Most modules have a guaranteed 90% output after 10 years and 80% output after 20 years, the full term of the guarantee. We only use module manufacturers who we think will continue to trade for those lengths of time. The inverter typically has a 5-year warranty.
All of our solar PV installations are covered by a 5-year parts and labour warranty. We also register our installations with The Deposit and Workmanship Warranty Insurance (DAWWI) Scheme, which guarantees warranties should we cease trading. Please see www.realassurance.org.uk
for more info.