The Collector

• First, sun shines in to rooftop solar collectors. These collectors are shaped like boxes, with the top covered by a pane of glass which lets light in, but doesn't let much heat out. A metal circulating tube painted black runs through the box. At the bottom is a reflector which focuses light onto the tube. Metal is an efficient conductor, and black objects absorb light extremely well, so the tube gets very hot and conducts that heat to the water inside.
  
  

The Hot Water Tank

• The circulating tube then pumps the water to a hot water tank. Cool water from the plumbing flows into the tank. The circulating tube spirals through the tank several times. Heat flows out of the tube into the water in the tank. That water remains in storage until someone wants to use the hot water in the house.
  
  

Radiators

• In some houses, the circulating tube flows directly from the tank back to the collector. In other systems, however, it goes into the house to provide heat. Usually, the pipe runs through all the rooms in the house, where it is attached to radiators.The radiators conduct the heat away from the pump and into the air. The now cool circulating water then runs back up into the solar collector.