PV system connection to the electrical installation

From Electrical Installation Guide

The integration of PV system into the electrical installation can be done through a connection:

  • to the main LV Switchboard
  • to a distribution LV Switchboard
  • upstream to the main LV switchboard
  • to the MV system

The corresponding schemes, field of application, advantages and drawbacks for each of these possibilities are detailed hereafter.

Connection at the main low voltage switchboard

With this configuration, the PV Installation architecture can include:

  • a single PV inverter, directly connected to the main LV switchboard
  • a group of PV inverters. The inverters’ outputs are gathered to a local generation switchboard and each in its turn feeds the main LV switchboard of the electrical installation – see Fig. P27. (Another possibility is to connect each inverter individually to the main LV switchboard, but this configuration is not recommended for cost, installation complexity and maintenance reasons)

The PV inverter power range used for self-consumption in commercial and industrial buildings being typically between 20kW and 60kW, it can be considered that for installed power up to 30kW a single inverter is used, and above this value a group of inverters is preferred.

Fig. P27 – PV installation connected to the main LV Switchboard

A configuration where the PV installation is connected to the main LV switchboard is used in the following cases:

  • PV system is located near the main LV switchboard
  • PV production is used both for self-consumption and export to the grid of the excess PV energy
  • PV system is associated with other local energy sources, e.g., storage or CHP. A connection at the main LV switchboard allows all local production to be gathered in a single area, which facilitates the maintenance and the operation of the installation. It is the ideal configuration for new electrical installations, or existing ones when the main LV switchboard is easily accessible (e.g., one- or two-floor buildings)
  • PV production capacity is between 10% to 100% of the building installed power. For smaller scale PV installations, a connection to a closer secondary switchboard can be preferred.

For larger PV installations, a connection upstream to the LV switchboard can be more suitable for existing installations.

Connection to a distribution switchboard

The PV system is connected to the closest switchboard.

This configuration is preferred in the following situations:

  • PV production does not exceed the consumption downstream to the switchboard it is connected to
  • the PV inverters are far from the main LV switchboard.

This configuration is typically used in multi-floor buildings characterized by:

  • A PV production at rooftop area significantly lower than the building energy consumption needs
  • a main LV switchboard usually located at the ground floor (utility incomer through ground cables).
Fig. P28 – PV installation connected to secondary LV switchboards

The connection to a secondary LV switchboard presents the following advantages:

  • The cable length between the PV system and its connection point to the electrical installation is minimized
  • The installation is easier and optimized.

Although, this configuration presents some limitations:

  • More complex maintenance if the number of PV sources multiplies - When a feeder is under maintenance, all power sources potentially supplying the feeder must be isolated. When connecting PV installations to the closest switchboard, the number of connected power sources is potentially higher and much more dispersed, which makes the isolation more complex
  • Limited upgradability – this configuration is much less evolutive than a connection to the main LV switchboard: an extension of the PV installation may require modifications in the existing building electrical installation (cables, switchboards and protections may need to be resized).

Connection upstream to the main low voltage switchboard

In this configuration, the PV installation is connected upstream to the main LV switchboard. A possible configuration is to connect all PV inverters and the utility incomer to a switchboard which feeds the main LV switchboard of the electrical installation. Another alternative, especially when the utility incomer and the local sources are not in proximity, is to connect a single output of the PV system to the utility incomer, before feeding the electrical installation.

This connection upstream to the main LV switchboard is used in existing buildings where the PV production capacity exceeds the load consumption for which the electrical installation is sized. In this case, a connection of the PV system to a secondary or main switchboard would overload the existing electrical infrastructure and will require its modification such as replacement of cables, switchboards and protection equipment. Coming as a better option, a connection upstream to the main switchboard does not require any modifications of the main LV switchboard or downstream to the installation.

The main advantage of this architecture is its capacity to integrate large-scale PV production without impact on the existing electrical installation infrastructure. It can be used both for self-consumption and export of PV production excess. A drawback can be the need for a dedicated, additional switchboard to gather all sources, which potentially increases the cost of the system.

Fig. P29 – PV installation connected upstream to the main LV switchboard

Connection to the MV system

A connection to the medium voltage side of the electrical installation is extremely rare, as the PV production and the electrical installation loads are in geographical proximity.

A medium voltage connection of the local PV production will require additional costs and will be less energy efficient, except if the PV production is far from the loads and with important production capacity.