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.

Fig. P22 – Grid connected <= 10kW

One three phase inverter with one string combiner 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.

Fig. P23 – 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.

Fig. P24 – 10-100kW multi single MPPT inverter

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 three phase inverter with one string combiner box except that it has more arrays, which requires array cable protection.
• Istc <= 400A, IAC <= 600A.

Fig. P25 – 150-500kW single MPPT inverter with N arrays > 2

Connection of PV system to the grid or to the private low voltage installation

Direct connection of PV system to the grid

When PV system is installed for "grid feeding", Utility that operates the grid will provide requirements for protection, disconnection, and metering function.

Each utility may have specific requirements according to local habits and grid specificity.

As a general rules the following functions are required :

• Energy meter (both direction)
• Disconnecting device (some countries require visual break)
• Over-current and earth fault protection according to earthing system
• Anti-islanding protection like VDE0126.

Connection of PV system to the private low voltage installation

See Photovoltaic architectures for self-consumption.