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

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


INDEX


Increasing the profitability of the plant from the design



Single-line diagram


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


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

6

Source: NASA

Solar resource evaluation: Solar Radiation maps


7

INDEX





Single-line diagram


OPTIMUM PROFITABILITY

8

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


9

INDEX





Single-line diagram


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:

10

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


11

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


12

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


13

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:


14

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


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


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


21

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

22

Cable FV

CABLE FV


23

Cable RZ

CABLE RZ


24

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


25

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


26

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”


27

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





Single-line diagram


30

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


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%.

31

100%

91%

87,4%

85,6%

83%

80,6%

77,3%

75,8%

System Losses evaluation


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

Keys to optimize the PR


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

33

Shadowing evaluation

FIX - GROUND SUNTRACKING-GROUND FIX - ROOF INTEGRATION


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.

34

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)

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

Fix - Ground

A practical example: Solar Plant in Valdecarabanos (Spain)

…Placement optimization

37

Suntracking - ground


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


39

…Location optimization. Shadowing study



40

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


41

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


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)

(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


44

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


45

System configuration

Source: PVsyst

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

46

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

47

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


48

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


49

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

50

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:


51

INDEX





Single-Line diagram


52

Single-line diagram

FUSE

DC MCB

DIFERENTIALPROTECTION

AC MCB

ELECTRICAL COMPANY DEVICE


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End of Session 1


Thank you for attending

Technology

Photovoltaic Training - Session 1 - Design