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 4.1. The EG4 FlexBOSS18 leads on warranty, efficiency and features. The EG4 12000XP wins on value and solar input. The EG4 12000XP costs $1,100 less ($2,099.99 vs $3,199.99).
EG4 12000XP
For off-grid homes that need whole-house 240 V power and a big solar array at a low price per kW. Grid-tied owners who want to sell power should look at a hybrid instead.
Signature Solar $2,099.99 Shop Solar Kits $2,099.99$2,099.99
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 EG4 FlexBOSS18 for warranty (10-year warranty vs 5-year warranty), efficiency (94% peak efficiency, 60 W idle vs 90.2% peak efficiency, 70 W idle) and features (UL 1741 listed, Wi-Fi app, parallel stacking, grid sell-back, battery communication vs UL 1741 listed, Wi-Fi app, parallel stacking, generator input, battery communication; no grid sell-back).
- Choose the EG4 12000XP for value ($175 per kW of continuous output vs $320 per kW of continuous output) and solar input (24,000 W of panels, 500 V max, 2 MPPTs vs 18,000 W of panels, 600 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 | EG4 12000XP |
|---|---|---|
| Overall rating | 4.4/5 | 4.1/5 |
| Value 30% | 76 $320 per kW of continuous output | 100 $175 per kW of continuous output |
| Solar input 20% | 82 18,000 W of panels, 600 V max, 2 MPPTs | 92 24,000 W of panels, 500 V max, 2 MPPTs |
| Efficiency 20% | 68 94% peak efficiency, 60 W idle | 38 90.2% peak efficiency, 70 W idle |
| Features 15% | 95 UL 1741 listed, Wi-Fi app, parallel stacking, grid sell-back, 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 | 44 5-year warranty |
Specifications
| EG4 FlexBOSS18 | EG4 12000XP | |
|---|---|---|
| Output | ||
| Output voltage | 120/240 V split-phase | 120/240 V split-phase |
| Continuous output | 10,000 W | 12,000 W |
| Surge | 20,000 W | 15,360 W |
| Peak efficiency | 94% | 90.2% |
| CEC efficiency | 97% | - |
| Idle draw | 60 W | 70 W |
| Transfer time | 20 ms | 10 ms |
| Parallel units | Up to 16 units | Up to 16 units |
| Solar | ||
| Max PV power | 18,000 W | 24,000 W |
| Max PV voltage (Voc) | 600 V | 500 V |
| MPPT range | 120 to 440 V | 120 to 385 V |
| MPPT trackers | 2 | 2 |
| PV current per tracker | 26 A | 35 A |
| Runs without battery | - | Yes |
| Battery and grid | ||
| Battery voltage | 48 V | 48 V |
| Battery types | Lithium, lead-acid | Lithium, lead-acid |
| Max charge current | 208 A | 250 A |
| Battery communication | Yes | Yes |
| Grid sell-back | Yes | No |
| Generator input | - | Yes |
| UL 1741 | UL 1741 SB | Yes |
| Build | ||
| App monitoring | Included | Included |
| Enclosure | NEMA 4X | IP20 |
| Dimensions | 30.43 x 22.28 x 11.22 in | 34.25 x 20.87 x 5.91 in |
| Weight | 115 lb | 104.7 lb |
| Warranty | 10 years | 5 years |
| Released | 2025-03 | 2024-11 |