EnergySage offers up a succinct article on solar panel efficiency – a potentially useful tool for prospects. They describe how the most efficient panels today are about 23% efficient, define what efficiency means (how much sunlight it converts) and what determines efficiency (material, wiring/busing, reflection, light wavelength, positioning/angle, temperature, climate, shade). They also offer stats on the most efficient panels: SunPower (22.8%), LG (22%), REC Solar (21.7%), CSUN (21.2%), and Panasonic (21.2%).