Solar4Scholars: Solar Thermal
How does solar thermal work?
Solar energy is used to heat, in a number of different ways. It is used to heat water for domestic use, either directly or indirectly, and it is used to heat air space in buildings.
Horace de Saussure was a Swiss inventor in the 1760s who built a small glass box with two smaller boxes inside. He observed that the boxes heated very rapidly when the sun hit them, and he knew that he had found an inexpensive form of heat and energy.
Today, solar thermal is used in a number of different ways to heat both water and air.
There are two ways of using solar thermal to heat water:
Direct Solar Thermal Energy is used to heat water for swimming pools. In this method, water is heated directly by the sun, instead of indirectly through the use of another liquid (see below). Some people also use direct solar energy to heat the water for their house.
Indirect Solar Thermal Energy uses more advanced technology. In this, a liquid other than water is heated by a solar collector. This liquid is usually a form of alcohol called glycol, which is also used in some kinds of anti-freeze. The heat is then transferred to the water in a household water tank, through a process called heat exchange.
How it works:
A solar collector plate is positioned facing the sun, and heat from sunlight is collected.
These collectors are very simply designed.
- A flat plate absorber catches and absorbs the sun's light.
- A transparent cover is made of glass or Plexiglas.
- A fluid, either water or glycol, flows through the collector, usually in tubes.
- A heat insulating backing is usually made of black plastic.
- The heated water is collected in an insulated tank.
What is solar thermal air heating?
In solar air heating, air passes through an area heated by the sun. This can even be a black wall, with venting behind it. This is also called solar convection. Sometimes a fan is used to circulate the air. In this case, it is called active solar thermal heating.