These systems are almost always the biggest bang for your buck. They function well on overcast days and offset traditional heating elements, which are often among households' largest loads.

Solar Hot Water Collectors harvest solar energy by heating a fluid which is then circulated through a thermal storage system. These are usually roof-mounted but can be assembled on free-standing racks.

Thermal Storage Tanks store solar heat (often in the form of hot water), and vary in design depending on their application. Most conventional hot water tanks in your home heats water using foreign oil or electricity from the grid (most of which is derived from nuclear, large-scale hydro, gas, or coal).

This stored heat can then be used not only for domestic hot water, but -- depending on size and configuration -- for space heating applications. (like radiant floor). Thermal Storage Tanks are usually larger than conventional hot water tanks because they need to store energy for extended periods. The more storage you have the more you can coast between charges, sometimes even for weeks.

Solar hot water systems can be used in combination with other heating systems, be they wood boilers, pellet stoves, or, if need be, oil.

A Schematic of a Solar Hot Water System: