Picking inverters for serviceability: a UK installer's bias list
After seven years of installing and maintaining commercial PV, we've developed opinions about which inverter brands are pleasant to look after and which are a pain. Here are ours, with reasoning.
The first time you specify an inverter for a commercial roof, you’re thinking about efficiency, warranty, lead time and price. The fifth or sixth time, you’re also thinking about whether you’ll still want to be looking after the site in five years. Those are different questions, and they sometimes give different answers.
This is our biased, operator-shaped view on the inverter brands we routinely work with in the UK C&I market. It’s not a buyer’s guide and it’s not a benchmark — it’s the bias list one installer has developed after seven years of putting steel on roofs and then coming back to fix what failed.
If you specify inverters for a living and you’d argue with all of this, that’s fair. We’re aware we’re a sample of one.
The brands we’ll talk about
We work daily with SolarEdge, Solis, and Sungrow on UK rooftops. We also occasionally encounter Huawei, SMA, Fronius and Sigenergy (the last increasingly, on hybrid systems with batteries). The rest of the field — Goodwe, Growatt, Delta, ABB, the assorted Chinese brands — we encounter on inherited fleets but rarely specify into new builds.
The framing below is about serviceability: how pleasant the inverter is to live with once it’s been on a roof for a few winters.
The serviceability axes
What actually matters for serviceability, in our experience:
- API access to operational data. Can you get string-level current, fault codes, and event logs out of the cloud platform, on a tier the customer can actually afford?
- Physical reliability. Does the box keep working? Cooling fans, capacitors, contactors, firmware quirks.
- Diagnostic accessibility on-site. Can a competent engineer with a multimeter and a laptop figure out what’s wrong without a vendor support call?
- Spare parts availability in the UK. Lead time from when you call to when a replacement is on a van.
- Firmware behaviour. Do updates auto-install in the middle of a sunny day? Do they break things? Is there a rollback path?
We’ll go brand-by-brand against those.
SolarEdge
The market leader in UK commercial rooftop. We’ve installed more SolarEdge than anything else over the years, and we’ll continue to specify it on certain site shapes — particularly anything where shading, mismatched orientations, or panel-level fire safety requirements (DC isolation) are part of the brief.
API access: a sore point. The standard monitoring API gives you site-level energy, inverter-level totals, and account-level alerts. Per-optimiser data — the thing that makes SolarEdge actually distinctive at install — is gated behind a higher API tier that’s not straightforward to negotiate. We’ve written about this gap in our fault detection post; it means most third-party platforms running on SolarEdge data are working with less granular signal than the SolarEdge web portal itself shows.
Physical reliability: solid. The single-phase residential inverters had a bad capacitor batch a few years back; the three-phase commercial units we put on rooftops haven’t given us much trouble. Optimiser failures happen but are usually isolated and detectable. The inverter cooling fans are user-replaceable, which is more than can be said for some.
On-site diagnostics: good. The inverter display surfaces fault codes, and the cloud portal — if you can get a logged-in browser onto a phone in the inverter cupboard — gives you string-level current. The SetApp tool for commissioning is genuinely better than most.
Spare parts: usually a 2-7 day lead from SolarEdge UK distribution. Critical-spare programme exists for high-value contracts.
Firmware: mostly well-behaved. We’ve had one or two cases where a firmware update changed an undocumented behaviour and confused our polling for a day; SolarEdge’s release notes could be more candid.
Net opinion: still our default for rooftops with shading or mismatch. The API tier issue is the thing we’d most like to see them change.
Solis
The price-competitive choice on most clean commercial roofs. We’ve put a lot of Solis on UK industrial sheds over the last three years.
API access: much better than SolarEdge for an integrator. Solis Cloud’s API exposes per-inverter, per-MPPT data on the standard tier. Polling intervals are short — we poll every 5 minutes against their public endpoints without hitting rate limits in normal operation.
Physical reliability: improved markedly over the last few years. The older RAI-series single-phase units had cooling issues; the current three-phase commercial range (S5/S6) has been reliable. AC contactor wear is the most common physical failure we see; usually a replaceable part.
On-site diagnostics: serviceable. The front-panel display is informative. The wiring diagram in the manual is accurate, which sounds like faint praise until you’ve worked with brands where it isn’t. DC isolation is on the inverter; some sites also have an external DC isolator. The string fuses are accessible.
Spare parts: Solis UK has improved here. AC contactors and fans are stocked. A full inverter swap is typically a 5-10 day lead.
Firmware: a known gotcha. Some Solis units default to auto-applying firmware updates when the cloud connection allows. We’ve had one case where a firmware update on a sunny weekend reset a site’s MPPT configuration; recoverable but annoying. We now disable auto-update at commissioning and pull updates manually during scheduled maintenance windows.
Net opinion: a strong second choice on clean rooftops. We’d specify it more often than we do, but customers often want the optimiser-level data that only SolarEdge provides.
Sungrow
Not currently a default for us — but the brand we’re watching most carefully. Sungrow’s recent string inverters and especially their commercial hybrid range are well-engineered, and the company is investing seriously in the UK market.
API access: improving but not yet at parity with Solis. The iSolarCloud API exposes the core metrics; advanced features require working with their integration team.
Physical reliability: good. The mechanical engineering on the larger string inverters is robust. We’ve put a handful on roofs and not had a unit failure yet (sample size small; not yet through enough winters to be conclusive).
On-site diagnostics: comparable to Solis. The fault code reference in the manual is comprehensive.
Spare parts: UK availability is improving but not yet at the level of SolarEdge or Solis.
Firmware: we have no significant gripes yet.
Net opinion: increasingly viable. We’d specify Sungrow on a large new commercial install today where we wouldn’t have three years ago. The Sungrow integration in SolarFleet is on the roadmap and will land in the next quarter or two.
SMA
The classic. SMA’s been making string inverters for longer than most operators have been in the industry. They are well-built, well-documented, and field engineers across the UK trust them.
API access: a story. SMA’s “Sunny Portal” works for residential and small commercial; their commercial-scale Ennexos platform is meant to be the modern path. The story is improving but historically third-party API access has been awkward.
Physical reliability: excellent. We have SMA units on rooftops we took over from previous installers that have been running for over a decade with minor servicing. They keep going.
On-site diagnostics: very good. The Sunny Boy and Sunny Tripower range have informative displays and well-documented error codes. The Bluetooth commissioning workflow is dated but functional.
Spare parts: the catch. SMA’s commercial UK distribution has been thinner than it was a few years ago. Lead times for replacement units have, in our experience, lengthened.
Firmware: SMA are conservative with firmware. This is mostly a virtue.
Net opinion: we’d be happy to inherit an SMA fleet. We rarely specify new SMA on UK commercial roofs in 2026 because the API and distribution story doesn’t compete with Solis on price-per-watt.
Fronius
The premium tier. Beautifully made. Genuinely excellent engineering.
API access: Fronius Solar.web works. We have third-party platforms talking to it routinely. The data is granular enough to be useful.
Physical reliability: very good. The mechanical design favours serviceability.
On-site diagnostics: among the best. The display, the documentation, the engineer training — all reflect a company that thinks about service.
Spare parts: variable depending on which series. The Symo line has good UK support; some of the larger commercial units have longer lead times.
Firmware: well-handled, well-documented.
Net opinion: if budget allows and the customer values service quality, Fronius is hard to argue with. The price-per-watt premium against Solis is significant on a 500 kWp project and that’s why it’s not always the answer.
Sigenergy
A newer entrant we’re seeing more often on hybrid systems with batteries. The integration of inverter, battery and EMS into a single mechanical and software stack is genuinely interesting.
We don’t have enough field data to give a confident serviceability opinion. The early units we’ve installed look well-built. The cloud platform and API are maturing fast. We’re cautiously positive and will write more once we have more sites through more winters.
The Sigenergy integration in SolarFleet is shipping; per-MPPT and per-battery-pack data is on the way through.
What the bias list says about specifying
If we strip the brand-specific commentary out and pull the general lessons:
- API access matters more than peak efficiency. A 0.5% efficiency gap on paper is dwarfed by a fault that hides for a fortnight because you couldn’t see string-level data.
- Distribution and lead time matter more than build quality. A brilliantly-made inverter you can’t replace inside two weeks costs the owner more, over the life of the system, than a slightly less brilliantly-made one with strong UK distribution.
- Firmware behaviour is a multi-year story. Specifying an inverter is also specifying a relationship with a firmware release process. Brands that auto-update without warning cause real operational pain.
Those three points have shifted the way we specify over the last few years. The “best inverter” question isn’t usefully answered without saying who’s going to look after the site.
Disclosure
We have no commercial relationship with any of the brands above beyond being a paying customer for parts, software, and training. We’ve taken zero marketing money to write this post. If a brand wanted to send us a free unit, we’d say no thanks — the bias list works because it’s based on what we’ve actually paid for.
If you’re an installer wrestling with the same trade-offs, get in touch. We’d rather talk through your specific situation than make this a more general piece of marketing.
SolarFleet runs SolarEdge and Solis Cloud on production sites today, and ships a Sigenergy adapter (beta). Other brands are demand-driven — see the integrations status. Start free with 2 sites.
Josh runs InspireGreen, a solar installer based in Cardiff, and builds SolarFleet — the O&M platform we use to monitor our own sites. Most posts here come straight out of the work: a case we dealt with, a feature we shipped, or a thing we wish we'd known earlier.