Architectures for integration of local sources

From Electrical Installation Guide

Local sources can be connected to the building electrical installation at different places: to the main low-voltage (LV) switchboard, to a secondary LV switchboard, or upstream of the main LV switchboard.

Fig. K50 – Main options for connecting local sources to an electrical installation: (1) to the main LV Switchboard, (2) to a secondary LV Switchboard, and (3) upstream of the main LV switchboard

Recommended design: connect to the main LV switchboard

A recommended option is to connect the local sources to the main low-voltage switchboard of the electrical installation. If the local power generation is achieved by more than one source (typically several solar inverters and energy storage system), it is recommended that the output of those inverters be grouped in a dedicated switchboard (local sources switchboard), which is then connected to the main LV switchboard at a single point.

This architecture is simple and safe to maintain because the local production can be disconnected at a single point. It is recommended for both new and existing buildings.

Fig. K51 – Electrical installation with local production connected to the main LV Switchboard

For existing buildings with small-scale PV production in grid connected Prosumer

Connecting PV generators to the closest secondary low-voltage switchboard is an architecture used mainly in existing buildings where the PV production is much lower than the building consumption. This approach is used primarily in existing multi-floor buildings, where the PV production, usually on the roof, is far from the main LV switchboard, which is usually at ground level. Indeed, in such situations, the cable length between the PV system and the main LV Switchboard can be considerable. Connecting the photovoltaic system to a secondary LV switchboard nearby can minimize cable length and facilitate the integration of the photovoltaic system.

However, this architecture presents important limitations, including:

  • Complexity of the design, management, and maintenance of the installation, especially if there are several dispersed PV-sources
  • Limited upgradability, because an increase in the PV system production capacity or the addition of other local production or storage may require significant changes such as resizing the existing electrical infrastructure
Fig. K52 – Electrical installation with photovoltaic production connected to secondary LV Switchboards

This architecture shall not be used for islandable Prosumer installation as the management of island mode would be very complex.

Local sources, at least grid forming source should be connected to the electrical installation close to the “Switching device for islanding”. See Islandable PEI

For existing buildings with local production exceeding the demand

Connecting the local sources upstream of the main low-voltage switchboard is frequently the approach taken in existing buildings when the local production being added is higher than the building’s consumption. In this case, connecting the local sources to a secondary or main switchboard would overload the existing electrical infrastructure and would require its modification, such as replacement of cables, switchboards, and protection equipment.

Making the connection upstream of the main switchboard provides a better option because it does not require any modification of the main LV switchboard or other downstream system components. However, the maximum short-circuit current including local sources shall be calculated and compatibility of existing installation with this maximum short-circuit current shall be checked.

Fig. K53 – Electrical installation with local production connected upstream of the main LV Switchboard