Pick any two string inverters from different brands and the brochures sound the same. Shade management, backup power, smart monitoring, long warranty. So the useful question is where the numbers diverge, and with Fronius and SMA they diverge in places most buyers never look.
This is a document comparison, not a field test, and I haven't installed either unit. I read the current North American datasheets, SMA's factory warranty text and the Fronius USA warranty page. Where a document says nothing, I say so. The pair is the Fronius Primo GEN24 7.7 and the SMA Sunny Boy Smart Energy-US 7.7 (SBSE7.7-US-50), because both are rated 7,680 W at 240 V and so share an AC output. If the battery side interests you more, the battery inverter comparison covers it. Here it's about the PV side.
How Do the 7.7 kW Datasheets Line Up?
| Specification | SMA SBSE7.7-US-50 | Fronius Primo GEN24 7.7 |
|---|---|---|
| AC rated power at 240 V | 7,680 W | 7,680 W |
| Max PV generator | 15,360 Wp (200%) | 11,520 Wp (150%) |
| MPP trackers | 3, one string input each | 2, two inputs each |
| Usable current per tracker | 15 A | 22 A each |
| Max DC voltage | 600 V | 600 V |
| Rated-power MPP window | 180 to 480 V | 260 to 480 V |
| Start-up voltage | 66 V | 80 V |
| Max efficiency | 98.1% | 97.5% at 240 V |
| CEC efficiency at 240 V | 97.5% | 97% |
| Weight | 38.6 lb | 45.97 lb |
| Enclosure | IP65 / Type 3R | Type 4X |
| Cooling | Natural convection | Active |
| Operating temperature | -13 to 140 F, with derating | -40 to 140 F |
| Standard warranty | 10 years | 10 years, extendable to 15 |
Two caveats. SMA's datasheet is one document for six power classes, and the 7.7 sits in the group of four non-"upcoming" units; I matched the 7.7 column by position, so confirm the row against your own model number. And SMA's unit is a hybrid that also takes a battery, which the Fronius only gains through a software upgrade.
Why Does the Tracker Layout Matter More Than Efficiency?
Because it decides what roof you can wire. SMA offers three trackers with one string input each. Fronius offers two trackers with two inputs each, and 22 A of usable current on both.
Take a roof with three faces, say east, south and west. SMA gives each face its own tracker. Fronius has to pair two faces on one tracker or leave one face off. That's a real limit. It's also not universal: a plain east-west roof fits Fronius perfectly, with one tracker per face and plenty of current headroom.
Current is where Fronius pulls ahead. SMA caps each tracker at 15 A usable, while Fronius allows 22 A. Whether 15 A is enough depends on the current of your chosen module, and the string configurator will show you where yours lands. One trap on the smaller Fronius units: footnote 2 of the datasheet says the 3.8, 5.0 and 6.0 kW models are 22 A on MPPT1 but only 12 A on MPPT2. The 7.7 and 10.0 give 22 A on both.
Then there's voltage. Fronius only guarantees rated power between 260 and 480 V on the 7.7. SMA's rated window starts at 180 V. A short string whose maximum power point sits near 220 V on a hot afternoon is inside SMA's window and below Fronius's. That's a hypothetical, but it's the kind of thing that shows up on small arrays and long wire runs.
How Much Oversizing Can You Actually Do?
SMA prints 200 percent DC/AC capability. Fronius lists 11,520 Wp on the 7.7, which works out to 150 percent of 7,680 W.
Here's the arithmetic with an assumption of mine, 400 W modules. SMA's ceiling is 15,360 Wp, so 38 modules (38.4 rounds down). Fronius's is 11,520 Wp, so 28 (28.8 rounds down). Ten panels of headroom on the same AC output.
Does that matter? On a roof with limited sun hours, a high DC/AC ratio clips a little at noon and pays back at the edges of the day. It's also a way to buy a smaller inverter, and with the grid connection capped, that's often the point. Check clipping in a design tool before you pay for panels the inverter can't use. Reading solar inverter data explains the rows involved.
Is the Efficiency Gap Worth Paying For?
Not by itself. SMA's datasheet prints a 98.1 percent peak and 97.5 percent CEC weighted at 240 V. Fronius prints 97.5 percent peak and 97 percent CEC for the 7.7. That's half a point on the figure that matters.
An illustration, and only that. Assume a system delivering 10,000 kWh a year at the inverter input and $0.15 per kWh, both my numbers. Half a point is 50 kWh, or $7.50 a year. Over a 10 year warranty that's $75. You'd never pick one box over the other for it.
I'd treat the efficiency row as a tiebreaker. Sizing, trackers and warranty fine print move the money far more. For a second case of a headline figure misleading, see the Fronius vs Solinteg comparison.
Does Either Have an Edge in Shade?
On paper, no. Both are string-level systems. Fronius calls its approach Dynamic Peak Manager, an algorithm that regularly scans the entire voltage curve and needs no components at module level. SMA's ShadeFix is software inside the inverter that finds the maximum power point despite shaded modules. Same idea, different name.
Both vendors publish only their own claims. Fronius's US page offers one example, a 3.3 kWp south-west system that produced 7 percent more on a sunny day with partial shading, and gives no scan interval. SMA's manual page gives none either. So who wins? Nobody has shown it.
The independent evidence treats the two as one class. IEA PVPS Task 13 says classic string inverters give the highest yields for light shading, where no more than a tenth of modules are in shade at once, and that optimizers earn their cost with medium to heavy shading. The 10 kW Fronius vs SolarEdge piece walks through that table. The practical takeaway: shade shouldn't pick between these two. Layout should.
What Happens When the Grid Goes Down?
Both offer a small solar-only outlet, with different caveats.
- SMA Backup Secure: 1,920 W at 120 V, activated manually. The datasheet adds that a Backup Start module is required in installations bound by NEC rapid shutdown requirements.
- Fronius PV Point: 1,560 VA at 120 V on the 7.7, switching in under 23 seconds. The 7.7 and 10.0 also list 2,860 VA at 220 V and 3,120 VA at 240 V.
Both stop when the sun does. For whole-home backup you need a battery, and then you're in the territory covered by the battery inverter article linked above: SMA is a hybrid out of the box, Fronius upgrades by software to the GEN24 Plus.
On rapid shutdown, SMA's datasheet is more explicit. It lists an integrated SunSpec-certified transmitter, an accessory Shutdown Initiator, and PV rapid shutdown equipment compliance with NEC 2020 and 2023. Fronius's datasheet lists emergency shutdown (WSD) and UL 1998 coverage including rapid shutdown equipment, but no module-level description. Get the pairing in writing from your installer.
What About Monitoring and Connectivity?
The two datasheets list different things, so a line-by-line match isn't possible. SMA names Webconnect and Speedwire, Modbus (SMA and SunSpec), WLAN, Ethernet, BAT-CAN and RS-485, and its brochure text mentions an integrated system manager and the SMA 360 app. Fronius names WLAN, two Ethernet ports, Solar.web, Modbus TCP and a JSON Solar API, plus six digital inputs for ripple control receivers and energy management. Neither datasheet lists per-panel data.
Which Warranty Reads Better?
Same headline, different fine print.
SMA's datasheet shows 10 years standard and optional extensions of 5, 10 and 15 years. SMA's factory warranty document, effective for purchases after 20 May 2026, ties the warranty start to commissioning or invoice date only if you register on SMA's site within 12 months. Miss that and the clock starts at delivery. The standard terms provide a replacement device, and the claimant bears transport and customs costs. The same document lists the USA as a Comfort Support country, where, if SMA decides to repair on site, materials and labor are covered for devices at ground level or a safely accessible roof. Slanted-roof access, lifts and travel aren't.
Fronius USA gives 10 years free if you register on Solar.web within 30 months of delivery. Warranty Plus extends to 15 years for a fee, has to be bought within 6 months of the warranty start, and covers materials, servicing and transport. The page says the term runs from manufacture in one sentence and from commissioning in another, so ask which.
Registration deadlines are the real difference. Twelve months against thirty. Put a reminder in your phone.
Who Wins at 7.7 kW?
My view, and an installer might disagree: pick on the roof, not the logo.
Three roof faces, a cramped array you want to oversize hard, or short strings? SMA fits. One or two faces, panels that draw a lot of current, and no plan for a battery? Fronius fits, mostly because of the 22 A trackers and the Type 4X enclosure. If noise matters, note Fronius lists under 52 dB(A) for the 7.7 and active cooling, while SMA's datasheet gives no noise figure and uses natural convection. That absence isn't proof of silence.
The older SMA Sunny Boy 6.0-US had the same three-tracker idea, and the Fronius Primo 8.2-1 is the older Fronius equivalent. For three-phase homes, start with the 3-phase power guide instead.
Summary
At 7.7 kW and 7,680 W AC, the Fronius Primo GEN24 and SMA Sunny Boy Smart Energy differ in layout, not efficiency. SMA brings three single-string trackers, a 200 percent oversizing limit, a 180 V lower MPP window and a 98.1 percent peak. Fronius brings two dual-input trackers at 22 A each, a 150 percent limit and Type 4X housing. Shade management is a draw on the evidence available, since both vendors publish only their own claims. Backup is a small solar-only outlet on both. Both start at 10 years, but the registration windows are 12 months for SMA and 30 months for Fronius.