Fortress Power Envy Duo 21
For homes with a large roof array that want whole-house backup and grid export from one outdoor unit. It takes more solar than the Envy True 12 for the same price.
Wind & Sun $4,898$4,898
The Fortress Power Envy Duo 21 is the better hybrid solar inverter overall, rated 4.3 to 4.1. The Fortress Power Envy Duo 21 leads on solar input and features. The SunGoldPower Freedom Pro 16K-48 wins on value. The SunGoldPower Freedom Pro 16K-48 costs $2,199 less ($2,699 vs $4,898).
SunGoldPower Freedom Pro 16K-48
A very large off-grid split-phase inverter for big homes, farms and shops that want one unit instead of a stack.
SunGoldPower $2,699$2,699
Prices were last checked October 23, 2026 and are subject to change; the price and availability shown by the retailer at the time of purchase apply.
Which should you buy?
- Choose the Fortress Power Envy Duo 21 for solar input (25,000 W of panels, 550 V max, 3 MPPTs vs 24,000 W of panels, 600 V max, 2 MPPTs) and features (UL 1741 listed, Wi-Fi app, parallel stacking, grid sell-back, generator input, battery communication vs UL 1741 listed, Wi-Fi app, parallel stacking, generator input, battery communication; no grid sell-back).
- Choose the SunGoldPower Freedom Pro 16K-48 for value ($169 per kW of continuous output vs $408 per kW of continuous output).
Scores side by side
Each factor is scored 0-100 against the same fixed reference points for every 120/240 V split-phase hybrid solar inverter; a clear win is highlighted. How we rank explains each one.
| Factor weight | Fortress Power Envy Duo 21 | SunGoldPower Freedom Pro 16K-48 |
|---|---|---|
| Overall rating | 4.3/5 | 4.1/5 |
| Value 30% | 58 $408 per kW of continuous output | 100 $169 per kW of continuous output |
| Solar input 20% | 100 25,000 W of panels, 550 V max, 3 MPPTs | 68 24,000 W of panels, 600 V max, 2 MPPTs |
| Efficiency 20% | 68 94% peak efficiency, 60 W idle | 54 94.3% peak efficiency |
| Features 15% | 100 UL 1741 listed, Wi-Fi app, parallel stacking, grid sell-back, generator input, battery communication | 85 UL 1741 listed, Wi-Fi app, parallel stacking, generator input, battery communication; no grid sell-back |
| Warranty 15% | 100 10-year warranty | 50 warranty not published (neutral score used) |
Specifications
| Fortress Power Envy Duo 21 | SunGoldPower Freedom Pro 16K-48 | |
|---|---|---|
| Output | ||
| Output voltage | 120/240 V split-phase | 120/240 V split-phase |
| Continuous output | 12,000 W | 16,000 W |
| Surge | 24,000 W | 32,000 W |
| Peak efficiency | 94% | 94.3% |
| CEC efficiency | 96.9% | - |
| Idle draw | 60 W | - |
| Transfer time | 20 ms | 10 ms |
| Parallel units | Up to 10 units | Up to 6 units |
| Solar | ||
| Max PV power | 25,000 W | 24,000 W |
| Max PV voltage (Voc) | 550 V | 600 V |
| MPPT range | 120 to 440 V | 120 to 550 V |
| MPPT trackers | 3 | 2 |
| PV current per tracker | 26 A | 36 A |
| Runs without battery | Yes | Yes |
| Battery and grid | ||
| Battery voltage | 48 V | 48 V |
| Battery types | Lithium | Lithium, lead-acid, user-defined |
| Max charge current | 250 A | 300 A |
| AC charge current | - | 300 A |
| Battery communication | Yes | Yes |
| Grid sell-back | Yes | No |
| Generator input | Yes | Yes |
| UL 1741 | UL 1741 SB | Yes |
| Build | ||
| App monitoring | Included | Included |
| Enclosure | IP66 (NEMA 4X) | IP20 |
| Dimensions | 22.3 x 35.2 x 11.2 in | 24.5 x 33.61 x 8.48 in |
| Weight | 125.7 lb | 105 lb |
| Warranty | 10 years | - |
| Released | 2026-01 | 2026-10 |