Fortress Envy Duo 21-US (16 kWh) Hybrid Inverter

Fortress Envy Duo 21 Whole Home Hybrid Inverter 

The Fortress Envy Duo 21 is a 48 V hybrid inverter designed for residential and light commercial solar-plus-storage systems. It supports up to 25,000 W of total PV array power across 3 independent MPPT trackers and delivers 12,000 W of continuous output power in grid-tied or off-grid modes. Featuring an integrated 200 A transfer switch, pre-installed AC/DC circuit breakers, and an APsmart rapid shutdown transmitter, it provides full backup power management in a single NEMA 4X / IP66 outdoor-rated enclosure.

Compatible with 120/240 V split-phase and 120/208 V three-phase electrical systems, the inverter handles high surge loads with peak outputs up to 16,000 W on 240 V connections. The transformer-less design connects to 48 V lithium battery systems and allows parallel scaling for up to 10 units to achieve 120 kW total system capacity. Weighing 125.7 lb, the unit features smart fan cooling and an active temperature range built for demanding installations.

Features and Specifications of Fortress Envy Duo

• 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): 21,000
• Max. PV ARRAY POWER (W): 25,000
• Paralleling Capability: Up to 10 units (120kW)
• Dimensions (W x H x D): 2.3 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

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
• THDV: <3%