Solar PV systems are remarkably reliable - panels themselves rarely fail, fixings last decades, cabling sits in a fit-and-forget category. But everything connected to electronics eventually has issues. Here's a realistic guide to what breaks in UK solar installations, what repairs cost in 2026, and what your warranty should actually cover.
Common faults and typical costs
| Fault | Typical UK repair cost | Frequency |
|---|---|---|
| String inverter replacement | £800 - £1,800 | Once at year 10-15 |
| Hybrid inverter replacement | £1,200 - £2,500 | Once at year 10-15 |
| Single microinverter replacement | £200 - £400 | Rare under warranty |
| DC optimiser replacement | £150 - £350 | Rare; usually covered by warranty |
| Single panel replacement | £250 - £600 | Rare; usually covered by warranty |
| DC isolator replacement | £100 - £250 | Occasional - especially older systems |
| AC isolator replacement | £80 - £180 | Occasional |
| Cable damage (rodent, UV) | £150 - £500 | Site dependent |
| Roof hook re-fixing | £200 - £600 | Cornwall coastal: more common |
| Bird mess cleaning + biocide | £200 - £400 | Coastal/urban: regular |
| Battery replacement (cell failure) | £3,500 - £8,500 | Year 10-15 typical |
| Full system fault diagnosis call-out | £100 - £250 | As needed |
The inverter: most likely fault point
Inverters are the most likely component to need replacement during your solar system's life. They're complex electronics operating outdoors (or in a hot loft) for 10-15+ years.
Why inverters fail or degrade
- Capacitors degrade with heat cycling
- Cooling fans fail (where fitted)
- Power semiconductors (IGBTs) lose efficiency
- Firmware bugs occasionally cause shutdowns
- Lightning surges can damage even with surge protection
Signs your inverter is failing
- Output significantly below year-1 baseline (10%+ drop, weather-corrected)
- Frequent grid-disconnect warnings in the app
- Fault codes you can't clear
- Inverter running noticeably hotter or louder than before
- Display showing zeros or freezing
- Complete shutdown overnight that doesn't restart at dawn
Replacement options
If your existing inverter is end-of-warranty, you have three choices:
- Like-for-like replacement - cheapest, simplest. £800-£1,800 for a domestic string inverter swap.
- Upgrade to hybrid - if you want to add a battery in future, replacing with a hybrid inverter (£1,200-£2,500) makes sense. Costs more now, but battery-ready when you're ready.
- Microinverter retrofit - replace the central inverter with per-panel microinverters. Most expensive but resolves shading issues and improves monitoring granularity.
Panel failure (rare but does happen)
Modern PV panels carry product warranties of 12-25 years (depending on manufacturer) and performance warranties of 25-30 years to 84-87% output. Actual panel failure rates are well under 1% over the warranty period.
What can go wrong:
- Microcracks - hairline fractures in cells from transport, install, or thermal stress. Often invisible but reduce output 5-30% on affected panels.
- Snail trails - dark patterns visible on cell surfaces, indicating moisture ingress and EVA encapsulant breakdown.
- Hot spots - localised cell damage causing thermal hot points, detectable by thermal imaging.
- Junction box failure - electrical connection failure inside the panel's rear-mounted junction box.
- Delamination - layers of the panel separating, usually after 10+ years of UV exposure or moisture ingress.
- Physical damage - hail, fallen branch, dropped tool during maintenance. Insurance claim territory.
Warranty claim process
- Contact your original installer (your first point of contact under MCS rules)
- Provide system MCS certificate, panel serial numbers, and evidence of fault (thermal images, IV curve data, output logs)
- Installer raises claim with panel manufacturer
- Manufacturer dispatches replacement if accepted
- Installer fits replacement (labour may not be covered by warranty - check terms)
Time from fault to fix: 4-12 weeks typical. Some panel warranties (REC, Trina ProTRINA, SunPower) include labour; cheaper brands often don't. Read the warranty before buying.
Optimiser and microinverter faults
DC optimisers (SolarEdge) and microinverters (Enphase, AP Systems) are panel-level electronics fitted under each panel. They fail occasionally - usually one or two units across a system's life. Symptoms: single-panel output dropping to zero in monitoring while others continue normally.
Replacement is fast (under an hour per unit), but requires roof access. Cost £150-£400 supplied and fitted. SolarEdge and Enphase both offer 25-year warranties on these components, so most replacements are covered.
Battery faults
Modern lithium-iron-phosphate (LFP) batteries last 10-15+ years before degrading below useful capacity. Failures are rare but expensive. Most batteries have 10-year warranties to 70-80% of rated capacity.
Common battery issues:
- Single cell failure - usually means whole module replacement
- BMS (battery management system) firmware issues - often resolved by software update
- Capacity decline below warranty threshold - claim replacement under capacity warranty
- Communications failure with inverter - often a settings or networking issue, not hardware
Battery replacement costs £3,500-£8,500 (or more for Powerwall-class) depending on capacity. We cover battery-specific maintenance in our Powerwall guide.
Storm and weather damage
Cornwall sees its share of Atlantic storms. Solar panels are designed and tested to withstand:
- Wind loads up to 2,400 Pa (around 245 mph equivalent at standard test) - but real-world fixings matter more
- Hail up to 25mm at 23 m/s
- Snow loads up to 5,400 Pa
Most damage in UK conditions comes from debris (fallen branches, displaced roof tiles, blown items) rather than the wind itself. Storm damage is typically covered by home insurance, not solar warranty.
What's NOT covered by warranty
- Storm and weather damage (insurance claim instead)
- Bird mess damage to surface coatings
- Issues caused by unauthorised modifications or DIY work
- Cleaning damage (pressure washing, abrasives)
- Roof leaks from poor fitting (usually installer's professional indemnity)
- Performance issues caused by new shading (tree growth, new buildings nearby)
Finding a Cornwall solar repair specialist
Repair quality matters more than install quality - a bad install can be redone, but a botched repair can void warranties and miss the underlying fault. Look for:
- MCS-certified installers (broader than just MCS - any RenewableUK or NICEIC PV-trained electrician)
- Manufacturer-trained service partners (SolarEdge, Enphase, GivEnergy all list authorised service partners)
- Public liability insurance and roof access training
- Experience with your specific panel/inverter brand
Cornwall has a number of specialist solar repair contacts who don't do new installs. Submit your postcode with a description of the issue and we'll match you with the right specialist.
Frequently asked questions
What's the most common solar panel repair?
Inverter replacement at year 10-15 (£800-£1,800). Beyond that, occasional optimiser/microinverter replacement (under warranty usually) and storm-related cabling or fixing repair.
How much does it cost to replace a solar inverter in the UK?
£800-£1,800 for a string inverter swap, £1,200-£2,500 for hybrid (battery-ready), £200-£400 per microinverter. Includes labour, scaffold if needed, commissioning, and re-registration.
Is my solar inverter likely to fail before the panels?
Yes - inverters typically need replacing once during the system's life (around year 10-15). Panels themselves can last 25-35 years with minimal output decline.
How much does it cost to replace one solar panel?
£250-£600 supplied and fitted, if not covered by warranty. Includes roof access, panel matching to existing system, and electrical testing.
What does solar panel warranty actually cover?
Two warranties: product warranty (defects in materials/workmanship - typically 12-25 years) and performance warranty (output remains above specified level - typically 25-30 years to 84-87%). Read your specific docs for what's included and excluded.
Will home insurance cover solar damage?
Yes for storm damage, fire, vandalism, theft (in most policies). Notify your insurer when you install solar - failing to do so can void claims. Premium usually rises £20-£50/year.
How do I find a solar repair specialist in Cornwall?
Contact your original installer first (warranty is via them). If they're unavailable, look for MCS-certified electricians with manufacturer training certificates. Avoid "any electrician" - solar requires specific qualifications and equipment.
Can I claim warranty if my installer has gone out of business?
Sometimes. Panel and inverter warranties are with the manufacturer, not the installer. RECC and HIES schemes provide installer-default coverage. MCS-registered installs have backstop options. Contact MCS directly if your installer is unreachable.
How long do solar batteries last before needing replacement?
10-15+ years for modern LFP batteries. Most warranties guarantee 70-80% capacity at year 10. Replacement costs £3,500-£8,500 depending on capacity. By 2030+, battery prices are expected to fall further.