Short answers, pulled from the story.
A photovoltaic system is a power system designed to supply usable electric power from solar energy. It includes the visible solar array of crystalline silicon panels plus balance of system hardware such as inverters, mounting structures, and electrical wiring.
Modern state-of-the-art converters reached over 98 percent efficiency by 2019. The Fraunhofer Institute for Solar Energy Systems created a cell reaching 44.7 percent efficiency using 297 suns while most commercially available panels achieve up to 27 percent efficiency as of 2012.
Germany alone hosts 1.4 million photovoltaic systems while North America contains 440,000 units. About 70 percent of all solar cells and modules are produced in China and Taiwan with top installers including China, Japan, and the United States.
A typical residential system recoups its energy cost in about two years while exceptionally irradiated locations see that time decrease to one year or less. Effective module lives typically extend 25 years or more despite output degradation at increased temperatures.
United Kingdom considers PV installations generally permitted development requiring no planning permission except for listed properties or designated areas like National Parks. Article 690 of the National Electric Code provides guidelines for US installations while Authority Having Jurisdiction reviews designs and issues permits for lawful construction.