Fortress Power Envy Duo 21 Inverter

Name: Fortress Power Envy Duo 21 Inverter
Brand: Fortress Power
SKU: Envy Duo 21
Price: 5499.0 USD
Availability: InStock

$5,499.00 - $5,499.00

$5,499.00

$5,499.00 - $5,499.00

$5,499.00

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Fortress Power Envy Duo 21 Inverter | 25kW PV Input | 12kW Continuous Output | Dual-Phase Compatible

Maximum Power. Dual-Purpose Design. Built for What’s Next.

The Fortress Power Envy Duo 21 is a high-output, 48V hybrid inverter built to meet the needs of advanced residential and light commercial energy systems. With up to 25kW of solar PV input, dual-phase compatibility, and seamless integration with Fortress Power’s 48V battery line, the Envy Duo 21 is the ideal solution for whole-home backup, net metering, and smart energy management.

Supporting both 240V split-phase and 208V three-phase systems (with parallel installation), the Envy Duo 21 delivers 12kW of continuous output and up to 16kW peak export—making it a powerhouse for demanding energy applications.

Key Features:

Massive PV Input Capacity: Bring in more solar with up to 25kW of PV input, allowing larger arrays to operate at full potential. Ideal for properties with high energy loads or oversized solar arrays.
Dual Voltage, Dual Purpose: Supports both 240V split-phase (residential) and 208V three-phase (light commercial) systems. Whether you're powering a home or a small business, the Envy Duo 21 adapts to your needs.
Note: Three-phase requires two or more inverters in parallel.
Whole-Home Backup with Fortress Battery Integration: Pairs perfectly with Fortress Power 48V batteries (e.g., eVault MAX, eFlex MAX, eForce), providing:
- 12kW of continuous output
- Up to 16kW of export power
- Reliable power for essential loads, appliances, HVAC systems, and more.
Scalable to 120kW Output: Parallel up to 10 Envy Duo 21 units for a total of 120kW of AC output, making it ideal for growing systems, small commercial sites, and microgrids.
Installer-Friendly with Built-In Hardware:
- Integrated AC/DC breakers
- Built-in rapid shutdown transmitter
- Simplifies installation and ensures NEC 2017/2020 compliance
- Reduces time, labor, and external hardware requirements
Smart Monitoring + Remote Updates: Control and monitor your system via the Fortress Power mobile app, featuring:
- Real-time solar, battery, and grid stats
- Historical performance analytics
- Remote firmware updates—no site visit needed

Applications:

Large residential solar + storage systems
Light commercial buildings
Off-grid & grid-tied backup systems
Net metering and load shifting
Time-of-use optimization and zero-export
Virtual Power Plant (VPP) participation

What’s Included:

1 × Fortress Power Envy Duo 21 Hybrid Inverter
Integrated AC & DC Breakers
Built-in Rapid Shutdown Transmitter
Mounting Hardware
Fortress Power Mobile App Access
User Manual & Warranty Card

Requires minimum of two inverters for 208V three-phase applications.

Specifications

PV Output Data
Number of MPPT	3
Inputs per MPPT	2:2:1
Max. usable input current (A)	26/26/15
Max. short circuit input current (A)	31/31/19
Start input voltage (V)	100
MPPT DC nominal voltage (V)	360
DC voltage range (V)	100-550
MPPt operating voltage range (V)	120-440
Max. Power (W)	21000
Max. PV ARRAY POWER (W)	25000
Backup Output Data
Nominal output current (A)	50@240V, 57.7@208V
Nominal output voltage (V)	(120/240), (120/208)
Continuous output power (VA)	12000@240V, 12000@208V
Operating frequency (Hz)	60 & 50
Peak power (VA)	2xPn, 0.5s
THDV	<3%
Switching Time (ms)	<20
General Data
Paralleling Capabiliy	Up to 10 units (120kW)
Dimensions	22.3 x 35.2 x 11.2 in (566 x 893 x 285 mm)
Weight	125.71 lbs (57 kg)
Degree of protection	NEMA4X / IP66
Cooling concept	Smart Cooling Fans
Topology	High Frequency Transformer-less
Relative humidity	0-100%
Altitude (m)	<6561ft. (<2000m)
Operating Temperature Range (ºC)	-25~60>40 Derating
Noise emission (dB)	<67
Idle Consumption AVG (W)	60
Display	Touch color screen
Communication interface	Rs485/ Wi-Fi/ CAN
AC Grid Output Data
Max. Output Current with pv (A)	66.7
Max. Output Power with pv (W)	16000@240V 13800@208V
Continuous power output with battery only (W)	12000@240V, 12000@208V
Rated voltage (V)	120/240, 120/208
Operating voltage range (V)	180-270
Operating frequency (Hz)	50/60
Operating frequency range (Hz)	55-65
Power Factor	0.99@full load
Reactive power adjust range	-0.8~+0.8 leadingAdjustable
THDI	<3%
Sync inrush current (A)	35
Efficiency
Max. EFFICIENCY PV to grid	97.50%
Max. EFFICIENCY battery to grid	94%
CEC Efficiency	96.90%
Battery Data
Type	Lithium battery/ No Battery
Max. charge current (A)	250
Max. discharge current (A)	250
Nominal voltage (V)	48
Voltage range (V)	40-60

Shopping Guide

Power Storage & Inverter

Item / Appliance	Typical Power (W)	Usage Time (hrs)	Total Energy Needed (Wh)	Battery Size Needed (Ah) (12V System)	Inverter Size Needed (W)
LED Light Bulb (10W)	10W	5 hrs	50 Wh	4.2 Ah	100W
Phone Charging	5–10W	2 hrs	10–20 Wh	0.8–1.7 Ah	100W
Laptop Charging	50–100W	3 hrs	150–300 Wh	12.5–25 Ah	200W
Ceiling Fan	75W	6 hrs	450 Wh	37.5 Ah	150W
LED TV (32")	60W	4 hrs	240 Wh	20 Ah	150–200W
Refrigerator (Mini)	100W (avg)	8 hrs	800 Wh	66.6 Ah	300–500W
Water Pump (1HP)	750W	1 hr	750 Wh	62.5 Ah	1000W
Microwave Oven	1000W	0.5 hr	500 Wh	41.6 Ah	1200–1500W
Electric Kettle	1500W	0.3 hr	450 Wh	37.5 Ah	2000W

Key Formulas

Purpose	Formula	Example
Energy Consumption (Wh)	`Watts × Hours`	60W × 4 hrs = 240 Wh
Battery Capacity (Ah)	`Watt-hours ÷ System Voltage (V)`	240 Wh ÷ 12V = 20 Ah
Inverter Size (W)	`Total Watts × 1.25 (for safety margin)`	300W × 1.25 = 375W → Use 400W inverter
Total Load Power (W)	`Sum of all appliance watts to be used at once`	Light (10W) + Fan (75W) = 85W
Runtime (hrs) of Battery	`(Battery Ah × Voltage) ÷ Total Load (W)`	(100Ah × 12V) ÷ 240W = 5 hrs

How To Choose The Right Products

Need / Application	Recommended Battery	Inverter Size	Notes
Basic lighting + phone charging	50Ah – 100Ah (12V)	100W–200W	For small backup setups
Home office (laptop, fan, TV)	150Ah – 200Ah (12V or 24V)	500W – 1000W	For moderate usage with 4–6 hours of backup
Home backup (fridge, lights)	200Ah+ (24V or 48V recommended)	1000W – 1500W	Ideal for longer backups or heavier loads
Business / shop power backup	300Ah+ (48V system)	2000W – 3000W	Suitable for commercial setups or extended power outages

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