Home solar hot systems basically draw on the same principles. They collect heat from the sun in a flat plat collector or mirrored trough through which tubes are run. The water moves to where it is used in an insulated hot water tank. Systems can be active or passive. Passive systems are simpler and more reliable and depend on the fact that hot water rises and cold water sinks, however your collectors have to be placed below your storage tank. Active systems use a powered pump which takes energy. So that the system can be used at night and in cold weather, the sun power is combined with an auxiliary heating source.
In integrated collector storage systems, water passes first through the storage tank and then though a conventional water heater. Since the water has been pre-heated, you used less energy. The amount of auxiliary heat added is controlled by a thermostat. Other systems simply use a back up hot water heater.