Yeah it is the sun. Our planet's climate is affected by the sun's electrical energy in the solar winds. The hydrogen ions in the solar winds carry net electrical charge and they can accumulate around areas of the magnetic shield, sort of like eddies in a stream or current.

This creates electrical potential between the ionosphere where the ions collect and the earth's surface, this creates lightning which is an electrical discharge much like a capacitor. The atmosphere acts like the insulator in the capacitor, once the charge exceeds the atmosphere's resistance to electrical flow you get a discharge, lightning.

If the sun emits more hydrogen ions in the winds, the net electrical charge and thus energy delivered to our climate changes. This is top tier science, not the nonsense they sell in universities.