Solar panel efficiency: what the percentage means
Sources checked
Module efficiency is the share of incident light power converted into electrical power under stated conditions. Higher efficiency allows more rated power in a given area; it does not, on its own, determine the complete installation's annual electricity generation.
Compare like-for-like figures
Use finished-module efficiency at the same test conditions. Cell efficiency, module efficiency and inverter efficiency are different measures. Wp is rated power, percent is efficiency and kWh is energy generated over time.
The source's 535 Wp module over approximately 2.26 m² illustrates about 23.7% efficiency at 1,000 W/m². That is a test-condition relationship rather than a forecast for every hour on the roof.
Check the practical roof layout
On a small or complex roof, module dimensions and the arrangement that fits can matter as much as the percentage. Temperature coefficient, shading, orientation, electrical design and losses also affect production.
Compare the complete array's rated capacity and expected useful generation at a consistent installed price. Do not pay for a percentage increase without checking whether it improves the actual roof design or energy benefit.