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48V Hybrid Inverter · 3 MPPT · GridBOSS-Ready · UL 9540
The EG4 FlexBOSS21 is rated for 12,000W of continuous output on its own, rising to 16,000W with solar actively assisting, backed by up to 21,000W of PV input across three MPPT trackers and five solar strings. It works grid-tied or fully off-grid, integrates directly with EG4's GridBOSS energy management hub, and carries a 10-year manufacturer's warranty inside a NEMA 4X all-weather enclosure.
Rated for 12,000W continuous on its own, and up to 16,000W when solar is actively contributing alongside the battery.
Three independent MPPT trackers split across five total input strings, pulling up to 21,000W utilized from the array.
Connects directly to EG4's GridBOSS hub for smart load management, AC coupling, and generator support at a system level.
Handles high-demand loads and grid integration with headroom beyond what most residential hybrid inverters offer.
UL 9540 certified for both grid-tied and off-grid installs with compatible batteries — the same unit covers either path.
Rated for direct outdoor installation and built to keep running through rain and snow, not just covered or indoor spaces.
Built-in rapid shutdown, ground fault, and arc fault protection for safe, code-compliant operation.
Scales from a single home installation up to large residential or commercial-style systems on the same platform.
The FlexBOSS21 sits at the top of EG4's hybrid lineup by power: 12,000W continuous on its own, 16,000W when solar is actively feeding in alongside the battery, and up to 21,000W of usable PV input spread across three MPPT trackers and five separate strings. That's more granular solar tracking than a typical 2-MPPT hybrid inverter, which matters on larger or more complex roof layouts with panels facing different directions.
Where it distinguishes itself further is the GridBOSS ecosystem: paired with EG4's GridBOSS hub (sold separately), it gains smart load management, AC coupling for retrofits, and generator support at a whole-system level rather than just at the inverter. It's UL 9540 certified for both grid-tied and off-grid installs with BigBattery ETHOS or EG4 batteries, wrapped in a NEMA 4X enclosure rated for direct outdoor installation, and backed by a 10-year manufacturer's warranty.
| Rated output (without PV) | 12,000 W |
| Rated output (with PV) | 16,000 W |
| Output voltage | 120/240V, 120/208V |
| Max output current | 66.7 A |
| Peak power (0.5s / 1s) | 24,000W / 18,000W |
| Power factor | 0.99 (full load) |
| Transfer time | 20ms default / 10ms configurable |
| MPPT channels | 3 (5 strings total) |
| Max utilized PV power | 21,000 W |
| Rec. max PV input | 25,000 W |
| DC input voltage range | 100–600 Vdc |
| MPPT voltage range | 120–440 Vdc |
| Max efficiency (PV to grid) | 97% |
| Nominal battery voltage | 48 Vdc |
| Battery voltage range | 40–60 Vdc |
| Max charge/discharge power | 12,000 W |
| Rec. battery capacity/inverter | >300 Ah |
| Max AC bypass | 90 A |
| Idle consumption | <65 W |
| Dimensions (D×W×H) | 11.3 × 22.3 × 30.5 in |
| Weight | 88 lbs |
| Enclosure rating | NEMA 4X (all-weather) |
| Operating temperature | -13°F to 140°F |
| Noise level | <50 dB @ 3 ft |
| Design topology | High-frequency, transformerless |
| Communication | RS485 / CANBus / Wi-Fi |
| Max parallel units | 16 |
| Brand / model | EG4 FlexBOSS21 |
| Warranty | 10 years |
Certification: UL 1741, UL 9540.
UL 9540 certified with closed-loop communication for both grid-tied and off-grid installs, when paired with:
12,000W is what the FlexBOSS21 delivers continuously on battery and grid power alone. 16,000W is the higher figure it can reach when solar is actively contributing at the same time — the same inverter, just with the sun helping out. Both numbers are accurate; they just describe different operating conditions.
The EG4 GridBOSS is a separate energy management hub (sold separately) that adds smart load management, AC coupling, and generator support at a whole-system level. It's an optional add-on — the FlexBOSS21 runs as a complete inverter on its own — but it's a natural pairing for larger or more complex installations.
Yes — it carries a NEMA 4X enclosure rating, built for direct exposure to rain and snow, unlike IP20-rated inverters that require an indoor or fully enclosed location.
It's UL 9540 certified for both grid-tied and off-grid installs with BigBattery ETHOS and EG4 batteries, with at least 300Ah of recommended capacity per inverter.
It depends on your total connected load. At 12,000–16,000W depending on solar contribution, it covers most homes comfortably, but a full load calculation is worth doing before sizing your system, especially for larger properties with heavy HVAC or well pump draw.
Yes, up to 16 units can be paralleled together, which is enough headroom to scale from a single large home up to bigger residential or commercial-style installations.
Given the voltages and currents involved, and the added complexity of a grid-interactive hybrid system, installation should be handled by a qualified, licensed electrician or solar installer familiar with your local code and utility interconnection requirements.
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To start a return: +1 (307) 317-7213, hello@ecosolarkits.com, or live chat. Read the full return and refund policy
