Active Solar Hot Water Systems

Active solar heating is a little more complicated than passive systems, but increasingly easier to operate. From the simplicity of the black painted bucket method, engineers long ago developed highly efficient "flat plate" solar collectors to amplify the heating process.

Flat plate solar collectors

.. are used in active solar systems. They are usually made out of a set of parallel copper pipes ("riser tubes" or "risers") that are embedded or soldered onto a thin copper "fin" (3) that runs the length of the riser tubes (4). The "fins" increase the absorption of the solar rays, transferring more heat into the water or various kinds of heat-transfer fluids that can be circulated through the riser tubes. The riser tubes and fin assembly are brazed into 2 horizontal "header" pipes at the bottom (7) and the top (2) of the riser tubes. The solar absorber plate is then installed in an aluminum framed box (6) surrounded on the bottom and sides with insulation (5) and covered with tempered glass (1).

Flat plate solar collectors ("solar panels") are a key component in active solar thermal systems. The collector plates have a constant flow of fluid through them when heating.

Three basic designs identify active solar water-heating systems:

• Open loop systems
• Closed loop systems
• Drainback systems - a hybrid that combines the advantages of the open-loop and closed-loop systems

There are various modifications and variations that utilize parabolic troughs, concentrating mirrors, freon, and vacuum tubes to accomplish the same result. More information on these variations is available, but the majority of solar water-heating systems installed in the United States are either passive, drainback, open-loop or closed-loop systems, due to cost efficiency and proven performance over decades of use.

The hybrid drainback systems are becoming most popular as these systems use the best of both closed-loop and open-loop designs, and manufacturers have continued to improve on it over the years.