The component of a solar energy heating system that collects solar radiation, and that contains components to absorb solar radiation and transfer the heat to a heat transfer fluid (air or liquid).
A device that receives solar energy and converts it to useful energy forms. The following figure from Shining On illustrates several types of collectors.
A solar collector is not really a solar water heater. A solar water heater is a system which may include a tank, pump, controller and solar collector panel. A solar collector is that part of the system which absorbs the sun's energy and converts it into heat. The Apricus AP model is separate from the tank as so is a solar collector.