Photovoltaic System Integration

8/13/2019 Photovoltaic System Integration

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Photovoltaic System Integration for

Roehampton Vale Campus, Kingston

University London

Omar Hamdan

Supervised by: Dr. Paul Wagstaff

MSc Renewable Energy Engineering

October 2012

Faculty of SEC, Kingston University


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Omar Hamdan | Kingston University London

Table of Contents

List of Figures ............................................................................................................................... VI

List of Tables............................................................................................................................... VIII

List of Equations ........................................................................................................................... IX

Chapter One .................................................................................................................................. 1

1.1.0 Introduction .......................................................................................................................... 2

1.2.0 Building Integrated PV System .............................................................................................. 5

1.3.0 Solar Radiation and Solar Constant ....................................................................................... 7

1.4.0 Geometrical Considerations: ................................................................................................. 8

1.4.1 The Declination angle............................................................................................................ 9

1.4.2 Solar Hour Angle ................................................................................................................... 9

1.4.3 The Latitude angle .............................................................................................................. 10

1.4.4 The Sunset Hour angle ........................................................................................................ 10

1.4.5 Slope Angle ......................................................................................................................... 10

1.4.6 Surface Azimuth angle ........................................................................................................ 10

1.4.7 Angle of Incident ................................................................................................................. 10

1.4.8 Zenith Angle ........................................................................................................................ 11

1.5.0 Solar Radiations reaches a specific tilted surface ................................................................. 11

1.5.1 Clearness Index: .................................................................................................................. 12

1.5.2 Calculating of Hourly Global and Diffused Irradiance ........................................................... 12

Chapter Two ................................................................................................................................ 15

2.1.0 System Components ........................................................................................................... 16

2.1.1 Solar Cell Basics: ................................................................................................................. 16

2.1.2 Light characteristics ............................................................................................................ 17

2.1.3 Electrical Characteristics of a PV-Cell: .................................................................................. 18

2.1.4 Voltage and Current in PV Plant .......................................................................................... 21

2.2.0 Electrical Power Output: ..................................................................................................... 22

2.3.0 Components Selection PV panel .......................................................................................... 23

2.3.1 PV Panel Selection Methodology ......................................................................................... 24

2.3.2 Chosen Panel ...................................................................................................................... 24

2.4.0 Inverter and Control............................................................................................................ 26

2.4.1 Maximum Power Point Tracking (MPPT): ............................................................................ 26

2.4.2 Connection of Inverter to Array........................................................................................... 26

2.4.3 Inverter, process and Functions .......................................................................................... 28


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2.4.4 Component Selection, Inverter ........................................................................................... 29

2.4.5 Summary ............................................................................................................................ 30

2.5.0 Shading: .............................................................................................................................. 33

Chapter Three ............................................................................................................................. 34

3.1.0 Project Demand and Hand Calculations ............................................................................... 35

3.1.1 Process of progression: ....................................................................................................... 35

3.1.2 Overview, System Demand and Electrical System Review:................................................... 36

3.2.1 Hand Calculation: ................................................................................................................ 38

3.2.2 Summary and Assumptions: ................................................................................................ 38

3.2.3 Calculating the hourly solar radiation on the system: .......................................................... 39

3.2.4 Calculation: ......................................................................................................................... 41

3.2.5 Hand Calculation Results and Analysis: ................................................................................ 46

3.2.6 Area optimising and assessment ......................................................................................... 52

3.2.7 shading consideration ......................................................................................................... 53

3.3.0 calculating the hourly electrical power produced through all the year ................................. 55

3.3.1 System sizing ...................................................................................................................... 55

Chapter Four ............................................................................................................................... 60

4.1.0 Project Simulation ............................................................................................................... 61

4.1.1 Preliminary Design .............................................................................................................. 61

4.2.0 Full Project Design .............................................................................................................. 64

4.2.1 Shade Simulation ................................................................................................................ 65

4.2.2 Electrical Layout .................................................................................................................. 70

4.2.3 Panel Layout Design ............................................................................................................ 71

4.2.4 Simulation Results and Review ............................................................................................ 73

Chapter Five ................................................................................................................................ 78

5.1.0 Electrical Configurations ..................................................................................................... 795.1.1 Measurement of the Energy Produced and Sold to the Grid ................................................ 80

5.2.0 Protection and Earthing of the System: ............................................................................... 81

5.3.0 Protection Against Over Current on AC Side: ....................................................................... 82

5.4.0 Comparison between Hand Calculation and Simulation....................................................... 82

Chapter Six .................................................................................................................................. 83

6.1.0 Economical Evaluation ........................................................................................................ 84

6.1.1 Assumptions ....................................................................................................................... 84

6.2.0 Sizing the System Based on Data from the Economic Model ................................................ 85


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6.2.1 Maximum Power Output ..................................................................................................... 85

6.2.2 System Limited by the Minimum Demand of December ...................................................... 87

6.2.3 Using the Data from Simulation for 20% of December System Size ...................................... 87

6.3.0 Analysis ............................................................................................................................... 93

Chapter Seven ............................................................................................................................. 94

7.1.0 Critical Review .................................................................................................................... 95

7.2.0 Further Work ...................................................................................................................... 95

Chapter Eight ............................................................................................................................... 96

7.1.0 Conclusion .......................................................................................................................... 97

References .................................................................................................................................. 98

Bibliographies ............................................................................................................................ 100

Appendix A ................................................................................................................................ 101

Appendix B ................................................................................................................................ 102

Appendix C ................................................................................................................................ 104


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List of Figures

Figure 1: GHG and CO2emissions by sector. (EC, 2010) ...................................................................... 3

Figure 2: Electricity consumptions by Sector. (DECC, 2009) ................................................................ 4

Figure 3: Electrical PV generation (European commission, 2010) ....................................................... 5

Figure 4: Grid-connected photovoltaic system. (Luque and Hegedus, 2011). ...................................... 6

Figure 5: Earth Positions around the sun (Scharmer, 2000) ................................................................ 8

Figure 6: Solar Geometry Angles (Duffie and Beckman, 2006). ......................................................... 11

Figure 7: Schematic of a solar cell. The solid white lines indicate the conduction and valence bands of

the semiconductor layers; the dotted white lines indicate the Fermi level in the dark. .................... 16

Figure 8: Light wavelength ranges ................................................................................................... 18

Figure 9 Equivalent circuit of Photovoltaic ....................................................................................... 19

Figure 10 Voltage-Current characteristics example (ABB, 2010) ....................................................... 20

Figure 11 Selected Panel Dimensions ............................................................................................... 25

Figure 12 photovoltaic panel curves with different irradiances. ....................................................... 25

Figure 13 typical circuit used in PV inverters. ................................................................................... 28Figure 14 inverter combination ....................................................................................................... 32

Figure 15 PWM DC to AC process .................................................................................................... 32

Figure 16 By-Pass diode under shading ............................................................................................ 33

Figure 17 system demand in kW ...................................................................................................... 37

Figure 18 Day Length for each month .............................................................................................. 47

Figure 19 Clearness Index and the diffused radiation ratio ............................................................... 47

Figure 20 total irradiance on a tilted surface per hour for each month............................................. 49

Figure 21 total estimated electrical output per hour each month. ................................................... 51

Figure 22 The monthly production of the system ............................................................................. 51

Figure 23 Roof Top of the Location. ................................................................................................. 52

Figure 24 calculating the area of shade effect .................................................................................. 54

Figure 25 Monthly Percentage of the total demand when maximum power produced. ................... 56

Figure 26 Percentage of the Supply to the Demand ......................................................................... 58

Figure 27 Monthly Demand Vs. Production. ..................................................................................... 58

Figure 28 Program's first interface page .......................................................................................... 61

Figure 29 Site data entry. ................................................................................................................. 62

Figure 30 mutual shading Visualisation/optimisation ....................................................................... 63

Figure 31 Sun Path and Mutual shading. .......................................................................................... 63

Figure 32 Preliminary Power Output, Horizontal and tilt surface comparison. .................................. 64Figure 33 Near Shading design tool interface ................................................................................... 64

Figure 34 building a new object to simulate the shading .................................................................. 65

Figure 35 the final built structure. ................................................................................................... 66

Figure 36 PV panels build user interface. ......................................................................................... 66

Figure 37 Final system before the shade simulation ......................................................................... 67

Figure 38 Top View, photovoltaic generator position ....................................................................... 68

Figure 39 Shading process ............................................................................................................... 68

Figure 40 shading when the system is placed at the eastern side of the building. ............................ 69

Figure 41 shading when the system is placed at the western side of the building............................. 70

Figure 42 System Design interface ................................................................................................... 72

Figure 43 Array power optimisation graph. ...................................................................................... 72
http://c/Users/Omar/Desktop/Final%20Dissertation.docx%23_Toc355166427http://c/Users/Omar/Desktop/Final%20Dissertation.docx%23_Toc355166427


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Figure 44 Module Layout design and layout tool interface. .............................................................. 73

Figure 45 Simulation Production vs. Demand ................................................................................... 74

Figure 46 loss Diagram of the whole system along the year. ............................................................ 75

Figure 47 Daily input/output diagram .............................................................................................. 76

Figure 48 Array voltage distribution ................................................................................................. 76

Figure 49 Daily Power output along the year. .................................................................................. 77

Figure 50 Performance Ratio for each month. ................................................................................. 77

Figure 51 Electrical System Layout. .................................................................................................. 80

Figure 52 kWh meter integration with the system ........................................................................... 81

Figure 53 Cash Flow when installing 250 kWp as maximum assumption .......................................... 87

Figure 54 Cash flow of system sized based on 20% of December demand. ....................................... 89

Figure 55 Cash flow of System sized based on 20% of December demand. Simulation results .......... 89

Figure 56 Saving on Electricity bill in first model .............................................................................. 92

Figure 57 Saving on Electricity bill in the second model ................................................................... 92

Figure 58 Demand and Production for the first model ..................................................................... 93Figure 59 Demand and Production for the second model ................................................................ 93


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List of Tables

Table 1 System Demand kW ............................................................................................................ 37

Table 2. Monthly Ground Reflectance, (Albedo) .............................................................................. 39

Table 3 Monthly average meteorological data (EUROPEAN COMMISSION) ...................................... 40

Table 4 Site Data and Calculated information for one hour of the year ............................................ 40

Table 5 Irradiance Htaccording to day hours for each month along the year.................................... 48

Table 6 Average kWh production per hour for each month. ............................................................. 50

Table 7 Maximum power system production and comparison with the system demand .................. 55

Table 8 Minimum Production considering 20% of the Demand in December. .................................. 57

Table 9 Shading factor for the beam radiation at different sun positions. ........................................ 70

Table 10 Simulation Data Output. .................................................................................................... 74

Table 11 Maximum power output applied on the built economical model (in ) .............................. 86

Table 12 20% of December production assumption applied on the built economical model (in ).... 88Table 13 20% of December production assumption applied on the built economical model/

simulation result (in ) ..................................................................................................................... 90


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List of Equations

Equation 1 Extraterrestrial Radiation ................................................................................................. 8

Equation 2 Declination Angle ............................................................................................................. 9

Equation 3 Solar Time ........................................................................................................................ 9

Equation 4 E value. ............................................................................................................................ 9

Equation 5 Sunset Hour Angle ......................................................................................................... 10

Equation 6 Incident Angle ................................................................................................................ 10

Equation 7 Zenith Angle .................................................................................................................. 11

Equation 8 Clearness Index .............................................................................................................. 12

Equation 9 global Hourly irradiance on horizontal surface ............................................................... 12

Equation 10 Diffused Radiation Ratio ws81.4............................................................................... 13

Equation 11 Diffused Radiation Ratio ws > 81.4............................................................................... 13

Equation 12 Average Daily irradiance .............................................................................................. 13

Equation 13 rt ratio ......................................................................................................................... 13

Equation 14 constant a .................................................................................................................... 13Equation 15 constant b .................................................................................................................... 13

Equation 16 Diffused irradiance ....................................................................................................... 13

Equation 17 Beam irradiance ........................................................................................................... 14

Equation 18 rd ratio......................................................................................................................... 14

Equation 19 Total irradiance on tilted surface.................................................................................. 14

Equation 20 RbValue ....................................................................................................................... 14

Equation 21 Photon Energy ............................................................................................................. 17

Equation 22 Atmospheric Mass ....................................................................................................... 18

Equation 23 Diode current............................................................................................................... 19

Equation 24 current delivered by the photovoltaic panel ................................................................. 19

Equation 25 Filling Factor ................................................................................................................ 21

Equation 26 Cell temperature effect on the cell Efficiency ............................................................... 22

Equation 27 Ambient temperature relation with the cell temperature ............................................ 22

Equation 28 tilt angle correction factor for the cell temperature ..................................................... 22

Equation 29 Energy supplied to the building and the electrical grid ................................................. 23


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Chapter One


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1.1 Introduction

Since the first public power distribution system was developed, in 1882, by the

famous Thomas Edison, our modern life style started to shape. Electricity made a

shift for human history, bringing all lifes modern luxuries into being (Chapman,

2005). Before electricity became available over 100 years ago, houses were lit with

kerosene lamps, food was cooled in iceboxes, and wood-burning or coal-burning

stoves warmed rooms. In other words, Electricity has changed that and become a

key driver in our modern life development.

Electrical power generation started in the form of cool power plants using

Steam turbines to drive Direct Current generators. That was followed by huge

developments in electrical power generation methods. Combined cycle power plant,

Nuclear Power Plant and Hydroelectric Power Plant are the latest forms of power

generation methods. Although those types of power plants are considered to have

high reliability and low loss of load probability (LOLP) fraction, they still suffer from

many major issues threatening the globe indirectly, by increasing Green House

Gases (GHG), and increasing the availability of some types of fuel, which might not

be available for all nations, either now or in the future.

Waldau A. J. et al, (2011) mentioned that "besides the increasing pressure on

the supply side of energy by the increasing world energy demand, environmental

concerns shared by a majority of the public and add to the list of weaknesses of

fossil fuels and the problems of nuclear energy. These concerns include the societal

damage caused by the existing energy supply system, whether such damage is of

accidental origin (oil slicks, nuclear accidents, methane leaks) or connected to

emissions of pollutants". Baker, (2004) added that generating electricity has made

major damages to the environment which might, in the end, cause global

catastrophes. Green House Gases (GHG) and CO2 emissions in particular cause

environmental damages. The Global warming or the expansion of the ozone hole,

which could lead to the melting of more ice in Antarctica and increase the water level

in the seas, represent clear examples of the danger of GHG. Such Issues have led

scientists to search for other alternatives, which might balance the scales.


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Renewable Power Generation is being strongly considered. The technology

offers a free fuel energy that is free of GHG emissions. Solar Power Generation has

a long history and a promising future. Generally, Photovoltaic Power Systems helped

to supply electricity to many rural places but since 1991, this case has changed. In

Aachen, Germany (1991), the first installation of building-integrated photovoltaic's

(BIPV) was realized.

In addition, the energy market in the UK is growing, according to many market

analysts. In December 1997, the European Council and the European Parliament

adopted the White Paper for a Community Strategy and action Plan. In this paper,

the aims are described as follows, Renewable energy sources may help to reduce

dependence on imports and increase security of supply. Positive effects also

anticipated in terms of CO2emissions and job creation. Renewable energy sources

accounted in 1996 for 6% of the unions overall gross internal energy consumption.

The unions aim is to double this figure by 2010(European Commission, 2010). The

UK government is stating policies to support renewable projects. Subsequently,

seeking sustainable and cleaner energy to provide a secure energy level of

consumption is an international concern.

Residential Buildings contribute in a large way to the total GHG and CO2

emissions. In the UK, residential CO2 and GHG emissions are 14% and 12%

respectively. The commercial institutions contribute in 3.8% and 3.2% (European

Commission, 2010). Figure (1) illustrates GHG and CO2emissions by each sector.

As well, Domestic and household consumption of electricity represents 32% of the

total electricity generation, while the commercial sector consumes 19% of the total

electricity produced. (DECC, 2010). Refer to Figure (2).

Figure 1: GHG and CO2emissions by sector. (EC, 2010)


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Figure 3: Electrical PV generation (European commission, 2010)

1.2 Building Integrated PV System

Examining Photovoltaic modules for building integration, produced as a

standard building product that fit into standard faade and roof structures (IEA,

1996). Since the first integration for Photovoltaic into buildings, it has become one of

the fastest growth market segments in photovoltaic (Benemann J. et al, 2001).

There are several reasons for the great interest in PV systems in buildings. Its

image as a high-tech and its futuristic technology makes it more interesting for

engineers, architect and consumers. As well, integration of PV is technically simple

to install compared with other solar technologies such as solar thermal (Fieber A.,

2005). Furthermore, the price of PV panel integration in building is economically

attractive where its profit expectation is promising.

A roof or faade element with photovoltaic can be used in all kind of building's

structures, curtain wall faade (with isolating glass), rear vented curtain wall faade ,

structural glazing and tilted faade . It is expected from the photovoltaic system to

cover day lighting, reduce the noise and produce electricity (Benemann J. Et al,

2001). While Thomas R. and Fordham M. argued (2001) that the reasons of why

Photovoltaic is attractive technology is that using it includes supplying all, or most

likely the largest portion, of the annual electricity requirement of a building, making a

contribution to the environment, making a statement about innovative architectural

1 13 4 3 4

810 11

1999 2000 2001 2002 2003 2004 2005 2006 2007

Gross Electricity Generation of

Photovoltaic GWh

Gross Electricity Generation of Photovoltaic GWh


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and engineering design and using them as a demonstration or educational project

(Thomas R. and Fordham M., 2001).

To integrate a PV system in any building, many considerations must be taken

into account by the designer and engineers. One of the crucial points is the

orientation of the building and tilt angle of the PV panel, solar irradiations and the

electrical system used including the proposed inverter and control methods.

In general, any BIPV system consists of Photovoltaic panel(s), inverter(s) and

accessories, which are usually referred to as Balance of System (BOS) and

switchgears. PV panels are the main component used to convert the energy carried

by the photons, particles that exist in sunlight, into electrical power. The inverter will

convert the produced DC electrical power by the PV panels to an AC usable

electrical power. The BOS includes kWh meter(s), cables, fuses, combiners, fittings,

grounding connections, switchgear and strings, DC and AC switches and

connectors.

The PV system integrated into a building would not need a storage system,

batteries; since the storage system is normally used to supply the load during the

night hours or when there is not enough radiation to produce electricity into the PVpanels. In this case, the national grid will act as a storage system (Luque and

Hegedus, 2011). Figure (4) illustrates a basic grid connected (On-Grid) schematic of

PV system. More details about each component of the system are presented later;

specifically on PV cell, module and array and on the conditioning system (inverter).

Figure 4: Grid-connected photovoltaic system. (Luque and Hegedus, 2011).


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To explain how the solar system does work, it is important to describe the

nature of the sun light and the radiations that fall on earth's surface. As well, a short

introduction about the sun and earth position should be presented to be able to

elucidate sunlight, radiation analysis and solar system.

1.3 Solar Radiation and Solar Constant

It is obvious that the Photovoltaic system is related to the sun and the earth's

movement around it, thus, studying this movement and the way the radiation will fall

into the earth's surface has great importance, in order to achieve the highest

possible performance. In addition, it is important to understand the geometric

relationships between a planet relative to the earth at anytime and the incoming

radiation. This will make it possible to find the power output for any system intended

to be installed.

The sun is a sphere containing hot gaseous matter and has a diameter of

1.39 x 109 m. On average, the earth is 1.5 x 1011meter away from the sun. This

distance equals about 12000 times the earth's diameter. The earth revolves around

the sun in an elliptical unusual orbit that varies the distance between the sun and theearth by 1.7%. The day of the closest approach in the northern hemisphere is known

as Perihelion and occurs on the 2nd of January, whilst on 2nd of July, the earth is at

its greatest distance from the sun, this distance is known as Aphelion, see Figure (5)

(Scharmer, 2000). The sun has an effective blackbody temperature of 5777 K. The

radiation emitted by the sun and its spatial relationship to the earth result in a nearly

fixed intensity of solar radiation outside the earth's atmosphere, often referred to as

extraterrestrial radiation. The extraterrestrial radiation's values, referred to as solar

constant, found in the literature vary slightly due to the measurement techniques or

assumptions for necessary estimations. The World Radiation Centre (WRC) has

adopted a value of 1367 W/m2, with 1% uncertainty (IEA, 1996).

The Solar Radiation outside the earth's atmosphere changes throughout the

year due to the change in the distance from the sun and the rotation of earth around

its axis. The solar radiation outside the atmosphere is then calculated depending on

the eccentricity correction factor () and the day of the year (Luque and Hegedus,


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2011). According to (Duffie and Beckman, 2006), depends on the distance of theearth from the sun, which will vary by 1.7% of its mean value , which is equal to1.49510

11m. A simple equation for engineering proposes combines the change in

the day and distance and defines the solar radiation outside the earth's atmosphere

as following:

Equation 1 Extraterrestrial Radiation

Where

Gsc: solar constant, 1367 W/m2.

n: is the day number of the year.

Figure 5: Earth Positions around the sun (Scharmer, 2000)

1.4 Geometrical Considerations:

To put a formula to find the radiation received on the system's surface, tilted

surface, by only knowing the total radiation on the horizontal surface. It is important

to know the direction from which the beam or the diffused radiations are received.

The geometrical properties should be studied. The next definitions and equations are

used in the calculation later in this paper.


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1.4.1 The Declination Angle:It is the key input for the solar geometry. It is defined by (UNESCO and NELP,

1978) as "the angle between the Equatorial Plane and the line joining the centre of

the Earth's sphere to the centre of the solar disk. The axis of rotation of the Earth

about the poles is set at an angle to that so called Plane of the Ecliptic. "The angle

varies along the Julian days between 23.45 and -23.45. The following equation

relates to the declination angle and the day number n, along the year.

Equation 2 Declination Angle

1.4.2 Solar Hour Angle:According to (PEN, 2012), is the angular displacement of the sun east and

west of the local meridian. It changes 1 each for minutes and 15 each hour. It

changes 15 each hour after the solar noon and -15 each hour before the solar noon.

The solar noon corresponds to the moment when the sun at the highest point in the

sky. So the solar noon does not depend on the local time but on the solar time. The

solar time can be found as following:

Equation 3 Solar Time

Where Lstis the standard meridian for the local time zone, L locis the longitudeof the specific location in degree. E is the equation of time in minutes which equals

to:

Equation 4 E value.


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1.4.3 The Latitude angle:It is the angular location north of the equator as positive and south of the

equator as negative. Its values range between -90 and +90.

1.4.4 The Sunset Hour angle:

According to (RETScreen International, 2005) is the angle of the sun at the

sunset solar hour. It can be found using the following equation:

Equation 5 Sunset Hour Angle

1.4.5 Slope Angle:This is the tilt angle where the Photovoltaic panel or array is tilted from the

horizontal. Generally, as a rule of thumb, to collect maximum annual energy, a

surface slope angle should be adjusted to be equal to the latitude angle. For the

summer maximum energy gain, slope angle should be approximately 10to 15less

than the latitude and for the winter, maximum energy gain can be acquired when the

angle is adjusted to be 10 to 15 more than the latitude. (Duffie and Beckman,

2006).

1.4.6 Surface Azimuth angle:This is the deviation of the projection, on a horizontal plane, of the normal to

the surface from local meridian. It is equal to zero when it is pointed to the south,

negative to the east and positive to the west. It ranges between .

1.4.7 Angle of IncidentThis is the angle between the beam radiation on a surface and the normal to

that surface. It can be calculated as follows:

Equation 6 Incident Angle


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1.4.8 Zenith Angle:

It is the angle between the vertical of the sun and the incident solar beam. Its value

must be between 0 and 90. For a horizontal surface the zenith angle can be

calculated using the following equation.

Equation 7 Zenith Angle

The following figure (6) illustrates the angles on a tilted surface. Please note

that the previous equations will be implemented in a hand calculation for the total

power output of the proposed system, later in this paper. The calculation will be done

using Microsoft Excel.

Figure 6: Solar Geometry Angles (Duffie and Beckman, 2006).

1.5 Solar Radiations reaches a specific tilted surface

The directions from which solar radiation reaches a specific tilted surface are

a dependent on conditions of cloudiness and atmospheric clarity (Duffie and

Beckman, 2006). Those radiations are considered to be distributed over the sky

dome. In general, the data of cloudiness and clarity are widely available.


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Equation 10 Diffused Radiation Ratio ws 81.4

For :

Equation 11 Diffused Radiation Ratio ws > 81.4

The average daily irradiance is now broken into hourly values. To do so, the

equation developed by Collares-Pereira is used in the calculations. The formulas are

as following:

Equation 12 Average Daily irradiance

Where is:

Equation 13 rt ratio

Where (a)and (b) arevalues can be found as follows:

Equation 14 constant a

Equation 15 constant b

Note that the values of sunset angle and the hour angles are in radians. Then

the values of both the diffused and the Beam irradiances can be calculated as

follows:

Equation 16 Diffused irradiance


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Equation 17 Beam irradiance

can be found using this equation:

Equation 18 rd ratio

The calculation of the total hourly irradiance is a combination of the three

irradiances values; the beam irradiance, diffused irradiance and the ground

reflectance. This equation was developed upon an Isotropic Model, which had been

derived by Jordan and Liu in 1963 (Duffie and Beckman, 2006). The equation equals

to:

Equation 19 Total irradiance on tilted surface

Where:

Equation 20 RbValue

Moreover, is the average diffused ground reflectance, Albedo.


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Chapter Two


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2.1 System Components

2.1.1 Solar Cell Basics:

The Solar cell is a solid-state device that absorbs light and converts part of its

energy- directly into electricity. The process is done within the solid work structure;

the solar cell does not have any moving parts (Richard J. K., 1995).

The photovoltaic cell is manufactured by combining two layers of

semiconductors differently doped, a p-type and an n-type layer. The combination will

result of a matching between holes and electrons which will lead to creating a

potential layer. This is why the solar cells are usually referred to as "Photovoltaic

cells", the photovoltaic effect. Photovoltaic effect is the electrical potential, developed

between the two dissimilar materials. When the two dissimilar material's common

junction, or what is called the depletion layer, is illuminated with radiation of photons,

thus an electrical potential gradient will be created (Mukund R. P., 1999).

Each photon, if it has enough energy, is capable of releasing an electron,

which has a negative charge, or creating a hole, which has positive charge. The

accumulated process will result in a current and potential difference on cell's sides,

the p-type and the n-type. The released electrons will be accelerated because of theresultant gradient, which is called Fermi level, and can then be circulated as a

current through an external circuit, see figure (7) (Mukund R. P., 1999).

Figure 7: Schematic of a solar cell. The solid white lines indicate the conduction and valence bands of the semiconductor

layers; the dotted white lines indicate the Fermi level in the dark.


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2.1.2 Light characteristics

All electromagnetic radiations can be viewed as being composed of particles

called Photons. According to the theory of quantum, the photons are particles that

travel in vacuum with the speed of light and have no mass. Each photon carriesspecific amounts of energy as a packet, referred to as an electron volt (ev). The

amount of energy is related to the proton's source spectral properties. The shorter

the wavelength of the proton, the larger the packet (Richard J. K., 1995).

The sunlight spectral is divided into three regions see figure (8). The first

region has a wavelength between 400 to 700 nanometres. At 700 nanometres, the

visible spectrum appears red and on the shorter end of 400 nanometres it appears

violate. All other colours appear in between. Our eyes are most sensitive to the

spectrum around 500 nanometres. At 400 nanometres and less, the spectrum is

called Ultraviolet (UV) wavelength and most of it is filtered or absorbed by the Ozone

or the transparent material before it reaches the earth's surface. Our skin perceives

the spectrum as radiant heat spectrums above 700 nanometres, which is referred to

as Infrared (Clark and Eckert, 1975). The water vapour, CO2and other substances in

our atmosphere absorb most of the Infrared spectrums. On the other hand, Most of

those absorptions become longer wavelengths than the wavelengths the solarsystem uses. While the solar system effectively collects wavelengths less than 2000

nanometres, thus its efficiency is not significantly affected (Duffie and Beckman,

2006). Photon's energy can be calculated as follows:

Equation 21 Photon Energy

Where is the wavelength, is Plank's constant ( ) and is thespeed of light (m/s).

As well as this, the energy held by a photon is affected by Air Mass. The Air

Mass is the path length which light takes through the atmosphere normalized to the

shortest possible path length (the shortest path is when the sun is directly overhead).

The Air Mass quantifies the reduction in the energy of light as it passes through the

atmosphere and is absorbed by air, dust, ozone (O3), carbon dioxide (CO2), andwater vapour (H2O) with the last three having a high absorption for photons that have


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energies close to their bond energies. The air mass (AM) is defined using the

following equation (noting that is defined later in this paper):

Equation 22 Atmospheric Mass

Figure 8: Light wavelength ranges

2.1.3 Electrical Characteristics of a PV-Cell:

A PV cell equivalent circuit is similar to that of the diode, since they have

similar structures. A photovoltaic cell is considered as a current generator and can

be represented by the equivalent circuit of Figure (9). The current I at the outgoing

terminals is equal to the current generated through the PV effect IPV by the ideal

current generator, decreased by the diode current Id and by the ground leakagecurrent Ish. The resistance in series Rsrepresents the internal resistance to the flow

of generated current and depends on the thickness of the junction P-N, the present

impurities and on contacts resistances.

The shunt resistance Rshtakes into account the current to earth under normal

operational conditions. In an ideal cell the values of Rsis zero while the value of Rsh

is maximum. On the contrary, in a high-quality silicon cell the typical value of R s is

around five milliohm and the shunt resistance is around 285 ohm. The conversion


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efficiency of the PV cell is greatly affected also by a small variation of Rs, whereas it

is not affected by the variation of Rshtoo much.

Figure 9 Equivalent circuit of Photovoltaic

The no-load voltage Voc, open circuit voltage, occurs when the load does not

absorb any current, i.e. ILequals zero, thus according to ohms law, the open circuit

voltage will be the current passing through the shunt resistance, times the shunt

resistance Voc=IshRsh(Luque and Hegedus, 2011)

In addition, the diode current is given by the classical formula for the direct

current:

Equation 23 Diode current

Where: ID is the diode's saturation current, Q is the charge of the electron

(1.610-19 C), A is the identity factor of the diode and it depends on the

recombination factor between the holes and electron inside the diode itself (for

crystalline silicon it is about 2). K is the Boltzmann constant (1.3810-23

J/K). Finally,T is the absolute temperature in Kelvin degree. Therefore, the current supplied to the

load is given by:

Equation 24 current delivered by the photovoltaic panel

The final term, the ground-leakage current, in practical cells is small

compared to Iphand ID, thus it can be ignored. The diode-saturation current can be


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determined experimentally by applying the open circuit voltage Voc in the dark (when

Iph is zero) and measuring the current going into the cell. This current is usually

referred to as the dark current or the reverse diode-saturation current. (Mukund R.

P., 1999).

The voltage-current characteristic curve of a PV module is shown in Figure10.

The generated current is at its highest under short-circuit conditions (Isc), whereas

with the circuit open, the voltage (Voc=open circuit voltage) is at the highest. Under

the two of those conditions, the electric power produced in the module is equal to

zero, whereas under all the other conditions, when the voltage increases, the

produced power rises too; at first, it reaches the maximum power point (Pm) and

then it falls suddenly near to the no-load voltage value. (Sera, D et al, 2007)

Figure 10 Voltage-Current characteristics example (ABB, 2010)

In summary, the electrical characteristics needed to be known about for a

photovoltaic module is as follows:

Iscshort-circuit current;


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Vocno-load voltage;

Pmmaximum produced power under standard conditions (STC);

Imcurrent produced at the maximum power point;

Vmvoltage at the maximum power point; FF filling factor: this is a parameter which determines the form of the

characteristic curve V-I. It can be defined as the actual maximum power

divided by the ideal power value; the ideal power is that value that would be

obtained under ideal conditions. i.e. when the voltage is equal to the open

voltage and the current is equal to the short circuit current. The filling factor is:

Equation 25 Filling Factor

It should be pointed that all those data can be found in the manufacturer data

sheet. Most of the information is experimentally distinguished. There are some

methods to calculate the series resistance value but it will not be needed in this

paper, thus it will not be presented.

2.1.4 Voltage and Current in PV Plant

PV modules generate a current from 4 to 10 A at a voltage from 30 to 40 V.

To achieve the projected peak power, the panels are electrically connected in series

to form the strings, which are connected in parallel. The trend is developing strings

constituted by as many panels as possible, given the complexity and cost of wiring,

in particular of the paralleling switchboards between the strings. The maximum

number of panels which can be connected in series (and therefore the highest

reachable voltage) to form a string is determined by the operational range of the

inverter and by the availability of the disconnection and protection devices suitable

for the voltage reached. In particular, the voltage of the inverter is bound, due to

reasons of efficiency, to its power. Generally, when using inverters with power lower

than 10 kW, the voltage range most commonly used is from 250V to 750V, whereas

if the power of the inverter exceeds 10 kW, the voltage range usually is from 500V to

900V. (ABB, 2010)


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2.2.0 Electrical Power Output:

The electrical power output of the system will depend on three values, the

total hourly irradiance, and the efficiencies of the electrical components used and the

total area of the panels. The values of total hourly irradiance will be found asdescribed previously in this thesis.

The efficiency of the Photovoltaic's arrays will be characterised by the

average module temperature Tc. Thus, the efficiency will depend on the ambient

temperature (RETScreen International, 2005). The efficiency equation using the

calculation for this study purpose is as follows:

Equation 26 Cell temperature effect on the cell Efficiency

Where is the temperature coefficient for the module efficiency and andare the efficiency and the temperature of the panel under the Standard TestingConditions (STC). Normally the testing temperature is equal to 25C. In addition, the

standard testing conditions will define the Nominal Operating Cell Temperature

NOCT. NOCT values normally ranges from 42C to 46C (Luque and Hegedus,

2011). The average module temperature Tcis related to the mean monthly ambient

temperature through the following equation, which had been developed by Evans in

1981 (Duffie and Beckman, 2006):

Equation 27 Ambient temperature relation with the cell temperature

Furthermore, the equation above is valid when the tilting angle is equal to the

latitude angle minus the declination angle, when the tilt angle is different, then the

right side of the equation has be multiplied by a correction factor defined as C f.

(RETScreen International, 2005). It can be found using the following equation:

Equation 28 tilt angle correction factor for the cell temperature

Where sM is equal to the latitude angle minus the declination angle and s is

the current tilt angle.


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On the other hand, STC efficiency will vary for each type of module. In

general, the efficiency values range between 5%, for example for a module of a-Si

type, up to about 15%, for example a mono-crystalline silicon module.

Finally, the power output of the PV generator can be defined as the total reached

irradiances multiplied by the final efficiency and the total area used S. Theequation can be shown below:

Equation 29 Energy supplied to the building and the electrical grid

To calculate the electrical power delivered by the PV generator, which is

received by the building or the grid, the EP must be multiplied by the inverter

efficiency and the electrical losses due to the wiring. As well, other miscellaneous

losses of the BOS should be deducted from the total power production (RETScreen

International, 2005).

In later sections, a method to calculate the power output will be presented and

illustrated systematically giving one example of the whole system. The codes and

work sheet of the hand model can be found in the appendix A.

2.3.0 Components Selection PV panel

In order to optimise the system for the best conditions, it is highly required to

choose the most suitable component in the system. Reliable, high efficient and low

cost components are the optimal components to choose. In the following, the

detailed process for the main component selection is presented.

There are many kinds of photovoltaic panels which vary in material used,

technology, manufacturing process and size. Looking into the features of each panel

then comparing it with its price and its installation cost can be a very difficult process,

especially if the life time of the PV panel, warranty, market availability and efficiency

are taken into account as well. Therefore, the selection process can be narrowed by

specifying the priority features needed in the panel.


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2.3.1 PV Panel Selection Methodology

The selection of the PV panel for this project was based on three aspect as

priority features; the efficiency of the photovoltaic panel, the panel price and the

market availability. In addition to those characteristics, an additional facet tookpriority when the economical evaluation had been completed. The project life-time

needed to be increased because the payback and the breakeven level of output, was

found to be longer than 20 years. Hence, the PV panel life-time and the entire project

studies have been extended to 25 years.

2.3.2 Chosen Panel

The panel which has the highest efficiency is mostly mono-crystalline, thus

the panel's types have been narrowed by only mono-crystalline panels. One of the

most established, experienced brands in the market of manufacturing panels is

SHARP, when the panel specifications have been studied, and only the panels with

life-time of 25 years are used. They had a higher level of efficiency was compared to

the other panels in the market.

The panel is mono-crystalline which has 14.14% efficiency and lower

sensitivity to the variation of the temperature, the voltage variation is only a

decreasing of 104 mV/C. The peak power of the panel is 185 WP. The voltage at

maximum power point is 24 while the current is 7.71 Amp. The filling factor is

71.75%. The Nominal Operation Cell Temperature (NOCT) is 47.5 C. The Panel

dimensions as show in figure 11 is 1.3180.994 m. the panel has a bypass diodes

which, as mentioned before, will minimise the loss in output when shading occurs.

The panel behaviour with different irradiances is shown in figure 12.

Additional data about the panel which might be useful for the installer:

156.5 mm 156.5 mm mono-crystalline solar cells

48 cells in series

2,400 N/m2 mechanical load-bearing capacity (245 kg/m2)

1,000 V DC maximum system voltage

IEC/EN 61215, IEC/EN 61730, Class II (VDE: 40021391)

Finally, a vital point need for economical evaluation purposes; a full

performance of the panel is guaranteed for five years, a 90% of the full performance


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for ten years and an 80% for twenty five years. Therefore, it will be possible to

extend the project life time to twenty five years. (A detailed data sheet is attached in

appendix C for the reader to refer to if needed).

Figure 11 Selected Panel Dimensions

Figure 12 photovoltaic panel curves with different irradiances.


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2.4.0 Inverter and Control

2.4.1 Maximum Power Point Tracking (MPPT):

A maximum Power Tracker is a device that keeps the impedance of the circuit

of the cells at levels corresponding to best operation. It also converts the resulting

power from the PV array, so its voltage is that required by the load. There is some

power losses associated with the power tracking process

Any PV array, however its size or sophistication, is only capable of producing

Direct Current (DC) power, thus for the system to be integrated into the building it is

necessary to have a methodology to convert the produced DC power into the

building integrated AC power system. The DC to AC Inverter, sometimes referred to

as converter, is used to achieve this function. The System might require more than

one inverter depending on the system size and sophistication.

2.4.2 Connection of Inverter to Array

For many systems, a three-phase inverter is used. In addition, in some cases,

single phase inverter is only needed with a final decision taken by knowing whether

the grid supply is single or three phases; this is because the system should be

coupled with the electrical grid. The system can be connected to the inverters with

three deferent methods depending on the rating of both the PV Generator and the

inverter.

The first method is a single inverter plant, which might consist of single or

several strings; a string is a connection of many modules to form one DC output,

positive wire and negative wire. The single inverter plant implies that the rating of

both the PV generator and the inverter required is relatively small. This method has

many advantages in terms of lower investment cost and low maintenance; but on the

other hand, using one inverter will reduce the reliability of the system since a total

stoppage of power production will occur in case of inverter failure. In addition, this

solution is not suitable for increasing the size of the system, since these increases

the problems of protection against over currents and the problems deriving from

different shading that is when the exposition of the panels is not the same in the

whole plant (Esram and Chapman, 2007).


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The second method is to have many strings with an inverter for each string. In

this layout, the blocking diode will prevent the source direction from being reversed;

it is usually included in the inverter. The diagnosis on production is carried out

directly by the inverter, which in addition can provide protection against the over-

current and under-voltage on the DC side. Moreover, having an inverter on each

string will reduce the coupling problems between the modules and inverters and the

reduction of the performances caused by shading or different exposition. Again, in

different strings, modules with different characteristics may be used, thus increasing

the efficiency and reliability of the whole plant. (Esram and Chapman, 2007).

Finally, the last method is to have a combination of large-size plants, the PV

field is generally divided into more parts (subfields), each of them served by an

inverter of ones own to which different strings in parallel are connected. In

comparison with the layout previously described, in this case there are a smaller

number of inverters with a consequent reduction of the investment and maintenance

costs. However it maintains the advantage of reducing the problems of shading,

different expositions of the strings and of those due to the use of modules that are

different from one another, if subfield strings with equal modules and with equal

exposition are connected to the same inverter. Besides, the failure of an inverterdoes not involve the loss of production of the whole plant (as in the case of single-

inverter), but of the relevant subfield only. It is advisable that each string can be

disconnected separately, so that the necessary operation and maintenance

verifications can be carried out without putting the whole PV generator out of service.

When installing a parallel switchboard on the DC side, it is necessary to provide for

the insertion on each string of a device for the protection against over-currents and

reverse currents so that the supply of shaded or faulted strings from the other ones

in parallel is avoided. Protection against over-currents can be obtained by means of

either a thermo-magnetic circuit breaker or a fuse, whereas protection against

reverse current is obtained through blocking diodes. With this configuration, the

diagnosis of the plant is assigned to a supervision system, which checks the

production of the different strings (ABB, 2010).


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2.4.3 Inverter, process and Functions

Inverters take a great role in photovoltaic electrical production; the inverter makes it

possible to convert the DC power to an AC power used in the building's systems. It

will add a great flexibility with dealing with the produced power since the dealing withDC power can often be difficult and dangerous.

It is important to present a brief introduction about the inverter in order to be

able to understand the basic methodology of how the inverter works. The circuit used

in the inverter is usually a three phase bridge inverter. This circuit is used to convert

the DC power to three phase AC power, which will make it easy to connect, and to,

integrate, the whole new photovoltaic system into the existing system in the building.

Moreover, after integrating both systems together; it is possible to connect their

integration to the electrical grid through a bidirectional kWh meter to calculate the

spending and selling. The typical circuit used in the inverter can be seen in figure 13.

Figure 13 typical circuit used in PV inverters.

The process of inverting the DC power to an AC power inside the

inverter is done using mostly a Pulse Width Modulator PWM to great a sinusoidal AC

output. The process can be explained using figure 13. The battery in the figure

represent the PV panels production, they are connected to the inputs of three legs,

two transistors, and are protected from the reverse current by a diode connected in

parallel with each of them. The DC voltage should be converted to a three phase,

lines, AC output, therefore, each transistor, of the six transistors, will be triggered

sequentially by a controller. The controller has a reference PWM wave, Sinusoidal


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form. The controller will trigger one of the transistors in a process and will form three

phase AC power. Each of the phases is shifted by 120 electrical degree.

Furthermore, in this process the inverter is able to vary the voltage and

frequency at the output. For the case of building integration, the frequency required

to be fixed to either 50 Hz in the UK or 60 Hz in other places. On the other hand, the

inverter need to be able to cope with the variation in the voltage level, hence the PV

generator, relatively, does not have a fixed voltage. The voltage variation can be due

to the change in the temperature of the cell or due to the voltage drop caused by the

resistance of wiring.

The output wave ought to be filtered to lower the effect of any ripples or

harmonics, which might be caused during the conversion process.

2.4.4 Component Selection, Inverter

In conjunction with the photovoltaic panel, the selection of an optimal inverter

to use for the project can be a difficult process since there are many issues to be

considered. One of the main issues when selecting an inverter is to consider the

Maximum Power Point Tracking MPPT voltage range which might affect the final

performance of the system. Any inverter with MPPT will be able to optimallydecrease the effect of shadowing.

In order to select a suitable inverter to be used in the system, some aspects

should be considered. The capability of the inverter to cope with the variation in

voltage is an important matter. The system size is determined according to much

iteration to evaluate the system technically and economically. According to the

system size the inverter rated power will be distinguished. Therefore, the options to

choose an inverter will be limited to a certain level. It is better to choose an inverter

rating half the system size. In this way, two inverters will be installed instead of one.

The main purpose of this is to increase the reliability of the system. When one of the

inverters is out of service only half of the system is lost. Under certain

circumstances, one inverter could be selected, especially if the system rating is low.

The inverter type chosen for this project is going to be able to handle the

whole system solely, since the system size is relatively small compared other

projects. After considering many aspects the system's voltage and current have been


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stated. Hence, the voltage rating is also known. The system voltage is ranging

between 540 V and 576 V, 576 V to be the maximum power point voltage. Now, the

options to choose an inverter, are narrowed, due to the fact that only the inverters

have voltages around this range. 25% of the maximum and the minimum voltage

are considered as a good estimation because a margin of variation above or below

the maximum or the minimum level must be considered. Finally, the market

availability, quality guarantee and the cost should be taken into account.

2.4.5 Summary

In summary, the selection of the inverter, depending on size, is carried out

according to the PV array rated power that the inverter should manage. The size of

the inverter can be determined, from 0.8 to 0.9 for the ratio between the active power

delivered to the network and the PV generator. This ratio considers the power under

real operational conditions (working temperature, voltage drops on the electrical

connection...etc) in addition to the efficiency of the inverter itself.

Finally, the choice of correct size, for the inverter, must be done by taking the

following considerations:

- DC Side:

rated power and maximum power;

rated voltage and maximum admitted voltage;

variation field of the MPPT tracking voltage under standard operating

conditions;

- AC Side:

rated power and maximum power which can be continuatively delivered by

the conversion group, as well as the field of ambient temperature at which

such power can be supplied;

rated current supplied;

maximum delivered current allowing the calculation of the contribution of the

PV plant to the short circuit current;

maximum voltage and power factor distortion;

maximum conversion efficiency;


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Efficiency at partial load and at 100%.

- Other:

Market availability

Life time

Cost

The chosen inverter is a tri-phased Sinvert 60 M from Siemens with 50 Hz

frequency and has a nominal power of 65 kVA (apparent). The inverter has a

minimum MPP voltage of 450 V and a maximum MPP voltage of 750 V. The power

conditioning unit consists of Isolated Gate Bipolar Transistor (IGBT) inverter, DC/AC

distribution, isolating transformer and a controller number SIMATIC S7. It also has a

MPP tracking for optimum utilisation of PV field power. In addition, it has an optional

Voltage Ampere Reactive (VAR) controller for three-phase network. The unit comes

with a control panel with display of operating states and actual values for the user to

interface in order to set the parameters of the inverter.

Furthermore, it does have a switch-over in both manual and automatic mode

by integrated key-switch. Moreover, the following features are included in the unit,

isolation monitoring with selective fault allocation and safety disconnection;

visualization and service software Power Protect solar; interface for process

visualization and an optional integration in management systems via Ethernet,

cabinets for floor mounting, forced ventilation by fan, air intake through lower cabinet

front and cabinet bottom, air discharge through the cabinet roof; cable entry at base

from. Figure 14 shows the component's internal combination. Figure 15 shows the

process in PWM to convert the DC power to an AC power.


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Figure 14 inverter combination

Figure 15 PWM DC to AC process


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2.5.0 Shading:

Taking into consideration the area occupied by the modules of a PV plant,

part of them (one or more cells) may be shaded by trees, fallen leaves, chimneys,

clouds or by PV panels installed nearby. In the case of shading, a PV cell consistingin a junction P-N stops producing energy and becomes a passive load. This cell

behaves as a diode, which blocks the current produced by the other cells connected

in series, thus jeopardizing the whole production of the module (Seung-Ho and Eun-

Tack, 2002). Moreover the diode is subject to the voltage of the other cells which

may cause the perforation of the junction due to localized overheating (hot spot) and

damages to the module. In order to avoid that one or more shaded cells prevent the

production of a whole string, some diodes which by-pass the shaded or damaged

part of module are inserted at the module level. Thus, the functioning of the module

is guaranteed even if with reduced efficiency. In theory, it would be necessary to

insert a by-pass diode in parallel to each single cell, but this would be too onerous

for the ratio costs/benefits. Therefore, by-pass diodes are usually installed for each

module (Kajihara and Harakawa, 2005). See figure 16

Figure 16 By-Pass diode under shading


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Chapter Three


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3.1.0 Project Demand and Hand Calculations

This approach is to decide whether the system will be feasible or not. The

feasibility study will be done through a hand calculation and system simulation using

PVsyst. The Use of both methods; hand and simulation will make it easier to decidethe system size and specification. In addition, the hand calculation will present a

power output at an hourly pace which then can be compared with hourly demand if

available. The hand calculation will make it easier to predict the hourly share of the

proposed system to set an economical plan for the building.

The first section will describe the hand calculation of the system. The

calculation will use one day, as an example to demonstrate the method. Starting with

only one monthly value, for each month, the hand calculation will find the hourly

estimated power output throughout the day, then, the estimated daily total kWh that

can be produced. It is important to note that the hand calculation does not consider

the system losses, since it is going to be considered in the simulation more precisely.

The simulation will be produced using PVsyst, as quoted from the user help

booklet of the program, "PVsyst is a PC software package for the study, sizing and

data analysis of complete PV systems. It deals with grid-connected, stand-alone,

pumping and DC-grid (public transport) PV systems, and includes extensive

meteorological and PV systems components databases, as well as general solar

energy tools."(PVsyst., 2012) Comparison between both calculations will be

presented.

3.1.1 Process of progression:

The system to be proposed will be installed in Kingston University London,

Roehampton campus. The campus is positioned at 15 26 and -00 15 latitude andlongitude. The system proposed is to integrate a photovoltaic system with the

existing electrical system.

The main objective of the project is to, fully or partially; supply the facilitys

electrical demand throughout the year. This will be done by:

This chapter:

- Calculating the system demand and electric system review,

- Calculating the hourly solar radiation on the system,


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- Hand Calculation the hourly electrical power produced annually,

- Optimising the area used and evaluating the available options, system sizing,

Next Chapters:

- Calculating the monthly power production, losses and shading effect using a

simulating program,

- Electrical consideration and power layout,

- Economical Evaluation of the project,

- Comparison of the hand calculation and the simulation results,

The integration of a PV system with a building will be carried out while carefully

considering all the aspects.

3.1.2 Overview, System Demand and Electrical System Review:

The site consists of a main building, which is composed of a library, lecture

rooms, and engineering laboratories, and a secondary building, which mainly

consists of lecture rooms. The buildings total area is approximately 4730 m2

, the

total useful area, which is above the main building, is around 3030 m2. The electrical

load main consumptions are air chillers, laboratories machines, wind tunnel; which is

used for experimental purposes and derived by two main electrical motors, lights,

personal computers and printers.

Similar to all the building's systems in the UK, the facility has 240 Volt/ 50 Hz

electrical systems, which will be supplied through a three phase main incomer

connected on the main board with electrical meters. The main electrical board is

located at the east gate of the building. This main incomer is supplying both buildings

through two sub-boards and connected to monitoring system.

The calculation of the electrical demand of the facility had been carried out

based on electrical monthly bill readings over a period of three years. This monthly

bills had been converted from kWh consumption to kW consumption. The final

monthly demand is shown in figure 17 and table 1. For the sake of comparison, the

electrical demand is kept in kWh in later sections.


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Figure 17 system demand in kW

Table 1 System Demand kW

Month Electrical Demand (kW)

January 345.4943727

February 324.6823017

March 264.0997798

April 200.4881069

May 182.0981522

June 152.2148372

July 156.0801467

August 164.6080031

September 219.5328399

October 287.221441

November 355.4871879

December 341.3481184

The data in both the figure and the table above shows the variation of the

electrical demand from one month to another. It can be shown that the highest

demand had been consumed in November while the least consumption takes place

in June. This situation, unfortunately, contradicts with the incident solar radiationsduring each month, i.e. the highest measured incident solar radiation occurs in June

and July when the lowest electrical consumption takes place, and the lowest

measured incident solar radiation occurs in November, December and January. This

is why system sizing should be carried out with cautious consideration of all the

aspects, since the main purpose of the project is only to supply the facility

consumption. Not taking this into account would lead to an unnecessary increase of

the investment cost. This point shall later be discussed in detail.

0100

200

300

400

January

February

arch

April

ay

June

July

ugust

Septe

ber

ctober

ove

ber

Dece

ber

Monthly

Average

System

Demand


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3.2.1 Hand Calculation:

The hand calculations have been done using a Microsoft Excel data sheet. All

the data and the codes can be found in appendix A. The calculations have been

done for all the days in the same method; therefore, one-hour example will bepresented to demonstrate the methodology of the power output calculation followed.

Power output calculation for a specific site will predict the long term system

performance. Many methods have been developed to calculate the power output of a

PV system. (Duffie and Bickman, 2006) demonstrated many theories, (the reader

can refer to this reference for further reading). For the purpose of this project, one

method has been selected for implementation, with occasional adjustments from

other theories.

3.2.2 Summary and Assumptions:

The aim of this calculation is to estimate the total irradiance on a tilted surface

with knowledge of only one value of, average monthly radiation on a horizontal

surface. Location latitude and the slope angle are primarily data in addition with the

monthly average radiation. Knowing that solar constant is equal to 1367 W/m2will

make it possible to find the extraterrestrial radiation on a horizontal surface and

likewise, the clearness index.

Ideally, the building should be oriented to the south to optimally make use of

the direct (beam) and diffuse radiation throughout the year. However, as the system

is planned to be installed on an already built building's surface azimuth angle might

be considered if the building conditions does not allow a south facing system. The

buildings for the proposed system do not face south, but south-east (SE) with an

angle estimated to be approximately 23.2 from the south or 156.8 from the north.The surface azimuth angle is calculated from the south, thus the used angle in the

calculation will be 23.2. The average daily monthly radiation on September is 2800

Wh/m2. The selected day is the 3rd of September and the selected hour is between

12:00 and 13:00 (day time). The ground reflectance can be found in the NASA solar

database and its average for September is 0.09. Monthly ground reflectance

(Albedo) can be seen in table 2.


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Table 2. Monthly Ground Reflectance, (Albedo)

Month Albedo Value Month Albedo value

January 0.1 July 0.11

February 0.1 August 0.1March 0.09 September 0.09

April 0.10 October 0.08

May 0.11 November 0.10

June 0.11 December 0.10

3.2.3 Calculating the hourly solar radiation on the system:

The hourly solar radiations that fall on the system will be calculated using the

methodology mentioned in previous sections of this paper. The calculation for one

hour in one day will be presented. The selected day is the 3rd of September and the

selected hour will be between 12:00 and 13:00 (day time).Table 3 shows the monthly

global irradiation data on the proposed location and its general information, while

table 4 shows the day information. All the metrological data is taken from European

Commission (EC) solar database.

It should be established that this calculation is done to find the maximum

power production in this specific day and hour based on the final total useful area

calculated later in area assessment section, 408 m2. The optimal area is found after

many iteration calculations to size the system.

Table 3 illustrates the basic information about the day of the study and the

specific hour, which has been carried out as follows.


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Table 3 Monthly average meteorological data (EUROPEAN COMMISSION)

Month H Wh/m2 Day Time Ave. Temperature C Ave. Temperature C Albedo

Jan 736 5.9 5.2 0.1

Feb 1360 6.5 5.8 0.1

Mar 2210 8.2 7.2 0.09

Apr 3680 10.4 9.4 0.1

May 4650 13.5 15.6 0.11

Jun 4820 16.4 15.6 0.11

Jul 4860 18.7 17.8 0.11

Aug 4140 19.2 18.2 0.1

Sep 2800 16.7 15.5 0.09

Oct 1690 13.3 12.2 0.08

Nov 902 9 8.1 0.1

Dec 527 6.1 5.4 0.1

Year 2697.916667 12 11.1 0.099

Table 4 Site Data and Calculated information for one hour of the year

Global Irradiation OnHorizontal Plane

(Wh/m2)

2800 Day Length13.174 Equals to

13h 27m

Day of Month 3 H0(J/m2) 28688146

Month 9 H (J/m2) 10080000

Day of Year 246 Kt 0.351365

Declination Angle 6.958 Hd/H 0.593271

Latitude Angle 51.43 Hd (J/m2) 5980176

Tilt Angle 51 Sunrise (hours) 06:16

Azimuth Angle -23.2 Sunset 19:4

Documents

Photovoltaic System Integration