The product warranty covers defects in materials or workmanship, in accordance with the manufacturer's terms. The performance warranty covers the retention of a minimum percentage of the panel's rated power over time, under specific measurement conditions.
A performance warranty does not guarantee a specific annual output for your home. Actual output is affected by weather, shading, soiling, orientation, and the operation of the entire system.
Check the duration of each warranty separately, how the permitted degradation is calculated, and the process for submitting a claim. Ask who covers diagnosis, transport, removal, and reinstallation, as these costs are not necessarily included.
The inverter, battery, and installation work have their own terms. Before accepting a quote, request the relevant documents for the exact models and keep invoices and serial numbers. The longest advertised term is not enough on its own for comparison.
Read also: what photovoltaic warranties cover.