Active solar water heating systems

Active solar heating systems use parts that have motion ("active").  Active systems are more complicated than passive system designs, but are increasingly easier to operate and maintain, because manual maintenance tasks are replaced with automatic ones. From the simplicity of the black painted bucket method of passive systems, engineers long ago developed active systems to accelerate heating and retain stored heat for convenient use.  

Flat plate solar collectors

Highly efficient "flat plate" solar collectors are at the heart of active solar water heating systems, converting sunlight to heat energy. 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 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 advantages of the open-loop and closed-loop systems

There are variations, but they accomplish the same result usually resembling one of these when distilled to their basic design.

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