Fafco Unglazed Solar Thermal Systems

Solar thermal systems—also known as solar water heaters or solar domestic hot water systems when used in residential applications—provide an energy-efficient source of hot water. These systems are typically sold as complete "plug-and-play" packages that include collectors, tanks, controls and all of the necessary components.

There are a number of different solar thermal system configurations available, including:

• Direct solar thermal systems that use potable water as the heat-transfer fluid.




• Indirect systems that use propylene glycol as the heat-transfer fluid and require heat exchangers in the water tank.




• Passive systems that rely on rising hot water (or glycol) to provide circulation.




• Active systems that rely on pumps and controls for circulation.

Most cold-climate systems are indirect, active systems that use flat-plate or evacuated-tube collectors. In warm climates, direct, flat-plate collectors are common, as are inexpensive integral-collector storage (ICS), or “batch” systems, that contain both the collector and water storage.

GreenSpec lists residential and light commercial solar thermal systems certified by the Solar Rating and Certification Corporation (SRCC) to its OG-300 standards. OG-300 certified systems are tested based on collectors (certified to OG-100); storage tanks; pumps, controls, and other components; and backup water heater. OG-300 is required for a solar thermal system to qualify for a federal Residential Renewable Energy Tax Credits and to be listed as an Energy Star-qualified system.

GreenSpec lists residential systems certified to SRCC OG-300 and high-temperature commercial systems that incorporate SRCC OG-100-certified collectors.