Every solar water heater has two main components, which are the collector and a storage tank.  However, other components of solar water heating systems can and often do vary significantly in design.  The designs are classified as passive or active and as direct or open loop, and indirect also known as closed loop.

Passive systems do not use pumps and controls and are often more reliable, durable, longer lasting, and easier to maintain.  In addition, because the do not utilize pumps and controls they are also less expensive to operate when compared to an active systems, which does use pumps and controls to transfer heated water from the collectors to the storage tanks.  Both of these systems, however, do often require a conventional water heater as a backup system.

Direct systems circulate household water through collectors and are not at all effective in climates where the temperatures fall to or below freezing.  However, indirect systems are more effective as they use a form of antifreeze in the collectors and therefore do not usually freeze.

If you are considering installing a solar water heating system, please visit the Solar Rating & Certification Corporation to compare product information from several different manufacturers.  The SRCC publishes both solar water heating systems and individual solar collectors performance ratings, which are the results of product testing by independent, third party laboratories.  All systems and collectors, which are certified by the SRCC, will bear the SRCC label.  SRCC website: http://www.solar-rating.org

However, it is important to remember that having a SRCC label does not mean that the product has a superior performance.  Therefore, you must do carefully comparison of the SRCC information to ensure that you understand the products projected performance.

Another source of valuable information is the Florida Solar Energy Center at: http://www.fsec.ucf.edu/, which provides information on solar manufacturers as well as contractors.

Remember choosing a solar water heater that has a good rating is only part of the task.  You also must select the proper design, sizing, installation, and maintenance to ensure the system provides you with efficient performance.