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 3.9. The Fortress Power Envy Duo 21 leads on warranty, solar input and features. The SunGoldPower SGN-11K15PRO wins on value. The SunGoldPower SGN-11K15PRO costs $2,048 less ($2,850 vs $4,898).
SunGoldPower SGN-11K15PRO
A grid-tied whole-home hybrid for homeowners who want to sell solar and keep the house running in outages, at a lower price than the big names.
SunGoldPower $2,850$2,850
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 warranty (10-year warranty vs 5-year warranty), solar input (25,000 W of panels, 550 V max, 3 MPPTs vs 15,000 W of panels, 600 V max, 3 MPPTs) and features (UL 1741 listed, Wi-Fi app, parallel stacking, grid sell-back, generator input, battery communication vs UL 1741 listed, Wi-Fi add-on, grid sell-back, generator input, battery communication).
- Choose the SunGoldPower SGN-11K15PRO for value ($250 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 SGN-11K15PRO |
|---|---|---|
| Overall rating | 4.3/5 | 3.9/5 |
| Value 30% | 58 $408 per kW of continuous output | 90 $250 per kW of continuous output |
| Solar input 20% | 100 25,000 W of panels, 550 V max, 3 MPPTs | 66 15,000 W of panels, 600 V max, 3 MPPTs |
| Efficiency 20% | 68 94% peak efficiency, 60 W idle | 50 efficiency and idle draw not published (neutral score used) |
| Features 15% | 100 UL 1741 listed, Wi-Fi app, parallel stacking, grid sell-back, generator input, battery communication | 82 UL 1741 listed, Wi-Fi add-on, grid sell-back, generator input, battery communication |
| Warranty 15% | 100 10-year warranty | 44 5-year warranty |
Specifications
| Fortress Power Envy Duo 21 | SunGoldPower SGN-11K15PRO | |
|---|---|---|
| Output | ||
| Output voltage | 120/240 V split-phase | 120/240 V split-phase |
| Continuous output | 12,000 W | 11,400 W |
| Surge | 24,000 W | 17,100 W |
| Peak efficiency | 94% | - |
| CEC efficiency | 96.9% | 96.5% |
| Idle draw | 60 W | - |
| Transfer time | 20 ms | 10 ms |
| Parallel units | Up to 10 units | - |
| Solar | ||
| Max PV power | 25,000 W | 15,000 W |
| Max PV voltage (Voc) | 550 V | 600 V |
| MPPT range | 120 to 440 V | 70 to 540 V |
| MPPT trackers | 3 | 3 |
| PV current per tracker | 26 A | 30 A |
| Runs without battery | Yes | No |
| Battery and grid | ||
| Battery voltage | 48 V | 48 V |
| Battery types | Lithium | Lithium, lead-acid |
| Max charge current | 250 A | 210 A |
| Battery communication | Yes | Yes |
| Grid sell-back | Yes | Yes |
| Generator input | Yes | Yes |
| UL 1741 | UL 1741 SB | UL 1741 SB |
| Build | ||
| App monitoring | Included | Optional add-on |
| Enclosure | IP66 (NEMA 4X) | NEMA 3R |
| Dimensions | 22.3 x 35.2 x 11.2 in | 448 x 901 x 270 mm |
| Weight | 125.7 lb | 103.6 lb |
| Warranty | 10 years | 5 years |
| Released | 2026-01 | 2025-07 |