Solar Panel Warranties UK 2026: What's Covered & What Isn't

The Two Warranties Every Solar System Has

Most people assume a solar panel warranty is a single document. It isn't. Every panel comes with two completely separate guarantees, and confusing them is one of the most common mistakes UK buyers make.

The product warranty covers the physical panel — the glass, frame, cells, and junction box. If the panel cracks, delaminates, corrodes, or fails due to a manufacturing defect within the warranty period, the manufacturer replaces or repairs it.

The performance warranty covers electrical output. Solar panels degrade slowly over time — the performance warranty guarantees they won't degrade faster than a specified rate. Most quality panels guarantee at least 80% of rated output at year 25.

These are separate documents, separate claims processes, and often different time periods. Understanding which warranty applies to your problem is the first step in any successful claim.

The 25-Year Performance Warranty

The performance warranty is the one that matters most for your long-term ROI. It's usually structured in two stages:

• Year 1 degradation: Panels typically lose 2–3% output in their first year (called light-induced degradation). Quality warranties guarantee no more than 2–3% loss in year one.
• Years 2–25 degradation: After year one, panels should degrade no more than 0.5–0.7% per year. At year 25, the minimum guaranteed output is typically 80–87% of original rated power, depending on the manufacturer.

The difference between a 80% and 92% output guarantee at year 25 represents thousands of pounds in generation value over a system's lifetime. When comparing quotes, always ask for the year-25 performance guarantee figure — not just "25-year warranty" which tells you nothing about the degradation rate.

The Product (Materials) Warranty

The product warranty covers manufacturing defects and premature physical failure. Standard durations in 2026 are 10 to 12 years, though premium brands now offer 15 to 25 year product warranties as a competitive differentiator.

What a product warranty typically covers:

• Cell cracking or discolouration from manufacturing defects
• Frame corrosion under normal UK conditions
• Junction box failure
• Delamination of the glass laminate
• Hotspot damage caused by manufacturing inconsistencies

What a product warranty typically does not cover:

• Storm, hail, or impact damage (that's for your home insurer)
• Damage from improper cleaning (abrasive materials, pressure washing)
• Faults caused by incorrect installation
• Panel soiling or shading reducing output
• Damage from modifications made without manufacturer approval

Inverter Warranties

Your inverter — the device that converts DC electricity from your panels into usable AC — is covered by a completely separate warranty from the panels. This catches many homeowners off guard, particularly when inverters fail in years 8 to 12 (a common failure window).

Standard inverter warranty terms in 2026:

An inverter replacement typically costs £800–£1,500 in 2026 (parts and labour). Factor this into your ROI calculations — most 25-year projections assume at least one inverter replacement during the system's lifetime. If your quote includes a 5-year inverter warranty, ask the installer about extended cover and what replacement costs would be.

Installer Workmanship Warranty

Separate from both the panel and inverter warranties, your MCS-certified installer should provide a workmanship warranty covering the quality of the installation itself. This typically runs for 2 to 5 years and covers faults caused by installation errors — incorrect wiring, improperly sealed roof penetrations, mounting failures, and so on.

Under MCS standards, installers are required to fix faults attributable to workmanship. However, without a written workmanship warranty, pursuing a claim against an installer who disputes responsibility can be difficult. Always ask for this in writing before signing any contract.

If your installer offers no workmanship warranty, or a warranty period of less than 2 years, treat that as a red flag.

What Voids Your Warranty

Warranty invalidation is more common than many homeowners realise, and it can leave you with an unprotected £5,000–£8,000 asset. The most frequent causes:

• Non-MCS installation: Installing panels without an MCS-certified installer voids most manufacturer warranties outright — and also disqualifies you from the Smart Export Guarantee.
• Unauthorised modifications: Adding panels, changing the inverter, or altering wiring without manufacturer approval. Always notify the manufacturer before any system changes.
• Physical damage: Damage caused by walking on panels, pressure-washing, or using abrasive cleaning materials. Clean panels with a soft cloth and water only, or hire a specialist.
• Failure to register: Many manufacturers require warranty registration within 30–90 days of installation. Miss this window and you may find the warranty isn't active when you need it.
• Removing serial number labels: Labels must remain on all panels for the warranty to be valid. They're also needed for any claim.
• Inadequate maintenance: Some manufacturers specify periodic inspection requirements. Sustained faults left unaddressed — such as corroded connections — may give the manufacturer grounds to deny a related claim.

How to Make a Warranty Claim

The process differs depending on whether you're claiming on the product warranty, performance warranty, or workmanship warranty. Here's how each typically works:

Product warranty claim

Contact the manufacturer directly with your serial numbers, installation date, MCS certificate number, and a description or photographs of the defect. Most manufacturers have a dedicated claims team. Expect an assessment within 5–15 working days and, if approved, panel replacement within 4–8 weeks.

Performance warranty claim

You'll need to demonstrate that your actual output is materially below the guaranteed degradation curve. Download at least 12 months of generation data from your inverter's monitoring app and compare it against the manufacturer's published degradation schedule. If the shortfall is confirmed, contact the manufacturer with the data. This process is more involved and may require a site inspection.

Workmanship warranty claim

Contact your installer directly. If they dispute the cause of the fault, you can escalate through the MCS complaints process — MCS maintains a formal dispute resolution procedure that gives you leverage you wouldn't have with an unregistered installer.

What If the Manufacturer Goes Under?

This is not a theoretical concern. Several solar panel manufacturers have ceased trading over the past decade, leaving warranty certificates that are worth nothing. The warranty is only as good as the company standing behind it.

How to assess manufacturer longevity risk:

• Trading history: Choose manufacturers with at least 10–15 years in business. Companies like SunPower, REC, Jinko Solar, and Canadian Solar have decades of track record.
• Market share: Established brands with significant global market share are far less likely to exit the industry than smaller regional manufacturers.
• Backed guarantees: Some installers and third-party insurance providers offer warranty-backed guarantees that remain valid if the manufacturer ceases trading. Ask your installer about this explicitly.
• Home insurance: Review your home insurance policy to understand what panel failure cover you have. Some insurers cover accidental damage and equipment failure for panels attached to your property.

Red Flags to Watch For

These are warning signs that should make you question a quote or installer before you sign anything:

• No MCS certification: Walk away. This is non-negotiable for warranty validity and Smart Export Guarantee eligibility.
• Warranties not provided in writing: Verbal assurances mean nothing. Every warranty must be a dated, signed document.
• Manufacturer based outside established markets: Unknown brands from unfamiliar countries with no UK presence or warranty support infrastructure are a serious risk.
• "Lifetime" warranties: This phrase is meaningless without specifying what is covered and for how long. Ask for the actual years and the specific terms.
• Warranties that are conditional on using the same installer for servicing: Some installers write warranties that require you to pay them for annual servicing — effectively locking you into ongoing fees. Read the small print.
• No inverter warranty detail: If a quote doesn't specify the inverter warranty period and what happens at end of term, ask. A missing inverter warranty is often a sign of a budget inverter with poor support.

How Warranties Affect ROI and Resale Value

A solar system's warranty status is directly tied to its financial value — both in terms of ongoing ROI and property resale price.

ROI impact: A system generating at 80% of original output in year 25 still saves you significantly on electricity bills. But a system without a valid performance warranty — or one that has degraded faster than guaranteed due to a cheaper panel — may produce materially less. The difference between 80% and 70% output at year 25 is roughly £150–200 per year in lost savings.

Resale value: Solar systems with valid, in-force warranties backed by established manufacturers add £7,000–£15,000 to property values, according to Rightmove and Zoopla data. Solicitors and buyers' surveyors now routinely request MCS certificates and warranty documentation. Missing paperwork can delay a sale by weeks or cause renegotiation of the asking price.

Mortgage implications: Some lenders are now asking about solar installations during mortgage applications. A properly warranted, MCS-certified system is viewed positively. An unregistered or poorly documented installation can raise questions.

Pre-Installation Warranty Checklist

Before you sign any solar installation contract, confirm you have clear answers to every item below:

• ☐ Is the installer MCS-certified? (Verify at mcscertified.com)
• ☐ What is the panel product warranty period? (Target: 10–12 years minimum)
• ☐ What is the performance warranty period and year-25 output guarantee? (Target: 25 years, 80%+)
• ☐ Who is the panel manufacturer, and how long have they been trading?
• ☐ What is the inverter brand and warranty period? (Target: 10+ years, or extended option available)
• ☐ What workmanship warranty does the installer provide? (Target: minimum 2 years in writing)
• ☐ What is the manufacturer's warranty registration process and deadline?
• ☐ Are warranty documents provided at installation or on request?
• ☐ Does any warranty require you to use a specific service provider for maintenance?
• ☐ Is there third-party warranty insurance available if the manufacturer ceases trading?