Photovoltaic for self-consumption - architecture and equipment requirements
When operating only grid-connected, PV systems used for self-consumption are simply connected to a switchboard of the electrical installation.
Loop configurations used to increase the energy availability in multi-source installations do not bring any benefit, as PV inverters stop operating in case of utility supply loss.
Automatic Transfer Operation
As described in the previous section, PV inverters operate in parallel with the grid. There is no transfer of operation from one source to another, thus Automatic Transfer Switch is not required for installations operating only grid-connected.
As the PV system for self-consumption is part of the electrical installation, the earthing arrangement of the electrical installation applies also to the AC side of the PV inverter. If the PV inverter is with distributed neutral, this one is connected to the same earth reference as the transformer neutral. The creation of two earth references inside the same building is forbidden as currents may circulate between both earths.
The earth reference remains the same as far as the installation operates gridconnected.
Regarding the DC side of the PV inverter(s), there are two options:
- galvanic isolation between the DC and the AC side of the PV system: the earthing at the DC side does not depend on the earthing system of the AC electrical installation
- no galvanic isolation (most common case): the system earthing at the DC side must be compliant with the earthing of the AC electrical installation
In case of utility supply loss, installations with local generation are required to guarantee that they do not inject power into the grid for utility workers’ safety.
For installations with PV production operating only grid-connected, this safety feature can be met by:
- the PV inverter (s) – most PV inverters integrate anti-islanding protection, which disconnects the PV inverter in case of power outage. The presence of this protection and its standard compliance is provided by the PV manufacturer
- a dedicated protection device installed at local sources feeders or at the utility incomer of the electrical installation.
Reverse power protection
Reverse power protection for PV inverters is not required as they are unidirectional devices and do not pass reverse current.
Reverse power protection may be required in the case of the presence of other local sources, such as diesel generators, where the flow of the current back to the generator may cause its failure.
Reverse power protection is usually not required to prevent the power injection into the grid in normal operating conditions, this function is assured through control of local sources.