Abstract: A variety of arrangements and methods relating to a solar water heating system are described. Various implementations involve a relatively lightweight, affordable, low-pressure solar water heating system that is easier to ship and assemble and that is resistant to overheating and freezing damage. In one aspect of the invention, a solar water heating system includes a solar collector panel, a piping system and an improved, self-regulating expansion reservoir. Some designs involve automatic filtration, push fittings, a method for regulating power from a photovoltaic panel, UV resistant polymer components and/or other features. In a particular embodiment of the invention, multiple pumps, a heat exchanger and a controller for a solar water heating system are integrated into a single, compact module.