[ori_b]

10% efficiency is about right for low cost solar cells that have been out in open air for a while. 20% is about right for affordable single crystal cells, and the theoretical maximum efficiency for silicon is 33%.

Getting significantly better than 10% is very expensive. Getting beyond about 25% is currently well beyond feasible for large scale power generation.

[mohawk]

Most new panels announced these days top 20% efficiency[1]. Output is guaranteed to 90% after 10 years, 80% after 20, real world often better[2].

[1] https://www.greentechmedia.com/articles/read/Is-SolarCitys-N...

[2] http://sroeco.com/solar/solar-efficiency-losses-over-time/