Photovoltaic Training - Session 1 - Design
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Transcript of Photovoltaic Training - Session 1 - Design
Photovoltaic Systems Training
Session 1 ‐ Design
http://www.leonardo-energy.org/training-pv-systems-design-construction-operation-and-maintenance
Javier Relancio & Luis RecueroGeneralia Group
September 14th 2010
PHOTOVOLTAIC SYSTEM
Design, Execution, Operation & Maintenance
FACILITY DESIGN
Javier Relancio. Generalia Group. 14/09/2010www.generalia.es
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INDEX
Evaluation of the solar resource
Increasing the plant profitability from the design
Choosing the components
Photovoltaic facilities calculations
Single-line diagram
3 http://www.leonardo-energy.org/training-pv-systems-design-construction-operation-and-maintenance
INDEX
Evaluation of the solar resource
Increasing the profitability of the plant from the design
Choosing the components
Photovoltaic facilities calculations
Single-line diagram
4 http://www.leonardo-energy.org/training-pv-systems-design-construction-operation-and-maintenance
Characteristics of the solar resource: random and variable
Great quantity and quality of measurement stations, both the global radiation and its
components: direct and diffuse
These stations are insufficient to allow the evaluation of any geographical location
or with changeable topography.
The usage of Geostationary satellites images are
a tool that can cover this gap
They are more reliable than the interpolation
of the data from closer meteorological stations
Solar resource evaluation
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Each day, we can find new
maps, which have less
uncertain measures
They allow a first approach to
the viability study for a solar
plant location
They can be considered
enough for small solar facilities
But, to get a completely certain measure, a rigorous solar radiation evaluation must
be done in situ.
Then, we could additionally compare them with the satellite information and
the closer meteorological stations
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Source: NASA
Solar resource evaluation: Solar Radiation maps
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INDEX
Evaluation of the solar resource
Increasing the plant profitability from the design
Choosing the components
Photovoltaic facilities calculations
Single-line diagram
http://www.leonardo-energy.org/training-pv-systems-design-construction-operation-and-maintenance
OPTIMUM PROFITABILITY
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Towards the profitability of the plant from the design
Resource evaluation System losses (PR)
• Shadows
• Disconnections & Breakdowns
• Panel tolerance
• Pollution, dispersion & reflectance
• Temperature
• Inverter
• Cables
• Latitude
• Longitude
• Altitude
• Data from closest
meteorological stations
• Data from satellites
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INDEX
Evaluation of the solar resource
Increasing the plant profitability from the design
Choosing the components
Photovoltaic facilities calculations
Single-line diagram
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The inverter can be considered as the heart of a solar facility
Its cost, in relation to the complete installation, is between 6% - 9%
Its performance is already between 95 %-97 %
It is important to know about their operation principles. We can find 3 options:
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Inverters: Trends
MULTI POWER STAGES ONE POWER STAGEMULTI CONTROLLED
POWER STAGES
The electrical companies can ask for galvanic isolation transformers when the connection
is in low voltage
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Inverters: features
The inverter main features are:
Maximum Input Voltage:
The PV generator voltage must be under the
inverter maximum input voltage
MPPT Voltage:
It is the range where the inverter is able to get
the Maximum Power Point from the PV
generator I‐V profile.
The PV generator voltage must be within this
range in the different conditions and weather
during the whole year.
Source: SolarMax
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Other important parameters are:
• Inverter efficiency:
• As it is shown in the graphic, the inverter has a different efficiency depending on the load. Usually,
the manufacturers give the maximum efficiency and the european efficiency, which is the weighting
of the different efficiencies when the load is: 5%, 10%, 30%...100%
• Inverter temperature range:
• This is really important, as in some places the temperature can reach over 40º, and extra cooling
might be considered
Inverters: Features
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Crystalline or Thin-film Panels
Visual identification:
Mono crystalline Poli crystalline Thin film A‐Si:H
Source: Atersa
They are cheaper, but they need larger surfaces & structures
The guaranteed output power is not as precise as in Mono/Poli crystalline modules
There are no references from facilities producing an important amount of years
Thin film panel observations:
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Crystalline or Thin film modules
CRYSTALLINE PANEL PRICE* TEMPERATURE INFLUENCE
Mono crystalline
Poli crystalline
THIN FILM PANEL
CGIS (Copper‐Gallium‐Indium Selenide)
CIS (Copper‐Indium Selenide)
CdTe (Cadmium telluride)
A‐Si:H triple (Amorphous silicon triple union)
A‐Si:H tandem (Amorphous silicon double union)
A‐Si:H single (Amorphous silicon)
EFFICIENCY REQUIRED SURFACE
* This information can be altered depending on each manufacturer price policy
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PV Module Specs
Source: Atersa
The most important electrical spec is the panel efficiency
The highest the efficiency is, we will require a smaller
surface to reach a certain output power
Voltage and current parameters are not determinant, as we
can connect the panels in series or in parallels to fit the
inverter input.
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PV Module Specs
Source: Atersa
Source: QS Solar
Among panels with different technologies: we can find big differences, as we can see in the technical
information below.
The losses due to temperature affect the production
specially in countries with latitudes between 0 – 35º
Among panels with the same technology: the
thermal coefficient is quite similar among the
different manufacturers & models
A: Si Polycrystalline
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Concentration technology is still being developed
Fresnel Lens (and other kinds)
Refractive optical system
Concentration up to 500x
Potential cost savings
Improvement in cell efficiency: from actual 30% towards 40%
Increasing the concentration: from actual 500x towards 1000x
Hardest challenges
Extremely accurate suntracking (Accuracy < 0.1 - 0.2º): High costs
Optical elements degradation
Cooling systems are required
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Concentration Panel
Source: Everphoton
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The protections to be installed are:
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Example: ABB S800PV (Specifications)
S800PV-S High Performance MCB
Versions: 2P, 3P & 4P
Current: Up to 80 A
Voltage: 800 Vdc with 2P & 1200Vcc with 3P & 4P
S800PV-M Switch-Disconnector
Versions: 2P, 3P & 4P
Current: Up to 125 A
Voltage: 800Vcc with 2P & 1200Vcc with 3P & 4P
Protections
ACMiniature Circuit Breaker (MCB)
ACDifferential
DCFuses
Source: ABB
DCMiniature Circuit Breaker (MCB)
AC sideDC side
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Overvoltage protections
To protect the installation against overvoltage we must install high energy varistors close to the element that we want to protect
The main aim of this device is to detect an overvoltage within a certain period of time and then divert it to the ground
The device may be destroyed depending on the power to be diverted to the ground
Type 150 275 320 385
According to standard IEC – 61643 – 1
Maximum voltage (AC/DC) Uc(L‐N/N‐PE) 150/200V 275/350V 320/420V 385/500V
Nominal discharge current (8/20) In (L‐N/N‐PE) 20/20 kA
Maximum discharge current (8/20) Imax(L‐N/N‐PE) 40/40 kA
Protection Level Up (L‐N)Up (N‐PE)
< 0.9 kV < 1.5 kV < 1.5 kV< 2 kV
< 1.9 kV
Tracking current If (L‐N/N‐PE) > 100 A RMS
Response time tA (L‐N/N‐PE) < 25 ns / 100 ns
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Cables
Cable Requirements for PV facilities
The facility has a lifetime of over 25 years
From solar panel to inverter: weatherproof for outdoor conditions and
suitable for indoor conditions (in houses or industries)
From inverters to meters: direct burial or inside cable ducts
If medium-voltage is required, it might be suitable:
For underground installation (inside cable ducts)
For aerial installation
Source: TopCable
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Cables
It is recommended to use*:
Specific PV usage cable
RZ Cable
Main features:
Conductor: electrolytic copper
Insulation: halogen free
Cover: fireproof; low emissions (corrosive gas & toxic smokes) in
case of fire
To avoid health damages and device damages
Obligatory in public locations
A comparative table can be found in next slides
Source: TopCable
* Based in previous slide considerations
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Cable FV
CABLE FV
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Cable RZ
CABLE RZ
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Typical elements (used in every electrical installation):
Earth peg: different sizes depending on the required depth
(from 1,5 to 2,5 meters)
Cable: copper without cover >35mm2.
Depending on the installation:
Low-power installations: it would be enough to use several
earth pegs connected by a copper cable (without cover)
High-power installations: a copper cable grid is usually used
(without cover). Depending on the physical measures, earth pegs
can be also used.
Earthing System
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Required elements for a Medium-voltage installation:
Transformer:
With the same power as the PV inverter output.
With the following features:
Mineral oil bath
Accessible neutral (in low-voltage)
Natural cooling
Three-phase voltage reduction: MV - LV
Medium-voltage cells:
We can find different types, such as:
Measurement cell
Automatic switch cell
They can be remotely controlled
Depending on each connection requirement, the company might
define the devices, and the cost may vary drastically.
Transformation stations
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The meter must be certified in the country where it will be used
Typical specifications to meet are:
Class 1.0 ( Class B)
Bidirectional
Optical & RS 485 outputs
Depending on the installed power the meter can be directly connected
or coil inductors are to be used.
Metering Device
Source: CircutorThe most usual cases are:
The grid connected PV facility exports all the generated electricity towards
the grid, except the consumption of its own devices: Inverters, Monitoring &
communications devices, Auxiliary services, Suntracking devices
The grid connected PV facility uses the network as a battery. This type is
known as “Net metering”
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Grid connection point
MT PV Facility
In order to avoid shadowing, MV cable will be buried underground
Usual voltage will be between 15 kV – 30 kV (Although it can be a
different one depending on each country)
An underground to aerial link will be done, to connect with the power line
of the electric company
Source: Centelsa
Main features for the copper cable
Density g/cm3 8,89
Resistivity Ohm – mm2/km 17.241
Conductivity (%IACS) 100.0
Breaking strength Mpa 220
Elongation % 25 – 30
Corrosion resistance Excellent
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Grid connection point
The MV cable requires a reinforcement to guarantee that the electrical
distribution is homogeneous.
This reinforcement is done in three layers (triple extrusion):
• Conductor reinforcement
• Insulation
• Insulation reinforcement
The cable requires also an external
cover to provide resistance to:
• Humidity
• Fire
• UV sunlight
• Impact
• Chemicals agentsSource: Centelsa
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INDEX
Evaluation of the solar resource
Increasing the plant profitability from the design
Choosing the components
Photovoltaic facilities calculations
Single-line diagram
http://www.leonardo-energy.org/training-pv-systems-design-construction-operation-and-maintenance
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Radiation (Wh/m2)
Electric Energy (Wh)
PR = 0,74 - 0.78
System Losses
Considerations:
1. The values considered in the following slides are estimated values and should only be used as an
approach. They may vary depending on each location.
2. A detailed Performance Ratio study is fundamental to evaluate the profitability of each solar facility
Towards the PR (Performance Ratio) definition
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1. Temperature. (9%) +10ºC 4% received energy
2. Inverter. We can consider about 6%. New inverters can reach 4%
3. Cable: AC, DC & other electric devices: < 2%
4. Panel tolerance. It shouldn’t be higher than 3%
5. Pollution, dispersion & reflectance.1. Fixed panel: aprox.3%2. Suntracking system: 2%.In urban areas, it should de increased by 2%
6. Shadowing. They should be below 4%. In case of using suntracking systems, a shadowing study might be necessary.
7. Other losses (incidences, etc).1. Fixed panel: 2%2. Suntracking system: 4%.
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100%
91%
87,4%
85,6%
83%
80,6%
77,3%
75,8%
System Losses evaluation
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Choose cool locations, as elevated areas
Select inverters with high efficiency and Maximum Power Point Tracking (MPPT)
Consider extra cable sizing avoiding long traces with voltage drops
Choose solar panels with tolerances between +/- 2-3%
Cleaning the modules in long periods without rain
Balance the separation between panel rows (to avoid shadowing) with the
optimization of the surface area
Minimize the impact of breakdowns, with a preventive maintenance.
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Keys to optimize the PR
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Depending on the type of installation, the shadowing study and the surface optimization,
the project profitability may vary.
The main aspect to study are:
Azimuthal deviation from the south (North hemisphere) or north (South hemisphere)
Tilt of the solar panel
Shadows of extern elements
Shadows of own elements
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Shadowing evaluation
FIX - GROUND SUNTRACKING-GROUND FIX - ROOF INTEGRATION
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1. Distance between panel rows
A basic rule would be to avoid shadows during the 4 central hours of the day, in
the day of the year with less radiation.
This implies calculating the angle of the sun (height regarding the line of the
horizon) to +/-2 hours regarding the solar midday. This angle will vary depending
on the latitude
The objective is to avoid that the top of the front panel projects a shadow to the
lowest part of the panel that is placed behind.
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Fix - Ground
d= h / k
Latitude 29° 37° 39° 41° 43° 45°k 1,600 2,246 2,475 2,747 3,078 3,487
2. Tilt angles
The optimum tilt angle of the solar panel can be expressed by the following
simplified formula: Tilt = Latitude – 10º
In Spain, tilt angles from 30 to 33º is considered as optimum, but tilt angles
between 20 – 40º don’t mean considerable system losses
Tilt angles below 15º in urban areas may cause system losses due to pollution
and dirt accumulation on the panels.
Local land slope will be logically taken into account, which can help reducing
distance between the panel rows to improve the surface profit. (Obviously, the
opposite effect can happen)
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Fix - Ground
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3. Orientation angle
The most favorable orientation is 0º South (North hemisphere).
An orientation deviation below 20º (East or West) cause negligible system losses.
The following graph (which is valid for a 40º latitude) shows how additional losses
may appear depending on the combination of orientation and tilt angle.
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Fix - Ground
A practical example: Solar Plant in Valdecarabanos (Spain)
…Placement optimization
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Suntracking - ground
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Previous tasks:
Environmental conditions
Urban conditions
Topography
External elements shadowing study (trees, electrical posts, etc)
Own elements shadowing study: direct & crossed (in suntracking cases)
Definition of the distance between suntrackers (or panel rows)
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Suntracking - ground
…Location optimization
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…Location optimization. Shadowing study
Suntracking - ground
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As grid connected solar facilities are considered as an investment, we have to choose
between the following cases:
To place the solar panels at the optimum tilt and orientation angle.
To adapt the solar panels to the roof shape
We should take into account:
Impact of angle orientation.
Impact of tilt angle.
Impact of shadows
Comparison between adapted VS optimum
Roof geometrical limits
Remarks: be careful with panels from
the same “row” in different planes
Fix - Roofs
OPTIMUM ANGLE & ORIENTATION
ROOF ADDAPTED
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Two possibilities:
To avoid visual impact, adapting the solar panels to the roof shape
To integrate the panel as a constructive element with a certain function:
Electricity generation
Sunshade effect: special panels which allow some sunlight to go
through
Innovative design: usually special structures are required, and this
may increase the installation costs
In architectural integration, the solar facility is not considered as just an
profitable investment, but also as an image and design element
Architectural integration
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We will consider that the radiation, in the south of Madrid (Spain), for a certain
year can be around 4.77 kW-h/m2 (Average)
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Annual production
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Production by kWp (installed)
(4.7 kW-h/ m2 –day x 0.74 x 1.15 x 365 day x 1 kW) / 1 kW/m2
Expected production for this horizontal radiation, with a PR = 0.74, would be: 1460 kW-h
STC
instincdaymedannual
IPyeardaysfPRHkWpE ××××
=− //
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Annual production
Hmed-day Average solar radiation per day
PR Performance ratio for the solar installation. Dimensionless
F inc Tilt coefficient: a ratio normally obtained from the optimum tilt for a fixed panel (Which optimizes its performance). In Spain (Latitude = 40º) it is 1.15
Pinst Installed solar power
ISTC Average irradiance in the horizontal plane
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Once the modules and inverters are selected, the configuration of the system allows to
maximize the produced energy
It is possible that in some cases we should consider the use of a different module or
inverter in order to improve the system performance.
The configuration of the systems takes into account:
Maximum input voltage of the inverter
Maximum input current of the inverter
Voltage and current at Maximum Power Point
When designing the solar panel configuration in series and parallels, we must take into
account that the voltage and current of the branch will change depending on the
temperature. Therefore it will be necessary to choose extreme values of the region for the
calculation.
System configuration
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System configuration
Source: PVsyst
A configuration example of a designing software for Solar Plants (PVSYS screen shot )
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It is very important to take into account:
Maximum current in the cables
Maximum allowed voltage drop.
If there is a long distance the main factor to determine the cable section will be the
voltage drop.
If there is a very short distance the current that flows along the cable will determine the
section of the cable
Tram
o
Long
.
V n
om (V
)
Wp inst (kWp)
Inom
(A)
Con
duct
.
∆V m
ax (%
)
∆V m
ax (V
)Seccion (mm2)
Sec
ción
cal
c. (m
m2)
Sec
cion
est
anda
r (m
m2)
Imax
_adm
isib
le
100% 70% 30% 100% 70% 30%
ZA01 93 541 72 50 22 133 93 40 35 1,0 5,4 131 92 39 97 150 338
ZA02 97 541 72 50 22 133 93 40 35 1,0 5,4 136 95 41 101 150 338
ZA03 115 541 72 50 22 133 93 40 35 1,0 5,4 162 113 48 120 150 338
ZA04 133 541 38 27 12 71 50 21 35 1,0 5,4 100 70 30 74 95 245
Electrical calculation
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Electrical design
In order to do a simplified earthing calculation, we can start with the following formulas
depending on the soil resistivity and the electrode characteristics
The average values of the resistivity, depending on the type of soil are:
Electrode Soil resistivity (Ohm)
Buried plate R = 0,8 ρ/P
Vertical peg R = ρ/L
Buried conductor R = 2 ρ/L
ρ, soil resistivity (Ohm x m)
P, Plate perimeter (m)
L, Peg or conductor length (m)
Type of Soil Soil resistivity (Ohm)
Cultivable and fertile soils, compact and wet soils 50
Cultivable non fertile soil, or other soils 500
Naked rock soils, and dried and permeable soils 3.000
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Electrical calculations
The cable sizing is based on the following formulas:
•Three Phases
•One Phase
• Considering:
• P = Power
• L = Cable length
• γ = Cable conductivity
• E = Allowed voltage drop
• U= Line voltage
• For example, for LV in Europe:
• 400V in Three-phase
• 230V in One-phase
TABLE OF CONDUCTIVITY DEPENDING ON THE TEMPERATURE
Material γ 20 γ 70 γ 90Copper 56 48 44
Aluminium 35 30 28
Temperature 20 ºC 70 ºC 90ºC
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A lightning may produce a transitory overvoltage of
short duration, with a huge amplitude.
The overvoltage produced due to network unbalances is
a permanent overvoltage, with a longer duration and a
lower amplitude.
In order to protect our installation against overvoltage,
electrical dischargers can be connected at the input and
output of each device to be protected.
There are three different protection levels:
High Middle Low
Over Voltage
Source: Cirprotect
DEVICE PROTECTION LEVEL
INVERTER
METER
CC CABINET
TRANSITORY OVERVOLTAGE
PERMANENT OVERVOLTAGE
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Transformers connection topology
RING
STAR
CABLE BREAK DOWN
NO PRODUCTION LOSSES
PRODUCTION LOSSES
In installations where more than one Medium Voltage transformer is required, it is
important to define the correct topology for the connection between all the MV
transformers and the main grid (Power line).
The possible connections options are:
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INDEX
Evaluation of the solar resource
Increasing the plant profitability from the design
Choosing the components
Photovoltaic facilities calculations
Single-Line diagram
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Single-line diagram
FUSE
DC MCB
DIFERENTIALPROTECTION
AC MCB
ELECTRICAL COMPANY DEVICE
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End of Session 1
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