Photovoltaic Training - Session 1 - Design

Photovoltaic Systems Training

Session 1 ‐ Design

Javier Relancio & Luis Recuero
Generalia Group

September 14th 2010

http://www.leonardo-energy.org/training-pv-systems-design-
construction-operation-and-maintenance

PHOTOVOLTAIC SYSTEM
Design, Execution, Operation & Maintenance

FACILITY DESIGN

Javier Relancio. Generalia Group. 14/09/2010
www.generalia.es
2
http://www.leonardo-energy.org/training-pv-systems-design-construction-operation-and-maintenance

INDEX

Evaluation of the solar resource

Increasing the plant profitability from the design

Choosing the components

Photovoltaic facilities calculations

Single-line diagram

3

INDEX


Increasing the profitability of the plant from the design



Single-line diagram

4

Solar resource evaluation

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

5

Solar resource evaluation:
Solar Radiation maps

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 Source: NASA

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

6

INDEX





Single-line diagram

7

Towards the profitability of
the plant from the design

Resource evaluation System losses (PR)

• Latitude
• Shadows
• Longitude
• Disconnections & Breakdowns
• Altitude
• Panel tolerance
• Data from closest
• Pollution, dispersion & reflectance
meteorological stations
• Temperature
• Data from satellites
• Inverter

• Cables

OPTIMUM
PROFITABILITY

8

INDEX





Single-line diagram

9

Inverters: Trends

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:

MULTI CONTROLLED
MULTI POWER STAGES ONE POWER STAGE
POWER STAGES

The electrical companies can ask for galvanic isolation transformers when the connection
is in low voltage

10

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
11

Inverters: Features

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

12

Crystalline or Thin-film Panels

Visual identification:

Mono crystalline Poli crystalline Thin film A‐Si:H

Source: Atersa

Thin film panel observations:

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

13

Crystalline or Thin film modules

CRYSTALLINE PANEL PRICE* TEMPERATURE EFFICIENCY REQUIRED
INFLUENCE SURFACE
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)

* This information can be altered depending on each manufacturer price policy

14

PV Module Specs

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.

Source: Atersa
15

PV Module Specs

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
Source: Atersa

Among panels with different technologies: we can find big differences, as we can see in the technical
information below.

A: Si Polycrystalline

Source: QS Solar

16

Concentration Panel

Concentration technology is still being developed

Fresnel Lens (and other kinds)
Refractive optical system
Concentration up to 500x

Potential cost savings Source: Everphoton

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
17

Protections

The protections to be installed are:

DC side AC side

DC AC AC
DC Miniature Circuit Miniature Circuit
Fuses Differential
Breaker (MCB) Breaker (MCB)

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 Source: ABB

Current: Up to 125 A
Voltage: 800Vcc with 2P & 1200Vcc with 3P & 4P

18

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) < 0.9 kV < 1.5 kV < 1.5 kV < 1.9 kV
Up (N‐PE) < 2 kV
Tracking current If (L‐N/N‐PE) > 100 A RMS
19 Response time tA (L‐N/N‐PE) < 25 ns / 100 ns

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

20

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

21
* Based in previous slide considerations

Cable FV

CABLE FV

22

Cable RZ

CABLE RZ

23

Earthing System

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.

24

Transformation stations

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.
25

Metering Device

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.
Source: Circutor
The 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”

26

Grid connection point

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

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

MT PV Facility
Source: Centelsa
27

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

Source: Centelsa
• Impact
• Chemicals agents

28

INDEX





Single-line diagram

29

Towards the PR (Performance Ratio)
definition

Electric Energy (Wh) System Losses

PR = 0,74 - 0.78

Radiation (Wh/m2)

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

30

System Losses evaluation

100% 1. Temperature. (9%) +10ºC 4% received energy

91% 2. Inverter. We can consider about 6%. New inverters can reach 4%

87,4% 3. Cable: AC, DC & other electric devices: < 2%

85,6% 4. Panel tolerance. It shouldn’t be higher than 3%

83% 5. Pollution, dispersion & reflectance.
1. Fixed panel: aprox.3%
2. Suntracking system: 2%.
80,6% In urban areas, it should de increased by 2%

6. Shadowing. They should be below 4%. In case of using suntracking
77,3% systems, a shadowing study might be necessary.

7. Other losses (incidences, etc).
1. Fixed panel: 2%
75,8% 2. Suntracking system: 4%.
31

Keys to optimize the PR

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.

32

Shadowing evaluation

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

FIX - GROUND SUNTRACKING-GROUND FIX - ROOF INTEGRATION

33

Fix - Ground

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.

d= h / k

Latitude 29° 37° 39° 41° 43° 45°
34 k 1,600 2,246 2,475 2,747 3,078 3,487

Fix - Ground

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)

35

Fix - Ground

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.

36

Suntracking - ground

…Placement optimization

A practical example: Solar Plant in Valdecarabanos (Spain)

37


…Location optimization

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)

38


…Location optimization. Shadowing study

39

Fix - Roofs

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 OPTIMUM ANGLE & ORIENTATION

We should take into account:
Impact of angle orientation.
Impact of tilt angle.
Impact of shadows
Comparison between adapted VS optimum
Roof geometrical limits ROOF ADDAPTED

Remarks: be careful with panels from
the same “row” in different planes

40

Architectural integration

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

41

Annual production

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)

42

Annual production

Production by kWp (installed)

Hmed − day × PR × finc × days / year × Pinst
Eannual / kWp =
ISTC
(4.7 kW-h/ m2 –day x 0.74 x 1.15 x 365 day x 1 kW) / 1 kW/m2

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

Expected production for this horizontal radiation, with a PR = 0.74, would be: 1460 kW-h

43

System configuration

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.

44

System configuration

A configuration example of a designing software for Solar Plants (PVSYS screen shot )

45 Source: PVsyst

Electrical calculation

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
Tramo

Seccion estandar (mm2)
Sección calc. (mm2)

Imax_admisible
∆V max (%)

∆V max (V)
V nom (V)

Conduct.
Inom (A)
Long.

Wp inst (kWp) Seccion (mm2)

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
46

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

Electrode Soil resistivity (Ohm)
Buried plate R = 0,8 ρ/P ρ, soil resistivity (Ohm x m)

Vertical peg R = ρ/L P, Plate perimeter (m)

Buried conductor R = 2 ρ/L L, Peg or conductor length (m)

The average values of the resistivity, depending on the type of soil are:

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

47

Electrical calculations

The cable sizing is based on the following formulas:

• Considering:
•Three Phases
• P = Power
• L = Cable length

• γ = Cable conductivity
•One Phase • 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 90
Copper 56 48 44
Aluminium 35 30 28
Temperature 20 ºC 70 ºC 90ºC
48

Over Voltage

A lightning may produce a transitory overvoltage of
short duration, with a huge amplitude.
TRANSITORY OVERVOLTAGE

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. PERMANENT OVERVOLTAGE

There are three different protection levels:
High Middle Low

DEVICE PROTECTION LEVEL

INVERTER

METER
Source: Cirprotect
CC CABINET
49

Transformers connection topology

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:
STAR

RING

PRODUCTION
LOSSES

CABLE BREAK DOWN

NO PRODUCTION
LOSSES

50

INDEX





Single-Line diagram

51

Single-line diagram

FUSE

DC
MCB

DIFERENTIAL
PROTECTION

AC
MCB

ELECTRICAL COMPANY
DEVICE

52

End of Session 1

Thank you for attending

http://www.leonardo-energy.org/training-pv-systems-design-
construction-operation-and-maintenance

53

Photovoltaic Training - Session 1 - Design

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