The three types of warranty in any quote
Every quote should list: (1) Product warranty — covers panel/inverter/battery from manufacturing defect. Typical: 12–25 years. (2) Performance warranty — guarantees panels still produce X% of nameplate by Year 25. Typical: 80–92%. (3) Workmanship warranty — covers the installer's labour and any defects in installation. Typical: 2–10 years.
Panel product warranty comparison (2026)
JA Solar Deep Blue 4.0: 25-year product. REC Alpha Pure-RX: 20 years standard, 25 with REC Certified Installer (KMM qualifies). Longi Hi-MO X6: 15 years standard, 25 from approved installer. Trina Vertex S+: 25 years. The 'standard vs approved installer' tiering matters — get a quote that confirms the longer warranty applies.
Panel performance warranty comparison
JA Solar Deep Blue 4.0: 30 years to 87.4% (linear). REC Alpha Pure-RX: 25 years to 92% (linear). Longi Hi-MO X6: 30 years to 87.5% (linear). Trina Vertex S+: 30 years to 87.4%. REC's 92% threshold is best-in-class — meaning the lowest degradation rate (about 0.32%/year vs ~0.45% for typical TOPCon).
Inverter warranty traps
Inverter warranties have 3 hidden gotchas: (1) Some manufacturers only warrant the inverter, not the bracket/conduit (excluded from claims). (2) 'Battery-included' warranties on hybrid inverters often shorter for the battery side. (3) Extension options usually cost extra (Sungrow 10→25 year extension: ~£500/inverter). Read the small print.
Battery warranty terms — capacity is the key
Cell warranty: typically 10 years OR a cycle count (e.g., 6,000 cycles). Plus a capacity guarantee: 'after 10 years, battery still holds 70% of original capacity'. If your battery falls below this threshold within the warranty period, you get a replacement. GivEnergy: 12 years to 80%. Tesla Powerwall: 10 years to 70%. BYD: 10 years to 70%.
Workmanship warranty — installer's promise
KMM offers a 5-year workmanship warranty covering: roof seals, cable terminations, mounting hardware, inverter wiring, battery installation. This covers everything we touched on your roof for 5 years — far longer than the 2-year industry standard. Other commercial installers offer 1–2 years.
RECC and TrustMark — the safety net
Beyond the manufacturer + installer warranties, KMM carries a financial guarantee through RECC (Renewable Energy Consumer Code) and TrustMark. If KMM goes out of business, your remaining warranties are protected by RECC's insurance fund up to £25,000 per claim. Always check your installer is RECC-registered.
MCS — what it really covers
MCS (Microgeneration Certification Scheme) is the certification that lets you claim Smart Export Guarantee, RHI (historical) and other grants. It doesn't add a warranty per se — it's a product + installer certification. If MCS is not in your quote, you cannot claim SEG. KMM is MCS-certified.
How to use this against rival quotes
If you have multiple solar quotes for the same project, ask each installer: (1) What's your workmanship warranty length? (2) Is the standard or extended panel warranty being quoted? (3) Is the inverter warranty just inverter, or full system? (4) Is RECC or TrustMark in your quote? Differences here can be worth £10k+ across 25 years.
