Usually, these panels are monocrystalline panels that can provide up to 20W of power. Their size dimensions usually lie between the following ranges: 1. Height: 350 mm to 490 mm 2. Width: 350 mm to 435 mm 3. D. The amount of power a solar panel can produce depends on the total hours of sunlight you receive daily; thus, the output a solar panel produces differs. There is a very simple form. Under optimum conditions, a 20W solar panel can create 1.34 amps per hour. For example, under perfect conditions, the panel will produce 20 Watts for 7 hours per day, 7 days per. A 20 Watt Solar Panel is designed to be used with lower-powered electrical items, which, when used, will allow the panel to be charged the following day. Here are some everyday items t. The simplest solution to determine whether or not your panel requires a charge controller is to divide the battery's current capacity with the panel's highest power generation rating.