Photovoltaic System, Hourly Electricity Generation. (Excel Calculation model and case study, Kingston University Building). Omar Hamdan Supervised by: Dr. Paul Wagstaff MSc Renewable Energy Engineering October 2012 Faculty of SEC, Kingston University
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This thesis is divided in a way to permit the reader to follow the content in a
logical sequence.
The main objective of this thesis is to design a photovoltaic system to be
optimally integrated with the electrical system in Kingston University London,
Roehampton Vale campus. This system main objective is to supply the electrical
demand of the facility.
The thesis presents a piece of work to calculate the power output of the
photovoltaic system in hand calculations and software simulation.
The thesis will evaluate the location of the installation by means of radiation
falls on the location, construction of the photovoltaic system, sizing the system by
evaluate the options according to area available and capital cost.
The hand calculation will present a model develop on excel to calculate the
power output by calculating the solar irradiances on a tilted surface, converting the
irradiances to electrical power and considering the effect of temperature on
photovoltaic cells.
The simulation part will present an entire design of the system by means of
calculating the power output, losses associated with the conversion process and
connection, shade study and result analysis
The sizing of the system was carried out through hand calculation, simulation
and economical analysis. Finally an economical evaluation for many models will be
presented.
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Table of Contents List of Figures ..................................................................................................................................... VI
List of Tables .................................................................................................................................... VIII
List of Equations ................................................................................................................................. IX
Chapter One ........................................................................................................................................ 1
5.1.1 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
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 Ht according 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 £) .... 88
Table 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
structural glazing and tilted façade . 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 1 3 4 3 4
8 10 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 PV
panels. 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 1011 meter 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 the
earth 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 the
earth from the sun, which will vary by ± 1.7% of its mean value , which is equal to
1.495×1011 m. 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 Lst is the standard meridian for the local time zone, Lloc is the longitude
of 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 10˚ to 15˚ less
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 Incident
This 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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In this paper radiations have been dealt with as three parts; Beam radiation,
Diffused radiations and Ground reflected or what is known as Albedo. The beam
radiations are the amount of radiations that have been received on a specific surface
without scattering; it will be represented as Hb. The diffused radiations are those
radiations, which their direction have been changed before they receive a specific
surface. Finally, the ground reflected radiations are the radiations received on a
specific surface after they have been reflected from the ground.
1.5.1 Clearness Index:
The Clearness index gives a measure of atmospheric transparency. It shows
the relation between solar radiation at the Earth's surface and extraterrestrial
radiation. It is related to the path of which the solar radiations have been received on
earth's surface, which will be illustrated in a later section, referred to as atmospheric
AM value. It also represents the composition and the cloud content of the
atmosphere (Luque and Hegedus, 2011). Thus, the Clearness Index is defined as:
Equation 8 Clearness Index
Where, is the monthly average daily solar radiation on a horizontal surface
and is the monthly average extraterrestrial daily solar radiation, which can be
found from the following equation:
Equation 9 global Hourly irradiance on horizontal surface
1.5.2 Calculating of Hourly Global and Diffused Irradiance
To calculate the hourly irradiances, a developed method by Erbs et al and
introduced by (Duffie and Beckman, 2006), was used. It is obvious that the amount
of the diffused radiations will be a function of Kt, thus the theory developed the
monthly average diffused fraction correlation. Equations for these correlations are as
following, for :
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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) are values 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 Rb Value
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 the
resultant 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 carries
specific 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, CO2 and 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 solar
system 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 the
speed 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), and
water 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 leakage
current Ish. The resistance in series Rs represents 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 Rsh takes into account the current to earth under normal
operational conditions. In an ideal cell the values of Rs is zero while the value of Rsh
is maximum. On the contrary, in a high-quality silicon cell the typical value of Rs 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 Rsh too 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. IL equals 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
(1.6×10-19 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 (1.38×10-23 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 Iph and 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:
Isc short-circuit current;
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Voc no-load voltage;
Pm maximum produced power under standard conditions (STC);
Im current produced at the maximum power point;
Vm voltage 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 as
described 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 and
are the efficiency and the temperature of the panel under the Standard Testing
Conditions (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 Tc is 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 Cf.
(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. The
equation 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 took
priority 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 1.318×0.994 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:
Looking at the first and the second model it can be seen that the payback
period for the first model is around 16.5 years while the second model payback
period is 13 years. Upon this it can be decided that it is better to decrease the
investment cost and, in the same time, the decrease the risk.
The produced kWh in the third model is less than the second model since the
losses were calculated in the simulation process. The payback time is less as
expected. On the other hand, the calculation in the simulation, occasionally, can be
inaccurate. The savings on the energy bill for both models, the first and the second,
are shown in figure 56 and figure 57. Figures 58 and 59 shows the demand and the
produced kWh in the first and the second model.
Figure 56 Saving on Electricity bill in first model
Figure 57 Saving on Electricity bill in the second model
-2000
-1500
-1000
-500
0
500
1000
1500
Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec
Elec
tric
ity
bill
(£
)
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Electricity Bill
New bill
Old bill
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Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Ele
ctri
city
bill
(£
)
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Electricity Bill
New electricity bill Old electricity bill
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Figure 58 Demand and Production for the first model
Figure 59 Demand and Production for the second model
6.3.0 Analysis
It can be seen that there is a huge different between the model when no
losses is considered and when the losses is considered. Therefore, the economical
evaluation must be done according to the closest power production value.
0
5000
10000
15000
20000
25000
30000
Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec
Chart Title
Produced kWh D (kWh)
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Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec
kWh
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Demand and production
New load Load
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Chapter Seven
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7.1.0 Critical Review
The approach to design this project was to evaluate the project characteristics
by hand calculations and then combining the hand calculations with a simulation.
The analysis of the site in terms of demand, solar radiation, useful area
available, obstacles and shading and other related issues help to set a methodology
to decide the system. London's solar irradiances and the clearness index values
were the main dampers of the electrical production the clearness index average
value was calculated to be 0.39. This value considers low compared with clearness
index values at other locations.
The facility demand played a great role of varying the system size since there
is a gap between summer's months and winter months. Considering the estimated
electrical production in summer is higher than the estimated production in winter
whilst the demand of the facility is higher in winter and less in summer.
The area assessment was done upon site survey and as built buildings
diagrams. Many trouble-shootings were done to estimate the size of the system but
the main challenging was the obstacles on the main building roof and the loading
withstand of the roof itself. Thus, an erected structure was suggested to overcome
this issue.
Hand calculation power production value and simulation power value were
quite different because in the hand calculation no losses were considered while the
simulation program presents realistic values.
7.2.0 Further Work
Any further work can be applied is to improve the hand calculation model by
adding equations to consider the system loss and attenuation losses. In addition, the
system size can be modified using different iterations. Those iterations can be
economically evaluated by the model presented in chapter six.
Finally, more economical analysis and evaluations can be added to this
project since this project was scientific oriented more than economical one.
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Chapter Eight
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Omar Hamdan | Kingston University London
7.1.0 Conclusion
The paper presents a method to design, size and evaluate photovoltaic
system. Many models were built to evaluate the system by means of electrical
configuration, structure and economical configuration.
Those models were evaluated using hand calculations, simulation of different
iterations of the project and an economical model to decide the system size and its
entire configuration. The size of the system is first assumed to use the maximum
area available for production. This model was modified after looking at both the
amount of production, according to hand calculation and simulation, and the
economical feasibility.
Later, another model was presented by limiting the production to 20% of the
demand of the month with the lowest solar electricity production. After evaluating the
model by hand calculation, simulation and an economical model presented, it was
found that the system size suggested is going to partially achieve the objectives of
the project. The system size was decided according to that.
Later an electrical design, shade simulation and system configurations were
presented for the selected system size. The system size decided to be 57.5 kWp,
which is expected to be injecting to either the facility electrical network of the national
electrical grid.
Number of arrays decided was 13 arrays in parallel accumulating of a current
equal to almost 102 A. A twenty four panel is decided to be connected in series and
accumulate a voltage of 543 V after considering the wiring voltage drop.
Total area used for the system is 858 m2 including only 409 m2 active area.
Number of panels decided to be 312 modules and one inverter with rated power of
60 kWp is decided to be installed with the system. Electrical configurations and
protection methods were stated.
After calculating the capital cost and the operation and maintenance cost, the
project is found to payback the capital in 13 years according to data from hand
calculations. A longer period is predicted according to power data from the
simulation. The payback period found to be 21 years.
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