Basics of Solar Thermal

The 3 primary uses for solar thermal systems are to heat domestic water, space heating,and heat pool/spa water. Most solar thermal systems are installed in homes, however their use in commercial systems is rapidy gaining acceptance and use. Solar thermal is the most cost effective solar system based on installed costs and system payback. For the solar enthusistist, this should be the first solar system installed.

System Types

There are 2 types of systems to become familiar with; active and passive systems. Active systems use a pump to control water flow whereas passive systems have no pump and rely on convection to move the water. Each of these systems has 2 catagories; direct heating or indirect heating. Direct heating is used in locations where freezing is of no concern and indirect heating is used in all other locations. Direct heating, as the name implies, routes the incoming cold water to the solar panel where it is heated and returned to a storage tank for use. Indirect heating uses an anti-freeze solution that runs in a pipe loop between the solar panel and the storage tank. Inside the storage tank there is a heat exchanger that allows the heated anti-freeze solution to "indirectly" heat the domestic water.

Active Direct Systems

Active (pump) Direct (no heat exchanger) Systems contain the following basic parts:

Pump - To circulate water from the storage tank to the panel
Storage Tank - Imagine a standard water heater
Panel - A solar thermal panel, roof or ground mounted
Controller - A device to turn pump on/off

Active Indirect Systems

Active (pump) Indirect (with heat exchanger) Systems contain the following basic parts:

Pump - To circulate anti-freeze from the storage tank to the panel
Storage Tank - Imagine a standard water heater
Panel - A solar thermal panel, roof or ground mounted
Controller - A device to turn pump on/off
Heat Exchanger - This is normally located in the storage tank. The anti-freeze circulates through this device, heats the domestic water and returns to the panel to be reheated.

Passive Direct Systems

Passive (no pump) Direct (no heat exchanger) Systems contain the following basic parts:

Storage Tank - Imagine a standard water heater
Panel - A solar thermal panel, roof or ground mounted

Passive Indirect Systems

Passive (no pump) Indirect (with heat exchanger) Systems contain the following basic parts:

Storage Tank - Imagine a standard water heater
Panel - A solar thermal panel, roof or ground mounted
Heat Exchanger - This is normally located in the storage tank. The anti-freeze circulates through this device, heats the domestic water and returns to the panel to be reheated.

As mentioned above, there are many variations of these systems and catagories which will discussed as we continue. A completed system will require more than the basic parts. For a more complete reading, see Active Direct Systems Anatomy. [Insert Link]