Product Description

The EG4 FlexBOSS18 is a hybrid solar inverter built for whole-home solar-plus-storage. Per EG4, it utilizes up to 18,000W of solar, delivers 13,000W of continuous split-phase 120/240V output with PV available (10,000W from battery alone), and supports grid-tied, backup, and off-grid operation from a NEMA 4X outdoor-rated enclosure. It is designed to pair with the EG4 GridBOSS MID for whole-home backup switching, smart loads, and generator integration.

Who This Is For

Homeowners building solar-plus-storage with room to grow: the FlexBOSS18 parallels up to 16 units per EG4, connects to GridBOSS for 200A whole-home backup, and carries EG4's grid-interactive certifications for utility interconnection where export is desired. If your service runs heavier simultaneous loads or you need more PV, step up to the FlexBOSS21.

Key Features

  • 13,000W continuous split-phase output with PV (10,000W battery-only), with surge to 20,000W for 0.5 s per EG4's spec sheet
  • Up to 18,000W of utilized PV — per EG4's spec sheet, two MPPTs with five string inputs (3 + 2), 26A rated per MPPT, 600 VDC max input
  • 48V battery charging/discharging up to 208A with closed-loop communications for EG4 batteries
  • Grid-interactive certifications per EG4: UL 1741 SA/SB with PCS CRD (EG4's product page also lists UL 3141), IEEE 1547, California Rule 21
  • GridBOSS-ready: connects to the EG4 GridBOSS MID for whole-home backup, smart load control, AC coupling, and generator management
  • NEMA 4X enclosure, -13 to 140 °F operating range, EMP-hardened per EG4
  • EG4 Connect monitoring via Wi-Fi, Ethernet, or cellular per EG4

Why EG4

EG4 Electronics is a US-based manufacturer with published spec sheets, manuals, and wiring diagrams for every product and US-based technical support. The FlexBOSS platform is the center of EG4's current residential ecosystem: FlexBOSS inverters, WallMount batteries, and the GridBOSS MID are designed and documented to work as one system with closed-loop communications.

Specifications

Specifications below are per EG4's published FlexBOSS18 spec sheet.

Continuous AC output 13,000W with PV/grid; 10,000W battery-only
Surge capacity 20,000W (0.5 s); 15,000W (1 s); 13,500W (1 min)
Output voltage Split-phase 120/240VAC or 120/208VAC
PV input 18,000W max utilized; 2 MPPTs, 5 string inputs (3/2)
MPPT voltage range 250–440 VDC full power (120–440 VDC operating; startup 200 VDC; max input 600 VDC)
PV current per MPPT 26A rated / 31A short-circuit (Isc)
Battery voltage 51.2V nominal (40–60 VDC range)
Max charge / discharge current 208A / 208A
AC input 120/240VAC or 120/208VAC; 90A pass-through
Transfer time 20 ms default
Efficiency 97% CEC; 97% peak PV-to-grid
Idle consumption <60W
Parallel capability Up to 16 units
Certifications UL 1741 SA/SB with PCS CRD; California Rule 21; CSA C22.2 107.1 & 330; IEEE 1547:2018 / 1547.1:2020 (UL 3141 also listed on EG4's product page)
Enclosure / environment NEMA 4X; -13 to 140 °F
Dimensions / weight 30.43 x 22.28 x 11.22 in; 115 lb
Communications / monitoring Wi-Fi, Ethernet, cellular; EG4 Connect app
Warranty 10 years per EG4 (registration required within first year)
SKU INV031

Grid-Tied, Backup, or Off-Grid

Grid-tied: solar powers your home and charges batteries, and surplus can be exported where your utility approves the interconnection — export capability and compensation vary by state and utility, and your installer files the application. Backup: when the grid fails, the FlexBOSS18 transfers to battery power in 20 ms per EG4; with a GridBOSS at the service entrance, backup extends to the whole 200A service with automatic load management. Off-grid: the same hardware runs with no utility at all. The operating mode and any utility-required settings are configured at commissioning.

Battery Compatibility

The FlexBOSS18 manages a 48V-class bank with closed-loop communications to EG4 WallMount batteries. The EG4 WallMount 314Ah all-weather battery (16 kWh) is the standard pairing — stack multiple units toward your storage target. Sizing rule of thumb: match storage to daily consumption, not to the inverter rating.

Installation

Licensed-electrician territory: the FlexBOSS18 interconnects with your main panel and — in grid-tied modes — with the utility, which requires an interconnection application before export. Residential energy storage installations are subject to local permitting and inspection. The NEMA 4X enclosure permits outdoor mounting; plan for 115 lb and EG4's published clearances. For whole-home backup rather than a critical-loads panel, install it with the EG4 GridBOSS 200A MID.

Warranty & Support

Per EG4, the FlexBOSS18 carries a 10-year warranty; registration within the first year (or proof of purchase from an authorized distributor) is required. OffGrid Horizon is a family-owned authorized EG4 dealer — call (302) 496-3554 for sizing help, commissioning questions, or warranty support.

Shipping

Ships within the contiguous United States. At 115 lb, the FlexBOSS18 ships LTL freight on a pallet. Inspect packaging before signing the delivery receipt and note any damage with the driver; call us right away if anything is wrong.

Frequently Asked Questions

FlexBOSS18 or FlexBOSS21?

Per EG4, the FlexBOSS18 delivers 13 kW with PV (10 kW battery-only) and 18 kW of PV; the FlexBOSS21 delivers 16 kW with PV (12 kW battery-only), 21 kW of PV, and an additional MPPT. Choose by your loads and array size — call us if you are on the fence.

How many MPPTs does it have?

Per EG4's spec sheet: two MPPTs with five total string inputs (three on MPPT 1, two on MPPT 2), 26A rated per MPPT — enough flexibility for arrays split across multiple roof faces.

Can it sell power back to the grid?

It carries EG4's grid-interactive certifications (UL 1741 SA/SB), but actual export depends on your utility approving your interconnection application. Rules and compensation vary by state and utility.

Do I need a GridBOSS?

Not strictly — a FlexBOSS18 can back up a critical-loads panel on its own. The GridBOSS is what turns the system into 200A whole-home backup with automatic switching, smart loads, and generator management.

Does it work with a generator?

Generator integration in a FlexBOSS system is handled through the GridBOSS, which provides a dedicated 125A generator input per EG4.

Can I add more inverters later?

Yes — per EG4, up to 16 FlexBOSS18 units can be paralleled.

Is it OK outdoors?

Yes — the enclosure is NEMA 4X rated with a -13 to 140 °F operating range per EG4.

Building a FlexBOSS system? Call OffGrid Horizon at (302) 496-3554 — we are a family-owned authorized EG4 dealer and will help you spec the inverter, GridBOSS, and batteries as one system.

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