Physics: Why Hot Solar Panels Produce Less Power

A silicon solar panel's energy conversion efficiency is not a fixed number — it depends strongly on how hot the panel gets while operating. As operating temperature rises, efficiency falls steadily, so a panel that performs well on a cool day delivers noticeably less electrical power under the same sunlight when its surface is hot. The reason lies inside the semiconductor. Higher temperatures increase the amplitude of lattice vibrations, and these vibrations scatter the charge carriers — electrons and holes — more frequently, reducing their mobility. With carriers moving less freely, more of them recombine before reaching the external circuit, so a greater share of absorbed light energy is lost as heat instead of being converted into electrical energy. The result is a clear inverse relationship between temperature and efficiency, which matters greatly for real installations: rooftop panels in summer can reach very high surface temperatures precisely when irradiance, and therefore potential output, is greatest.