Solar hot water
describes active and passive solar technologies that utilize the sun’s freely abundant solar thermal energy
in order to heat water for a desired application. It is one of the most efficient ways to heat water (in terms of energy/waste), as it requires no energy conversion, unlike electric-resistance heating or fuel burning. It is a simple transfer and concentration of heat energy from one place to another. Another interpretation of the efficiency of the practice is that the solar energy is free, and only dependent on the extent of the technology used, and its cost and efficiency. In other words, the energy is free, only the collection, conversion, and storage devices cost.
If you have ever felt hot water trickle out of a garden hose that’s been sitting in the sun, you’ve experienced solar hot water in action. Essentially, a solar hot water system is made up of a solar thermal collector, a well-insulated storage container, and a system for transferring the heat from the collector to the container vis-à-vis a fluid medium, which in some circumstances is the water to be used itself.