1. BASIC PRINCIPLES FOR DESIGN AND CONSTRUCTION OF PHOTOVOLTAIC PLANTS
TRAINING COURSE
BASIC PRINCIPLES FOR DESIGN AND CONSTRUCTION OF PHOTOVOLTAIC PLANTS
Ing. Salvatore Castello
ENEA - Renewable Energy Technical Unit - Photovoltaic Lab

2. Summary Criteria for selecting PV modules Strings and PV generator
Supporting structures
Fire prevention
Power conditioning unit
The connection to the grid
Design documentation

3. THE CONNECTION TO THE GRID
Is generally regulated by
Administrative rules that define
relationship between the User and the electric Utility
administrative cost
grid balancing fees
value of energy fed into the grid or exchanged
Technical standards for the connection to the LV or MV grid
define the modality and characteristics of the components necessary for the connection to the grid

4. INDICATIVE SOLUTIONS FOR THE CONNECTION
Popwer [kW]
Voltage level of Utility grid
≤ 6
LV single phase
≤ 100 LV
LV or MV (*)
200 – 6 000 MV
6 000 – 10 000
MV or HV (*)
> HV
(*) depending on the characteristics of the grid and loads connected

5. GENERAL DIAGRAM OF CONNECTION
delivery and accounting equipment
Utility grid
Point of connection
User grid
General device
loads
Interface device
loads able to operate
In islanding mode
Generator device
PV generator (controller for ordinary conditions management)

6. CONNECTION TO THE LV GRID
GENERAL DEVICE (GD)
Disconnect the User grid from the Utility grid in case of faults on the User grid
can be composed of multiple Line General Devices (DGL) up to a maximum of 3
must be placed immediately downstream the point of connection (PoC) and a connecting cable (C) of negligible length
Utility grid
Counter
Connecting cable
PoC
User lines

7. CONNECTION TO THE LV GRID
INTERFACE DEVICE (ID)
Disconnect the User from the grid in case of malfunctioning on the grid
Is managed by an Interface Protection System (IPS)
for systems with multiple generators
usually a single ID managed by a single IPS
more ID managed by more IPS acting in OR logic (the anomaly detected by an IPS causes the release of all ID)
In small plants The ID and the IPS can be integrated in the inverter
in large plants is foreseen a backup device in case of failure of the interface device
The resetting of the backup device is performed manually

8. FURTHER REQUIREMENTS IN LV PLANT
DC components fed into the grid
The production facilitry must be equipped with a system able to limit the DC fed into the grid by means of :
LF transformer
Protection device able to disconnect the inverter from the grid when DC component > %
Unbalance among phases
Permanent: generated in three-phase systems made ​​with different single-phase units The Utility generally allow unbalance within fixed limit
Transient: can be generate in particular operating conditions The plant should be equipped with an automatism that returns the umbalance within the limits allowed

9. REVIEW OF MAJOR CASES IN LV
The general scheme can be applied in different ways according to plants size and
to the grid voltage level

10. LV GRID CONNECTION Single generator 21/04/2017 LV Utility grid
kWh < >
PoC GD
LV loads
ID =
Generator Device
IPS
The interface device managed by the interface protection system can be integrated in the inverter
Inverter

11. LV GRID CONNECTION Multiple generators 21/04/2017 LV Utility grid
kWh < >
PoC
a single interface device managed by a interface protection system
Genarl Device of line
GDL FV
LV load ID
IPS
for large systems must be foreseen a reinforcement device
Generator Device N
Inverter 1
Inverter 2
Inverter N

12. LV GRID CONNECTION Multiple generators 21/04/2017 LV Utility grid
kWh < >
PoC GD
multiple interface device managed by more interface protection system acting in OR logic
LV loads
ID=
Gen. Dev.
ID=
Gen. Dev.
IPS
IPS
IPS
OR logic
Typically for N>3
Inverter 1
Inverter 2
Inverter N

13. THE CONNECTION TO THE MV GRID
Interface Device (ID) and Interface Protection System (IPS)
For systems with multiple inverters
the ID is normally unique
can be used more ID + IPS (one for each inverter) in OR logic
The IPS must be equipped with protection able to detect
Grid voltage or frequency out of fixed limits
single-phase faults to ground
Faults between two-phase
three-phase faults isolated from ground

14. THE GENERAL PROTECTION IN MV
21/04/2017
THE GENERAL PROTECTION IN MV
General Protection System
Manages The GD
must be integrated with the protection able to detect:
overcurrent of phase
Maximum vectorial sum of the 3 currents of phases
fault to ground (only for long distances from GD to ID
GPS DG
General Device

15. CONNECTION TO THE MV GRID multiple inverter system
21/04/2017
MV Utility grid
kWh < >
PoC
MV User grid GD
GPS
MV loads
the ID is normally unique
The ID can be installed in LV or MV side D Y
LV loads ID
IPS
Generator Device (can be integrated into the inverter)
Inverter 1
Inverter 2
Inverter N

16. CONNECTION TO THE MV GRID multiple inverter system
21/04/2017
MV Utility grid
kWh < >
MV User grid GD
GPS
MV loads
Can be used multiple ID + IPS (one for each inverter) operating in OR logic
LV loads
kWh
IPS
IPS
ID=genD
IPS
OR logic
Inverter 1
Inverter 2
Inverter N

17. THE CONFORMITY OF GRID INTERFACE DEVICES
the declaration of conformity to applicable rules
Is typically issued by the manufacturer, in the form of self-certification
Is required by the Utility for the connection to the grid
contain the information necessary to identify the device
The environmental compatibility (insulation, and EMC) is tested by Accredited Laboratory
It also state that the device has been produced in the framework of quality system (ISO 9001)
To certify that the quality levels remain constant over time must be produced Factory Inspection Certificate issued by a Certification body
To identify the origin of the product (Inverter made ​​in EU countries) is produced Factory Inspection Attestation  

18. GRID STABILITY
In order to contribute to the stability of the grid, the inverter must be able to:
maintain the insensitivity to rapid voltage drops;
increase the selectivity of the protections in order to prevent the untimely disconnection of the PV system;
allow disconnection from the grid as a result of a remote command;
avoid the possibility that the inverter can supply the loads in the absence of voltage in the grid cabin;
enable the delivery or absorption of reactive power;
limit the power fed into the grid (to reduce voltage variations of the grid);

19. THE CONNECTION TO THE GRID
OPERATING RANGE OF THE PRODUCTION SYSTEMS
In order to guarantte the grid stability, IPS must be able to keep the production system connected to the grid (by means of the ID) for
Grid voltage values at the point of delivery, ranging between
85% Vn ≤ V ≤ 110% Vn
and grid frequency values ranging
47.5 Hz ≤ f ≤ 51.5 Hz

20. BEHAVIOUR OF PLANTS AT GRID VOLTAGE TRANSIENT
The PV plants are maintained connected to the grid during rapid voltage drop
Typical limit allowed
60% drop for 400 ms
100% drop for 200 ms

21. BEHAVIOR AT GRID FREQUENCY TRANSIENT
To reduce grid voltage variations, the production system should have the possibility to reduce the power fed into the grid in response to frequency raise
The restart should be
conditioned to a stabilized frequency
increasing the power gradually

22. SELECTIVITY OF INTERFACE DEVICES
Adopted to prevent untimely disconnection
If the Utility make a “grid failure “ signal available (ground faults in LV or MV) then the operating range of IPS
47,5 (4s) ≤ f ≤ 51,5 (1s) in absence of fault
While is restricted to 49,7(0,1s) ≤ f ≤ 50,3 (0,1s) in presence of fault
If the Utility don’t make available a “grid failure “ signal, the operatin range is: 47,5(0,1s) ≤ f ≤ 51,5(0,1s)
grid fault signal
Delayed tripping 4s
Delayed tripping 1s
Delayed tripping 0.1s
Grid frequency
remote trip
instantaneous tripping

23. DESIGN DOCUMENTATION

24. THE DESIGN OF THE PLANT
ensemble of studies that produces the necessary information for the construction of the plant in accordance with
applicable rules
performance requirements
consists of
Preliminary draft
defines the qualitative features and the performance to be provided
Final draft prepared on the basis of the preliminary draft,
contains the elements necessary for the request of authorization for plant construction
Working design
defines completely and in full detail the components and the action to be executed for plant construction

25. THE DESIGN DOCUMENTATION
Depends on plant size and typology
Includes
Technical Report
Wiring diagrams
Lay out and drawings
Executive calculations
Maintenance Plan
Safety Plan
Estimated bill of quantities
Time schedule

26. TECHNICAL REPORT Desig data Description of the system
Criteria adopted for the design choices
Description
protection measures
operating modes of the system
calculation criteria, methods of implementation and results
Reference standards
List of documents

27. TECHNICAL REPORT DESIGN DATA Site identification
weather and climate data (solar radiation, temperature, wind, snow)
description of the building, or the place of installation
bearing capacity of the roof
any architectural constraint
power supply data
voltage level
contractual power committed
average consumption
performance requirements
expected production PR

28. TECHNICAL REPORT PLANT DESCRIPTION
Electrical characteristics of the PV generator, strings and sub- array
Functional, electrical and mechanical properties of PV modules
String box and AC switchboards features
Supporting structures
Power conditioning unit
Grid connection section (LV or MV)
Wiring and grounding network

29. TECHNICA REPORT CRITERIA ADOPTED FOR THE DESIGN CHOICES Plant size
Maximizing the collection of solar radiation
Limitation of losses and systematic shading
Module technology
Working Voltage
Plant configuration and conversion system
Management PV generator
protections against overcurrent, overvoltage, direct and indirect contacts, lightning
Interfacing with the grid
Modalities for the observance of any architectural constraints
Solutions that allow to place adequately the photovoltaic generator on buildings or on ground

30. ELECTRICAL DIAGRAM Must show the following details: number of strings
number of modules per string
switchboards components for string and subarray parallels
number of inverters and connection mode
Components in electrical cabinets in AC
Any protection devices external to the inverter on DC side
connection point to the utility grid
protection devices on AC side
counters (energy produced, to/from the grid)

31. STRING BOX AND SUBARRAY SWITCHBOARD
To the inverterr
194,4 kW
Subarray switchboard A V
21,6 kW
String box
string (18 modules series connected; Pnom = 200 W)

32. UNIFILAR ELECTRICAL DIAGRAM conversion system
Generator Device
INVERTER

33. UNIFILAR ELECTRICAL DIAGRAM MV section
Energy Counter
GD & ID
General Protection Syste
IPS

34. GRAPHIC DOCUMENTS Planimetry excerpt of the area
Site plan showing the location of
rows of modules
equipment room
String box
Layout
Conduit
grounding grid and LPS
Plan of equipment room with electrical equipment positioning
Constructive details
cables disposal
grounding network and lightning protection system
Assembly and construction details of supporting structures

35. PLANIMETRY EXCERPT OF THE SITE
North
1:5000 scale
PV Site
GPS

36. GENERAL PLAN OF PV ARRAY
XX street
Subarray 1
Subarray 2
rows of modules
equipment room
North
Subarray 3
YY street

37. AND STRING BOX POSITIONING
CONDUITS LAYOUT
AND STRING BOX POSITIONING
50 m
North
String box
50 m
conduit
Subarray box

38. GROUNDING SYSTEM LAYOUT
cabin

39. Protection devices and counters
ELECTRICAL EQUIPMENT ROOM
14 m
2.80 m
Protection devices and counters
MV transfor.
INVERTER 1
INVERTER 2
INVERTER 3
3,5 m

40. MODULE SUPPORTING STRUCTURES
Lateral view
Construction details
300 cm
PV module
180 cm
String box
50 cm
cordoli
275 cm
Front view
8,40 m
180 cm

41. CONSTRUCTIVE DETAILS Conduits and cables disposal
grounding network detail
Copper stake

42. EXECUTIVE CALCULATIONS
should be related to the operating conditions and must enable to
evaluate the expected energy production
sizing:
electric cables
Switchboards (thermal)
Supporting structures
Grounding network
LPS
Must be carried out in conjunction the design of the building in order to forecast space, shafts, passages

43. FINAL DOCUMENTATION OF PLANT
After PV plant completion, will be released to the customer
user manual
maintenance manual certificate issued by an accredited laboratory regarding compliance with standards
Modules
inverter (interface device)
warranty certificates of installed components
warranty of the whole plant
warranty on plant performance

44. THANK YOU FOR YOUR KIND ATTENTION
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