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 3.8. The Fortress Power Envy Duo 21 leads on solar input, warranty and features. The ECO-WORTHY Synch 12KP wins on value. The ECO-WORTHY Synch 12KP costs $1,928.01 less ($2,969.99 vs $4,898).
ECO-WORTHY Synch 12KP
For grid-connected homes that want battery backup and solar export from one 12 kW unit. Off-grid buyers can get the same power for less from an off-grid model.
Amazon ECO-WORTHY $2,969.99$2,969.99
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 13,200 W of panels, 550 V max, 2 MPPTs), warranty (10-year warranty vs 5-year warranty) 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, parallel stacking, grid sell-back, generator input, battery communication).
- Choose the ECO-WORTHY Synch 12KP for value ($247 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 | ECO-WORTHY Synch 12KP |
|---|---|---|
| Overall rating | 4.3/5 | 3.8/5 |
| Value 30% | 58 $408 per kW of continuous output | 91 $247 per kW of continuous output |
| Solar input 20% | 100 25,000 W of panels, 550 V max, 3 MPPTs | 48 13,200 W of panels, 550 V max, 2 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 | 90 UL 1741 listed, Wi-Fi add-on, parallel stacking, grid sell-back, generator input, battery communication |
| Warranty 15% | 100 10-year warranty | 44 5-year warranty |
Specifications
| Fortress Power Envy Duo 21 | ECO-WORTHY Synch 12KP | |
|---|---|---|
| Output | ||
| Output voltage | 120/240 V split-phase | 120/240 V split-phase |
| Continuous output | 12,000 W | 12,000 W |
| Surge | 24,000 W | 24,000 W |
| Peak efficiency | 94% | - |
| Max efficiency | - | 97.5% |
| CEC efficiency | 96.9% | 96.5% |
| Idle draw | 60 W | - |
| Transfer time | 20 ms | - |
| Parallel units | Up to 10 units | Up to 6 units |
| Solar | ||
| Max PV power | 25,000 W | 13,200 W |
| Max PV voltage (Voc) | 550 V | 550 V |
| MPPT range | 120 to 440 V | 125 to 450 V |
| MPPT trackers | 3 | 2 |
| PV current per tracker | 26 A | 25 A |
| Runs without battery | Yes | - |
| Battery and grid | ||
| Battery voltage | 48 V | 48 V |
| Battery types | Lithium | - |
| Max charge current | 250 A | 200 A |
| AC charge current | - | 120 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 | - |
| Enclosure | IP66 (NEMA 4X) | IP65 |
| Dimensions | 22.3 x 35.2 x 11.2 in | 29.5 x 17.3 x 9.4 in |
| Weight | 125.7 lb | 93 lb |
| Warranty | 10 years | 5 years |
| Released | 2026-01 | 2026-08 |