Photovoltaic system: electrical equipments selection

Grid connected PV system ≤ 10kW (Residential)

One single phase inverter

Typically, a 5kW grid-connected single-phase inverter. with UOC MAX ≤ 600V. One or two strings – Isctc < 25A, IAC < 32A. In this design there is no string protection.

A PV main switch is necessary. When the inverter is indoors, an additional remote controlled switch at the DC cable entry point is recommended for emergencies services.

Needs	String junction box	PV array main switch	Inverter	AC box (400V)
Switchgears and control (Q)
- Isolation	•	•		•
- Switching (Making & breaking rated current	• DC21B	• DC21B		•
- Control	•	•		•
- Over-current protection				•
- Protection against Insulation fault				RCD type B or A SI
Surge protection (SPD)		• type 2		• type 1 or 2
Enclosure (E)	Outdoor Double insulation	Indoor Double insulation		Standard AC requirement + grid code requirement
Metering			Inverter relevant parameters	Energy

[a]  PV array main switch could be included in the inverter. This solution makes inverter service or replacement more difficult.
[b]  Remote switching for emergency services located as closely as possible to the PV modules or to the point of entry of DC cables in the building.
[c]  No protection is required when the number of string does not exceed 2.
[d]  Service and emergency switching
[e]  Inverter shall include a protection for anti-islanding (in accordance with VDE 0126 for example)
[f]  Overload and short-circuit protection B curve recommended.
[g]  If the inverter provides no galvanic separation a RCD protection is necessary on AC side. IEC 60364-712 specifies RCD type B. Some local regulations require RCD type A SI

Fig. P22 – Grid connected <= 10kW

10 to 100kW grid connected PV system (Small building)

One three phase multi input inverter without array box

• Typically, 10kW to 36kW grid-connected inverters, U_{OC MAX} probably higher than 600V (i.e. 800V or 1000V), Isctc < 125A, Iac < 63A.
• In this range of power, inverters usually have between 2 and 4 maximum power point tracking (MPPT) inputs, so the number of strings in the same DC sub-network is equal to one or two.
• There is no need for string protection. A PV main switch for each MPPT input is necessary.
• When an inverter is indoors, additional remote-controlled switches at DC cable entry point are recommended for emergencies services.

Needs	String junction box	PV array main switch	Inverter	AC box (400V)
Switchgears and control (Q)
- Isolation	•	•		•
- Switching (Making & breaking rated current	• DC21B	• DC21B		•
- Control	•	•		•
- Over-current protection				•
- Protection against Insulation fault				RCD type B or A SI
Surge protection (SPD)		• type 2		• type 1 or 2
Enclosure (E)	Outdoor IP5x Double insulation	Indoor IP5x Double insulation		Standard AC requirement + grid code requirement
Metering				Energy

[a]  PV array main switch could be included in the inverter. This solution makes inverter service or replacement difficult.
[b]  Remote switching for emergency services located as closely as possible to the PV modules or to the point of entry of DC cables in the building.
[c]  No protection is required when the number of string does not exceed 2.
[d]  Service and emergency switching
[e]  Inverter shall include a protection for anti-islanding (in accordance with VDE 0126 for example)
[f]  Overload and short-circuit protection (B curve recommended).
[g]  If there is no SPD in the inverter or if the distance between String junction box and inverter exceeds 10m a SPD is necessary in this box.
      If the inverter provides no galvanic separation a RCD protection is necessary on AC side. IEC 60364-712 specifies RCD type B. Some local regulations require RCD type A SI
      If the inverter provides at least simple separation
       - Without functional earthing: insulation monitoring is necessary, it's usually done by the inverter in this range of power.
       - With functional earthing: the earthing shall be done with a DC MCB breaker (C60PV 4P series 2 – 10A) or a fuse.

Fig. P23 – 10-100kW single multi MPPT inverter

One three phase inverter with One Array box

• Typically, 30kW to 60kW grid-connected inverters. U_{OC max} is generally higher than 600V (up to 1000V), Isctc does not exceed 200A, Iac does not exceed 100A.
• This design has more than 2 strings.
• Reverse current protection is therefore necessary.
• A main PV switch is required. When an inverter is inside, additional remote-controlled switch at DC cable entry point is recommended for emergencies.

Needs	String / Array junction box	PV array main switch	Inverter	AC box (400V)
Switchgears and control (Q)
- Isolation	•	•		•
- Switching (Making & breaking rated current	• DC21B	• DC21B		•
- Control	•	•		•
- Over-current protection	•			•
- Protection against Insulation fault				RCD type B or A SI
Surge protection (SPD)		• type 2		• type 1 or 2
Enclosure (E)	Outdoor IP5x Double insulation	Indoor IP5x Double insulation		Standard AC requirement + grid code requirement
Metering				P, Q, PF, Energy

[a]  PV array main switch could be included in the inverter. This solution makes inverter service or replacement difficult.
[b]  Remote switching for emergency services located as closely as possible to the PV modules or to the point of entry of DC cables in the building. The main switch in array box can be equipped with tripping coil and motor mechanism for remote reclosing for that purpose.
[d]  Service and emergency switching
[e]  Inverter shall include a protection for anti-islanding (in accordance with VDE 0126 for example)
[f]  Overload and short-circuit protection (B curve recommended).
[g]  If there is no SPD in the inverter or if the distance between String / Array junction box and inverter exceeds 10m a SPD is necessary in this box.
[h]  If the inverter provides no galvanic separation a RCD protection is necessary on AC side. IEC 60364-712 specifies RCD type B. Some local regulations require RCD type A SI.
      If the inverter provides at least simple separation
       - Without functional earthing: insulation monitoring is necessary
       - With functional earthing: the earthing shall be done with a DC MCB breaker (C60PV 4P series 2 – 10A) or a fuse.

Fig. P24 – 10-100kW single MPPT inverter

Multi single phase inverters design

• Typically, 6x5 to 20x5kW grid-connected inverters.
• The design used for residential building can be duplicated as often as necessary.
• In that case, the DC system is very simple and the AC system is very similar to usual AC systems.

Needs	PV arraymain switch	Inverter		AC box (400V)
Switchgears and control (Q)	See ≤10kW design
Surge protection (SPD)	• type 2			• type 1 or 2
Enclosure (E)	Outdoor IP5x Double insulation			Standard AC requirement + grid code requirement
Metering			Energy	P,Q, PF, Energy, unbalance

Fig. P25 – 10-100kW multi single MPPT inverter

Three phase inverter with two Array boxes (Na ≤ 2)

Typically, 60kW to 100kW grid-connected inverters with 2 arrays. Array cable protection is not necessary for 2 or 3 arrays.

The I_sctc array ≤ 200A, I_sctc ≤ 400A, and I_max AC ≤ 200A. A PV main switch is required close to the inverter. Remotely operated switches in array boxes allow disconnects to be located close to the PV modules in the event of emergencies.

Needs	String / Array junction box	PV array main switch	Inverter	AC box (400V)
Switchgears and control (Q)
- Isolation	•	•		•
- Switching (Making & breaking rated current	• DC21B	• DC21B		•
- Control	•	•		•
- Over-current protection	•			•
- Protection against Insulation fault				RCD type B or A SI
Surge protection (SPD)		• type 2		• type 1 or 2
Enclosure (E)	Outdoor IP5x Double insulation	Indoor IP5x Double insulation		Standard AC requirement + grid code requirement
Metering				P, Q, PF, Energy

[a]  PV array main switch could be included in the inverter. This solution makes inverter service or replacement difficult.
[b]  If switching for emergency services is required, the main switch in array box can be equipped with tripping coil and motor mechanism for remote reclosing.
[c]  No protection is required when the number of arrays ≤ 3 (No cable sizing benefit)
[d]  Service and emergency switching
[e]  Inverter shall include a protection for anti-islanding (in accordance with VDE 0126 for example)
[f]  Overload and short-circuit protection.
[g]  If there is no SPD in the inverter or if the distance between DC box and inverter exceeds 10m a SPD is necessary in this box.
      If the inverter provides no galvanic separation a RCD protection is necessary on AC side. IEC 60364-712 specifies RCD type B. Some local regulations require RCD type A SI
      If the inverter provides at least simple separation
      - Without functional earthing: insulation monitoring is necessary
      - With functional earthing: the earthing shall be done with a DC MCB breaker (iC60PV 4P series 2 – 10A) or a fuse.

Fig. P26 – 10-100kW single MPPT inverter with 2 arrays

150kW to 500kW Grid connected PV system (Large building and farm)

Three phase inverter with more than two Array boxes

• Typically, 150kW to 500kW single inverter.
• This design is very similar to the previous one except that it has more arrays, which requires array cable protection.
• Istc <= 400A, IAC <= 600A.

Needs	String	Array junction box	Generator junction box	Inverter	AC box 400V or other voltage (Transfoless inverter)
Switchgears and control (Q)
- Isolation	•	•	•		•
- Switching (Making & breaking rated current		• DC22A	• DC22A	•	•
- Control		•		•	•
- Over-current protection	•		•		•
- Protection against Insulation fault				•	•
Surge protection (SPD)			• type 2		• type 1 or 2
Enclosure (E)		Outdoor IP5x Double insulation	Indoor Double insulation		Standard AC requirement + grid code requirement
Metering					P, Q, PF, Energy, Alarm, THD, individual harmonics

[a]  PV array main switch could be included in the inverter. This solution makes inverter service or replacement more difficult.
[b]  If switching for emergency services is required, the main switch in array box can be equipped with tripping coil and motor mechanism for remote reclosing.
[c]  Array cable protection is recommended to prevent cable oversizing. To ensure fast trip of protections 6 to 8 arrays are recommended.
[d]  Service and emergency switching
[e]  Inverter shall include a protection for anti-islanding (in accordance with VDE 0126 for example)
[f]  Overload and short-circuit protection.
[g]  If there is no SPD in the inverter or if the distance between DC box and inverter exceeds 10m a SPD is necessary in this box.
[h]  Galvanic insulation is provided by LV/MV transformer,
      - PV system without functional earthing: insulation monitoring is necessary: IMD - IM20 and accessory IMD-IM20-1700
      - PV system with functional earthing: the earthing shall be done with a DC MCB breaker (C60PV 4P series 2 – 10A) or a fuse.

Fig. P27 – 150-500kW single MPPT inverter with N arrays > 2

Multi three phases inverters design without array box

Typically 10x20 to 20x30kW grid connected inverters

U_oc max ≤ 1000V one or two string per inverter. IAC max 50A for one inverter.

Needs	String junction box			AC Combiner box
Switchgears and control (Q)	See 10 to 36kW design
Surge protection (SPD)	• type 2			• type 1 or 2
Enclosure (E)	Outdoor IP5x Double insulation			Standard AC requirement + grid code requirement
Metering			Energy	P, Q, PF, Energy, Alarm

Fig. P28 – 150-500kW multi 3-phases inverters

Multi MW Grid connected PV system (Large building and farm)

• Typically 500kW-630kW inverters with LV/MV transformers and MV substation.

Needs	String	Array junction box	Generator junction box	Inverter		AC box 400V or other voltage (Transfoless inverter)
Switchgears and control (Q)				DC side	AC side
- Isolation	•	•	•	•	•	•
- Switching (Making & breaking rated current		• DC22A	•	• DC22A or 23A	• AC1	•
- Control		•		•	•	•
- Over-current protection	•		•	No	•	•
- Protection against Insulation fault			•	•		•
Surge protection (SPD)			• type 2			• type 1 or 2
Enclosure (E)		Outdoor IP5x Double insulation	Indoor Double insulation
Metering		Energy				P, Q, PF, Energy, Alarm, Power quality

[a]  PV array main switch is usually included in the inverter panel.
[b]  If switching for emergency services is required, the main switch in array box can be equipped with tripping coil and motor mechanism for remote reclosing.
[c]  Array cable protection is recommended to prevent cable oversizing. To ensure fast trip of protections 6 to 8 arrays are recommended.
[d]  Overload and short-circuit protection.
[e]  If there is no SPD in the inverter or if the between DC box and inverter >10m a SPD is necessary in this box.
[f]  Galvanic insulation is provided by LV/MV transformer,
      - PV system without functional earthing: insulation monitoring is necessary: IMD - IM20 and accessory IMD-IM20-1700
      - PV system with functional earthing: the earthing shall be done with a DC MCB breaker (C60PV 4P series 2 – 10A) or a fuse.

Fig. P29 – 500-630kW inverters with LV/MV transformers