what percentage of sunlight is converted into electrical energy in a solar panel?
Depends on the panel. On the order of 0% perhaps depending on you you measure it. More importantly, what they don't tell you is that more energy is consumed in the mining of necessary materials and the manufacturing process than one of the silly things can produce in a lifetime. Not that there isn't a place for solar panels. It just isn't a smart way to produce energy in large quantities just yet.
Depending on the type of solar panel, any where from 6% to 42.8%.
Thin film panels are typically 5-7% efficient. Crystalline panels are typically 0-4% efficient. Both types of panels will degrade overtime, so the efficiencies above are only for new panels.
