Inverters

Fortress Power Envy Duo 21 Hybrid Inverter | 48V | 25kW PV Input | 12kW Backup | 240V Split-Phase & 208V 3-Phase | Parallel to 120kW | 10-Year Warranty

$ 5,759.54USD · price may vary

BrandFortress Power

Model: Envy-Duo-21-US
Specifications: 0

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Overview

Power larger solar + storage systems with the Fortress Power Envy Duo 21, a high-capacity 48V hybrid inverter built for demanding residential and light commercial energy needs. With up to 25kW PV input, dual-voltage compatibility (240V split-phase / 208V three-phase), and scalable paralleling up to 120kW, it’s a future-ready solution for backup power, off-grid setups, zero-export, TOU optimization, and more.

Key Features & Benefits:

High PV input capacity: Supports up to 25kW PV array power for larger residential or light commercial solar arrays

Dual voltage compatibility: Works with 120/240V split-phase and 120/208V three-phase configurations

Reliable backup output: 12,000W continuous backup power (240V or 208V) with <20ms switching time

Higher grid output with PV: Up to 16,000W @ 240V (or 13,800W @ 208V) when PV is available

Seamless battery integration: Designed to pair with Fortress Power 48V batteries (40–60V range) for stable backup performance

Scalable system design: Parallel up to 10 units (120kW total) to expand as energy demands grow

Install-friendly, code-compliant hardware: Built-in AC/DC breakers + integrated rapid shutdown transmitter

Remote monitoring + updates: Monitor production/consumption and perform remote firmware updates via Fortress Power mobile app (where supported)

Built for tough environments: NEMA 4X / IP66 enclosure, smart cooling fans, and touch color display

Quick Specs:

MPPTs: 3 (inputs per MPPT: 2:2:1)

Max PV Array Power: 25,000W | Max PV Power: 21,000W

Continuous Output (Battery Only): 12,000W @ 240V or 208V

Max Output w/ PV: 16,000W @ 240V | 13,800W @ 208V

Efficiency: 97.5% max PV-to-grid | 96.9% CEC

Comms: RS485 / Wi-Fi / CAN

Size / Weight: 22.3 x 35.2 x 11.2 in | 125.71 lb

Warranty: 10 Years

What’s in the Box (Unboxing):

1 x Envy inverter with hole knockout caps

1 x Wall mount bracket

2 x L-shaped braces

1 x Battery RJ45 adapter

1 x Installation/User manual

2 x Current transformers (CT) (connected by one cable)

1 x Dongle

2 x Battery-to-inverter comm cable + inverter-to-inverter comm cable

4 x RJ45 terminals

6 x Mounting screws (wood)

6 x expansion screws

4 x Cross head screws: L-brace + dongle

1 x Knockout hole template

User Manual / Documents:

Fortress Power Envy Duo 21 Hybrid Inverter Data Sheet

Fortress Power Envy Duo 21 Hybrid Inverter Installation Manual

Fortress Power Envy Duo 21 Hybrid Inverter Warranty

Reading the specifications

Detailed specifications for Fortress Power Envy Duo 21 Hybrid Inverter | 48V | 25kW PV Input | 12kW Backup | 240V Split-Phase & 208V 3-Phase | Parallel to 120kW | 10-Year Warranty have not been published yet. Fortress Power lists this inverter in the Inverters, and we add fields as the manufacturer releases them — in the meantime, ask your distributor for the datasheet before ordering.

For an inverter, the figures that matter most are the MPPT voltage window, which decides how many panels go in a string, peak and weighted (European/CEC) efficiency, typically 96–98.5%, topology — on-grid, off-grid, hybrid or micro and continuous AC output in kW, which caps the load you can run at once. It is the component that decides what a solar system can do: how much power you can draw at once, whether you can export to the grid, whether the system keeps running in a blackout, and how well the panels and battery are managed day to day.

Before you buy an inverter

The checks below apply to any inverter. Run them against the specification table above — most disappointing solar purchases are compatible-on-paper units that fail one of these in practice.

Size the inverter against the loads you need to run simultaneously, not against the total wattage of every appliance in the building — a 5 kW inverter comfortably runs a fridge, fans, lights and a couple of ACs, but not all of them plus a water pump starting at the same time.
Keep the panel array between roughly 1.0 and 1.3 times the inverter's rating. Slight oversizing (a higher DC-to-AC ratio) captures more energy on cloudy mornings and winter days; going far beyond it wastes generation through clipping.
Check the surge rating if you run motors — deep-well pumps, compressors and older air conditioners can draw two to three times their running current for a few seconds at start-up.
Choose a hybrid inverter if a battery is in your plan now or later; retrofitting storage onto a pure grid-tie inverter usually means buying a second unit or an AC-coupled battery system.

Where buyers lose money

Overlooking the IP rating. An outdoor installation needs at least IP65; indoor-rated units mounted outside fail early.
Buying on peak-watt price alone. A cheap inverter with a narrow MPPT window forces awkward string layouts and can strand a portion of the array.
Ignoring the ambient temperature rating. Inverters derate in heat, so a unit rated 5 kW at 25 °C may deliver noticeably less on a hot roof-adjacent wall at 45 °C.

Price and availability in United States

Fortress Power Envy Duo 21 Hybrid Inverter | 48V | 25kW PV Input | 12kW Backup | 240V Split-Phase & 208V 3-Phase | Parallel to 120kW | 10-Year Warranty is listed at $ 5,760 (USD) for United States. Solar pricing moves with supply, import duties and exchange rates, and distributors set their own margins, so treat this as a comparison reference and confirm the current figure before you order.

SolarBazaar compares equipment rather than selling it. Shortlist here on specification and price, then buy from an authorised distributor or installer in United States: warranty cover on solar hardware is normally honoured through the channel you bought from, so confirm who supports Fortress Power locally before ordering.

Fortress Power Envy Duo 21 Hybrid Inverter | 48V | 25kW PV Input | 12kW Backup | 240V Split-Phase & 208V 3-Phase | Parallel to 120kW | 10-Year Warranty — frequently asked questions

Fortress Power Envy Duo 21 Hybrid Inverter | 48V | 25kW PV Input | 12kW Backup | 240V Split-Phase & 208V 3-Phase | Parallel to 120kW | 10-Year Warranty is listed at $ 5,760 (USD) for United States. The figure is indicative — solar prices move with supply, duties and exchange rates, and each distributor sets its own margin — so confirm the current price with a supplier before ordering.

Fortress Power Envy Duo 21 Hybrid Inverter | 48V | 25kW PV Input | 12kW Backup | 240V Split-Phase & 208V 3-Phase | Parallel to 120kW | 10-Year Warranty is a Fortress Power product, listed under inverters with model reference Envy-Duo-21-US. The Fortress Power brand page lists the rest of its range so you can compare across the catalogue.

That depends on what it has to connect to. For an inverter, check surge or peak rating, which covers the brief inrush of motors and compressors, maximum PV input and the number of MPPT trackers, which set how many panel strings you can connect and the MPPT voltage window, which decides how many panels go in a string against the rest of your equipment before price enters the decision. Look at the warranty term and what it covers. Five years is the common baseline, ten is offered by stronger brands, and extensions are often cheaper bought with the unit than later.

SolarBazaar lists and compares equipment rather than selling it. Use the specifications and price here to shortlist, then buy through an authorised distributor or installer in United States — buying in-channel is what keeps the manufacturer's warranty valid.

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