Operation of electrical installation with local PV production
From Electrical Installation Guide
Normal operating conditions
In normal operating conditions, electrical installations with PV production for self-consumption are characterized by two operating modes:
- The electrical installation operates supplied by the grid only when there is no PV production (e.g., during the night)
- The PV installation may be disconnected - as an option - through its protection device
- The electrical installation operates supplied both by the grid and by the PV installation when there is a PV production. The output waveform of the PV inverter(s) is synchronized with the grid voltage and frequency. This function is ensured by the PV inverter(s) embedded control.
- The produced PV power goes to the loads, as the electricity takes in priority the path of least resistance. Consequently, there is no need of specific equipment redirecting the flow of electrons.
Management of excess PV production
In case where the PV production exceeds the instantaneous consumption needs of the electrical installation, one of the following management strategies can be adopted:
- Inject the excess power in the grid where it is consumed by other users.
- The injected power can be remunerated at the wholesale price of electricity, or at other tariff, or not given value at all depending on the agreement with the energy provider
- Limit the PV production - Some energy providers do not allow the injection of excess PV power in the grid, or authorize a restricted injection only
- Use storage
- Share the PV excess with a community, with a private electrical network if allowed by the local regulation
PV systems create some limited disturbances in the electrical installation, coming mainly from the operation of the PV inverters. Those are:
- Harmonics: as most electronic equipment, PV inverters generate harmonics. The harmonics emission is specified by the PV manufacturers, generally they are below 3%THDI.
- DC residual currents: In case of an earth fault on the DC part of the network, the feeding of a DC residual current at the AC side of the installation depends on the isolation between the DC and AC side of the PV system:
- Galvanic isolation between DC and AC side of the PV installation guarantees that DC residual currents will not pass at the AC side.
- When there is no galvanic isolation between the DC and the AC side, a DC residual current may be present at the AC side of the installation and must be eliminated, unless the PV inverter is designed to prevent, limit or avoid such situation.
When an electrical installation requires the installation of Residential Current Device (RCD) of the AC circuit, the type (AC, A or B) should be selected in function of the residual current that can be present. PV inverters manufacturer usually specify the injected by the PV inverters maximum DC residual current and the RCD type that should be used with this inverter.
Utility supply loss
In installations operating grid-connected only, the PV inverters shut down automatically in the case of utility supply loss. They are not designed to provide back-up power during utility outages.
Fault inside the electrical installation
In the case of fault in the electrical installation, a high short-circuit current flows from the utility incomer to the fault location. The PV inverters also contribute to the fault providing their maximal current, which usually does not exceed two times the nominal PV inverter current (The maximal short-circuit current value is provided by the PV inverter manufacturer).
Electrical faults in installations with PV systems for self-consumption are localized and isolated by overcurrent protections, and specific protection functions or devices are not required.
The presence of PV inverters does not affect earth fault protection in the AC side of the installation.
PV inverters and DC side shall be protected against earth fault according to IEC 712.421.101.