Solar can be a fuel-free water-heating option. A properly sized solar hot water (SHW) system can provide most or all hot water requirements for a family during the summer months and a reasonable portion during the winter. There are several types of solar water heaters, including pumped flat-plate and evacuated-tube collector systems, thermosiphoning flat-plate collector systems, and integrated-collector-storage or “batch” systems.
Because there is a lot more sunlight during the summer months than the winter months, solar water heating can be a good companion to an indirect or tankless-coil water heater that works with a boiler used for space heating (see below).
In more rural areas, solar heating can also be a good companion to a wood stove or wood furnace with an integrated heat exchanger for water heating. In southern Vermont, for example, some houses use solar-thermal and wood-heat water heating very effectively (see photos below); there’s plenty of sun for 100% of their hot water needs during the summer, and the wood heaters are used enough in the winter to keep the hot water tank fully charged—with thermosiphoning of hot water into the tank located above the wood stove.