BASIC PRINCIPLES FOR DESIGN AND CONSTRUCTION OF PHOTOVOLTAIC PLANTS

1. TRAINING COURSE BASIC PRINCIPLES FOR DESIGN ANDCONSTRUCTION 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

5. GENERAL DIAGRAM OF CONNECTION deliveryand accounting equipment Utility grid Point of connection User grid Generaldevice loads Interface device loads able to operate In islanding mode Generatordevice 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 Connecting cable User lines Counter Utility grid PoC

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 LV Utility grid kWh < > PoC GD LV loads ID = Generator Device The interface device managed by the interface protection system can be integrated in the inverter IPS Inverter

11. LV GRID CONNECTION Multiple generators LV Utility grid kWh < > PoC a single interface device managed by a interface protection system GDL FV Genarl Device of line 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 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 • 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 GRIDmultiple inverter system 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 GRIDmultiple inverter system 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 IPS IPS IPS LV loads kWh ID=genD 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 producedFactory 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 • Typical limit allowed • 60% drop for 400 ms • 100% drop for 200 ms • The PV plants are maintained connected to the grid during rapid voltage drop

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 absenceof fault • Whileisrestrictedto 49,7(0,1s) ≤ f ≤ 50,3 (0,1s) in presenceof 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) Delayed tripping 4s Delayed tripping 1s Delayed tripping 0.1s Grid frequency grid fault signal 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 V A 21,6 kW 1 2 3 4 5 6 7 8 9 String box 1 2 3 4 5 6 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. CONDUITS LAYOUT AND STRING BOX POSITIONING 50 m North String box 50 m conduit Subarray box

38. GROUNDING SYSTEM LAYOUT cabin

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

40. MODULE SUPPORTING STRUCTURES Lateral view Construction details 300 cm PV module String box 180 cm 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 manualcertificate 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 for information: salvatore.castello@enea.it