Envy Duo 21 Inverter
Maximum Power. Dual-Purpose Design.

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The Fortress Power Envy Duo 21 is a powerful 48V hybrid inverter designed to handle demanding residential and light commercial energy needs. With a maximum PV input of 25kW and dual-phase compatibility (240V split-phase and 208V three-phase), it delivers 12kW of continuous output power across both configurations, with peak outputs of 16kW (240V) and 13.8kW (208V).

Perfectly matched with Fortress PowerÆs 48V battery systems, the Envy Duo 21 supports multiple applications. Its integrated AC/DC breakers, rapid shutdown transmitter, and parallel scalability up to 120kW make it a versatile, future-ready solution.

High PV Input Capacity

• Accepts up to 25kW of PV input-ideal for large residential or small commercial solar arrays seeking maximum generation potential.

Dual Voltage Compatibility

• Supports both 240V split-phase and 208V three-phase applications, making it flexible for a wide range of grid configurations.

Seamless Battery Integration

• Pairs with Fortress Power 48V batteries to deliver 12kW of continuous power and up to 16kW peak, ensuring stable, whole-home or light commercial backup.

Scalable System Design

• Parallel up to 10 units for a total output of 120kW, expanding as energy demands grow without the need for complete system redesign.

Integrated Install-Friendly Hardware

• Includes built-in AC/DC breakers and an integrated rapid shutdown transmitter for faster, code-compliant installations.

Remote Monitoring and Firmware Updates

• Monitor your solar production, battery performance, and grid consumption anytime via the Fortress Power mobile app. The Envy also supports remote firmware updates, ensuring your system stays up to date without the need for onsite visits.

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
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

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