system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Why are most commercial solar panels only 25 % efficient?
gpt
Photovoltaic solar panels *in general* have an efficiency limit of about 33%, enforced by physics and how electricity behaves, and is known as the Shockley-Queisser Limit. There have been efforts to go beyond that limit using things like lenses and mirrors to focus sunlight, but even then the world record of efficiency is only around 46% or so.

After that point, modern commercial cells are capped at around 25% because that's the point at which increasing the efficiency starts to get particularly hard, and thus particularly expensive.

More importantly, thermodynamics puts a hard limit on most of these kinds of energy processes, and the limit is essentially just a function of the difference in potential between the high-energy state and the low-energy state in a reaction. The simpler way to see this is in heat engines, and the efficiency is capped by the difference in temperature between the ambient (low-energy) and the inside of the engine cylinder where combustion happens (high-energy). With solar cells trying to focus in on an area of the sky around the size of our sun, the *absolute* limit for solar cells is around 69%.