Sizing of electrical installation with solar production

The sizing of all electrical installation equipment must be done considering all operating modes and the worst-case constraints.

For example, as shown in the figure below:

• Cables and busbars are sized based on maximum load current (1),
• Transformers are sized based on maximum power flow (2),
• Protective and switching devices are selected according to maximum load current, and minimum and maximum short-circuit currents (3).

Fig. K57 – Components potentially impacted by the integration of photovoltaic production in existing installation

When the photovoltaic production capacity is lower than the power demand

There is little or no impact on the electrical installation sizing:

• the current flow through cables and busbar does not increase when adding photovoltaic production,
• the transformer power flow is lower due to the contribution of the photovoltaic system.

When the photovoltaic production capacity exceeds the power demand

The impact on the electrical installation sizing must be considered, as current and power flows in the installation can be higher.

In new constructions, the higher power and current flow constraints are considered at the early design phase, and the installation can be sized accordingly.

However, for existing buildings, consider the following:

• Connecting the photovoltaic system upstream to the main busbar avoids the need for changes in the main switchboard
• Using a control system to limit the photovoltaic production can avoid the need to replace the transformer and its protection device.

Fig. K58 – In existing buildings: the use of a control system or integration upstream to the main LV switchboard can reduce the impact on the existing electrical infrastructure