EG4 18kPV vs FlexBOSS21
The maker calls the FlexBOSS21 an enhanced cousin of its 18kPV, designed to work with the GridBOSS interconnect device. On paper they overlap, with…
EG4 18kPVHybrid inverter12 kW output48 VDC battery21,000 W solar input0 datasheet edges
EG4 FlexBOSS21Hybrid inverter12 kW (50 A), battery only output51.2 VDC battery21 kW solar input2 datasheet edgesDatasheet scoreboard: 8 lines where both datasheets list a number. It counts who has the bigger (or, for idle draw, smaller) figure; it is not a quality rating and says nothing about reliability.
The short version
Near-twins on paper: the FlexBOSS21 adds output and peak power, and wants a much bigger battery.
- 18kPV: You want the maker’s flagship hybrid.
- FlexBOSS21: You plan to pair it with a GridBOSS, as the maker intends.
The maker calls the FlexBOSS21 an enhanced cousin of its 18kPV, designed to work with the GridBOSS interconnect device. On paper they overlap, with both at 21 kW of recommended solar, but the output figures, battery guidance and certifications differ in ways that change how you would build around each.
EG4 18kPV vs FlexBOSS21: specs head to head
| Spec | EG4 18kPV | EG4 FlexBOSS21 |
|---|---|---|
| Model number | 18KPV-12LV | IV-12000-HYB-AW-XX | IV-16000-HYB-AW-FX-XX |
| Continuous output | 12,000 W @ 240 V | 10,400 W @ 208 V | 12 kW (50 A), battery only |
| Surge | With PV: 14,700 W (10 min), 15,500 W (5 min). Without PV: 13,500 W (10 min) | 0.5 s: 24,000 W · 1 s: 18,000 W · 6 min: 15,000 W · 12 min: 13,200 W |
| Battery voltage (nominal) | 48 VDC | 51.2 VDC |
| Max battery charge/discharge current | 250 A | 250 A |
| PV input voltage range | 100–600 VDC | 600 VDC |
| MPPT voltage high protection (inverter faults here; plan strings below it) | 550 VDC | 550 VDC |
| MPPT operating voltage range | 140–500 VDC | 250 – 440 VDC (operating range 120 – 440 VDC) |
| Number of MPPTs | 3 | 3 |
| Max usable PV input current | 25 A (MPPT 1) | 15 A (MPPT 2) | 15 A (MPPT 3) | 26 A (MPPT 1) | 26 A (MPPT 2) | 15 A (MPPT 3) |
| Recommended max solar input | 21,000 W | 21 kW |
| Recommended battery capacity per inverter | ≥300 Ah | 600 Ah |
| Idle consumption (normal | standby) | ~70 W | ~18 W | <65 W @ 25 °C |
| Efficiency, battery to grid (max) | 94% | 94% |
| Max units in parallel | 10 | 16 |
| Warranty (as listed) | 10-year standard warranty | 10 years |
| Outdoor rating | NEMA 4X | NEMA 4X |
| Weight | 121 lbs (55 kg) | 121 lbs (55 kg) |
| Dimensions (H×W×D) | 34.3×20.5×11.2 in (870×520×285 mm) | 30.43×22.28×11.22 in (773×566×285 mm) |
| Continuous output with PV and grid (at 25 °C) | not on datasheet | 16 kW (66.7 A) |
Highlighted = the better figure where both datasheets give a number (higher is better, except idle draw). More is not always better: a larger solar input, for example, needs a bigger battery and wiring to use it. Sources: EG4 18kPV datasheet · EG4 FlexBOSS21 datasheet. Checked September 30, 2026. “Not on datasheet” means the sheet does not list that line, not that the product lacks it.
What the 18kPV and FlexBOSS21 numbers mean
- Output: the 18kPV is rated 12,000 W at 240 V (10,400 W at 208 V). The FlexBOSS21 gives 12 kW on battery alone and 16 kW with PV and grid at 25 °C.
- Peak power: the FlexBOSS21 lists 24,000 W for half a second, 18,000 W for one second, 15,000 W for 6 minutes and 13,200 W for 12 minutes; the 18kPV lists 14,700 W for 10 minutes and 15,500 W for 5 minutes with PV.
- Battery guidance: the 18kPV recommends at least 300 Ah per inverter, the FlexBOSS21 a minimum of 600 Ah. The FlexBOSS21 is listed at 51.2 V nominal, the 18kPV at 48 V.
- Solar: both recommend up to 21 kW; the 18kPV has three MPPTs at 25 A, 15 A and 15 A, the FlexBOSS21 three at 26 A, 26 A and 15 A.
- Paralleling: up to 10 units for the 18kPV and 16 for the FlexBOSS21.
- Certifications: the maker’s pages list UL 1741 SB, CEC and CSIP badges for the 18kPV and UL 3141 and UL 1741 for the FlexBOSS21; the datasheets of both list UL 1741 and California Rule 21. NEMA 4X, which both carry, is an enclosure rating, not a certification.
18kPV or FlexBOSS21: who should pick which
Pick the 18kPV if…
- You want the maker’s flagship hybrid.
- Your battery bank will be around 300 Ah per inverter rather than 600 Ah.
- You do not plan to add a GridBOSS.
Pick the FlexBOSS21 if…
- You plan to pair it with a GridBOSS, as the maker intends.
- You want more continuous output with PV and grid (16 kW) and a higher short-term peak.
- You are building a bank of 600 Ah or more per inverter, or a large parallel system of up to 16 units.
EG4 18kPV vs FlexBOSS21: questions people ask
Is the FlexBOSS21 just a bigger 18kPV?
The maker describes it as an enhanced cousin of the 18kPV designed to work with GridBOSS. The datasheets differ in output, peak ratings, battery guidance and certifications, so compare the lines rather than the names.
Which needs the bigger battery?
The FlexBOSS21: its datasheet recommends a minimum of 600 Ah per inverter, against at least 300 Ah for the 18kPV.
Specs change with new revisions; check the current datasheets before you buy. Checked 2026-09-30. Next: size a system or compare any two models.