Problem Description
- Fault Name: Lights Flicker During Grid/Backup Transfer
- The customer reports that the house lights flicker significantly, and sometimes computers reboot, when the grid power fails (switching to battery backup) and when the grid is restored. The inverter brand is Solis. Previous installations by an old installer did not have this issue, but systems installed by a new installer experience this flickering.
Symptoms
- The transition time between On-Grid and Off-Grid (EPS/UPS mode) takes visibly longer than the standard <20ms.
- Lights blink or dim momentarily during the transfer in both directions.
- The monitoring chart (as shown in the image) shows rapid, sharp compensations between the Grid and the Battery.
Possible Causes
- Neutral Wire Shared (Wiring Error): The new installer mixed the Grid Neutral (N) and the Backup Neutral (N) on the same busbar in the distribution box.
- UPS/Seamless Switch Mode Disabled (Settings Error): The new installer forgot to enable the fast-switching "UPS Mode" or "Seamless" feature in the Solis inverter's hidden settings.
- External Contactor Delay: The installer used an external AC contactor for an entire-home backup setup, which inherently takes 50-100ms to switch, causing a flicker.
How to Verify
First, check the Inverter LCD settings for the switching mode. If the settings are correct, open the AC distribution box and visually trace the Neutral (N) wires from the Inverter's "Backup/EPS" port. See if they share the same Neutral busbar with the Grid Neutral.
Required Tools
- Multimeter
- Screwdriver (to open the AC Distribution Box)
- Inverter Installer Password (for Solis, usually 0010)
Diagnostic Procedure
- Step 1: Go to Solis Inverter LCD -> Advanced Settings -> Backup Mode. Ensure that "Backup" is turned ON, and if there is a "Seamless" or "UPS Mode" option, ensure it is enabled.
- Step 2: Open the AC distribution box. Power off the system. Use a multimeter in continuity mode. Measure the resistance between the Grid Neutral bar and the Backup Neutral bar. If it beeps (resistance is 0), the Neutral wires are incorrectly shared.
- Step 3: Check if the installer added an external ATS (Automatic Transfer Switch). An external ATS will always cause a flicker compared to the inverter's internal relay.
Root Cause
Why the N-Wire matters: Modern hybrid inverters use internal high-speed relays to achieve <20ms switching. They require the Grid AC-N and the Backup AC-N to be strictly separated on different busbars. If the new installer was lazy and tied all the Neutral wires to a single busbar (a common habit from traditional grid-tied solar), the inverter's internal zero-crossing detection gets confused by the grid's floating voltage during an outage. This forces the inverter to delay its switching time for safety, downgrading a 10ms seamless switch into a 500ms hard blink.
Corrective Actions
- Rewire the Neutral: Have an electrician separate the AC distribution box into two distinct sections: The "Grid side" and the "Backup/EPS side". Install a separate Neutral busbar for the Backup loads. Ensure Backup-N and Grid-N are physically isolated.
- Enable UPS Mode: Access the Solis installer menu and verify that the switching time is optimized for UPS (<20ms) rather than standard EPS.
⚠ ⚠️ Sharing the Neutral wire in off-grid mode can not only cause flickering but can also disable the function of RCDs (Residual Current Devices) or Earth Leakage breakers, creating a severe shock hazard for the homeowner.
💡 💡 “A good inverter can be ruined by a lazy wireman.” The fact that the "Old installer was fine, but the new one flickers" is the ultimate proof that this is a workmanship issue. Traditional electricians are used to tying all Neutrals together. Hybrid ESS installations require a strict "Two-Neutral-Bar" mindset. Training your new installers on the exact AC wiring schematic will fix this instantly.