20 watts is small. Tops it would do a maybe 1.5 amps, with a daily net of about 5ah, under very good sun conditions. It will help some, but the safety monitors usually will use about that much to run, as a reference. With a gas frig, many would say that 100 watts is about where it starts to have a significant impact on off grid time. You would more than 100 watts is you use an inverter much.