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EG4

EG4 FlexBOSS21 Hybrid Solar Inverter | 21 kW PV / 16 kW AC | Split-Phase | 4 MPPT

SKU INV027

Regular price: $3,779.99

Regular price: $3,779.99

✅ Order by 12:00 PM EST and processing starts the same day (ships within 1–2 business days). Free, insured US shipping — delivery in 4–7 business days. Oversized items ship via LTL freight and we coordinate delivery with you by phone.

Quantity

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Shipping: how fast & how it works

Free standard shipping on every US order — no shipping charges at checkout, no hidden fees, and every shipment is insured against loss or damage.

Processing: 1–2 business days. Order before 12:00 PM EST and processing begins the same day.
Delivery: 4–7 business days via USPS, UPS or FedEx. Tracking is emailed the moment your order ships.
Large items (solar kits, batteries, shelters): delivered by LTL freight carriers such as FedEx Freight, Old Dominion or XPO. The carrier calls ahead to schedule a delivery window — please inspect the pallet and note any damage on the delivery receipt before signing, and we’ll take care of the rest.

Questions about delivery to your location? Call (302) 496-3554 (Mon–Fri, 9am–4pm EST) — we’re happy to check before you order.

What is your Return Policy?

At OffGrid Horizon, we want every customer to shop with confidence. If something doesn’t go as planned, we’ve made returns and refunds simple and fair. Here’s how it works:

1. Return Window

You can request a return within 30 days of receiving your order. Unfortunately, we’re unable to accept returns after that time frame.

2. Who Pays for Return Shipping?

If your item arrives damaged, defective, or incorrect, we’ll cover the return shipping cost — and you’ll receive a full 100% refund or replacement, including any original shipping costs.
If you’re returning an item because you changed your mind, you’ll be responsible for return shipping, and a 25% restocking fee applies.

3. Damaged or Defective Items

Received something broken or not working properly? Contact us within 30 days. We’ll provide a prepaid return label and once the item is returned and inspected, we’ll issue either a full refund or a replacement.

4. Changed Your Mind?

If you no longer want the item, you can return it within 30 days — as long as it’s unused, unopened, in its original packaging, and in resellable condition.

5. Refund Processing

Once we receive and approve your return, we’ll send a confirmation email and issue a refund to your original payment method within 7 business days. Please allow additional time for banks or credit card companies to process and reflect the refund.

How to start a return: email sales@offgridhorizon.com or call (302) 496-3554 (Mon–Fri, 9am–4pm EST) with your order number — we’ll send return instructions and your RMA right away.

Product Description

The EG4 FlexBOSS21 is the higher-output model in the FlexBOSS line, accepting up to 21 kW of solar PV input across four MPPT channels and delivering 16 kW of continuous split-phase AC output. It supports grid-tied, off-grid, and battery-backup operation, parallels for larger systems, and includes remote Wi-Fi monitoring — the inverter to choose when your home runs heavy simultaneous loads or your array spans multiple orientations.

Why the FlexBOSS21

21 kW of PV input across 4 MPPT channels — handles large, complex arrays split over multiple roof faces
16 kW of continuous split-phase 120/240V output — central air, well pump, range, and shop tools at the same time
Three operating modes: grid-tied self-consumption, off-grid, and battery backup with automatic transfer
Scalable: parallel multiple FlexBOSS units for even larger systems
Remote Wi-Fi monitoring included — production, consumption, and battery state in the app
Closed-loop communication with compatible 48V LiFePO4 banks, including EG4 WallMount and BigBattery ETHOS

Who it's for

Larger homes and properties where 13 kW isn't enough headroom — or where a big array needs four MPPT channels. Pairs with the EG4 GridBOSS MID for whole-home backup switching and smart load management. For pre-matched systems, see our FlexBOSS21 kits with EG4 WallMount batteries (16–48 kWh) or BigBattery ETHOS modules (10.24–30.72 kWh).

Specifications

Solar (PV) input	Up to 21 kW, 4 MPPT channels
AC output	16 kW continuous, split-phase 120/240V
Operating modes	Grid-tied, off-grid, battery backup
Battery voltage	48V nominal
Battery communication	Closed-loop with EG4 WallMount, BigBattery ETHOS, and other compatible banks
Scalability	Parallel-capable for larger systems
Monitoring	Remote Wi-Fi app monitoring included
SKU	INV027

Warranty

The EG4 FlexBOSS21 carries a 10-year full parts-or-product replacement manufacturer warranty. EG4 requires warranty registration within the first year of purchase (or proof of purchase from an authorized distributor) to keep coverage valid.

Common questions

FlexBOSS21 or FlexBOSS18?

Choose the 21 for 16 kW of output and a fourth MPPT. If your loads and array are moderate, the FlexBOSS18 covers most homes at a lower price.

Do I need an electrician?

Yes — a hybrid inverter interconnects with your main panel and, in grid-tied modes, with the utility. Installation should be performed by a licensed electrician, and residential energy storage installations are subject to local permitting.

Which battery should I pair it with?

EG4 WallMount batteries for a native single-brand system, or BigBattery ETHOS for stackable modular storage — both are available in matched FlexBOSS21 kits in the store.