Growatt's SPE US series is a 120/240 V split-phase, 48 V off-grid inverter built for American homes, available in four sizes from the SPE 6000 US to the SPE 12000 US. This post covers the two ends of the range, explains how the smart load output works, and compares both models with the off-grid inverters US homeowners most often shortlist.
Why it matters: more homes across the US want backup that runs the whole house, rides through multi-day outages from storms, wildfires and grid strain, and can lean on a generator when the sun is short. An all-in-one inverter that combines solar charge controllers, a battery inverter/charger and a transfer switch in one box is the simplest way to get there. The SPE US series is built for exactly that job, and it is listed to UL 1741 (with CSA C22.2 and FCC), so it fits permitted installs under the NEC.
Built for off-grid first. The SPE US runs your home from solar and battery, and treats the grid or a generator purely as a backup source for charging and pass-through. It does not export power back to the utility. That keeps the design simpler and the price lower, and it suits both fully off-grid properties and grid-connected homes that want self-powered backup without a net-metering interconnection agreement.
SPE 6000 US vs SPE 12000 US at a glance
Both models share the same chassis, PV front end and protection features; the 12000 US doubles the AC output, the PV array size and the battery current.
| Spec | SPE 6000 US | SPE 12000 US |
|---|---|---|
| Continuous AC output | 6,000 W | 12,000 W |
| Max. output current | 25 A | 50 A |
| Max. recommended PV (STC) | 9,000 W | 18,000 W |
| Max. input per MPPT | 4,500 W | 9,000 W |
| MPPTs / strings per MPPT | 2 / 2 | 2 / 2 |
| Max. PV voltage / MPPT range | 550 V / 60–480 V | 550 V / 60–480 V |
| Max. input current per MPPT | 22 A | 27 A |
| Battery charge / discharge current | 140 A / 140 A | 250 A / 280 A |
| Grid passthrough / generator input | 70 A / 70 A | 70 A / 70 A |
| Transfer time | ≤20 ms (single), ≤30 ms (parallel) | ≤20 ms (single), ≤30 ms (parallel) |
| Parallel units | Up to 9 | Up to 9 |
| Size / weight | 550 × 465 × 150 mm / 21.5 kg (47 lb) | 550 × 465 × 150 mm / 21.5 kg (47 lb) |
| Certification | UL 1741, CSA C22.2, FCC | UL 1741, CSA C22.2, FCC |
| ROCKSOLAR price (USD) | $1,399.99 | $1,799.99 |
What stands out:
- UL 1741 listed. The certification inspectors and AHJs expect to see on a permitted residential install.
- 1.5 DC/AC ratio. You can oversize the array by 50%, so mornings, evenings and cloudy winter days still deliver useful power.
- High-current MPPTs. At up to 27 A per tracker (22 A on the 6000 US), the SPE US handles today's large 182 mm and 210 mm-cell modules without clipping, and two strings per tracker simplify wiring.
- 550 V maximum PV voltage. Longer strings mean fewer combiners and thinner wire runs to a detached or ground-mount array.
- Generator charging. A dedicated 70 A generator input lets a gas, propane or diesel generator top up the battery and carry loads on dark stretches.
- Scales with the home. Up to 9 units run in parallel, and three units can form a 208 V three-phase system for shops, farms and small commercial sites.
- Fast backup. A ≤20 ms switch time keeps computers and networking gear running through an outage, and 10-second overload capability (104–120%) helps with well pump and AC compressor starts.
- Covered and connected. Built-in Wi-Fi monitoring, CAN/RS485 battery communication, lithium or lead-acid support, and a 5-year standard warranty.
How the smart load function works
Smart load turns one of the inverter's AC ports into a second, automatically switched 120/240 V output. It powers non-essential, high-draw circuits only when there is energy to spare, so they never drain the battery you need overnight.
The hardware. The SPE US has three AC terminal blocks: Grid, Load (main output) and GEN/Smart Load. Program 90 sets the GEN/Smart Load port as either a generator input (default) or a smart load output. The smart load can carry up to the inverter's full rating: 6,000 W on the SPE 6000 US and 12,000 W on the SPE 12000 US.
The logic. The inverter switches the smart load circuit on and off using rules you set on the LCD or in the app:
| Program | What it controls | Default (range) |
|---|---|---|
| 59 | Battery level at which smart load turns off | 48.0 V (44–54 V); lithium: 60% SOC (20–95%) |
| 60 | Battery level at which smart load turns back on | 53.0 V (48–58 V); lithium: 90% SOC (20–100%) |
| 61 | Minimum PV power before smart load turns on | 0 kW (up to the inverter's rating) |
| 58 | Up to three daily time windows when smart load may run | All day |
| 57 | Keep smart load on whenever the grid is present | Disabled |
With the lithium defaults, the smart load circuit runs until the battery falls to 60%, then waits until it is recharged to 90% before switching back on. Add a PV threshold, say 4 kW, and the circuit only runs when the array is producing a real surplus.
Where smart load pays off
- Water heaters and pool pumps. Heat water or run the pool pump from midday solar surplus instead of from the battery at night.
- EV charging. Put a Level 2 charger on the smart load port and charge from the sun, with the battery floor protected automatically.
- Central AC and mini-splits. Pre-cool the house in the afternoon on solar surplus; the main output keeps the fridge, lights and internet on through the evening.
- Workshops, barns and outbuildings. Run a shop sub-panel only between set hours, so a forgotten compressor can't empty the bank.
- Grid-assisted homes. Enable Program 57 and the smart load circuit stays on whenever utility power is available, then sheds automatically in an outage.
Design trade-off to plan for. Because smart load and generator input share one port, a single SPE US uses one function or the other. Sites that need both can parallel two units, or feed a generator through the grid input with an external transfer switch. Ask your installer which layout fits your loads.
How the SPE US compares with EG4 and Sol-Ark
The closest match for the SPE US is EG4's XP series, which are also off-grid inverters: they can charge from the grid but do not export to it. The Sol-Ark 12K is a different class of product, a grid-interactive hybrid certified to sell power back to the utility (UL 1741 SB, IEEE 1547, California Rule 21). That grid-export certification, plus extras such as an outdoor enclosure, is a big part of why it costs more. If you don't plan to export, you would be paying for features you won't use. Specs are from each maker's current datasheet; competitor prices are typical US online prices as of November 2026 and vary by dealer.
6 kW class: SPE 6000 US vs EG4 6000XP
| Spec | Growatt SPE 6000 US | EG4 6000XP |
|---|---|---|
| Inverter type | Off-grid (grid as backup, no export) | Off-grid (grid as backup, no export) |
| Continuous output | 6,000 W | 6,000 W |
| Max. PV input | 9,000 W | 8,000 W utilized (10,000 W recommended max.) |
| Max. PV voltage / MPPT range | 550 V / 60–480 V | 480 V / 120–385 V |
| Current per MPPT / strings | 22 A / 2 per MPPT | 17 A / 1 per MPPT |
| Grid / generator bypass | 70 A | 50 A |
| Battery charge / discharge | 140 A / 140 A | 125 A / 140 A |
| Smart load | Yes: SOC/voltage, PV threshold, 3 time windows | Yes |
| Parallel units | 9 (three-phase capable) | 16 |
| Operating temperature | 14 to 122 °F (−10 to 50 °C) | 32 to 113 °F (0 to 45 °C) |
| Weight / noise | 47 lb / <75 dB | 53 lb / <58 dB |
| Certification | UL 1741 | UL 1741 |
| Warranty | 5 years | 5 years |
| Price (USD) | $1,399.99 at ROCKSOLAR | about $1,550–$1,700 |
The SPE 6000 US costs less, accepts more solar, works across a far wider string-voltage window, and passes 40% more grid or generator current. Its 14 °F rating also suits unheated garages and cabins in northern states, and its 122 °F ceiling gives more margin in a hot Southwest garage. EG4 counters with a quieter fan profile and the ability to stack up to 16 units.
12 kW class: SPE 12000 US vs EG4 12000XP vs Sol-Ark 12K
| Spec | Growatt SPE 12000 US | EG4 12000XP | Sol-Ark 12K-2P-N |
|---|---|---|---|
| Inverter type | Off-grid (no export) | Off-grid (no export) | Grid-interactive hybrid (exports to grid) |
| Continuous output (battery) | 12,000 W | 12,000 W | 9,000 W |
| Max. PV input | 18,000 W | 24,000 W utilized | 13,000 W |
| Max. PV voltage / MPPT range | 550 V / 60–480 V | 480 V / 120–385 V | 500 V / 175–425 V |
| Current per MPPT | 27 A | 35 A | 20 A |
| Grid passthrough | 70 A | 100 A | 63 A |
| Battery charge / discharge | 250 A / 280 A | 250 A / 250 A | 185 A / 185 A |
| Smart load | Yes, on GEN port | Yes, separate port from GEN | Yes, on GEN port |
| Parallel units | 9 | 6 | 9 |
| Transfer time | ≤20 ms | <10 ms | 4 ms |
| Operating temperature | 14 to 122 °F | 32 to 113 °F | −13 to 131 °F |
| Enclosure / weight | IP20 / 47 lb | IP20 / 105 lb | NEMA 3R / 78 lb |
| Certification | UL 1741 | UL 1741 | UL 1741 SB, IEEE 1547 (grid export) |
| Warranty | 5 years | 5 years | 10 years |
| Price (USD) | $1,799.99 at ROCKSOLAR | about $1,900–$2,600 | about $4,000–$4,500 |
The SPE 12000 US delivers the full 12 kW from the battery at the lowest price in this group, and at 47 lb it is less than half the weight of the 105 lb EG4 12000XP, so one installer can hang it. It also offers the highest battery discharge current (280 A) and more parallel units than the 12000XP.
Where rivals lead: the EG4 12000XP takes a bigger array (24 kW) and has separate generator and smart load ports. The Sol-Ark 12K switches in 4 ms, is rated for outdoor mounting, carries a 10-year warranty and can sell power back to the grid. If net metering isn't part of your plan, the SPE 12000 US gives you 3 kW more continuous output for well under half the price.
Smart load, side by side
All three brands offer a smart load output, but the controls differ. The SPE US combines a battery cut-off and recovery point (in volts or SOC), a minimum PV power threshold and up to three daily time windows, plus a "keep on while grid is present" option. That PV threshold is useful: the circuit runs only on a real solar surplus, not just whenever the battery happens to be full.
Which SPE model fits your home?
Pick the SPE 6000 US for cabins, small homes and critical-load panels; pick the SPE 12000 US for whole-home backup or a full off-grid house.
- SPE 6000 US (6 kW, $1,399.99): a cabin, tiny home, RV pad or hunting property, or a backup sub-panel covering fridge, furnace blower, well pump, lights and internet. Pair it with a 9 kW array and at least 200 Ah of 48 V battery.
- SPE 12000 US (12 kW, $1,799.99): a full-size home with 240 V loads such as a well pump, central AC or mini-splits, or an electric range. Pair it with up to 18 kW of PV and at least 400 Ah of 48 V battery.
- Two or more units: large homes, ranches and shops. Up to 9 units run in parallel, and three or more can build a 208 V three-phase system.
In every case, put flexible loads like a water heater, pool pump or EV charger on the smart load output. They will run on spare solar and switch off before they touch your overnight reserve.
Ready to size a system? Contact the ROCKSOLAR team with your monthly kWh usage, your largest motor loads and your roof or ground space. We can help confirm string sizing, battery capacity and smart load settings for your site.
Specifications are from Growatt's preliminary SPE 6000–12000 US datasheet and user manual and may change. Prices are in US dollars as of November 2026. Always follow the NEC and your local AHJ's requirements, and use a qualified installer.
Sources
- Growatt SPE 6000–12000 US datasheet (preliminary)
- Growatt SPE 6000–12000 US user manual
- Growatt SPE 6000–12000 US product page (UL 1741 / CSA C22.2 and FCC certificates)
- EG4 6000XP data sheet v1.4.4
- EG4 12000XP spec sheet v1.2
- Sol-Ark 12K-2P-N datasheet