, the forbidden band has a wide

energy (for example Eg = 9 eV for SiO2) neither thermal energy nor an electric field is able to

raise the energy of an electron to send it into the conduction band. Due to the absence of free

electrons for conduction, the material behaves as an insulator. On the contrary, in a conductor the

conduction band is partially superimposed to the valence band. As a consequence, there are many

electrons available for conduction and an electric field can give them sufficient energy to

perform conduction.

In a semiconductor, the two bands are separated but the energy of the forbidden band is low

(Eg = 1.12 eV for Si at T = 300 K) and it is easy to give energy to an electron to go into the

conduction band. In this case, the hole in the valence band contributes to the conduction as well

as the electron in the conduction band.

The forbidden band amplitude varies with temperature, for Si the amplitude is:

(1.2)

The temperature coefficient is negative, it means that the forbidden band amplitude decreases

with temperature.

2.4.3 Absorption of Light:

The radiated energy interacts with the matter, including semiconductors, as photons, whose

energy is , and momentum

The excitation of an electron from the valence band to the conduction band is called fundamental

absorption and, as a consequence, a hole appears in the valence band. Both the total energy and

the momentum must be conserved; in particular, for direct band-gap semiconductors (GaAs,

GaInP, CdTe, and CU (InGa) Se2) a transition can occur remaining constant the momentum of

the photons. The crystal momentum is equal to where l is the lattice constant and it is bigger

than the photon momentum. Being the wavelength of sunlight of the order of 10 -4 cm and the

lattice constant of 10-8 cm, it can be assumed that the conservation law can be applied only to the

photon momentum. The probability of an induced transition from a level E1 into the valence

band to a level E2 into the conduction band for a photon with energy is given by a coefficient

that depends on the difference between the photon energy and the forbidden band gap.

(1.3)

Some semiconductors allow only transitions with , in such cases:

(1.4)In indirect band-gap semiconductor, like Si and Ge, the maximum of the valence band and the

minimum of conduction band occur for different values of the momentum .as shown below

Figure 1.4 Energy versus momentum representation of the energy band structure for indirect band-gap semiconductor

Conservation of the momentum implies in this case the emission or the absorption of a phonon.3

In particular, if the photon energy is greater than the difference between the starting electron

energy level in the valence band and the final level in conduction band, a phonon is emitted. On

the contrary, if the photon energy is lower than the difference between the starting electron

energy level in the valence band and the final level in conduction band, a phonon is

Absorbed. The absorption coefficient is different depending on absorption or emission

phenomenon.

(1.5)

(1.6)

Where Eph is the phonon energy. It should be noted that for indirect band-gap semiconductor,

the absorption of a photon depends on the availability of energy states, and on the

absorbed/emitted phonons as well. This makes the absorption coefficient for indirect transition

smaller than the corresponding one for direct transition. As a result, light is able to penetrate

more inside an indirect band-gap semiconductor.

2.4.4 Doping: The conductivity of a semiconductor can be varied by introducing specific dopants. it can benoted that phosphorous has five valence electrons (3s23p3) whereas boron has three valence

electrons (3s23p1). If phosphorous atoms are introduced in a silicon crystal, one of its five

valence electrons becomes available for conduction, the remaining four electrons are tied with

covalence bonds of silicon lattice. This kind of dopant is said donor. In the same way by

introducing boron, its three valence electrons are tied

Figure 1.5 a) n-type doping with Phosphorous b) p-type doping with Boron

with covalence bonds of silicon lattice and a hole remains as shown in above fig 1.5 This kind of

dopant is said acceptor. From the point-of-view of energy levels, the presence of donor

introduces additional energy levels near the conduction band (within few kT), hence thermal

energy can allow the added electron to move to the conduction band. In the same way, the

presence of an acceptor introduces additional energy levels near the valence band.

In case of donor introduction, electrons are the primary source of conduction and the

semiconductor is said n-type, on the contrary, if an acceptor is introduced, conduction is due to

hole, and the semiconductor is said p-type. The atoms of donors (ND) or acceptors (NA) are

usually completely ionized, as a consequence for n-type semiconductor and for p-type

semiconductor

This hypothesis will be maintained in the following, throughout the chapter. The presence of

dopant changes the Fermi level compared to an intrinsic semiconductor, this value can be

recalculated for an n-type semiconductor.

(1.7)Compared to an intrinsic semiconductor the Fermi level is increased.For a p-type semiconductor.

(1.8)

and the Fermi level is lower compared to the intrinsic semiconductor holds even for doped

semiconductors, for an n-type:

(1.9)

and the donors concentration can be expressed versus the Fermi level for an intrinsic

semiconductor:

When is obtained by using below I and II equation with the position of

(I) (1.10)

.... (II) (1.11)

Then for P-type we can get

(1.12)

In an n-type semiconductor, electrons represent majority carriers and holes minority carriers.

Usually, if necessary, their concentration symbol includes a pedex to indicate the semiconductor

type. Hence, in an n-type semiconductor there are majority carriers and minority carriers. In a

p-type semiconductor, there are pp majority carriers and np minority carriers. If necessary, to

specify the equilibrium conditions a further pedex o can be added. When double doping with

both donors and acceptors is performed, the type of the semiconductor is determined by the

greatest impurity concentration.

2.4.5 PN Junction:A pn junction can be conceptually conceived as a two doped semiconductor of n-type and p-

type that have a surface in common. When both semiconductors are separated, they are

electrically neutral. As soon as they get in touch, majority carriers of n-type semiconductors (the

electrons) begin to diffuse into the p-type semiconductor and vice versa. As a result, near the

surface of separation between the two semiconductors, in n-type semiconductor, holes coming

from p-type semiconductor tend to combine with electrons and the positive charge of the

corresponding ionized donors is not more compensated by majority carriers. Inside the n-type

region, near the junction, where there are no more majority.

Figure 1.6 Schematic representation of a pn junction

charges, a depletion is observed and the corresponding zone remains with fixed positive charges.

In the same way, in p-type side, electrons coming from n-type semiconductor tend to combine

with holes and the negative charge of the ionized acceptors is not more compensated by majority

carriers. Inside the p-type region, near the junction, where there are no more majority charges, a

depletion is observed and the corresponding zone remains with fixed negative charges. As the

fixed charges are uncovered, an electric field is produced and the diffusion process is slowed

down. A pn junction is drawn in Fig. 1.6 in 1D representation; the origin (x = 0) is the junction

surface, xp and Wp are the depletion boundary at the end of p-type region, while -xn and -Wn are

the depletion boundary at the end of n-type region. It should be noted that, if a semiconductor is

more doped than the other (usually indicated with apex +), the greater quantity of free carrier

diffused in the other semiconductor cause a more extended depletion. It is assumed a uniformed

and no degenerated doping and that dopants are fully ionized. The whole zone in which there are

f ixed uncompensated charge is called depletion region or space charge region. The remaining

zones can be considered as neutral (often called quasi neutral). The electric field due to the fixed

charges origins an electrostatic potential difference called built-in voltage. The Poissons Eq.)

can be rewritten as:

(1.13)

Where is the electrostatic potential, p0 and no are the hole and electron equilibrium

concentration, is the concentration of ionized donors (positive fixed charges), and is the

concentration of ionized acceptors (negative fixed charges).

Figure 1.7 Electric symbol and voltage versus current diode characteristic

When the forward bias voltage approaches Vbi the depletion zone tends to vanish and the current

is limited by the semiconductor and ohmic contact, as well. In this case, the voltage versus

current characteristic is approximated by straight line. When a reverse bias is applied, it means

that a positive voltage is applied to the n zone contact, can be still utilized. As a matter of fact,

the exponential term is negligible and a reverse saturation current is obtained. In this case, the

obtained small current is given only by carriers generated inside the junction and it does not

depend on the applied reverse bias. the voltage versus current characteristic of a diode. From

what explained above, it is clear that a diode allows the current to pass from p zone to n zone

when it is forward biased. The ohmic contact belonging to the p zone is called anode while the

ohmic contact belonging to the n zone is called cathode.

2.4.6 Optical Generation Rate:As we know only photons with wavelength can contribute to generate holeselectrons couples.

The generation rate depends on a grid shadowing factor s, on the reflectance on the absorption

coefficient and on incident photon flux according to the equation 1.14

( 1.14)

Physical Model of a PV Cell:On the basis of Kirchhoffs current law (KCL) an equivalent circuit can be deduced. It represents

a physical circuit model of a PV cell. This circuit is drawn in

Figure 1.8 Physical model of a PV cell

It should be noted that the output current is the sum of a current given by a generator that

depends on solar irradiance minus the current that flows through the two diodes.The first current

corresponds to

In equation ( 1.15)

(1.15)

and the second current corresponds to

and the third current corresponds to

As a matter of fact, the second and the third term of (Eq.1.15) can be considered as Shockley

diode equations. Finally, the output voltage is obtained by the diodes direct bias due to the

current generator. During operating conditions, when solar radiation occurs, the generator current

flows through the diodes and a voltage appears at the terminals. If no load is applied this voltage

is an open circuit voltage, i.e., the voltage of a directly polarized pn junction and it is the

maximum value achievable by a PV cell. If a load is connected, a part of the current of the

generator flows into the load, voltage decreases and electric power is supplied to the load. The

conversion process is completed. Starting from solar radiation, electric energy has been obtained.

It should be noted that if the load is raised (it corresponds to a lower resistance) current rises too

and voltage decreases; the supplied power reaches a maximum and then decreases until the short

circuit condition.

Figure 1.9 a) structure of crystalline b) Monocrystalline c) amorphous silicon

When no solar radiation is present, the generated current is null and consequently the voltage at

terminals. However, this does not correspond to a short circuit behavior on the contrary; the PV

cell does not allow negative current flow imposed by external circuits.

Crystalline Silicon:Crystalline silicon is considered as an ideal structure where the pattern is regular throughout the

whole surface. All theory explained above is developed with reference to this structure. The main

advantage consists of highest ratio solar irradiance produced electric power. With

Monocrystalline silicon, power conversion efficiency ranging from 20 to 24 % is expected, with

GaAs, power conversion efficiency ranging from 20 to 29 % is expected. Crystalline silicon, on

the other hand, is expensive owing to manufacturing process. For this reason, several alternative

cheaper silicon structures have been developed.

Multicrystalline:Multicrystalline and polycrystalline silicon can be produced by a less sophisticated technique

compared with crystalline. However, in this case, the presence of grain boundaries must be taken

into account. In particular, cell performance is reduced because at the boundaries the carriers

flow is blocked, the level structure is altered, and the current that would flow across pn junction

is shunted away. Some remedies have been devised as, for example, the use of grains of few

millimeters to cover the entire distance from the back to the front of the cell with minimum

number of grains. With Polycrystalline silicon, a power conversion efficiency ranging from 13 to

18 % is expected.

Amorphous:Amorphous silicon presents a less regular structure with unsatisfied bonds. These dangling

bonds are passivated by hydrogen by allowing doping (otherwise impossible) and raising the

band gap form 1.1 eV of crystalline silicon to 1.7 eV; in this way, photons of higher energy can

be absorbed and the required thickness of the material is lower. As a consequence, amorphous

silicon can be used as a thin film form deposited on glass or other substrates for low cost

applications. The band structure of amorphous materials is similar to the crystalline material over

short distance and a mobility gap, in which conduction occur, can be defined. However, there are

a great number of localized energy states within mobility gap.

2.5.1 Basic Structure of PV:

PV cells are the basic building blocks of the PV modules, for almost all applications the one halfvolt produced by a single cell. Therefore cells are connected together in series to increase thevoltage. Several of these series strings of cells may be connected together in parallel to increasethe current. So in basic structure of PV model there must be include the effects of series andparallel resistance of the PV, so when the first Kirchhoffs law is applied to one of the nodes ofequivalent circuit, the current supply by the PV, at a specified temperature.

PV Model in PSIM:

Figure 1.10 PV model in PSIM

Chapter 3

Off-Grid PV System:

In the stand alone PV system the battery energy storage is necessary to help get a stable and

reliable output from PV generator. In this case we need a battery charge regulator to protect the

battery against overcharge and deep discharge which shorten the battery life time.

Figure 3.1 Charge controller

Above figure shows a charge controller system this system consist a PV system, filter and battery

charger. In PV system block it contains a PV array, and buck boost converter. Buck boost

converter is implemented to the system to maintain the output voltage at the required value.

When the PV gets the max or min voltage from the sunlight, the converter will use to control the

output voltage at the required value to charge the battery.

Figure 3.2 Battery charger

Above figure (3.2) shows a Battery Charger which is consist of a boost converter with controller.

The output connection of this circuit to the PV system is usually dc-dc converter mainly boost

chopper in order to boost the voltage to the predefined levels. Figure (3.3) show a boost

converter in battery charger block.

Figure 3.3 Power boost converter

Off - grid inverter:In this below block we show design of an Off-grid inverter Figure (3.4) shows the inverter

design for a PV system. First stage consists of a battery regulator with the value 48 Volts and a

boost converter for amplication of the battery voltage to the required value amount to 192 V dc.

The boost converter parameters are L=10010-3 H, C= 100010-6 F, f switching=100 kHz, Duty

cycle=75% .

Figure 3.4 Inverter design for PV electricity generation system

DC/AC Inverter Analysis:Here we analyzed, inverter architectures, single phase wave form of inverter and six-step of

three-phase will be analyzed for photovoltaic system. Detailed modulation strategies of the space

vector modulation will be described for the three-phase inverter.

Single phase full bridge DC/AC inverter:In photovoltaic system, the DC/AC inverter is used to converts the power of the source by

switching the DC input voltage (or current) in a pre-determined sequence to generate AC voltage

(or current) output. Figure (3.5) shows the equivalent circuit of single-phase inverter. This has

four switches that turn on and off to obtain a sinusoidal output.

Figure 3.5 Equivalent circuit of the full bridge single phase inverter.

The load of the inverter is a single-phase AC load or connected to single-phase grid power. The

topology of the single-phase inverter is shown in figure (3.6). The single-phase inverter has four

switches and four anti-parallel protective diodes. It provide path for the inductive current to flow

when the switches are open and protect the switches from the large voltage by interrupting the

inductive current.

Figure 3.6 Topology of a single phase inverter with filter and load

To generate an AC waveform in single-phase inverter, the switches S1, S2 ON and S3, S4 off for

period t1 and t2 as shown in figure (3.7). For that period, the output is a positive voltage.

Figure 3.7 Output current for S1,S2 ON; S3,S4 OFF for t1 < t < t2

For period t2 to t3 in figure (3.8), the switches S3, S4 are on and S1 and S2 are off to obtain

negative voltage.

Figure 3.8 output current for S3, S4 ON;S1,S2 OFF for t2 < t < t3

Switches S1 and S4 should not be closed simultaneously, the same for switches S3 and S2.

Otherwise short circuit of the DC bus will occur. By following the switching scheme, the inverter

output voltage will alternate between positive and negative as figure (5.5), and the sinusoidal

fundamental component is obtained as shown in figure (5.6).

Impact of solar radiation on I-V characteristic curve of photovoltaic module:

Standard sunlight conditions on a clear day are assumed to be (1000 W/m^2). This is

sometimes called one sun or a peak sun . Less than one sun can reduce the current output of

the module by a proportional amount, for example if only one-half sun (500w/m^2) is available,

the amount of current is roughly cut in half.

Figure 3.1 I-V characteristics at t=25 C, By PSIM different irradiances [y-axis: current (A): X-axis: voltage(volt)].

Impact of temperature on I-V characteristic Curve of Photovoltaic Module:

The temperature of PV cell is an important parameter that has to be taken into consideration inPV system operation. The PV cell has given temperature coefficients for both the current and thevoltage (). The current coefficient is mostly negligible; hence it is mainly the voltagetemperature coefficient that is considered during calculations. For Silicon based cells thecoefficient ()=2mV/C_ Per cell.

Figure 3.2 I-V characteristic at 1000w/m2, By PSIM with Different temperature [Y-axis: Current (A), X-axis: Voltage (volt)]

Impact of shading on I-V Characteristic curve of photovoltaic module:

Solar Pv panel is a power source having non-linear internal resistance. A major challenge inusing a PV source containing a number of cells in series is to deal with its non-linear internalresistance. The problem gets all the more complex when the array receives non-uniforminsolationand covert it into heat. This heat may damage the illuminated cells under certainconditions. To relieve the stress on shaded cells, bypass diodes are added across the module.

Battery:

Battery stores direct current electrical energy in chemical form for later use. In PV system, theenergy is used at night and during cloudy weather.

A battery charging when energy is being put in and discharging when energy is being takenout .A cycle is considered one charge-discharge sequence, when often occurs over a period ofone day in residential PV systems. The following types of batteries are commonly used in PVsystem.

1. Lead acid batteries

2. Liquid vented

3. Alkaline batteries

4. Nickel Cadmium

5. Nickel iron

The performance of storage batteries is described below. Ampere-hour capacity: The number ofamp-hours a battery can deliver is simply the number of amps of current it can discharge,multiplied by the number of hours it can deliver that current. System designers use amp-hourspecifications to determine how long the system will operate without any significant amount ofsunlight to recharge the batteries. This measure of "days of autonomy" is an important part ofdesign procedures. Theoretically, a 200 amp-hour battery should be able to deliver either 200amps for one hour, 50 amps for 4 hours, 4 amps for 50 hours, or one amp for 200 hours.

Charge and discharge rates: If the battery is charged or discharged at a different rate thanspecified, the available amp-hour capacity will increase or decrease. Generally, if the battery isdischarged at a slower rate, its capacity will probably be slightly higher. More rapid rates willgenerally reduce the available capacity. The rate of charge or discharge is defined as the totalcapacity divided by some number. For example, a discharge rate of C/20 means the battery is

being discharged at a current equal to 1/20th of its total capacity. In the case of a 400 amp-hourbattery, this would mean a discharge rate of 20 A.

Temperature: Batteries are rated for performance at 80oF. Lower temperatures reduce amphour capacity significantly. Higher temperatures result in a slightly higher capacity, but this willincrease water loss and decrease the number of cycles in the battery life.

Depth of discharge: This describes how much of the total amp hour capacity of the battery isused during a charge-recharge cycle. As an example, "shallow cycle" batteries are designed to discharge from 10% to 25% of theirtotal amp-hour capacity during each cycle. In contrast, most "deep cycle" batteries designed forphotovoltaic applications are designed to discharge up to 80% of their capacity withoutdamage. Even deep cycle batteries are affected by the depth of discharge. The deeper thedischarge, the smaller the number of charging cycles thebattery will lost.

Block Diagram :