The Fortress Power Envy Duo 21 is a cutting-edge hybrid inverter engineered to bridge the gap between residential and light commercial energy storage. True to its “Duo” name, it offers native dual-voltage support for both 120/240V split-phase (homes) and 120/208V three-phase (commercial) applications. With a massive 25kW PV input and 16kW of grid-tied power, it is the most powerful 48V inverter in the Fortress lineup.

Why Choose Envy Duo 21

The Envy Duo 21 is the ultimate “future-proof” inverter. It eliminates the need to choose between residential and commercial distinct models. Its massive 25kW solar input capability (significantly higher than the industry standard 15-18kW) allows for oversized arrays that guarantee full battery charging even on cloudy days. Whether you are powering a large luxury estate or a small business with 3-phase motors, the Duo 21 handles it all without external transformers.

Benefits of Envy Duo 21

• Dual Voltage Versatility: The “Duo” capability allows it to output native 208V 3-phase power for commercial equipment or 240V split-phase for standard homes, making it a single solution for mixed-use properties.

• Industry-Leading Solar Input: With 3 MPPT trackers supporting up to 25kW of PV, you can maximize energy harvest and ROI, ensuring you have ample power to run loads and charge massive battery banks simultaneously.

• Whole-Premise Backup: Features a 200A AC pass-through (grid-tied), allowing it to sit between the meter and the main panel to back up the entire electrical service without a critical loads panel.

• Seamless Integration: Designed to pair perfectly with the Fortress eBoost, eForce, and eVault MAX batteries using closed-loop communication for “plug-and-play” setup and optimized performance.

General Data

• Dimensions (H x W x D): 35.2″ x 22.3″ x 11.2″ (894 x 566 x 285 mm)

• Weight: 126 lbs (57 kg)

• Enclosure Rating: NEMA 4X / IP65 (Outdoor Rated)

• Cooling: Smart Fan Cooling

• Operating Temperature: -13°F to 140°F (-25°C to 60°C)

• Stackable: Yes (Up to 10 units for 120kW)

Frequently Asked Questions

Q1: What does “Duo” stand for?

“Duo” refers to the inverter’s dual-voltage capability. It can be configured to output standard residential 120/240V split-phase power OR commercial 120/208V three-phase power without needing external transformers.

Q2: How much solar can I connect?

You can connect up to 25,000 Watts (25kW) of solar panels. This is one of the highest PV input ratings in its class, allowing for aggressive oversizing to ensure performance in winter or low-light conditions.

Q3: Is this the same as the Envy True 12?

The Envy Duo 21 is the evolution of the 12kW platform. While both offer 12kW backup, the Duo 21 features the upgraded 25kW PV input (vs 21kW) and explicit dual-voltage 208V/240V firmware and hardware support.

Q4: Can I stack them?

Yes. You can stack up to 10 units in parallel. In a commercial 208V setup, this allows for a massive 120kW / 1.2MWh energy storage system.

Q5: Does it work with the Fortress eBoost battery?

Yes. The Envy Duo 21 is the recommended inverter companion for the new Fortress eBoost battery, as well as the eForce and eVault MAX, fully supporting closed-loop communication for all of them.

If you have any questions about the item or your order, please feel free to message before purchasing. Thank you!