Some solar PV inverters offer a backup circuit that can be used even without the presence of batteries. This backup circuit offers the ability to power a small load, when the PV system is generating energy and when the grid is unavailable. Examples of these inverters include the following:
1. Fronius GEN24 Plus (with “PV Point”)
- The PV Point on the Fronius GEN24 inverter provides basic backup power directly from the solar panels, but only when the sun is shining. It does not require or use a battery system. This circuit can power small, essential loads but will not work if there is insufficient solar generation (e.g., at night).
2. SMA Sunny Boy (with “Secure Power Supply – SPS”)
- The SPS feature of SMA Sunny Boy inverters works similarly to the Fronius PV Point. It supplies backup power directly from the solar panels when they are generating energy during the day, without requiring a battery. Like the Fronius, this backup only works during daylight hours and can only supply small, essential loads.
3. Goodwe DNS Inverter (with EPS):
- Some of Goodwe’s inverters, such as the DNS series with an Emergency Power Supply (EPS) function, can also provide direct power from solar panels without the need for batteries, though this backup feature is dependent on adequate solar energy production.
Whilst this backup functionality without the need for batteries can be an important and/or attractive functionality for owners, it is critical that this backup circuit is protected appropriately.
As per the AS/NZS 3000:2018 (Wiring Rules), Clause 2.6 addresses Additional Protection by Residual Current Devices and specifically Clause 2.6.3 discusses Additional Protection by Residual Current Devices on final subcircuits. This clause states that:
- RCD protection is required on all final subcircuits with a rated current not exceeding 20A that supply power to socket outlets, lighting, and certain other circuits. The standard specifies that these RCDs must have a maximum residual current of 30mA.
This is directly relevant to solar PV inverter backup supplies, as these are considered a final subcircuit and must be protected by a 30mA RCD to comply with Australian wiring standards and to ensure personal safety.
Below is an excerpt from the Fronius Gen24 installation manual which reiterates this point to provide additional clarity.
Figure 1 – Excerpt from Fronius Gen24 Installation Manual