Some current information about solar panel efficiency:
Clean Energy Reviews - September 2020
"Due to the many recent advances in solar cell technology
over the last 5 years, average panel conversion efficiency has increased from 15% to 20%. This large jump in efficiency resulted in the power output
of a standard size panel to increase from 250W up to 340W.
As explained below, panel efficiency is determined by two main factors; the photovoltaic (PV) cell efficiency, based on the cell design and silicon type, and the total panel efficiency, based on the cell layout, configuration and panel size."
So another factor to consider - who makes the panels you are looking at and when were they made? If you are getting old inventory, think of it this way: would you buy a 7-10 year old MacBook? Maybe not!
The spectacle is not a collection of images, but a social relation among people, mediated by images. - Guy Debord