A solar PV system has two assets with very different design lives. The panels, on a Tier-1 specification, run 25-30 years with linear performance warranty. The inverter, even on premium brands, runs 15-20. That mismatch means almost every commercial PV system installed in the UK between 2010 and 2015 is now either due for or actively going through inverter replacement. The first wave hit around 2022-2024; we are mid-wave through 2025-2027. This page covers what fails, what it costs, what your warranty position is, and what the upgrade options look like in 2026.
Why inverters wear out
A solar inverter is a continuous-duty power-electronics device. It runs 4,000-5,500 hours per year converting DC from the panels into AC for the building or grid. The dominant wear-out mechanisms are well understood.
Electrolytic capacitor ageing. Inverters use large DC-link capacitors to smooth the voltage between panel-side and inverter-side. These are typically aluminium electrolytic capacitors with an electrolyte that slowly evaporates through the seal. As electrolyte volume drops, capacitance drops and equivalent series resistance rises. The inverter still operates but efficiency declines. Capacitor ageing is the main driver of the slow 1-3 percent annual efficiency decline observed on 12-15 year old inverters.
IGBT power module fatigue. The Insulated Gate Bipolar Transistors that switch the high-current power flow undergo thermal cycling — heating up under load, cooling between cycles. After roughly 1.5 to 3 million switching cycles, the wire bonds and solder layers in IGBT modules fatigue and fail. Failures are typically sudden, not gradual.
Cooling fan wear. String inverters above 25 kW typically have at least one forced-air cooling fan. Bearings wear, blades become unbalanced, eventually fans fail. Fan failure leads to thermal stress on the rest of the electronics — accelerating IGBT and capacitor wear-out.
DC isolator failure. Many 2010-2015 era inverters have integrated DC isolators that have aged poorly — particularly Solis, Aurora, and some early SMA Sunny Mini Central units. Isolator burnout has caused several documented fire incidents and is one of the most common reasons for forced replacement.
Typical replacement cost in 2026
Like-for-like commercial inverter replacement headline cost in 2026:
| System size | Like-for-like replacement | Per kW |
|---|---|---|
| 10-25 kW | 2,500-4,500 pounds | 180-200 per kW |
| 25-50 kW | 4,500-7,000 pounds | 140-180 per kW |
| 50-100 kW | 7,000-13,500 pounds | 120-150 per kW |
| 100-250 kW | 13,500-30,000 pounds | 100-130 per kW |
| 250-500 kW | 30,000-55,000 pounds | 90-115 per kW |
| 500 kW-1 MW | 55,000-95,000 pounds | 80-105 per kW |
The replacement cost is materially lower than the original install (roughly 10-15 percent of the original capex) because the existing wiring, mounting, panels, AC connection, isolation, monitoring, and DNO interface remain in place. The work is essentially a unit swap — disconnect the old inverter, mount the new one on the same bracket where compatible, reconnect DC and AC, commission, and re-register with the manufacturer monitoring portal.
Upgraded replacement (where 2010-2015 technology is replaced with 2026 technology featuring meaningful efficiency, monitoring, and grid-feature improvements) typically costs 20-40 percent more than like-for-like — but adds 1-2 percent annual yield over the next 15 years which usually justifies the premium.
Brand-by-brand parts and replacement landscape
SolarEdge
The dominant residential-and-light-commercial inverter brand in the UK 2015-2022, with a growing commercial product range (SolarEdge Synergy commercial line). HD-Wave inverters carry 12-year product warranty with extension options to 25 years. DC optimisers carry 25-year warranty as standard. Parts availability strong, UK service infrastructure mature. Many 2015-2018 era HD-Wave units are now starting to fail capacitors and are typically replaced under extended warranty (where purchased) or replaced like-for-like by us.
SMA Solar
The dominant commercial inverter brand in the UK 2010-2018 — Sunny Tripower, Sunny Highpower (now Sunny Highpower Peak3), Sunny Boy. German engineering, very long support tail. SMA still services and supplies parts for Sunny Mini Central units installed in 2010-2012, although those units are reaching end of useful life and we typically recommend replacement rather than repair. Newer Sunny Tripower 50-110 kW commercial inverters are the gold-standard replacement specification on commercial replacements.
Fronius
Austrian, premium-engineered commercial inverters. Symo (sub-25 kW commercial), Eco (commercial), Tauro (commercial-utility, modular). Tauro's modular field-replaceable card design is unique and means individual sub-component replacement extends service life materially — repair-rather-than-replace economics on Tauro are very strong. Older Fronius IG-Plus units are less serviceable and typically replaced.
Sungrow
Chinese, increasingly dominant in UK commercial 2020-2026 driven by cost-quality balance. SG series (residential and small commercial) and SG-CX series (commercial-utility). 10-year standard warranty, extension to 25. Strong UK distributor presence. Replacement parts good. We specify Sungrow on price-competitive commercial replacement projects.
Huawei FusionSolar
Chinese, geopolitical risk on US public-sector procurement but routine on UK private-sector commercial. SUN2000 commercial range. Strong AI-driven monitoring and string-level optimisation features. 10-year warranty standard. UK presence growing through specialist distributors. Replacement parts good for newer units; less long-term track record on legacy.
Solis (Ginlong)
Chinese, mid-tier-priced, popular on small-commercial 2017-2024 installs. Cost-competitive replacement product. 10-year standard warranty. UK distributor presence good. Some 2017-2019 era integrated-DC-isolator units have failed at higher rates than peer brands and we have replaced a number under warranty claims.
Power-One / FIMER (legacy)
Power-One Aurora was a major Italian-American inverter brand 2008-2014. Acquired by ABB, then sold to FIMER. Parts availability for Aurora units is patchy in 2026 and we generally recommend full replacement rather than repair. FIMER continues to manufacture commercial inverters but the legacy Aurora cohort is reaching end of useful life across the board.
Discontinued or limited-service brands
SMA Sunny Mini Central (2009-2013) — service available but unit life is essentially up.
Diehl Ako (2010-2014 commercial) — limited UK service capability, replacement recommended.
Sputnik Engineering / SolarMax (2011-2015) — Swiss, brand in administration. No UK service path — replacement is the only route.
Schneider Electric Conext (2012-2018 commercial) — Schneider exited the inverter market 2018-2020 with patchy ongoing parts. Replacement recommended on units past 10 years.
Bonfiglioli (2010-2015 utility commercial) — exited UK market, parts very patchy.
Replace versus repair — the decision matrix
A practical rule we apply on every maintenance call.
Repair when: the inverter is under 12 years old AND the fault is a single component (cooling fan, single capacitor, DC isolator, communications card) AND the manufacturer brand has good UK service capability AND the repair cost is under 25 percent of replacement cost.
Replace when: the inverter is over 15 years old, OR the manufacturer brand has limited UK service, OR the repair fault is multi-component (multiple capacitors, IGBT module failure, transformer failure), OR the repair cost exceeds 35 percent of replacement cost, OR the inverter is exhibiting greater-than-5-percent efficiency drop against the PVSyst-modelled expectation.
The 12-15-year band is the judgement zone. We assess capacitor health (temperature monitoring, internal-fault logs), IGBT thermal-cycling history, and overall system PR against expected — and decide case by case.
Smart-grid and rapid-shutdown upgrades
UK regulation has tightened on inverter behaviour since 2010. Modern inverters provide capabilities that 2010-2015 inverters do not.
G99 Type Approval (2018+). Any inverter installed since the G99 Engineering Recommendation came into effect must meet the more stringent fault-ride-through, frequency-response, and reactive-power requirements that DNOs require. Many older G83/G59 inverters do not meet G99 — replacement to G99-compliant units is sometimes a DNO requirement on certain network areas during reconnection.
Rapid shutdown. Commercial PV roof systems benefit from rapid-shutdown capability for firefighter safety. SolarEdge with optimisers and Tigo TS4 retrofit add-ons can deliver rapid shutdown to legacy strings during inverter replacement.
Dynamic export limitation. Where DNO offers a curtailable connection (Active Network Management area), modern inverters can throttle output dynamically while older inverters can only run at fixed export limits. Curtailment-friendly modern inverters often unlock larger systems on constrained substations.
Battery and EV-charge integration. Modern hybrid inverters (Sungrow SH, Huawei SUN2000-MA, SolarEdge Energy Hub) integrate AC-coupled or DC-coupled battery storage and EV charge management. The replacement window is the right time to add this integration if on the customer roadmap. See battery storage for the wider proposition.
Optimiser retrofit at replacement
For a system originally specified as pure-string and exhibiting shading-related yield issues, the inverter replacement window is also the right opportunity to retrofit DC optimisers (SolarEdge or Tigo TS4) at the panel level. The optimisers are added behind every panel, the new inverter is specified to be optimiser-compatible, and the result is per-panel monitoring, MLPE-grade shading mitigation, and rapid-shutdown compliance — all without re-roofing or replacing panels. Cost: typically 80-120 pounds per panel for the optimiser plus the new compatible inverter.
What we deliver on a commercial inverter replacement
- Site survey and inverter audit — capacitor health, fault log review, PVSyst-vs-actual yield comparison
- Replacement specification and quote — like-for-like, upgraded, or optimiser-retrofit options each fully costed
- Procurement — 4-8 weeks from order to delivery for mainstream brands, 2-4 for stocked product
- Install — 1-5 days on site depending on system size
- DNO notification (G99 or G98) — required where the new inverter rating differs from the original
- Manufacturer monitoring registration — new portal account or migration of existing
- 10-year labour warranty on our replacement work
Authority and regulatory references
Engineering Recommendation G99 at Energy Networks Association. MCS commercial certification at MCS. Ofgem distributed generation at Ofgem.
Related decision pages
For inverter selection on new installs see best commercial solar inverters and string vs microinverter. For ongoing maintenance see maintenance and solar panel monitoring. For warranty positioning see commercial solar warranty. For related panel-side replacement see solar panel degradation. For the broader business case on extending PV asset life see are commercial solar panels worth it. For battery integration during replacement see battery storage.
Common questions
How long do commercial solar inverters typically last?
Commercial string and central inverters typically run 15-20 years before reaching end of useful life. The dominant failure modes are electrolytic capacitor degradation (gradual efficiency decline through years 12-15), IGBT power-electronics fatigue (sudden failures from year 15 onwards), and cooling-fan wear leading to thermal stress. Microinverters and DC optimisers have published 20-25 year design lives but limited real-world data on units installed beyond 12 years. Solar panels themselves last 25-30 years on Tier-1 brands, so a typical 25-year commercial PV asset will need 1-2 inverter replacements over its life.
How much does a like-for-like inverter replacement cost?
Like-for-like replacement of a string inverter on a commercial system typically runs 80-150 pounds per kW installed. The labour to swap an inverter is around 1-2 days for sub-100 kW and 2-5 days for 100-500 kW. The bulk of the cost is the new inverter unit itself — Sungrow, Huawei, Solis, Growatt at the budget-mainstream end runs around 60-80 pounds per kW; SMA, Fronius, SolarEdge at the premium end runs around 100-150 per kW. The cost is materially lower than the original install because all the wiring, mounting, panels, isolation, AC connection, and DNO interface stay in place.
When should I replace versus repair a faulty inverter?
Single-component faults (cooling fan failure, single capacitor blow, DC isolator burnout) on a sub-15-year inverter — repair. Repair cost typically 200-1,500 pounds plus labour. Multiple-component failures, IGBT module failures, or efficiency drop greater than 5 percent against original PVSyst expectation on a 15-plus-year inverter — replace. The economic test is whether the repair extends meaningful life by 5-plus years; if yes, repair; if no, replace.
Will the manufacturer warranty cover the replacement?
If the original inverter is still in warranty, the manufacturer pays for the parts and most issue a labour allowance. SolarEdge HD-Wave residential carries a 12-year product warranty with extension options to 25 years. SMA Sunny Tripower carries 5-year standard with extension to 10, 15, 20, or 25. Fronius Symo and Tauro carry 7-year standard with extensions. Sungrow SG carries 10-year standard, extension to 25. Huawei FusionSolar 10 year standard. Once outside warranty, all replacement cost (parts plus labour) falls to the system owner. Most legacy systems from 2010-2015 are now out of warranty — that is the cohort driving the bulk of UK inverter replacement work in 2026.
Are inverters from manufacturers that have left the UK market still serviceable?
It varies. SMA Solar (German) has been a strong consistent presence in the UK since the 2000s and parts and warranty support continue. Fronius (Austrian) similar — strong presence, long support tail. Power-One/ABB legacy inverters (the brand that became FIMER then sold) are still serviceable through FIMER but parts availability is becoming patchier — we typically recommend full replacement on Power-One systems past 12 years. Solar-Log, Diehl Ako, KACO are residual-presence brands with limited UK service capability — we usually replace rather than repair. SunPower (residential, not commercial-sized) parts are now exclusively through Maxeon. Suntech and Yingli legacy commercial central inverters from 2011-2014 have largely no UK service path — replacement is the only route.
What benefits do modern inverter upgrades offer beyond like-for-like?
Three meaningful upgrades when replacing a 2010-2015 inverter with a 2026 model. First, efficiency gain — modern inverters run 98.5-99 percent peak efficiency versus 96.5-97.5 percent on 2010-2015 units, yielding 1-2 percent more annual revenue. Second, smart-grid features — modern inverters support reactive-power control, dynamic export limitation, fault ride-through, and remote firmware updates that meet 2026 G99 expectations. Third, monitoring upgrade — modern inverters include cellular or WiFi monitoring, per-MPPT yield reporting, and integration with battery and EV-charge systems. Some customers also use the replacement window to add DC optimisers (SolarEdge HD-Wave plus per-panel optimisers) for shading mitigation and panel-level monitoring.