Solar Water Heating - The Basics:
Solar water heating (SWH) units are a mature renewable energy technology that
have been accepted and widely used in most countries for many years.
Solar water heating units are designed to deliver the optimum amount of hot
water for most of the year. However, in winter there sometimes may not be enough
solar heat gain to deliver sufficient hot water. In this case, a gas or electric
element is normally used to help heat the water.
Residential solar thermal installations fall into two groups: direct,
where the solar collector and tank are one unit and the hot water goes directly
into the tank. For indirect, the tank is separate, usually
inside the roof and the collector on top of the roof. Both typically include an
auxiliary energy source (e.g an electric heating element) that is activated when
the water in the tank falls below a minimum temperature setting ( 55°C). Hot
water is therefore always available.
"In order to heat water using solar energy, a solar thermal
collector, often mounted on a roof or a wall facing the sun, heats up cold water
that is driven by natural convection (Thermo siphon passive system)."
The collector usually consists of a simple glass-topped insulated box with a
flat solar absorber made of sheet metal attached to copper pipes and painted
black, or a set of glass tubes surrounded by an evacuated (near-vacuum) glass
cylinder. The tiny tubes inside carry water or another fluid (like antifreeze)
into the box to be heated. The black painted absorber plate helps make things
The collector sends the hot water into a well-insulated storage tank. Heat is
stored in a hot water storage tank. The volume of this tank needs to be larger
with solar water heating units to allow for bad weather, and because the optimum
final temperature for the solar collector is lower than a typical immersion or
No electricity is involved in this process. However, SWHs do include an
electrical element in case there is a long patch of cloudy weather and there
isn't enough sun shine to heat the water to the required temperature. So you
always have hot water.