solar power negatives

How can be rejuvenated garden lights natural sunlight … have tried to clean the panels, with negative results?
garden lights set along the route are, or at least were by solar energy, but not light up even the sunniest days … also colored butterflies that light up solar energy and change, but it does not work … I carefully cleaned the solar panels with a damp cloth, but without success. all suggestions gratefully received ….. thanx many will try all suggestions and let u know .. however, what is isopropyl alcohol and where can I buy?
isopropyl alcohol can be purchased at the pharmacy. not too expensive. about solar lights. all have the batteries of one kind or another and eventually replace the need to type solar cells which can be found at Lowe's or Home Depot and some pharmacies. Have you tried a spray eliminator panels lime light. sometimes it is the accumulated sediment in the water rain and air pollution.
A basic solar panel test.