Solis Hybrid Black Start Capability Application Note

Note: This letter only applies to Solis hybrid inverter series being sold in North America.  Please scroll to the bottom to download this letter for your utility or AHJ.

June 8th, 2026

Solis Hybrid Black Start Capability Application Note

Subject: This application note serves as official documentation from the manufacturer regarding the "Black Start" capabilities and automated system recovery logic of Solis hybrid inverters during extended grid outages, explicitly addressing system architectures both with and without string-level Rapid Shutdown (RSD) devices.

Part 1: Black Start Architecture for Systems Utilizing Rapid Shutdown (RSD)

When a hybrid system with backup incorporates rapid shutdown equipment (such as Tigo or APS ), the system encounters a technical catch-22 during an extended power outage where during the night the battery depletes to the over discharge state-of-charge (SOC) point: In the morning the next day the inverter requires PV voltage to wake up; however, the rapid shutdown equipment in the PV array requires an active Power Line Communication (PLC) "keep-alive" signal from the RSD transmitter to provide that voltage to the inverter. Without the signal, the PV array is stuck in “safety mode”. 

Because the inverter is completely shut down with no power from the battery or the grid, it cannot power the transmitter, and the system cannot natively perform a black start using only the sun. To enable Black Start capability on RSD-equipped systems, an external auxiliary power loop must be installed to bridge this gap.

The Auxiliary Black Start Loop: Installers must integrate a small external 12V lithium-ion battery as an emergency power supply to independently power the RSD transmitter in the event the inverter is completely shut down. The recommended architecture includes:

• 12V DC UPS Controller & AC-to-DC Converter: Powered by a single phase (120VAC) from the inverter's backup port. While the inverter is running, this powers the transmitter and float-charges the auxiliary battery.
• 12V LiFePO4 Auxiliary Battery: A compact (e.g., 3Ah–5Ah) lithium-ion battery equipped with an internal Battery Management System (BMS) to protect against overcharging and deep discharge.
• Trigger Mechanism: A 12V photocell relay (daylight sensor) or a manual momentary push-button installed inline between the auxiliary battery and the transmitter.
• System Behavior & Recovery: During an extended outage where the main home/building battery system depletes, the Solis inverter shuts down, dropping power to the backup port. The 12V DC UPS shifts to the auxiliary battery once the sun comes up and the photocell relay closes.

1. Overnight Drain Protection: To prevent the transmitter from draining the small 12V battery overnight, the photocell relay opens the circuit once it is dark, ensuring the transmitter remains off until the sun comes up the next morning.

2. Morning Wake-Up: At dawn, the photocell detects sunlight and closes the circuit. The auxiliary battery powers the RSD transmitter.

3. Black Start Activation: The transmitter sends the PLC signal to the roof modules. High-voltage DC is restored to the inverter, waking it up to take over the load, re-energize the backup port, and resume normal battery charging.

Part 2: Black Start Architecture for Systems Not Utilizing Rapid Shutdown

For systems where string-level Rapid Shutdown is not utilized or required by the local AHJ, the Solis hybrid inverter system is engineered with integrated Black Start hardware and firmware logic to automatically reboot itself using only solar power once environmental conditions permit.

1. System Behavior During Battery Depletion: During an extended outage, the home relies on PV generation and battery storage. If local load demand exceeds solar production, the battery will discharge to support the backup panel. Once the battery reaches its programmed over-discharge State of Charge (SOC) limit, the inverter's internal DSP will systematically shut down the AC backup output. This is a critical self-preservation mechanism designed to prevent deep discharge and permanent chemical damage to the connected energy storage system. In this state, the inverter powers down and enters a low-energy hibernation mode.

2. Automated PV Wake-Up & Recovery Logic: The true Black Start capability activates the following morning. When the sun comes up and solar irradiance hits the panels, the PV strings begin generating DC voltage. The Solis inverter is designed to detect this incoming DC string voltage independently of the grid and the depleted battery.

Once the PV voltage crosses the inverter's minimum startup threshold:

• The system utilizes the raw PV power to wake up its internal communications and processing components.
• It turns itself back on and closes the necessary internal relays to re-establish communication with the battery's BMS.
• The system bypasses normal AC load support and directs 100% of the available PV power to start recharging the batteries from PV only.

3. Resumption of Load Support: To prevent a cycle of immediate brownouts, the inverter will not immediately restore power to the home's backup loads. The system will continue to charge the battery using strictly PV power until the battery recovers to a safe, pre-programmed restart SOC threshold. Once this healthy baseline is achieved, the inverter will automatically restore AC output to the backup loads, resuming standard off-grid operation without requiring any manual intervention or external generator jump-starts.

Official Confirmation

Solis officially confirms that our hybrid inverter series supports Black Start functionality. The system will safely shut down to protect the energy storage system at the over-discharge SOC and will automatically wake up via PV power from the sun to recharge the battery when sufficient solar energy is available.

Should your engineering or installation team require further technical clarification regarding SOC thresholds, PV startup voltages, or designing external RSD auxiliary circuits, please reach out to the US Solis Support team for assistance.

Email: usservice@solisinverters.com & Phone: +1(866)438-8408

Michael Allen

Product Manager

michael.allen@solisinverters.com

Solis North America

Ginlong Technologies Co., Ltd.