Scientific Bulletin of the Electrical Engineering Faculty – Year 10 No. 3 (14)
ISSN 1843-6188
CONCERNING THE DESIGN OF A SOLAR FIELD
Ioana Iulia MICLE1, Horia ANDREI2, Helga SILAGHI1,
Ulrich L. ROHDE3, Alexandru Marius SILAGHI1, Mircea PANTEA1
1
Faculty of Electrical Engineering and Information Technology, University of Oradea,
2
Faculty of Electrical Engineering, University Valahia Targoviste 18-20 Blv. Unirii
3
Department of Communications, Technical University of Cottbus, GERMANY
E-mail: mcl_ioana@yahoo.com
Abstract: This paper presents several advantages both
financial and maintenance of using renewable energy. The
paper illustrates an application using photovoltaic panels
connected to the electrical network, the user being able to sell
the energy produced by these modules, and also it's
comparing energy generated, the profit and the period for the
depreciation of PV, for the case in which keeps unchanged
the angle of inclination of the PV throughout the year and
change the angle of inclination of PV, one for the summer
and one for winter.
Keywords: electrical energy from renewable sources,
photovoltaic panels connected to the network
1. INTRODUCTION
Figure 1. Solar radiation [12]
Nature of new of the project is given by current energy
trends of renewable energy sources, characterized by
wide spread of these sources (e.g. in this case is the
Sun). An application of renewable energy technology is
the installation of photo voltaic systems that generate
power without emitting pollutants and requiring no fuel.
Passing through the Earth atmosphere, a part of solar
radiation is absorbed, warming air, another part is pieces of
air molecules, water vapor, dust in the atmosphere
(constituting solar radiation release), but most end up in the
Earth's surface (constituting Solar radiation directly), [1].
Solar radiation intensity depends direct on the atmosphere
condition and the position in the world, the daily
variations in the annual function of terrestrial globe
movement, this being the changes in temperature from
day to night and from a season to another (Figure 1).
Solar radiation varies with geographic latitude, season, and
time of day due to the various sun positions in the sky.
Hence, the problem of designing the optimal tilt angle and
the orientation of a solar panel arises for maximizing solar
radiation collection at fixed latitude [3], [4].
Energy produced by Sun radiation contains a whole
spectrum of wavelengths and constitutes small packs of
particles of energy called photons. Light is composed of
those visible wavelengths for human eye. Light is
moving at a speed of 300 000 km/s.
2. THE SPECTRUM OF RADIATION
The spectrum of radiation depends on the wavelength
and shows absorptions due to the presence of water or
carbon dioxide in the atmosphere, shown in Figure 2.
Figure 2. Spectrum of radiation [4]
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Scientific Bulletin of the Electrical Engineering Faculty – Year 10 No. 3 (14)
Photoelectric effect, represents the conversion of solar
energy (“photon”) into electricity (“volt”) and it was
discovered in 1839 by physicist Edward Becquerel
[5],[6]. This effect is based on three simultaneous
physical phenomena that are closely linked:
• Absorption of light by materials
• Energy transfer from photons to electrical charges
• Collecting tasks
One of the uses of solar radiation is to transform it into
electricity through the
photoelectric
process.
Photoelectric cell is not a source of constant voltage or
constant current source, a photoelectric cell can be
assimilated to a photosensitive diode, its operation based
on the property of semiconductor materials. The ratio of
electricity and radiant energy incident on the surface
determines the efficiency of solar cell, modules. Actual
construction of photovoltaic cells based on basic
properties of semiconductor materials that are able to
release electrons when photons are bombarded. The
problem of the evaluation of incident solar radiation on a
surface can only be tackled with cautious approximation
because of many variables are involved and their
unpredictability (presence of clouds, atmosphere
transparency, etc.), [7].The solar radiation incidence
depends on two fundamental parameters: height of the
sun and its position. Figure 4 shows the position of the
sun along its apparent trajectory during the identified
day by two angles:
β: Solar elevation angle provided by the right that joins
respectively the centers of the earth and the sun with the
horizontal plane;
Ψ: Azimuth (or azimuth angle) is the angle that the
projection of the normal to the surface, receiving the
horizontal plane, makes with the south direction. Can
take values between -180 ° and 180 °. It is invalid (0°) if
it coincides with the projection direction south - is
positive if the projection falls in the eastern half plane is negative in the opposite case.
The azimuth angle describes the deviation plan in which
the panel is, from a southerly direction, this means that
when the panel is oriented towards south, azimuth angle
is 0°. Since solar radiation is stronger during the noon,
plane collectors must be oriented as possible to the
south.
energy can be taken if the plan in which the panel is
perpendicular to sunlight. As the angle of incidence of
radiation depends on the hour and the season, plan the
panel should be positioned to meet the sun's position in
the range of maximum radiation.
Figure 4. Global radiation on an slope plan. [12]
Analyzing the diagram, we see that the optimum tilt
angle to capture solar radiation is 15 - 55 °, and
deviation from a southerly direction may be between ±
40 ° without affecting the ability to capture solar energy.
Even collectors mounted vertically, with a deviation of
up to ± 20 ° to the south, may recover 80% of solar
radiation. Arguably, the solar collectors to the horizontal
orientation and to south, there is an issue as sensitive.
The diagrams of the trajectories of the Sun (in terms of
height and azimuth from the sun) in a day, for several
days of the year are shown in Figure 5. The days - one per
month - are chosen so that the declination of the solar day
is the average of the month. In the reference polar, rays
joining points of equal azimuth, while the concentric
circles, join points of equal height. Here the circles are
drawn with steps of 10 ° from the outer circumference
(height = 0 °) to the central point (height = 90 °).
Figure 5. Solar diagram
Figure 3. Solar trajectory [12]
But in the Cartesian reference, the solar azimuth angle
and height are set respectively on the axes of abscissas
Angle of inclination of the solar panels is the angle
between the horizontal and panel. Largest quantity of
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Scientific Bulletin of the Electrical Engineering Faculty – Year 10 No. 3 (14)
and ordinates (Figure 6). In both diagrams, a dashed line
shows the time-related: it is true solar time, which
differs from the average time marked by the usual
clocks.
ISSN 1843-6188
ratio of diffuse light intensity radiated by a body and the
intensity of light falling on that body. Albedo is a
measure of the reflection of an object (albedo of 1.0 for
a perfectly reflecting object, and albedo of 0.0 for an
object that absorbs all the light), the ratio of light
reflected by an object and the light incident (Figure 7).
3.
SIZING THE PHOTOVOLTAIC
INSTALLATIONS
As an application of renewable energy technology we
can make an installation of photovoltaic systems that
generate power without emitting pollutants and
requiring no fuel.
The methods of dimensioning of a photovoltaic plant
differ substantially according to its intended to energy
supply, customers isolated or customers connected to the
electricity network.
Photovoltaic power systems are generally classified
according to their functional and operational
requirements, their component configurations, and how
the equipment is connected to other power sources and
electrical loads.
The two principle classifications are grid-connected or
utility-interactive systems and stand-alone systems.
Photovoltaic systems can be designed to provide DC
and/or AC power service, can operate interconnected
with or independent of the utility grid, and can be
connected with other energy sources and energy storage
systems.
Figure 6. Tilt and azimuth angle of the sun
Once the angles are known, it is possible to determine
the instantaneous solar position, in order to assess the
energy flow of incident solar radiation on a surface that
allows the determination of the incidence angle between
the normal to the surface and the solar rays (sun-surface
right).
If the surface is inclined, it receives less diffuse
radiation from atmosphere, but it can receive an
additional amount of reflected radiation due to the
reflection from the ground. The reflection factor is
called albedo. It varies considerably depending on the
nature of the soil, vegetation, etc.
Figure 8. Photovoltaic panel
The main component in grid-connected photo voltaic
systems is the inverter, or power conditioning unit (PCU).
Conditional power unit converts the direct current power
produced by photovoltaic arrays in AC power and
automatically stops supplying energy to the utility grid
when it is not powered. At night and during other periods
when electrical loads are greater than the output of the
photovoltaic system, balance of power necessary for
charge carriers is received from the utility electrical
power. This safety measure is necessary to all network
connected photovoltaic systems, and ensures that the
photovoltaic system will continue to operate and refuel to
the utility grid when the grid is in service or repair.
Figure 7 . Albedo angle [11]
Albedo (White in Latin) is a measure of reflectivity on a
surface or body. It is a photometric quantity equal to the
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ISSN 1843-6188
Scientific Bulletin of the Electrical Engineering Faculty – Year 10 No. 3 (14)
Photovoltaic cells are connected electrically in series or
in parallel circuits to produce voltage, current and higher
power levels. This connection must be compliance with
certain specific criteria, given the imbalances that are
created during operation in a network of photocells.
Basically, even if many cells forming a generator are
virtually identical, because of the inevitable dispersion
of production, they have different characteristics.
Furthermore, lighting and temperature cells are not the
same for all cells in the network. When connected in
parallel, the voltage at the terminals of all cells is the
same, the current result by the sum of all cell currents
components. Feature is given by the sum of all currents
provide cell components at a certain voltage (Figure 9).
to determine a power peak [Wp] (Watt peak) as high per
m2.
First calculate the solar radiation (W/m2) under standard
conditions (25 ° C, 1000 W/m2, 1.5 AM). Depending on
the panel area S = (L * l) (panel sizes to be processed in
m), I’ll make the following transformation:
S = L * l = 1.58 [m] * 0.8 [m] = 1264 [m2]
(1)
For this paper we choose panels model AL-180M35W;
Mono Silicon Crystalline terrestrial photovoltaic
models.
Knowing that in the data provided by the manufacturer
gives us power (this power is provided by panel testing
under standard test conditions (STC).
Standard Test Conditions are defined by a module (cell)
operating at a temperature of 25 ° C and solar radiation
index level of 1000[W/m2] as an air mass of AM 1.5 .
Global solar lights indicate weakening the earth's surface
depending on latitude desired browsing a large air
masses proportional to the latitude (in this case is
considered latitude 50 °), [8], [9].
This corresponds to Central European summer
conditions in northern Italy until Southern Sweden. In
winter conditions corresponding to values of AM 4 to
AM 6.The absorption spectrum of atmospheric and light
falling on the panel is moved.
Global indicates that light is composed both of light and
in the direct run.
Pp = 180 [W] are given a power of 1000 [W/m2]
(2)
Figure 9. Diagram of modules in a complete photovoltaic
field diodes for protection.
This project was started by location on map and by
drawing surface boundaries and objects that may cause
shading panels (Figures 10, and 11).
Pin = 1000 [W/m2] * 1.26 [m2] = 1264 [W]
For this model of panel, power out is:
Pout = 180 [W]
(3)
(4)
η = Pout / Pin = 180/1264 = 14.24 [%]
(5)
The panel efficiency η is chosen.
(Pp=power peak; Pin= power in; Pout = power out)
The simulation tool SOLARITALY of ENEA Italian
Institute was used and applied to measure solar radiance
data performed by ENEA from 1995) we can get the real
radiation W/m2 by entering the following data:
- latitude = 44 ° 56 ',
Figure 10. Location of the land with Google Map
Figure 11. Using Rhinoceros for drawing land limits and
buildings that can produce the shadowing of the panels
Determine the longitude and latitude of the surface (that
it will use in finding the proper inclination of the panels
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Scientific Bulletin of the Electrical Engineering Faculty – Year 10 No. 3 (14)
- longitude = 11 ° 03 ',
- Albedo coefficient (0.25),
- Azimuth angle (0°),
- Inclination angle of the panels (34°)
Regarding the angle inclination of the panels (Figure
12), we have two possibilities: to put the panels at 34 °
and maintain it throughout the year or to have two
distinct angles of bending the panels (15 ° in summer,
and 50 ° in winter), shown in Figure 13. This requires a
change twice a year (summer and winter).
The optimum tilt angle values for winter months are
very different from the values relative to summer
months. This fact suggested the idea of planning semi
fixed solar panels, whose tilt angle can be changed twice
a year to obtain an advantageous energy gain without
onerous maintenance costs such as the case of solar
tracking systems.
May
June
July
August
September
October
November
December
absent
absent
absent
absent
absent
absent
absent
absent
ISSN 1843-6188
5.67
5.93
6.09
5.57
4.87
3.68
2.71
2.06
kWh/m2
kWh/m2
kWh/m2
kWh/m2
kWh/m2
kWh/m2
kWh/m2
kWh/m2
-
Annual global radiation on inclined surface: 1608
kWh/m2 (year conventional 365.25 days), shown in
Table 1.
Yearly power production (at the cables) = global annual
radiation on inclined surface (kWh/m2) * Total surface
(m2) * STC efficiency of the modules (to dim) * BOS
(a-dim) =? kWh
Wout = 1608 [kWh/m2] * 1264 [m2] * 0.1424 [a-dim] *
0.8 [a-dim] = 231,543 [kWh]
(6)
BOS (balance of system) is a term typically refers to
photo voltaic and wind power and expressed as a
percentage of energy losses that occur in the plant due to
various factors such as the coupling between the various
PV modules, the links with the / converters / s, the losses
in paintings, in Conductors, etc. Given the significant
investment to overcome for the construction of large
facilities and powers involved one or more points in
more or less in BOS may mean, sometimes, several
thousand per year.
ηB.O.S = 75 to 80 [%]
When we calculate the energy we have to keep account
of module efficiency and energy losses (due to the
inverter, cables, conductors, etc..). So but the energy
they have available to be used is given by
Figure 12. Panel orientation [10]
Pout = Pin * ηBOS * ηmodul
The energy emitted by the sun reaches the panel, and
then depending on the efficiency of the cell goes into the
panel whether it is a generation 1, 2, 3, will support a
transformation. This transformation Ein (Pin), in Eout
(Pout) is exactly the form of electricity current. Further
current bear some loss in stand turned up when ηBOS
noted that counting the energy obtained.
With an average annual radiation of 1608 [kWh/m2],
with a panel with an efficiency of 14.24% and loss of
ηBOS we get Wout = 231.543 [kWh], with a catchment
area of 1.264 [m2] against an angle of 34 °. The problem
still is the fact that the set of a surface (S = 14.561 m2) in
conditions which are opting to change the angle of
inclination of the panels for summer and winter. During
winter, when the sun is very low due to very long
shadows, consequently occupy a surface on which a
panel is larger, it will not be able to install the same
number of panels that in summer so will result in a
smaller number of kWp installed.
Figure 13. Drawing the panels orientation on the field at an
angle inclination of 34°, with Rhinoceros
Table 1. Monthly average daily global solar radiation
(Madgsr) on inclined surface five-year average calculate
for all year
Month
January
February
March
April
Obstacle
absent
absent
absent
absent
Madgsr on incl. surf
2.66
kWh/m2
3.61
kWh/m2
4.73
kWh/m2
5.20
kWh/m2
(7)
Error
-
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ISSN 1843-6188
Scientific Bulletin of the Electrical Engineering Faculty – Year 10 No. 3 (14)
Shading on the panels can be (Figure 14).
Shading caused by panels between them (line 2 will be
overshadowed by turn 1), if we don’t respect the distance
between rows. The resulting calculations as binding
between them, row n +1 will be overshadowed by row n.
Shading caused by buildings, trees, hedges that are up to a
distance of 100 m. These shadows are very important
because in winter, the sun is very low and the shadows are
very long.
Month
January
February
March
Obstacle Madgsr on incl. surf Error
absent
2.95 kWh/m2
absent
3.84 kWh/m2
2
absent
4.77 kWh/m
Present
April
1.90 kWh/m2
all day
Present
May
2.23 kWh/m2
all day
Present
June
2.37 kWh/m2
all day
Present
July
2.28 kWh/m2
all day
Present
August
2.04 kWh/m2
all day
Present
September
1.64 kWh/m2
all day
October
absent
3.82 kWh/m2
2
November absent
2.95 kWh/m
December
absent
2.29 kWh/m2
Annual global radiation on slope surface: 1006 kWh/m2
(year conventional 365.25 days)
Figure 14. Simulation shadow produced by the objects
around the field
Wyear = 1006[kWh/m2]* 1.264 [m2]* 0.1424 [%] * 0.8
[%]= 144.858 [kWh]
(8)
Summer: For azimuth=0[º]; inclination=15[º];
Input data:
- Latitude: 44 ° 56'55'',
- Longitude: 11 ° 03'56''
- Azimuth: 0 °
- tilt from the horizontal plane: 15 °
- Model for calculating the fraction of scattered radiation
than the global ENEA-SOLTERM
- Reflection coefficient of soil: 0.25
- Units: kWh/m2
Summer+Winter:WoutS
+
WoutW
[kWh]+144.858[kWh]= 322.259[kWh]
(9)
4.
Obstacle
Present all day
Present all day
Present all day
absent
absent
absent
absent
absent
absent
Present all day
Present all day
Present all day
177.401
CALCULATION OF REAL ENERGY
The area which occupies a panel on a surface is given by
the area of the panel and by the shadow that formed;
these calculations are made for worst day of the year,
December 22th, the day when the sun has the lowest
height. So for a panel with an area of 0.8 [m] wide and
3.61 [m] length (length panel + shadow) follows an area
occupied by panel
Spanel = 0.8 [m] * 3.61 [m] = 2.88 [m2]
(10)
Table 2. Monthly average daily global solar radiation
(Madgsr) on inclined surface five-year average calculate
for summer
Month
January
February
March
April
May
June
July
August
September
October
November
December
=
Madgsr on incl. surf Error
0.75 kWh/m2
2
1.10 kWh/m
1.55 kWh/m2
2
5.16 kWh/m
2
5.93 kWh/m
6.35 kWh/m2
2
6.47 kWh/m
5.66 kWh/m2
2
4.64 kWh/m
1.28 kWh/m2
2
0.86 kWh/m
2
0.65 kWh/m
-
To find the number of panels that can be installed in a
fixed area:
Sfield = 14561 [m2]:
(11)
Sfield / Spanel = 5041 [panels]
Peak power is the maximum value power point
corresponding to standard test conditions Pp = 180 [Wp]
, this is the value for one panel, which means that 5041
panels will have a peak power of:
Pp = 180 [ Wp] * 5041 = 907.38 [kWp]
(12)
Table 3. Monthly average daily global solar radiation
(Madgsr) on inclined surface five-year average calculate
for winter
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Scientific Bulletin of the Electrical Engineering Faculty – Year 10 No. 3 (14)
Stot = 1.264 [m2]*5041[panels] = 6371.82 [m2]
5.
Erad = 1608[kWh/m2]*6371.82[m2] = 10245886 [kWh]
ISSN 1843-6188
CONCLUSIONS
1. Experience from past projects can help to improve the
quality of new projects and to avoid problems in current
and future large-scale projects.
(13)
Eyear = 10245886.56[kWh] * 0.1424[a-dim] * 0.8 [adim] = 1 167 211 [kWh]
(14)
2. The environmental impact of solar field is limited to,
the only space and the visual impact, since there are no
polluting, thermal and acoustic emissions. Of course, in
the context of the energy balance and environment must
be taken into account the emissions and energy
consumption resulting from the production phase of
photovoltaic modules. Of course, high values are
obtained in the case of plants connected in network and
installed in areas with high sunshine.
For an inclination angle of 15 °, maintained during the
summer:
Spanel = 0.8 [m] * 2.59 [m] = 2072 [m2]
(15)
Sfield / Spanel = 7027 [panels]
(16)
3. It is relevant for the PV community to be informed on
the performance of PV systems, information is vital in
this area, any delay in promoting recent discoveries may
slow the implementation of solar energy to global scale.
PpS = 180 [Wp] * 4372[panels] = 786 [kWp] (17)
Stot = 1.264 [m2] * 4372 [panels] = 5526 [m2]
(18)
4. Time of use is expected to be 30 years, in which case
their yield should not fall below 80% of the baseline. As
can be seen the period of depreciation of all investments
represent 30% of life guaranteed modules solar energy
system by using national network for selling the energy
produce by the photovoltaic panels, and by changing the
angle of inclination of the panels, one for summer (15
degrees) and one for winter (50 degrees). This change of
angle of inclination of the panels will yield three million
Euros, compared with keeping a certain angle of
inclination (34 degrees) throughout the year.
Erad = 1232 * 5524.2 = 6 808 288.2 [kWh]
(19)
Esummer = 6 808 288.2 * 0.1424 [a-dim] * 0.8 [a-dim] =
775 600[kWh]
(20)
For an inclination angle of 50 °, maintained during the
winter:
Spanel = 0.8 [m] * 4.17 [m] = 3.33 [ m2]
(21)
6.
[1]
Mario Pagliaro, Giovanni Palmisano, Rosaria Ciriminna
– Il nuovo fotovoltaico, Dal film sottile alle celle a
colorante; Dario Flacovio Editore, 2008.
[2]
[3]
Daniele Cocco, Chiara Palomba, Pierpaolo Puddu Tehnologie delle energie rinovabili; SGEditoriali Padova
Gabriele Zini - Conto energia e analisi economica di
impianti fotovoltaici;Universita di Modena e Reggio
Emilia, 4 Novembre 2008.
[4]
Gabriele Zini – Sistemi fotovoltaici; Universita di
Modena e Reggio Emilia, 4 Novembre 2008.
[5]
A.Lay-Ekuakille, G. Vendramin. A. Fedele, L. Vasanelli
and A. Trotta, PV maximum power point tracking
through pyranometric sensors: Modeling and
characterization, Vol.1, Nr. 3, September 2008.
[6]
A.C. de Keizer, E.W. ter Horst, E.C. Molenbroek,
W.G.J.H.M. van Sark - 22nd European Photovoltaic
Solar Energy Conference, 3-7 September 2007, Milan,
Italy; Evaluating 5 years performance monitoring of
1MW building integrated PV project in Nieuland
Amersfoort, The Netherlands - Utrecht University, Dept.
Science, Technology and Society, Copernicus Institute
for Sustainable
Sfield / Spanel = 4372 [panels]
PpW = 180 [Wp] * 4372 [panels] = 786.96 [kWp]
Stot = 1.264 [m2] * 4372 [panels] = 5524.2[m2]
Erad = 1006 [kWh/m2] * 5524 [m2] = 5557345[kWh]
(22)
Ew = 5557345.2 * 0.1424 [a-dim] * 0.8 [a-dim]
=633092[kWh]
(23)
Winter:
PpW = 786.96[kWp]
Etot = Es + Ew = 775600 [kWh] + 633092 [kWh]
=1408692 [kWh]
(24)
92
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ISSN 1843-6188
Scientific Bulletin of the Electrical Engineering Faculty – Year 10 No. 3 (14)
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[11] www.energyeducation.tx.gov/.../img/albedo.gif
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