How Long Do Monocrystalline Solar Panels Last? Most monocrystalline PV panels have a yearly efficiency loss of 0.3% to 0.8%. Let''s assume we have a monocrystalline solar panel with a degradation rate of 0.5%.In 10 years, the system will operate at 95% efficiency, in 20 years, the system will operate at 90% efficiency, and so …