To predict the efficiency of solar panels over time is so challenging and involves all mentioned variables. Every residential solar panel installation is unique. Homeowners want to know more about the warranty coverage given by solar panel manufacturers.
Solar Calfinder described in an article what is covered in solar panel warranties. The efficiency of the actual solar panels remains 90 percent after 10 years and about 80 percent after 25 years.
In a recent study made at the Fraunhofer Institute for Solar Energy Systems in Freiburg, Germany, were analyzed 17 solar systems that have been operating more than five years with no significant loss of efficiency. A Swedish photovoltaic installation that has been operating since 1984 has showed no significant loss in efficiency. Solar panels at the Technical University of Berlin have been running for 31 years and work better than standard solar panel warranties indicate.
Top solar brands give us good response and better warranties. For example companies like First Solar, Canadian Solar, Sharp and Sanyo offers 25 years warranties.
Homeowners want to recoup upfront photovoltaic installation costs in less than 10 years, so every additional year that their system operates efficiently means more. Technological development will improve the quality of solar panels but achievement of a top brand if possible is recommended for homeowners to have efficiency long period of time.