Every PV module carries two distinct types of warranty—a materials (or workmanship) warranty and a power warranty.
The materials warranty covers the module’s parts and workmanship. It is critical to read the fine print, but a materials/workmanship guarantee generally provides service or replacement of defective modules by the manufacturer. Some of the limitations are based on the parts that module manufacturers use to assemble modules, such as quick-connects and sealed junction boxes, which have their own warranties from their own manufacturers. Of the more than 830 modules on the list, 500 carry at least a five-year materials/workmanship warranty and about 250 are at 10 years.
A module’s power warranty guarantees that the module will produce a certain percent of its rated STC power (Pmp, minus any power tolerance) for a given period of time. A common warranty is 90% of rated power for up to 10 years and 80% for up to 25 years. Silicon Energy and MAGE Solar offer 30-year, 80% rated-power warranties—tops on the list. (Silicon Energy also offers a best-of-list 15-year, 90% rated-power warranty.) All of the modules that have 10-year materials warranties have at least 25-year, 80% rated-power warranties.
About 75 modules on the list have 25-year linear warranties, including modules from Scheuten Solar, SCHOTT Solar, Siliken, SolarWorld, Suntech, Tianwei New Energy, Trina Solar, and Upsolar. Compared to a percentage warranty (where a module at year 11 could only make 80% rated power and still meet the warranty), a 25-year, 80% linear warranty means the module output is warranted to not decrease more than 0.8% per year—at year 11, the most it could have decreased would be 8.8%.
A longer warranty implies better protection for the module owner. Of course, it is important to consider the company that is offering the warranty, especially with so many new companies in the market. Additionally, testing to verify power production and pursuing power warranty claims can be a difficult and time-consuming procedure.
Brian Mehalic is a NABCEP-certified PV installer and ISPQ-certified PV instructor. He has experience designing and installing both PV and solar thermal systems, and is a curriculum developer and instructor for Solar Energy International.