EG4 FlexBOSS18
For grid-tied homes that want net metering and whole-home backup at a lower price than the FlexBOSS21. Choose the 21 if you need more battery-only output or a third tracker.
Signature Solar $3,199.99$3,199.99
The EG4 FlexBOSS18 is the better hybrid solar inverter overall, rated 4.4 to 3.6. The EG4 FlexBOSS18 leads on value and solar input. The EG4 FlexBOSS18 costs $2,228.58 less ($3,199.99 vs $5,428.57).
Sol-Ark 12K-2P
For installers matching existing 12K systems or homes that want a proven Sol-Ark on a critical-loads panel. Most new buyers get more for less from the Limitless 12K-2P-LL.
altE $5,428.57$5,428.57
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 EG4 FlexBOSS18 for value ($320 per kW of continuous output vs $603 per kW of continuous output) and solar input (18,000 W of panels, 600 V max, 2 MPPTs vs 12,000 W of panels, 500 V max, 2 MPPTs).
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 | EG4 FlexBOSS18 | Sol-Ark 12K-2P |
|---|---|---|
| Overall rating | 4.4/5 | 3.6/5 |
| Value 30% | 76 $320 per kW of continuous output | 19 $603 per kW of continuous output |
| Solar input 20% | 82 18,000 W of panels, 600 V max, 2 MPPTs | 59 12,000 W of panels, 500 V max, 2 MPPTs |
| Efficiency 20% | 68 94% peak efficiency, 60 W idle | 66 60 W idle |
| Features 15% | 95 UL 1741 listed, Wi-Fi app, parallel stacking, grid sell-back, battery communication | 95 UL 1741 listed, Wi-Fi app, parallel stacking, grid sell-back, battery communication |
| Warranty 15% | 100 10-year warranty | 100 10-year warranty |
Specifications
| EG4 FlexBOSS18 | Sol-Ark 12K-2P | |
|---|---|---|
| Output | ||
| Output voltage | 120/240 V split-phase | 120/240 V split-phase |
| Continuous output | 10,000 W | 9,000 W |
| Surge | 20,000 W | 16,000 W |
| Peak efficiency | 94% | - |
| Max efficiency | - | 97.5% |
| CEC efficiency | 97% | 96.5% |
| Idle draw | 60 W | 60 W |
| Transfer time | 20 ms | 4 ms |
| Parallel units | Up to 16 units | Up to 9 units |
| Solar | ||
| Max PV power | 18,000 W | 12,000 W |
| Max PV voltage (Voc) | 600 V | 500 V |
| MPPT range | 120 to 440 V | 150 to 500 V |
| MPPT trackers | 2 | 2 |
| PV current per tracker | 26 A | 20 A |
| Battery and grid | ||
| Battery voltage | 48 V | 48 V |
| Battery types | Lithium, lead-acid | Lithium |
| Max charge current | 208 A | 185 A |
| Battery communication | Yes | Yes |
| Grid sell-back | Yes | Yes |
| UL 1741 | UL 1741 SB | UL 1741 SB |
| Build | ||
| App monitoring | Included | Included |
| Enclosure | NEMA 4X | IP65 / NEMA 3R |
| Dimensions | 30.43 x 22.28 x 11.22 in | 29.5 x 17.7 x 10 in |
| Weight | 115 lb | 78 lb |
| Warranty | 10 years | 10 years |
| Released | 2025-03 | 2021-02 |