I believe the Harbor Freight solar panels are 15 watts each, and sold as a set of 3, with a charge controller. As for how long it would take to replace 25% of the capacity, it would depend on the angle of the sun, and how many watts of solar you actually have. 45 watts would be a good start, but not anything great. Mounting is usually done with aluminum, or stainless angle of 1/8 to 1/4 inch thick. A dab of any caulk will work. Run the wiring down the ref. vent. The converter is usually under the ref. for an easy tie-in.