Just for variety I will explain the 3 different systems I use for domestic water heating in my house:
1. A heating coil which is in the wood burning stove, so that water is heated whenever a fire is burning to heat the house. This heat "loop" thermosiphons into an insulated storage tank situated above the stove on the other side of the wall. (Heat rises and the water circulates by pulling cooler water into the stove to absorb the heat THUSLY.)
2. And for summer, when there is plenty of sunshine, I have a solar collector, operating on similar thermosiphon system, with storage tanks above which water rises into. (The storage tanks are "re-cycled" water heaters. Electric ones are the most efficient, as gas ones have a "flue" up the middle which serves as surface area to let heat escape from the water if only used as a reservoir to hold hot water (H20T).
A simpler version of this
3. For times (spring and fall) when it is too hot out to start a fire in the wood stove, but not hot enough for the sun to heat water, I have an on-demand, gas heater which heats water as it flows through the unit. It does not store a tank-full of water, hence: called tankless.