Choosing a 48V split-phase hybrid inverter usually comes down to three brands: Growatt, EG4 and Sol-Ark. All three make all-in-one units that combine solar charging, battery inverting, grid-tie export and whole-home backup. All three carry a 10-year warranty, and all three are certified to UL 1741 for grid connection in the US. The differences show up in the details: how much solar each unit can take, how fast it switches to backup, and how much battery current it can move.
This guide compares the functions and specifications of the new Growatt SPH 9600–18000TL-HU-US series with the EG4 18kPV, the EG4 FlexBOSS21, the Sol-Ark 15K-2P-N and the Sol-Ark 18K-2P-N. Every number comes from each manufacturer's published spec sheet. Sources are listed at the end.
The Growatt SPH 9600–18000TL-HU-US series at a glance
The SPH series comes in four sizes that share the same chassis, the same 3-MPPT solar input and the same 200 A grid passthrough. Only the power rating and the battery current change from one size to the next:
| Model | Continuous AC / backup output | Max recommended PV | Battery charge/discharge |
|---|---|---|---|
| SPH 9600TL-HU-US | 9,600 W | 19,200 W | 200 A / 9,600 W |
| SPH 11500TL-HU-US | 11,500 W | 23,000 W | 240 A / 11,500 W |
| SPH 15000TL-HU-US | 15,000 W | 30,000 W | 312.5 A / 15,000 W |
| SPH 18000TL-HU-US | 18,000 W | 36,000 W | 334 A / 18,000 W |
Growatt lists these key functions:
- UPS-class backup with a switchover time under 10 ms
- 2.0 DC/AC ratio: up to twice the inverter's AC rating in solar panels, spread across 3 MPPTs with 2 strings each
- DC-coupled, AC-coupled and AC-retrofit installs, so you can add batteries to an existing grid-tie solar system
- Generator charging, with up to 30,000 W of generator input
- Up to 6 units in parallel, and the option to build a 208 V or 220 V three-phase system
- Type II surge protection on both the DC and AC sides, plus built-in AFCI
- 200% overload for 10 seconds to help start motors, well pumps and compressors
Head-to-head specification comparison
The table lines up the two largest Growatt SPH models against EG4's and Sol-Ark's 48V flagship units.
| Specification | Growatt SPH 15000TL-HU-US | Growatt SPH 18000TL-HU-US | EG4 18kPV | EG4 FlexBOSS21 | Sol-Ark 15K-2P-N | Sol-Ark 18K-2P-N |
|---|---|---|---|---|---|---|
| Continuous AC output | 15,000 W | 18,000 W | 12,000 W | 16,000 W with PV and grid; 12,000 W on battery only | 15,000 W | 18,000 W |
| Max PV array | 30,000 W recommended | 36,000 W recommended | 18,000 W usable (21,000 W recommended max) | 21,000 W recommended | 19,500 W usable | 28,800 W usable |
| Max DC input voltage | 550 V | 550 V | 600 V | 600 V | 500 V | 500 V |
| MPPT voltage range | 150–450 V | 150–450 V | 140–500 V | 120–440 V | 150–500 V | 150–425 V |
| MPPTs / max current per MPPT | 3 / 40 A | 3 / 40 A | 3 / 25 A, 15 A, 15 A | 3 / 26 A, 26 A, 15 A | 3 / 26 A | 3 / 36 A |
| Battery voltage range | 40–60 V | 40–60 V | 40–60 V | 40–60 V | 43–63 V | 41–63 V |
| Max battery charge/discharge | 312.5 A | 334 A | 250 A | 250 A | 275 A | 350 A |
| Max grid passthrough | 200 A | 200 A | 200 A | 90 A | 200 A | 200 A |
| Backup transfer time | <10 ms | <10 ms | 20 ms default (10 ms configurable) | 20 ms default (10 ms configurable) | 5 ms | Not stated on spec sheet |
| Units in parallel | Up to 6 | Up to 6 | Up to 10 | Up to 16 | Up to 12 | Up to 12 |
| Peak / CEC efficiency | 98.1% / 97.0% | 98.1% / 97.0% | 97.5% / 96.9% | 97% / 97% | 97.5% / 96.5% | 97.6% / 97.0% |
| Enclosure | IP65 | IP65 | NEMA 4X | NEMA 4X | IP65 / NEMA 3R | IP65 / NEMA 3R |
| Operating temperature | −25 to 60 °C | −25 to 60 °C | −25 to 60 °C | −25 to 60 °C | −25 to 55 °C | −40 to 60 °C |
| Net weight | 63 kg (138.9 lb) | 63 kg (138.9 lb) | 55 kg (121 lb) | 55 kg (121 lb) | 61.2 kg (135 lb) | 62.1 kg (137 lb) |
| US grid codes | UL 1741 SA/SB, IEEE 1547, CA Rule 21, HECO Rule 14, UL 1699B, UL 3141 | UL 1741 SA/SB, IEEE 1547, CA Rule 21, HECO Rule 14, UL 1699B, UL 3141 | UL 1741 SA/SB/PCS CRD, IEEE 1547, CA Rule 21, HECO 14H | UL 1741, IEEE 1547, CA Rule 21 | UL 1741 SB/SA/CRD-PCS, IEEE 1547.1, CA Rule 21, HECO 14H, UL 1699B | UL 1741 SB/CRD, IEEE 1547, HECO SRD 2.0, UL 1699B |
| Warranty | 10 years | 10 years | 10 years | 10 years | 10 years | 10 years |
Ratings are taken from each manufacturer's spec sheet (versions available November 2026). Manufacturers measure "max PV" differently: some publish a recommended array size and others a usable figure. Always confirm against the current datasheet and your local code before you design a system.
Where each inverter stands out
Solar input: Growatt SPH takes the most panels
Growatt's 2.0 DC/AC ratio is the biggest functional difference. The SPH 18000 accepts up to 36 kW of panels, compared with 28.8 kW usable on the Sol-Ark 18K and about 21 kW on the EG4 units. Each Growatt MPPT also accepts 40 A, which leaves room for today's high-current bifacial panels without splitting strings. The trade-off is voltage. Growatt's 550 V maximum sits between Sol-Ark (500 V) and EG4 (600 V), so EG4 allows the longest strings and Sol-Ark the shortest.
Backup switchover: Sol-Ark is fastest, Growatt is close behind
Sol-Ark's 15K lists a 5 ms transfer. The Growatt SPH series is under 10 ms out of the box. EG4's units default to 20 ms but can be set to 10 ms (they stay at 20 ms in parallel). All of these are fast enough for most homes. Desktop computers and some sensitive electronics ride through more reliably at 10 ms or less.
Battery power: the large Growatt and Sol-Ark models move the most current
Battery current decides how much of your home the inverter can run from batteries alone at night. The Sol-Ark 18K (350 A) and Growatt SPH 18000 (334 A) lead, followed by the Growatt SPH 15000 (312.5 A). The EG4 units are capped at 250 A, and the FlexBOSS21 drops from 16 kW to 12 kW continuous when it runs on battery alone. If you want full-rated output off-grid at night, pay attention to this row.
Whole-home passthrough: most units handle a 200 A service
The Growatt SPH, EG4 18kPV and both Sol-Ark models pass up to 200 A of grid power through to your loads, so they can sit in front of a typical 200 A main panel. The FlexBOSS21 is rated for 90 A passthrough and is designed to pair with EG4's separate GridBOSS for whole-home setups.
Efficiency and build
Growatt publishes the highest peak efficiency in this group (98.1%). CEC-weighted efficiency is close across the board at 96.5–97.0%. All six inverters are rated for outdoor installation. EG4 uses NEMA 4X enclosures, while Growatt and Sol-Ark are IP65. For cold-climate sites, the Sol-Ark 18K lists the widest range (down to −40 °C); the others are rated down to −25 °C. In very cold climates, an indoor or sheltered location helps every brand.
Retrofit and generator support
All three brands support AC coupling, so you can add batteries to an existing grid-tie solar system. Growatt also supports AC-retrofit installs and charging from a generator with up to 30 kW of input. Sol-Ark builds in automatic generator start (AGS) with a 2-wire start signal. EG4 handles generators through its AC bypass input and its Gen Boost feature.
Which one fits your project?
- Big roof or ground-mount array, whole-home backup: Growatt SPH 15000 or SPH 18000. They take the most PV per inverter, support 200 A passthrough and have high battery current.
- Mid-size home, 10–12 kW loads: Growatt SPH 9600 or SPH 11500, or the EG4 18kPV. Compare the solar input you need (19–23 kW on the Growatt models vs about 18 kW usable on the EG4).
- Fastest switchover and a large installer network: Sol-Ark 15K or 18K.
Every model here is UL 1741 certified, so the right choice depends on your loads, your array size and your batteries. Check the manufacturer's approved battery list before pairing any inverter with a battery.
Need help sizing a system? Browse our hybrid inverters or the Growatt SPH 18000TL-HU-US, or contact the ROCKSOLAR team for a free system design.
Sources
- Growatt SPH 9600–18000TL-HU-US datasheet (2026-10), us.growatt.com
- EG4 18kPV-12LV spec sheet
- EG4 FlexBOSS21 spec sheet
- Sol-Ark 15K datasheet (Rev 5, June 2025)
- Sol-Ark 18K-2P datasheet
EG4 and Sol-Ark are trademarks of their respective owners. ROCKSOLAR is not affiliated with EG4 or Sol-Ark. Specifications may change; confirm with the manufacturer before purchase.