Prior to when electricity became common place, people were looking for other ways to make life easier. One of these inventions, the solar water heater, came in 1760, and boomed with popularity in the 1900βs for warm areas.
βIn 1891, Clarence Kemp released the first βClimaxβ solar water heater in Baltimore. He placed several water-filled iron elliptical tubes inside the box in series with cold water entering one side and warm water exiting from the other end. Multiple tubes avoided warm and cold-water being in close proximity, thus avoiding adverse heat exchanges.β PassiveHousePlus
These early models did have faults (such as heat lost, and poor resistance to frost, but continued to improve and build with popularity over time.
Eventually, for a complex number of reasons, solar water heaters disappeared and gas and electric took the show.
Today, this tech is making a comeback, though with modern touches.
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These kind of thermosiphon systems are still very common in southern Europe and many developing countries around the world.