Table of Contents

Part 1

Chapter 1

Introduction ......................................................................................................................................... 1.1 Motivation of the search .......................................................................................................................

1.2 PV History ..............................................................................................................................................

1.3 PV operation ..........................................................................................................................................

Chapter 2

PV systems and system components ..................................................................................................... 2.1 PV systems types .....................................................................................................................................

2.2 Inverter ...................................................................................................................................................

2.3 Battery.....................................................................................................................................................

2.4 Battery charger ......................................................................................................................................

Chapter 3

Protection and Troubleshooting ........................................................................................................... 3.1 Protection system ..................................................................................................................................

3.2 Troubleshooting and maintenance .........................................................................................................

Chapter 4

Load estimation and sizing .................................................................................................................. 4.1 Load estimation .....................................................................................................................................

4.2 PV design and Sizing ..............................................................................................................................

Chapter 5

Economical and technical studies ......................................................................................................... 5.1 Environmental effects .............................................................................................................................

5.2 Economic study using PV program .........................................................................................................

Part2

Chapter 6

Tracking system to obtaining the maximum power point from PV ..................................................... 6.1 Introduction ...........................................................................................................................................

6.2 Installation for PV module .....................................................................................................................

6.3 Tracking system using arduino and stepper motor.................................................................................

Photovoltaic (Solar Electric) Photovoltaic (PV) devices generate electricity directly from sunlight via an electronic process that occurs naturally in certain types of material, called semiconductors. Electrons in these materials are freed by solar energy and can be induced to travel through an electrical circuit, powering electrical devices or sending electricity to the grid.

PV devices can be used to power anything from small electronics such as calculators and road signs up to homes and large commercial businesses.

Photovoltaic (PV), the technology which converts sunlight into electricity, is one of the fastest growing sectors of the renewable energy industry. It is already well established in many countries and looks set to become one of the key technologies of

The 21st century. The market is being driven by concerns about carbon emissions, energy security and the rising price of fossil fuels.

History of Photovoltaic Technology The photovoltaic effect was observed as early as 1839 by

Alexander Edund Becquerel .it was the subject of scientific inquiry through the early

Twentieth century. In 1954 Bell Labs in U.S

Introduced the first solar PV device that produced a usable amount of electricity.

In 1958 solar cells were being used in a Varity of small scale scientific and commercial applications. the begging of using PV in homes and businesses was in 1970.but the high price made it impractical to be used in large applications. After that industry and research began to make it feasible, low price and increasing production. The end of 2011, total of 67.4GW had been installed, sufficient to generate 85 TWH/year and by the end of 2012 the 100 GW installed capacity was achieved. Solar PV is now ,after hydro and wind power the third most important renewable energy source in terms of globally installed capacity .more than 100 countries use solar photovoltaic.

Photovoltaic Operation:

Photovoltaic (PV) use some of the properties of semiconductors to directly convert light into electricity.

There are many different kinds of PV technology commercially available and under research each with their own strengths and weaknesses. Our discussion focuses on one material: silicon. This is the same material that many integrated circuits (computer chips) are made from. It is currently the workhorse of the commercial market.

We begin by looking at the physics that allows this technology to convert sunlight directly into electricity.

A discussion of efficiency follows. Efficiency for any energy production technology is a complex issue and PV is no exception.

Physics of Photovoltaic Operation: The fundamental unit of a PV panel is the cell. The main material of the cell is some kind of semi conducting material. There are cells made from gallium arsenide, crystalline silicon, amorphous silicon and others. These all are different types of semi conducting material. The discussion of the basic operation will focus on explaining the behavior of crystalline silicon cell. It is the most common type. Because of its conduction level we can get semiconductors to exhibit some behavior. We have the ability to add conductors to a semiconductor allowing us to choose not only the quantity of conductors but also the type. There are two types of conductors we can add: positive conductors and negative conductors.

The negative ones known as electrons. The positive ones are a little more conceptually difficult s they are halls, or lack of electrons.

A semiconductor with more positive conductors is called a p type and one with more negative conductors is called n- type.

Do not however get the impression that we are adding a charge to the semiconductor. We are merely increasing the number of current carriers (so charges that are free to move about) but each one is balanced out by a charge of the opposite type so the overall charge of the semiconductor remains neutral. A PV cell requires both p and n type semiconductors. Figure a show two pieces of semiconductor. The one with the plus signs is the p-type and they are distributed evenly over the material.

. Again, the plus and minus signs represent the polarity of the carriers not the overall charge of the material.

If the p and n type semiconductors are then brought together and a junction formed so that charges can flow between them an interesting thing happens as shown in Figure .

The loose positive and negative carriers are attracted to each other so some of the electrons in the n-type material migrate into the p-type material and vice-versa. The attraction of unlike charges is counterbalanced by the electric field that is created as the charge of the material is changed when it loses some of its charged particles.

This region surrounding the junction is called the depletion region and is what gives the p-n junction the ability to convert light into electricity.

It is possible to excite an electron away from the atom it is attached to by having it absorb some energy.

When light of sufficient energy hits the p-n junction an electron can be separated from its associated atom. If this electron is not re-absorbed by another atom before reaching the depletion region, it gets swept through the electric field created by the charge separation to a higher potential.

This electron can then be collected by an electrode placed on the top of the junction (N-type) and used in a circuit to do some work. This is how the p-n junction creates usable electricity.

Clearly the direction the sun comes from must have a transparent coating. The electron can be reabsorbed by the silicon before it gets to the electrode.

If this happens that energy is lost and never makes it out of the panel. To reduce the occurrence of electron reabsorbing it is desirable to have the electrodes as close together as possible. Too many electrodes will shade the panel, however, so a balancing act ensues.

The smallest unit of PV system is solar cell it produces small power, so cells are connected in series and parallel to form larger unit with higher power called (Module). Modules also connected in series and parallel to form (Array).

Solar radiation

The sun as an energy source

The sun supplies energy in the form of radiation, without which life on Earth could not exist. The energy is generated in the sun's core through the fusion of hydrogen atoms into helium. Part of the mass of the hydrogen is converted into energy. In other words, the sun is an enormous nuclear fusion reactor. Because the sun is such a long way from the Earth, only a tiny proportion (around two-millionths) of the sun's radiation reaches the Earth's surface. This works out at an amount of energy of 1 x 101 8 kWh/a.

worldwide distribution of annual solar irradiance in kWh/m2

4H+2e4He+2neutrinous+6photons

The amount of energy involved is 26Mev each time the above reaction take place.

90% of the generated by the sun comes from this fusion reaction.

Distribution of solar radiation Global Horizontal Irradiance/Irradiation (GHI)

GHI is the most important parameter for calculation of PV electricity yield. In simple language, Global Horizontal Irradiation (GHI) = Direct Horizontal Irradiation (DHI) + Diffused Horizontal Irradiation (DIF)

DHI is the irradiation component that reaches a horizontal Earth surface without any atmospheric losses due to scattering or absorption.

DIF is the irradiation component that reaches a horizontal Earth surface as a result of being scattered by air molecules, aerosol particles, cloud particles or other particles. In the absence of an atmosphere there would be no diffused horizontal irradiation.

The ratio between DHI and DIF can be variable in time and spatial context. It plays an important role when comparing various technology options.

The GHI varies throughout months of year and from somewhere to another.

Sunlight as it passes through the atmosphere.

Angle definition Angle definition is important for calculating irradiance value and the yields of solar energy system.

Solar angles used in power calculations for PV panels

The angle at which the sun hits a PV panel is the basis for understanding how to design the most efficient PV array for a specific location. This is one of the first topics presented in solar engineering textbooks.

Zenith Angle, z: This is the angle between the line that points to the sun and the vertical basically, this is just where the sun is in the sky. At sunrise and sunset this angle is 90.

Solar Altitude Angle, s: This is the angle between the line that points to the sun and the horizontal. It is the complement of the zenith angle. At sunrise and sunset this angle is 0.

Solar Azimuth Angle, s: This is the angle between the line that points to the sun and south. Angles to the east are negative. Angles to the west are positive. This angle is 0 at solar noon. It is probably close to -90 at sunrise and 90 at sunset, depending on the season. This angle is only measured in the horizontal plane; in other words, it neglects the height of the sun.

Angle of Incidence, : This is the angle between the line that points to the sun and the angle that point straight out of a PV panel (this is also called the line that is normal to the surface of the panel). This is the most important angle. Solar panels are the most efficient when pointing at the sun, so engineers want to minimize this angle at all times. To know this angle, you must know all of the angles listed and described next.

Hour Angle, : This is based on the sun's angular displacement, east or west, of the local meridian (the line the local time zone is based on). The earth rotates 15 per hour so at 11am, the hour angle is -15 and at 1pm it is 15.

Surface Azimuth Angle, : This is the angle between the line that points straight out of a PV panel and south. It is only measured in the horizontal plane. Again, east is negative and west is positive. If a panel pointed directly south, this angle would be 0.

Collector Slope, : This is the angle between the plane of the solar collector and the horizontal. If a panel is lying flat, then it is 0. As you tip it up, this angle increases. It does not matter which direction the panel faces.

Declination, : This is the angle between the line that points to the sun from the equator and the line that points straight out from the equator (at solar noon). North is positive and south is negative. This angle varies from 23.45 to -23.45 throughout the year, which is related to why we have seasons.

Latitude, : This is the angle between a line that points from the center of the Earth to a location on the Earth's surface and a line that points from the center of the Earth to the equator.

Electrical properties of solar cells

A solar cell looks like a large scale diode .the characteristic curve of a silicon diode is shown below. if a positive potential is present at the anode and negative potential is present at the cathode, the diode is connected in forward biased direction. The characteristic curve in the first quadrant applies Starting from a particular voltage (the threshold voltage here is 0.7V), current flows. If the diode is connected in reverse-biased direction, current flow is prevented in this direction. The characteristic curve in the third quadrant applies. Only starting from a high breakdown voltage (here, 150V) does the diode become conductive? This can also lead to the destruction of the diode.

Current voltage curve for silicon diode

An un-illuminated solar cell is described in the equivalent circuit diagram by a diode. Accordingly, the characteristic curve of a diode is also applicable. For a mono crystalline solar cell, one can assume a forward voltage of approximately 0.5V and a breakdown voltage of 12V to 50V (depending upon the quality and cell material).

Dark equivalent circuit diagram and characteristic curve

V =VD

I =-ID

Illuminated equivalent circuit diagram and characteristic curve

V=VD

I=IPh -ID

When light hits the solar cell, the energy of the photons generates free charge carriers. An illuminated solar cell constitutes a parallel circuit of a power source and a diode. The power source produces the photoelectric current (photocurrent) I p h. The level of this current depends upon the irradiance. The diode characteristic curve is shifted by the magnitude of the photocurrent in the reverse-biased direction (into the fourth quadrant).

Extended equivalent circuit diagram

This extended equivalent circuit diagram is termed a single-diode model of a solar cell and is used as a standard model in photovoltaic. In the solar cell, a voltage drop occurs as the charge carriers migrate from the semiconductor to the electrical contacts. This is described by the series resistor Rs, which is in the range of a few milliohms. In addition, what are known as leakage currents arise, which are described by the parallel resistor. Both resistors bring about a flattening of the solar cell characteristic curve. With the series resistor, it is possible to calculate current/voltage characteristic curves of solar cells at different irradiances and temperatures.

Equivalent circuit models of solar cell

Solar cell character I-V Curves

If light falls on an unloaded solar cell, a voltage of approx. 0.6V builds up. This can be measured as the open-circuit voltage Voc at the two contacts. If the two contacts are short circuited via an ammeter, the short-circuit current ISC can be calculated. In order to record a complete solar cell characteristic I-V curve, one requires a variable resistor (shunt), a voltmeter and an ammeter

Current/voltage characteristic curve (l-V curve) for crystalline silicon

Solar cell

FF=Vmpp*Impp/Voc*Isc

Where:

Mpp: maximum power point. The maximum power point (MPP) value is the point on the I-V curve at which the solar cell works with maximum power. Impp: current at maximum power point

Vmpp: voltage at maximum power point

Voc: open circuit voltage with crystalline cells, approximately 0.5V to 0.6V, and for amorphous cells is approximately 0.6V to 0.9V.

Isc: short circuit current is approximately 5 per cent to 15 per cent higher than the MPP current. With crystalline standard cells (10cm x 10cm) under STC,

FF: fill factor it measures the quality of PV cell. If FF=1 this means the best quality of PV cell.

Standard test conditions (STC) Uniform conditions are specified for determining the electrical data with which the solar cell characteristic I-V curve is then calculated. 1 vertical irradiance E of 1000 W/m2; 2 cell temperature T of 25C with a tolerance of 2C; 3 defined light spectrum (spectral distribution of the solar reference irradiance

Irradiance dependence and temperature characteristics: The electrical output and the I-V curves of PV modules depend upon (Temperatures & irradiance). 1) Effect of irradiance: >> During the course of a day the irradiance varies more than the temperature. >> The changes in irradiance affect the module current since the current is directly dependent upon the irradiance. Note: -When irradiance drops by half, the electricity generated also reduces by half.

(I-V) curves for varying irradiance and constant temperature.

- By contrast, the MPP voltage stays approx. constant with changing irradiance. 2) Effect of temperature: >> The voltage is most affected by the temperature. -Where the voltage is inversely proportional to temperature. In summer: Temp is high .. so there is (-10 volts). In winter: Temp is low so there is (+10 volts). - By contrast, the current increases slightly with increasing temperature.

(I-V) curves at different module temperatures and with constant

irradiance of 1000W/m2. Problem: >> During summer, the 0/p power of a module at high temperatures can be 35 % less than under STC. As shown in Figure (***). Solution: >> In order to minimize this power loss, the PV modules should be able to dissipate heat easily (sufficient ventilation)

Different module temperatures with constant irradiance

Effect of ventilation of the cells:

(Hot spots), (bypass diodes) and (shading): - Hot spot: it is a spot on the solar cell which is hot when there is a shadow. >> This can happen, for instance, when relatively high reverse current flows through the unlit solar cell) shading cell). 1) Hot spot reduces the power of the solar cell. 2) The probability of cell failure. 3) And hence, the probability of module failure. Bypass diodes: First standard module with 36 cells is irradiated by the sun. The current generated in the solar cells is used by a load (resistance R). As fig

If a leaf falls on the solar module so that a solar cell (C36 in Figure) is darkened, this solar cell becomes an (electricity load). - No more current is generated in this cell. - It uses the current from the other cells so the direction of the voltage is reversed in the shaded cell.

- This current flow is then converted into heat. If there is a large enough current, this can lead to the hot spot effect already mentioned. To prevent a hot spot from developing, the current is diverted past the solar cells via bypass diodes. See following fig:

Number of bypass diodes: - One diode for each (18 to 20 cells). - Modules with (36 to 40) cells have two bypass diodes. - Modules with (72) solar cells have four bypass diodes.

Solar cell types

Crystalline silicon cells 1. Polycrystalline silicon or multicrystalline silicon.

2. Mono crystalline.

3. Mono-like-multi silicon.

4. Ribbon silicon.

Thin films 1. Cadmium telluride solar cell.

2. Copper indium gallium selenide.

3. Gallium arsenide multijunction.

4. Light-absorbing dyes (DSSCQuantum Dot Solar Cells (QDSCs).

5. Organic/polymer solar cells.

6. Silicon thin films Indium Gallium Nitride.

Hybrid solar cell The most common solar cell and higher sails is poly crystalline.

Maximum efficiencies in photovoltaic

Solar cell material Cell efficiency (laboratory) (%)

Cell efficiency (production) (%)

Module efficiency (series production) (%)

Monocrystalline silicon 24.7 21.5 16.9

Polycrystalline silicon 20.3 16.5 14.2

Ribbon silicon 19.7 14 13.1

Crystalline thin- film silicon 19.2 9.5 7.9

Amorphous silicon 13.0 10.5 7.5

Micromorphous silicon 12.0 10.7 9.1

CIS 19.5 14.0 11.0

Cadmium telluride 16.5 10.0 9.0

lll - V semi conductor 3 9. 0 27.4 27.0

Dye-sensitized call 12.0 7.0 5.0

Hybrid HIT solar cell 21 18.5 16.8

The cell we use is Polycrystalline silicon.

What is crystalline silicon?? The most important material in crystalline solar cells is silicon. After oxygen, this is the second

most abundant element on Earth and, hence, is available in almost unlimited quantities. It is present not in a pure form, but in chemical compounds, with oxygen in the form of quartz or sand. The undesired oxygen has to be first separated out of the silicon dioxide. To do this, quartz sand is heated together with carbon powder, coke and charcoal in an electric arc furnace to a temperature of 1800C to 1900C.This produces carbon monoxide and what is known as metallurgical silicon, which is about 98 per cent pure. But 2 per cent impurity in silicon is still much too high for electronics applications. Only billionths of a per cent are acceptable for photovoltaic, which falls to ten times less for the semiconductor industry (electronic grade silicon).

Because the purity requirements for silicon used in manufacturing solar cells aren't as high as for electronic grade silicon, the solar industry primarily uses waste products from the semiconductor industry. Since 1998, however, there has not been enough silicon waste to cover the rapid growth in demand. The shortfall has mostly been made up using ultra-pure silicon, but which, in some cases, is of a slightly lower quality. Over the same period, processes have been developed that now make it possible to produce silicon with the quality required for solar cells (solar grade silicon and solar silicon), but involving less cost, time and energy expenditure.

Efficiency of solar cells and PV modules

The efficiency of solar cells is the result of the relationship between the power delivered by the solar cell and the power irradiated by the sun. Hence, it is calculated from the MPP the solar irradiance E and the area A of the solar cell as follows

In PV modules, the module surface area is used for A. On the data sheets, the efficiency is always specified under standard test conditions (STC):

This yields the nominal efficiency of solar cells and modules:

The efficiency of solar cells depends upon irradiance and temperature. The efficiency at a particular irradiance or temperature is the result of the nominal efficiency minus the change in efficiency.

With the radiation factor s, the change in efficiency with irradiances deviating from STC can be calculated

For example, s = 0.5 means the radiation factor is at half STC irradiance and, hence, irradiance is at 500W/m2 .The approximate change in efficiency with crystalline silicon cells results with constant temperature as follows:

The efficiency also depends on temperature as follow.

:

PV Systems

There are two types of PV systems:

1. Stand alone system 2. Grid connected system

Stand-alone PV systems are systems that are not connected to the public electricity grid. They are generally much smaller than grid-connected systems, and because they are very often in rural areas, the PV modules are frequently ground mounted as space is usually not a problem. The three main categories are:

systems providing DC power only; systems providing AC power through an inverter; Hybrid systems: diesel, wind or hydro.

Stand-alone photovoltaically powered systems with peak PV powers can have from mill watts to several kilowatts. They do not have a connection to an electricity grid. In order to ensure the supply of the stand-alone system with electric power also in the times without radiation (at night) or with very low radiation (at times with a strong cloud cover), stand-alone systems mostly have an integrated storage system (battery system). If the systems are used only during the time when the radiation is sufficient to supply the system with electric power directly, a storage system is not necessary.

At present, a very great variety of stand-alone system exists. Example range from solar calculators and watches to systems for traffic control systems those are able to supply one or several buildings in remote areas with electric power. They can be dc systems with or without storage battery they can be ac systems with an inverter.

Grid connected PV system is the most popular solar electric system on the market today. Grid-connected systems are so named because they are connected directly to the electrical grid. A grid-connected system consists of five main components: PV array An inverter The main service panel or breaker box safety disconnects Meters.

To understand how a battery-less grid-connected system works, lets begin with the PV array. The PV array produces DC electricity. It flows through wires to the inverter, which converts the DC electricity to AC electricity. The inverter doesnt just convert the DC electricity to AC; it converts it to grid-compatible AC that is, 60 cycles per second, 120-volt (or 240-volt) electricity. Because the inverter produces electricity in sync with the grid, inverters in these systems are often referred to as synchronous inverters. The 120-volt or 240-volt AC produced by the inverter flows to the main service panel, aka the breaker box. From there, it flows to active loads (electrical devices that are operating). If the PV system is producing more electricity than is needed to meet these demands which is often the case on sunny days the excess automatically flows on to the grid. After the electricity is fed to the grid, the utility treats it as if it were its own. End users pay the utility directly for the electricity you generate (thats only occurs at smart Grid).

Solar Inverter Inverter is one of the most important components in grid connected

system. Inverter is semiconductor device which used to convert DC (direct

current) electricity into AC (alternating current) electricity. Some modern

inverters make process of conversion with small losses. Sometimes we

dont need battery bank in grid connected system as Electricity Company

act as battery .But many people preferred to use battery bank to act as

back up when grid is failure. When PV feed dc load, it become more

efficient as in this case dont need to use inverter

Inverter Ratings: 1- Continuous Rating :

This is the amount of power you could expect to use continuously without the inverter overheating and

shutting down.

2-Half Hour Rating:

This is handy as the continuous rating may be too low to run a high energy consumption power tool or

appliance, however if the appliance was only to be used occasionally then the half hour rating may well

suffice.

3- Surge Rating:

A high surge is required to start some appliances and once running they may need considerably less

power to keep functioning. The inverter must be able to hold its surge rating for at least 5 seconds.

4- IP Rating :

Define the ability of inverter to be used to prevent water and dust ingress

5- Peak Efficiency:

Represent high efficiency inverter can achieve.

Types of Solar Inverter 1) standalone inverter:

Used in isolated system and do not need an anti-islanding system.

2) battery backup inverter:

Special type of inverter which required an anti-islanding protection

3) grid tie inverter:

Is the most common type used in grid connected solar system. It takes the direct current voltage from

battery or pv array and convert it to ac voltage to be used in homes and business. The output of grid tie

inverter must be in phase with Grid to have the ability of selling the remaining energy back to Grid and

reduce consumer bill. This process called net metering which.

Grid Controlled Inverter:

The basic assembly of a grid-controlled inverter is a bridge circuit with thyristors inlarger PV systems,

thyristor inverters are also used, as well as the predominantinsulated gate bipolar transistor (IGBT)

inverters.For the single-phase inverters with lower powers (< 5kWp), there are now only afew

manufacturers who still build inverters on this principle.

Self commuted inverter

can be turned on and off are used in the In self-commutated inverters, Principle of grid controlled

inverter semiconductor elements that bridge circuit. Depending upon the system performance and

voltage level, the following semiconductor elements are used:

Metal-oxide semiconductor power field effect transistors (MOSFETs);

Bipolar transistors;

8 gate turn-off thyristors (GTOs) (up to 1 kHz);

insulated gate bipolar transistors (IGBTs).

These power-switching devices, using the principle of pulse width modulation, enabla good reproduction

of the sinusoidal wave.

Principle of self-commutated inverters

Grid Tied Inverter:

Grid connected inverter also known as grid tied inverter or synchronous inverter.These types of inverters

can not used in standalone system.In grid-connected PV systems, the inverter is linked to the mains

electricity griddirectly or via the building's grid. With a direct connection, the generated electricity isfed

only into the mains grid. With a coupling to the building's grid, the generated solar is first consumed in

the building, then any surplus is fed to the mains electricity grid.

Principle operation of grid tied inverter

In order to feed the maximum power into the electricity grid, the inverter must workin the MPP of the

PV array. The MPP of the PV array changes according to Climatic conditions. In the inverter, an MPP

tracker ensures that the inverter is adjusted to the MPP point. Since the modules' voltage and current

vary considerably depending upon the weather conditions, the inverter needs to move its working

pointing order to function optimally. To do this, an electronic circuit is used that adjusts the Voltage so

that the inverter runs at the point at which the PV array achieves its maximum power (MPP).

Modern grid-connected inverters are able to perform the following functions:

Conversion of the direct current generated by the PV modules into mains-standardalternating current;

Adjustment of the inverter's operating point to the MPP of the PV modules (MPP tracking)Pv system up

to5kwp or size of 50 m^2 we use single phase inverter and with large system the feed is three phase

inverter.

Principle of connecting PV systems to the grid with a single-phase and three-phase inverter

Grid Connected Inverter Types and Construction Size in Various power Class: Grid connected inverter classified into three groups:

1-centeral inverter 2-string inverter 3-module inverter

Central inverter with low output power range (single phase)

Type: Top Class III - TCG 2500/6.

Manufacturer: ASP.

Concept: self-commutated inverters with LF transformer.

DC nominal power: 2.5kW.

MPP voltage: 82V to 120V.

Size: 456mm x 320mm x 211mm.

Weight: 22kg.

Central inverter with high output power range (three phase):

Type: invert solar 100

Manufacture: Siemens AG

Concept: self commuted inverter with LF transformer

MPP voltage: 460v to 750v

Size: 13.725*950*850 mm^3

Weight: 750kg

String inverter:

Type: Sunny Boy 2100TL.

Manufacturer: SMA Technology AG.

Concept: transformer less, self-commutated inverter.

DC nominal power: 2kW.

MPP voltage: 125V to 600V.

Size: 295mm x 434mm x 214mm.

Weight: 25kg.

Module inverter:

Type: DMI 150/35.

Manufacturer: Dorfmiiller Solar anlagen GmbH.

Concept: self-commutated inverter with LF transformer. DC nominal power: 120W.

MPP voltage: 28V to 50V.

Size: 80mm x 200mm x 100m^3

Weight: 2.8kg.

Characteristics and Properties of Grid Tied Inverter:

Conversion efficiency (N, C 0 N)

The conversion efficiency describes the losses that arise when converting direct current into alternating

current. In inverters, these comprise the losses caused by the transformer (in devices that have

transformer), the power switching devices and by own consumption for management, control, recording

operating data, etc.

N, con=Pac (input real power)/Pdc (input real power)

Tracking efficiency :( R | T R).

A state-of-the-art grid-connected inverter in a grid-connected PV system has to ensure optimum

adaptation to the characteristic curve of the PV array connected to it (I-V curve). During the day, the

operating parameters in the PV array are constantly changing. The differing irradiance and temperature

conditions change the PV array's maximum power point (MPP). In order to always transform the

maximum solar power into alternating current, the inverter must automatically set and track the

optimum operating point (MPP tracking). The quality of this inverter adjustment to the optimum

operating point is described by the tracking efficiency:

R | T R=Pdc (instantaneous input real power)/Ppv (maximum instantaneous pv array power).

Instantaneous values (red line) of insulation compared to hourly values (blue line) on a cloudless day (left) and on a cloudy day

Static efficiency:

Static efficiency is formed as the product of conversion

and tracking efficiency. Generally, only the conversion

efficiency that is achieved during operation in the

inverter's nominal range (Vnand In) is stated as the

nominal efficiency on the data sheets. In addition, the

maximum efficiency is also often stated, which usually

lies in the partial load range of 80 per cent to 50 per cent of the nominal power.

Characteristic curves for various inverter types (according to manufacturers' specifications)

Inverter installation site: When choosing the installation site, it is required that the environmental conditions specified by the manufacturer are maintained

(essentially humidity and temperature).The ideal installation site for inverters is cool, dry, dust free and indoors. It makes sense to install

inverters next to the meter cupboard or close by. If the environmental conditions permit, the inverter can be installed close to the PV array

combiner/junction box. This reduces the length of the DC main cable and lowers the installation costs. The ventilation grilles and heat

dissipaters need to be kept uncovered to ensure optimum cooling. For the same reason, the devices should not be installed right on top of

each other if this can be avoided. The noise produced by the inverter should also be taken into account when choosing the installation site.

The units should be protected from aggressive vapors, water vapor and fine particles.

Criteria for Inverter Selection: Checklist when considering selecting a Solar PV Inverter

AC Voltage:

AC operating voltages as well as single or three-phase systems;

120/240- single phase is used in residential applications. Inverters would connect to 240VAC in this application.

240- three-phase is used for power loads in commercial and industrial buildings. This is a delta configuration. Across any one (of 3

transformers) theres 240V. On one side (only) of the delta there is a center-tapped transformer which is connected to neutral.

Thus providing 2x 120VAC for outlets.

208Y/120-V three-phase four wire distribution is commonly used in commercial buildings with limited electrical loads. 120V is

available between a pole and ground, while 208V is available between any two poles.

480- Three phase delta is commonly used in commercial and industrial buildings with substantial motor loads.

480Y/277- is used to supply commercial and industrial buildings. Between any two poles theres 480V, and between any pole and

neutral theres 277V. The 277V is used for ballasted lighting. Local step-down transformers are typically inserted to provide

208Y/120-V power for lighting, appliances and outlets.

DC Voltage:

The Maximum Power Point Transfer (MPPT or MPP) voltage range. a solar PV string should be

sized such that the inverter can normally operate within this range.

Maximum DC voltage; a solar PV string with no load (Vo) must under no circumstance ever

exceed an inverters maximum DV voltage. When considering this factor, one must assume the

lowest possible solar PV panel temperature while exposed to bright sunlight

Minimum DC voltage; for tracking systems:

. During cloud cover, a solar

PV strings DC voltage can drop to a very low level, so inverter will stop production and

shutdown.

We can select grid tied inverter according to the following table: When select grid tie inverter we should take in our mind some consideration such as: how much power generated, sizing of building, energy

use changes over the time and type of solar panel Inverter can be selected according to the following table:

SYSTEM SIZE NO. PANELS INVERTER ROOF AREA AVG DAILY

OUTPUT ANNUAL OUTPUT

1.0kW 6 1700WR 7.8m 4.7kWh 1715kWh

1.5kW 9 1700WR 11.7m 7.0kWh 2555kWh

2.1kW 12 2300WR 14.3m 9.3kWh 3487kWh

2.6kW 15 3300WR 19.5m 11.7kWh 4270kWh

3.1kW 18 3300WR 23.4m 14.3kWh 5219kWh

3.5kW 20 4600WR 27.3m 15.6kWh 5694kWh

4.2kW 24 4600WR 31.2m 18.7kWh 6825kWh

Inverter efficiency: Inverter efficiency can be defined as how much output power from inverter as percentage of power

input to the inverter. Inverter efficiency is depending on power as there is direct relation between power

and efficiency. As the power increase inverter efficiency will increase. Inverter uses power from battery

even we are not drawing AC current from it which reduce efficiency of inverter. Some inverters have the

facility called sleep mode which improve overall efficiency of inverter. So sensor is required with inverter

to sense if AC power is required or not. If not power used it will shut down the inverter so inverter dont

draw power from battery and increase efficiency. Which means that the appliances can not be put in

stand-by mode .Another factor may be affects on inverter efficiency is waveform and inductive load. In

case of non pure sine wave will be less efficient when powering an inductive load. The most common

disadvantages of inverter are harmonic problems.

How to solve harmonic problem? A large portion of the losses are caused by the return of current between the output inductor and the

input capacitor. If we decouple the capacitor and the inductors then it is impossible for a return current

to flow and electro-magnetic disturbances cannot occur at the input as a result of voltage spikes.

Inverter failure: Solar inverters may fail due to transients from the grid or the PV panel, component aging and operation beyond the designed limits.

Causes of failure:

capacitor failure:

Voltage stress

Continuous operation under maximum voltage

Current stress

Mechanical stress

Vibration

2-inverter bridge failure:

Over voltages and over currents

Thermal shock

Thermal overload

Extremely cold operating temperature

Other malfunction components

3-electro mechanical wear:

Extreme temperature conditions

Component stress

Contamination at contact

What can market provide for you? Market can provide two types of inverter:

Low Cost:

These inverters are available from electrical stores, hardware stores and electronic suppliers are

commonly available.. These inverters usually lack devices such as auto-start or any form of

adjustability.

Performance may or may not be as stated (or even not properly stated at all). However they are not all

bad. Consider one if your needs are modest and your budget is limited. Usually they present no

problems for TV and video, computers and smaller appliances. High output models can be good "power

tool" inverters. We don't sell them.

High Quality:

There is no substitute for quality. You will find only a small handful of companies worldwide who

make high quality power inverters.

Battery selecting and voltage regulation In Stand-alone PV system In stand-alone photovoltaic systems, the electrical energy produced by the PV array cannot always be used when it is produced. Because the demand for energy does not always coincide with its production, electrical storage batteries are commonly used in PV systems. The primary functions of a storage battery in a PV system are to:

1. Energy Storage Capacity and Autonomy: to store electrical energy when it is produced by the PV array and to supply energy to electrical loads as needed or on demand.

2. Voltage and Current Stabilization: to supply power to electrical loads at stable voltages and currents, by suppressing or 'smoothing out' transients that may occur in PV systems.

3. Supply Surge Currents: to supply surge or high peak operating currents to electrical loads or appliances.

The battery's capacity for holding energy is rated in amp-hours: 1 amp delivered for 1 hour = 1-amp hour

Battery capacity is listed in amp hours at a given voltage, e.g. 220 amp-hours at 6 volts. Manufacturer's typically rate storage batteries at a 20-hour rate:

220 amp-hour batteries will deliver 11 amps for 20 hrs

This rating is designed only as a means to compare different batteries to the same standard and is not to be taken as a performance guarantee. Batteries are electrochemical devices sensitive to climate, charge/discharge cycle history, temperature, and age. The performance of your battery depends on climate, location and usage patterns. For every 1.0 amp-hour you remove from your battery, you will need to pump about 1.25 amp-hours back in to return the battery to the same charge state of charge. This figure also varies with temperature, battery type and age.

Wattage, Volts, Amps, etc Electrical appliances in the United States are rated with wattage, a measure of energy consumption per unit of time. One watt delivered for one hour equals one watt-hour. Wattage is the product of current (amps) multiplied by voltage.

Watt = amps x volt

One amp delivered at 120 volts is the same amount of wattage as 10 amps delivered 12 volts:

1 amp at 120 volts = 10 amps at 12 volts

Wattage is independent of voltage:

1 watt at 120 volts = 1 watt at 12 volts

To convert a battery's amp-hour capacity to watt-hours, multiply the amp-hours times the voltage. The product is watt-hours. To figure out how much battery capacity it will require to run an appliance for a given time, multiply the appliance wattage times the number of hours it will run to yield the total watt-hours. Then divide by the battery voltage to get the amp hours.

For example, running a 60-watt light bulb for one hour uses 60 watt-hours. If a 12-volt battery is running the light it will consume 5 amp-hours (60 watt hours divided by 12 volts equals 5 amp-hours)

How big a battery do I need for a PV System?

Ideally, a battery bank should be sized to be able to store power for 5 days of autonomy during cloudy weather. If the battery bank is smaller than 3 day capacity, it is going to cycle deeply on a regular basis and the battery will have a shorter life. System size, individual needs and expectations will determine the best battery size for your system.

Where:-

Wel: power from PV

Autonomy Days: Number of days of non-sunshine often 2 days b: is the battery efficiency often (80%)

DOD: depth of discharge (80%)

SYSTEM Voltage: (12 or 24 volt)

In our case 50 watt PV module and system voltage is 12 volt after regulation assume Autonomy Days is only one day max DOD is 70%

so we need

(50/12)*2/(.8*.7) 15 AH battery

Wide variations exist in charge controller designs and operational characteristics. Currently no standards, guidelines, or sizing practices exist for battery and charge controller interfacing.

Battery Cycles Batteries are rated according to their "cycles". Batteries can have shallow cycles between 10% to 15% of the battery's total capacity, or deep cycles up to 50% to 80%. Shallow-cycle batteries, as those for starting a car, are designed to deliver several hundred amperes for a few seconds, then the alternator takes over and the battery is quickly recharged. Deep-cycle batteries or the other hand, deliver a few amperes for hundreds of hours between charges. These two types are designed for different applications and should not be interchanged.

AhDODMax

DaysAutonomy Voltage System

W

zeBattery siB

el

.*

*

Battery classifications Primary Batteries Primary batteries can store and deliver electrical energy, but cannot be recharged. Typical carbon-zinc and lithium batteries commonly used in consumer electronic devices are primary batteries. Primary batteries are not used in PV systems because they cannot be recharged Secondary Batteries A secondary battery can store and deliver electrical energy, and can also be recharged by passing a current through it in an opposite direction to the discharge current. Common lead-acid batteries used in automobiles and PV systems are secondary batteries.

Batteries used in PV systems

Lead Acid Batteries

Nickel Cadmium Batteries

Lead-Acid Batteries - How they work The lead-acid battery cell consists of positive and negative lead plates of different composition suspended in a sulfuric acid solution called electrolyte. When cells discharge, sulfur molecules from the electrolyte bond with the lead plates and releases electrons. When the cell recharges, excess electrons go back to the electrolyte. A battery develops voltage from this chemical reaction. Electricity is the flow of electrons. In a typical lead-acid battery, the voltage is approximately 2 volts per cell regardless of cell size. Electricity flows from the battery as soon as there is a circuit between the positive and negative terminals. This happens when any load (appliance) that needs electricity is connected to the battery.

Good care and caution should be used at all times when handling a battery. Improper battery use can result in explosion. Read all documentation included with your battery in its entirety.

At the positive plate or electrode:

Pbo2 +4H

++2e- pb2++2H2o Pb2++so4

-2v pbso4 At the negative plate or electrode: Pb pb2++2e-

Pb2++so4

2- pbso4 Overall lead acid cell reaction:

Nickel-Cadmium Battery Chemistry At the positive plate or electrode:

At the negative plate or electrode:

Overall nickel cadmium cell reaction

The nominal voltage for a nickel-cadmium cell is 1.2 volts, compared to about 2.1 volts for a lead-acid cell, requiring 10 nickel-cadmium cells to be configured in series for a nominal 12 volt battery. The voltage of a nickel-cadmium cell remains relatively stable until the cell is almost completely discharged. Nickel-cadmium batteries can accept charge rates as high as C/1, and are tolerant of continuous overcharge up to a C/15 rate. Nickel-cadmium batteries are commonly subdivided into two primary types; sintered plate and pocket plate. Where c is the charge rate Charge rate is often denoted as C or C-rate and signifies a charge or discharge rate equal to the capacity of a battery in one hour.[1] For a 1.6Ah battery, C = 1.6A. A charge rate of C/2 = 0.8A would need two hours, and a charge rate of 2C = 3.2A would need 30 minutes to fully charge the battery from an empty state, if supported by the battery. This also assumes that the battery is 100% efficient at absorbing the

charge.

Comparison between different PV batteries types

BATTERY CHARGE CONTROLLERS IN PV SYSTEMS

The primary function of a charge controller in a stand-alone PV system is to maintain the battery at highest possible state of charge while protecting it from overcharge by the array and from over-discharge by the loads.

Although some PV systems can be effectively designed without the use of charge control, any system that has unpredictable loads, user intervention, optimized or undersized battery storage (to minimize initial cost) typically requires a battery charge controller.

The algorithm or control strategy of a battery charge controller determines the effectiveness of battery charging and PV array utilization, and ultimately the ability of the system to meet the load demands. Additional features such as temperature compensation, alarms, meters, remote voltage sense leads and special algorithms can enhance the ability of a charge controller to maintain the health and extend the lifetime of a battery.

Important functions of battery charge controllers and system controls are:

Prevent Battery Overcharge: to limit the energy supplied to the battery by the PV array when the battery becomes fully charged.

Prevent Battery Over-discharge: to disconnect the battery from electrical loads when the battery reaches low state of charge.

Provide Load Control Functions: to automatically connect and disconnect an electrical load at a specified time, for example operating a lighting load from sunset to sunrise.

Overcharge Protection A remote stand-alone photovoltaic system with battery storage is designed so that it will meet the system electrical load requirements under reasonably determined worst-case conditions, usually for the month of the year with the lowest insolation to load ratio.

When the array is operating under good-to-excellent weather conditions (typically during summer), energy generated by the array often exceeds the electrical load demand. To prevent battery damage resulting from overcharge, a charge controller is used to protect the battery.

A charge controller should prevent overcharge of a battery regardless of the system sizing/design and seasonal changes in the load profile, operating temperatures and solar insolation.

Charge regulation is the primary function of a battery charge controller, and perhaps the single most important issue related to battery performance and life.

The purpose of a charge controller is to supply power to the battery in a manner which fully recharges the battery without overcharging.

Without charge control, the current from the array will flow into a battery proportional to the irradiance, whether the battery needs charging or not.

If the battery is fully charged, unregulated charging will cause the battery voltage to reach exceedingly high levels, causing severe gassing, electrolyte loss, internal heating and accelerated grid corrosion.

In most cases if a battery is not protected from overcharge in PV system, premature failure of the battery and loss of load are likely to occur.

Charge controllers prevent excessive battery overcharge by interrupting or limiting the current flow from the array to the battery when the battery becomes fully charged.

Charge regulation is most often accomplished by limiting the battery voltage to a maximum value, often referred to as the voltage regulation (VR) set point. Sometimes, other methods such as integrating the ampere-hours into and out of the battery are used.

Depending on the regulation method, the current may be limited while maintaining the regulation voltage, or remain disconnected until the battery voltage drops to the array reconnect voltage (ARV) set point.

Over-discharge Protection During periods of below average insolation and/or during periods of excessive electrical load usage, the energy produced by the PV array may not be sufficient enough to keep the battery fully recharged.

When a battery is deeply discharged, the reaction in the battery occurs close to the grids, and weakens the bond between the active materials and the grids.

When a battery is excessively discharged repeatedly, loss of capacity and life will eventually occur. To protect batteries from over-discharge, most charge controllers include an optional feature to disconnect the system loads once the battery reaches a low voltage or low state of charge condition.

In some cases, the electrical loads in a PV system must have sufficiently high enough voltage to operate. If batteries are too deeply discharged, the voltage falls below the operating range of the loads, and the loads may operate improperly or not at all. This is another important reason to limit battery over- discharge in PV systems.

Over-discharge protection in charge controllers is usually accomplished by open-circuiting the connection between the battery and electrical load when the battery reaches a pre-set or adjustable low voltage load disconnect (LVD) set point. Most charge controllers also have an indicator light or audible alarm to alert the system user/operator to the load disconnects condition. Once the battery is recharged to a certain level, the loads are again reconnected to a battery.

Non-critical systems loads are generally always protected from over-discharging the battery by connection to the low voltage load disconnect circuitry of the charge controller.

If the battery voltage falls to a low but safe level, a relay can open and disconnect the load, preventing further battery discharge.

Critical loads can be connected directly to the battery, so that they are not automatically disconnected by the charge controller. However, the danger exists that these critical loads might over-discharge the battery.

An alarm or other method of user feedback should be included to give information on the battery status if critical loads are connected directly to the battery.

Charge Controller Set Points

The battery voltage levels at which a charge controller performs control or switching functions are called the controller set points.

Four basic control set points are defined for most charge controllers that have battery overcharge and over-discharge protection features.

The voltage regulation (VR) and the array reconnect voltage (ARV) refer to the voltage set points at which the array is connected and disconnected from the battery.

The low voltage loads disconnect (LVD) and load reconnect voltage (LRV) refers to the voltage set points at which the load is disconnected from the battery to prevent over-discharge.

Figure 11 shows the basic controller set points on a simplified diagram plotting battery voltage versus time for a charge and discharge cycle. A detailed discussion of each charge controller set point follows.

Voltage Regulation (VR) Set Point The voltage regulation (VR) set point is one of the key specifications for charge controllers.

The voltage regulation set point:

Is defined as the maximum voltage that the charge controller allows the battery to reach, limiting the overcharge of the battery.

Once the controller senses that the battery reaches the voltage regulation set point, the controller will either discontinue battery charging or begin to regulate (limit) the amount of current delivered to the battery.

Proper selection of the voltage regulation set point may depend on many factors, including:

1. The specific battery chemistry and design.

2. Sizes of the load and array with respect to the battery.

3. Operating temperatures.

4. Electrolyte loss considerations.

An important point to note about the voltage regulation set point is that the values required for optimal battery performance in stand-alone PV systems are generally much higher than the regulation or 'float voltages' recommended by battery manufacturers.

This is because in a PV system, the battery must be recharged within a limited time period (during sunlight hours), while battery manufacturers generally allow for much longer recharge times when determining their optimal regulation voltage limits. By using a higher regulation voltage in PV systems, the battery can be recharged in a shorter time period, however some degree over overcharge and gassing will occur. The designer is faced selecting the optimal voltage regulation set point that maintains the highest possible battery state of charge without causing significant overcharge.

Array Reconnect Voltage (ARV) Set Point In interrupting (on-off) type controllers, once the array current is disconnected at the voltage regulation set point, the battery voltage will begin to decrease.

The rate at which the battery voltage decreases depends on many factors, including the charge rate prior to disconnect, and the discharge rate dictated by the electrical load.

If the charge and discharge rates are high, the battery voltage will decrease at a greater rate than if these rates are lower.

When the battery voltage decreases to a predefined voltage, the array is again reconnected to the battery to resume charging. This voltage at which the array is reconnected is defined as the array reconnects voltage (ARV) set point.

If the array were to remain disconnected for the rest of day after the regulation voltage was initially reached, the battery would not be fully recharged. By allowing the array to reconnect after the battery voltage reduces to a set value, the array current will 'cycle' into the battery in an on-off manner, disconnecting at the regulation voltage set point, and reconnecting at the array reconnect voltage set point. In this way, the battery will be brought up to a higher state of charge by 'pulsing' the array current into the battery.

Voltage Regulation Hysteresis (VRH) The voltage span or difference between the voltage regulation set point and the array reconnect voltage is often called the voltage regulation hysteresis (VRH). The VRH is a major factor which determines the effectiveness of battery recharging for interrupting (on-off) type controllers. If the hysteresis is too great, the array current remains disconnected for long periods, effectively lowering the array energy utilization and making it very difficult to fully recharge the battery.

If the regulation hysteresis is too small, the array will cycle on and off rapidly, perhaps damaging controllers which use electro-mechanical switching elements.

The designer must carefully determine the hysteresis values based on the system charge and discharge rates and the charging requirements of the particular battery.

Most interrupting (on-off) type controllers have hysteresis values between 0.4 and 1.4 volts for nominal 12 volt systems. For example, for a controller with a voltage regulation set point of 14.5 volts and a regulation hysteresis of 1.0 volt, the array reconnect voltage would be 13.5 volts. In general, a smaller regulation hysteresis is required for PV systems that do not have a daytime load.

Low Voltage Load Disconnect (LVD) Set Point Over-discharging the battery can make it susceptible to freezing and shorten it's operating life. If battery voltage drops too low, due to prolonged bad weather for example, certain non-essential loads can be disconnected from the battery to prevent further discharge.

This can be done using a low voltage load disconnect (LVD) device connected between the battery and non-essential loads.

In controllers or controls incorporating a load disconnect feature, the low voltage load disconnect (LVD) set point is the voltage at which the load is disconnected from the battery to prevent over-discharge. The LVD set point defines the actual allowable maximum depth-of-discharge and available capacity of the battery operating in a PV system.

The available capacity must be carefully estimated in the PV system design and sizing process using the actual depth of discharge dictated by the LVD set point.

In more sophisticated deigns, a hierarchy of load importance can be established, and the more critical loads can be shed at progressively lower battery voltages. Very critical loads can remain connected directly to the battery so their operation is not interrupted.

The proper LVD set point will maintain a healthy battery while providing the maximum battery capacity and load availability. To determine the proper load disconnect voltage, the designer must consider the rate at which the battery is discharged.

Because the battery voltage is affected by the rate of discharge, a lower load disconnect voltage set point is needed for high discharge rates to achieve the same depth of discharge limit. In general, the low discharge rates in most small stand-alone PV systems do not have a significant effect on the battery voltage.

Typical LVD values used are between 11.0 and 11.5 volts, which correspond to about 75-90% depth of discharge for most nominal 12 volt lead-acid batteries.

A word of caution is in order when selecting the low voltage load disconnects set point. Battery manufacturers rate discharge capacity to a specified cut-off voltage which corresponds to 100% depth of discharge for the battery.

For lead-acid batteries, this cut-off voltage is typically 10.5 volts for a nominal 12 volt battery (1.75 volts per cell).

In PV systems, we never want to allow a battery to be completely discharged as this will shorten it's service life. In general, the low voltage load disconnect set point in PV systems is selected to discharge the battery to no greater than 75-80% depth of discharge.

Load Reconnect Voltage (LRV) Set Point The battery voltage at which a controller allows the load to be reconnected to the battery is called the load reconnect voltage ('LRV). After the controller disconnects the load from the battery at the LVD set point, the battery voltage rises to its open-circuit voltage.

When additional charge is provided by the array or a backup source, the battery voltage rises even more. At some point, the controller senses that the battery voltage and state of charge are high enough to reconnect the load, called the load reconnect voltage set point.

The selection of the load reconnect set point should be high enough to ensure that the battery has been somewhat recharged, while not to high as to sacrifice load availability by allowing the loads to be disconnected too long.

Low Voltage Load Disconnect Hysteresis (LVDH) The voltage span or difference between the LVD set point and the load reconnect voltage is called the low voltage disconnect hysteresis (LVDH). If the LVDH is too small, the load may cycle on and off rapidly at low battery state-of-charge (SOC), possibly damaging the load or

controller, and extending the time it takes to fully charge the battery. If the LVDH is too large, the load may remain off for extended periods until the array fully recharges the battery.

With a large LVDH, battery health may be improved due to reduced battery cycling, but with a reduction in load availability. The proper LVDH selection for a given system will depend on load availability requirements, battery chemistry and size, and the PV and load currents.

Charge Controller Designs Two basic methods exist for controlling or regulating the charging of a battery from a PV module or array - shunt and series regulation. While both of these methods are effectively used, each method may incorporate a number of variations that alter their basic performance and applicability.

Simple designs interrupt or disconnect the array from the battery at regulation, while more sophisticated designs limit the current to the battery in a linear manner that maintains a high battery voltage.

The algorithm or control strategy of a battery charge controller determines the effectiveness of battery charging and PV array utilization, and ultimately the ability of the system to meet the electrical load demands. Most importantly, the controller algorithm defines the way in which PV array power is applied to the battery in the system. In general, interrupting on-off type controllers require a higher regulation set point to bring batteries up to full state of charge than controllers that limit the array current in a gradual manner.

Some of the more common design approaches for charge controllers are described in this section. Typical daily charging profiles for a few of the common types of controllers used in small PV lighting systems are presented in the next section.

1. Shunt controller design: Since photovoltaic cells are current-limited by design (unlike batteries), PV modules and arrays can be short-circuited without any harm. The ability to short-circuit modules or an array is the basis of operation for shunt controllers.

Most shunt controllers require a heat sink to dissipate power, and are generally limited to use in PV systems with array currents less than 20 amps.

1- Shunt-Interrupting Design

The shunt-interrupting controller completely disconnects the array current in an interrupting or on-off fashion when the battery reaches the voltage regulation set point.

2- Shunt-Linear Design

Once a battery becomes nearly fully charged, a shunt-linear controller maintains the battery at near a fixed voltage by gradually shunting the array through a semiconductor regulation element.

2. Series Controller Designs As the name implies this type of controller works in series between the array and battery, rather than in parallel as for the shunt controller. There are several variations to the series type controller, all of which use some type of control or regulation element in series between the array and the battery.

While this type of controller is commonly used in small PV systems, it is also the practical choice for larger systems due to the current limitations of shunt controllers.

1- Series-Interrupting Design

The most simple series controller is the series-interrupting type, involving a one-step control, turning the array charging current either on or off. The charge controller constantly monitors battery voltage, and disconnects or open-circuits the array in series once the battery reaches the regulation voltage set point

2- Series-Interrupting, 2-step, Constant-Current Design

This type of controller is similar to the series-interrupting type, however when the voltage regulation set point is reached, instead of totally interrupting the array current, a limited constant current remains applied to the battery.

3- Series-Interrupting, 2-Step, Dual Set Point Design

This type of controller operates similar to the series-interrupting type, however there are two distinct voltage regulation set points. During

the first charge cycle of the day, the controller uses a higher regulation voltage provides some equalization charge to the battery. Once the

array is disconnected from the battery at the higher regulation set point, the voltage drops to the array reconnect voltage and the array is

again connected to the battery, This type of regulation strategy can be effective at maintaining high battery state of charge while

minimizing battery gassing and water loss for flooded lead-acid types.

4- Series-Linear, Constant-Voltage Design

In a series-linear, constant-voltage controller design, the controller maintains the battery voltage at the voltage regulation set point. The series regulation element acts like a variable resistor, controlled by the controller battery voltage sensing circuit of the controller. The series element dissipates the balance of the power that is not used to charge the battery, and generally requires heat sinking. The current is inherently controlled by the series element and the voltage drop across it.

Series-linear, constant-voltage controllers can be used on all types of batteries. Because they apply power to the battery in a controlled manner, they are generally more effective at fully charging batteries than on-off type controllers. These designs, along with PWM types are recommended over on-off type controllers for sealed VRLA type batteries.

Charge Controller Selection The selection and sizing of charge controllers and system controls in PV systems involves the consideration of several factors, depending on the complexity and control options required. While the primary function is to prevent battery overcharge, many other functions may also be used, including low voltage load disconnect, load regulation and control, control of backup energy sources, diversion of energy to and

auxiliary load, and system monitoring. The designer must decide which options are needed to satisfy the requirements of a specific application. The following list some of the basic considerations for selecting charge controllers for PV systems.

System voltage PV array and load currents Battery type and size Regulation algorithm and switching element design Regulation and load disconnect set points Environmental operating conditions Mechanical design and packaging System indicators, alarms, and meters Over current, disconnects and surge protection devices Costs, warranty and availability

Sizing Charge Controllers

Charge controllers should be sized according to the voltages and currents expected during operation of the PV system. The controller

must not only be able to handle typical or rated voltages and currents, but must also be sized to handle expected peak or surge

conditions from the PV array or required by the electrical loads that may be connected to the controller. It is extremely important that the

controller be adequately sized for the intended application. If an undersized controller is used and fails during operation, the costs of

service and replacement will be higher than what would have been spent on a controller that was initially oversized for the application.

Typically, we would expect that a PV module or array produces no more than its rated maximum power current at 1000 W/m2 irradiance

and 25 oC module temperature. However, due to possible reflections from clouds, water or snow, the sunlight levels on the array may be

"enhanced" up to 1.4 times the nominal 1000 W/m2 value used to rate PV module performance. The result is that peak array current could

be 1.4 times the nominal peak rated value if reflection conditions exist. For this reason, the peak array current ratings for charge controllers should be sized for about 140% or the nominal peak maximum power current ratings for the modules or array.

The size of a controller is determined by multiplying the peak rated current from an array times this "enhancement" safety factor. The total current from an array is given by the number of modules or strings in parallel, multiplied by the module current. To be conservative, use the short-circuit current (Isc) is generally used instead of the maximum power current (Imp). In this way, shunt type controllers that operate the array at short-circuit current conditions are covered safely.

Operating Without a Charge Controller In most cases a charge controller is an essential requirement in stand-alone PV systems. However there are special circumstances where a charge controller may not be needed in small systems with well defined loads. Beacons and aids to navigation are a popular PV application which operates without charge regulation. By eliminating the need for the sensitive electronic charge controller, the design is simplified, at lower cost and with improved reliability.

The system design requirements and conditions for operating without a charge controller must be well understood because the system is operating without any overcharge and over-discharge protection for the batteries.

There are two cases where battery charge regulation may not be required:

(1) When a low voltage "self-regulating module" is used in the proper climate;

(2) When the battery is very large compared to the array.

1. Using Low-Voltage "Self-Regulating" Modules

The use of "low-voltage" or "self-regulating" PV modules is one approach used to operate without battery charge regulation. This does not mean that the modules have an electronic charge controller built-in, but rather it refers to the low voltage design of the PV modules. When a low voltage module, battery and load are properly configured, the design is called a "self-regulating system".

Typical silicon power modules used to charge nominal 12 volt batteries usually have 36 solar cells connected in series to produce and open-circuit voltage of greater than 21 volts and a maximum power voltage of about 17 volts.

Why do we generally use modules with a maximum power voltage of 17 volts when we are only charging a 12 volt battery to maybe 14.5 volts? Because voltage drops in wiring, disconnects, over-current devices and controls, as well as higher array operating temperatures tend to reduce the array voltage measured at the battery terminals in most systems. By using a standard 36 cell PV module we are assured of operating to the left of the "knee" on the array I-V curve, allowing the array to deliver it's rated maximum power current.

Even when the array is operating at high temperature, the maximum power voltage is still high enough to charge the battery. If the array were operated to the right of the I-V curve "knee", the peak array current would be reduced, possibly resulting in the system not being able to meet the load demands.

Self-Regulation Using Low-Voltage Module

In the case of using "self-regulating" modules without battery charge regulation, the designer wants to take advantage of the fact that the array current falls off sharply as the voltage increases above the maximum power point. In a "self-regulating" low voltage PV module, there are generally only 28-30 silicon cells connected in series, resulting in an open-circuit voltage of about 18 volts and a maximum power voltage of about 15 volts at 25

oC. Under typical operating temperatures, the "knee" of the IV curve falls within the range of typical battery

voltages. Figure above shows a comparison of operating points between a 36-cell and 30-cell PV module. As the battery voltage rises, there is a more dramatic reduction in current from the 30-cell module. In the afternoon, in this example, the battery voltage has risen to about 14.4 volts, and the current from the 30-cell module is almost one third that from the 36-cell module.

Using a "self-regulating module" does not automatically assure that a photovoltaic power system will be a self-regulating system. For self-regulation and no battery overcharge to occur, the following three conditions must be met:

The load must be used daily. If not, then the module will continue to overcharge a fully charged battery. Every day the battery will receive excessive charge, even if the module is forced to operate beyond the "knee" at current levels lower than its Imp. If the load is

used daily, then the amp-hours produced by the module are removed from the battery, and this energy can be safely replaced the next

day without overcharging the battery. So for a system to be "self-regulating", the load must be consistent and predictable. This

eliminates applications where only occasional load use occurs, such as vacation cabins or RV's that are left unused for weeks or months.

In these cases, a charge controller should be included in the system to protect the battery.

The climate cannot be too cold. If the module stays very cool, the "knee" of the IV curve will not move down in voltage enough, and the expected drop off in current will not occur, even if the battery voltage rises as expected. Often "self-regulating modules" are used in

arctic climates for lighting for remote cabins for example, because they are the smallest and therefore least expensive of the power

modules, but they are combined with a charge controller or voltage dropping diodes to prevent battery overcharge.

The climate cannot be too warm. If the module heats up too much, then the drop off in current will be too extreme, and the battery may never be properly recharged. The battery will sulfate, and the loads will not be able to operate.

A "self-regulating system" design can greatly simplify the design by eliminating the need for a charge controller, however these type of designs are only appropriate for certain applications and conditions. In most common stand-alone PV system designs, a battery charge controller is required.

2. Using a Large Battery or Small Array A charge controller may not be needed if the charge rates delivered by the array to the battery are small enough to prevent the battery voltage from exceeding the gassing voltage limit when the battery is fully charged and the full array current is applied.

In certain applications, a long autonomy period may be used, resulting in a large amount of battery storage capacity. In these cases, the charge rates from the array may be very low, and can be accepted by the battery at any time without overcharging.

These situations are common in critical application requiring large battery storage, such as telecommunications repeaters in alpine conditions or remote navigational aids. It might also be the case when a very small load and array are combined with a large battery, as in remote telemetry systems.

In general a charging rate of C/100 or less is considered low enough to be tolerated for long periods even when the battery is fully charged. This means that even during the peak of the day, the array is charging the battery bank at the 100 hour rate or slower, equivalent to the typical trickle charge rate that a controller would produce anyway.

Solar tracking

OBJECTIVE: The aim of our projects is to utilize the maximum solar energy through solar panel. For this a digital based automatic sun tracking system is proposed. This project helps the solar power generating equipment to get the maximum sunlight automatically thereby increasing the efficiency of the system. The solar panel tracks the sun from east to west automatically for maximum intensity of light.

Basic concept: Sunlight has two components, the "direct beam" that carries about 90% of the solar energy, and the "diffuse sunlight" that carries the remainder - the diffuse portion is the blue sky on a clear day and increases proportionately on cloudy days. As the majority of the energy is in the direct beam, maximizing collection requires the sun to be visible to the panels as long as possible

Solar tracker: (mechanism) Is a device that orients a payload toward the sun. Payloads can be photovoltaic panels, reflectors, lenses or other optical devices.

This mean Tracking mechanism with the PV installation that enables it to follow the sun as it moves across the sky makes the system produce more energy and provide the biggest returns in net metering.

The idea behind using trackers is that solar panels are static while the sun isn't at any time of the day - so trackers are used to help optimize the incidence angle at which the sun's rays reach them.

Solar tracker increases the system's output by 50 percent in the summer months and by 20 percent in the winter months.

Types of solar trackers:

one axis tracking

two axis tracking

1. Single axis tracking systems:

Solar panels with single axis tracking systems. The panels can turn around the center axis.

Single axis trackers have one degree of freedom that acts as an axis of rotation. The axis of rotation of single axis trackers is typically aligned along a true North meridian. It is possible to align them in any cardinal direction with advanced tracking algorithms.

Single axis tracking system: Single axis trackers increase electricity output by 27 to 32%, and are an impressive simple way of improving the potential performance of a commercial solar installation while keeping cost in check. There are several common implementations of single axis trackers.

These include horizontal single axis trackers (HSAT), vertical single axis trackers (VSAT), tilted single axis trackers (TSAT) and polar aligned single axis trackers (PSAT). The orientation of the module with respect to the tracker axis is important when modeling performance.

2-Dual axis trackers: Dual axis trackers have two degrees of freedom that act as axes of rotation. These axes are typically normal to one another. The axis that is fixed with respect to the ground can be considered a primary axis. The axis that is referenced to the primary axis can be considered a secondary axis.

They are classified by the orientation of their primary axes with respect to the ground. Two common implementations are tip-tilt dual axis trackers (TTDAT) and azimuth-altitude dual axis trackers (AADAT).

The orientation of the module with respect to the tracker axis is important when modeling performance. Dual axis trackers typically have modules oriented parallel to the secondary axis of rotation.

Dual axis trackers allow for optimum solar energy levels due to their ability to follow the sun vertically and horizontally. No matter where the sun is in the sky, dual axis trackers are able to angle themselves to be in direct contact with the sun.

Dual axis trackers increase a systems energy output by 35 to 40%; that is an additional 6% on average compared with the single axis trackers.

How the Track Rack follow the sun:

1. Sunrise "Wake- Up The Track Rack begins the day facing west.

As the morning sun rises in the east, then the tracker move to the sun by sensors and motor drive which control the tracker.

2. Mid-Morning The Track Rack moved by the shifting according to motion of sun.

3. Mid-Afternoon As the sun moves, the Track Rack follows

(At approximately 15o per hour)

4. Sunset The Track Rack completes its daily cycle facing west. It remains in this position overnight until it is "awakened" by the rising sun the following morning.

How control the tracker to track the sun:

1-Fabricate a stepper motor control interfaced with driver circuit, as will be explained in its own partial.

2-Design an electronic circuit to sense the intensity of light and to control stepper motor driver for the panel movement.

3-use programmable device such as plc. or arduino (used in our prog.) which send pulses to motor drive to control the movement of mechanism (tracker) .

What is stepper motor??

STEPPER MOTOR Introduction: Stepper motor is called also stepping motor as its rotor shaft rotate with fixed angular step in response to each pulse received by its field winding from digitally controller and its three type we will Talking about them. We used the steeper motor in our project as it has more advantage and special applications and we will showed its advantages; applications and also dis advantage to avoid it

.Types of stepper motor 1-permenent magnet (PM) This type of step motor has a permanent magnet rotor. The stator can be similar to single stack variable reluctance .Usually construct from two phase winding each one has two teeth and rotor is two poles of permanent. Now we speak for its way of operation and its advantage and dis advantage.

Operation of (PM) Each winding ( A ,B) has two terminal we excited stator winding control the polarity of excited current ( A+,B+,A-,B-,.) and the rotor poles are attracted To excited phase and make one step . Direction of rotation depends on the polarity of excited coil.

1-One mode operation (full step): At which excited phase (A) with positive current then change excitation to phase (B) with positive current make the rotor rotate one step at clock-wise direction. sequence of pulse for rotation clock-wise ( A+,B+,A-,B-,A+,..).sequence of pulse for rotation anti clock-wise (A+,B-,A-,B+,A+ ,B+ ,). We can obtain that step angle for PM motor B =90 for full step fig1

2-Two phase operation mode:

In this method two stator winding excited at same time that make generate torque from both phases make rotor set at mid-way Between two excited phase by sequence (A+B+,B+A-,A-B-,B-A+,).Make stepper rotate at clockwise with full step .excited phase by sequence(A+B-,B-A-,A-B+,B+A+,A+B-,).Make stepper rotate anti clockwise with full step .fig2

3- Half step operation: is alternative between one phase and two phase mode we can obtain it by give sequence (A+,A+B+,B+,B+A-,A-,A-B-,B-,B-A+,A+,).make rotation with clock-wise steps . We can obtain that step angle for PM motor B =45 for half step fig3

Advantage: 1-dont required external exciting current.

2-Need low power.

3-has high detent torque compared with variable reluctance.

4-has high moment of inertia and slower acceleration

Disadvantage: 1-to reduce step angle we need increase rotor poles but it is difficult to manufacture small