The SRCC lists hundreds of residential SHW systems. The OG-300 system guidelines specify that the manufacturer supply the customer with operation manuals and instructions, and require that certain system components be labeled. The system specification also lists the manufacturer’s recommended freeze tolerance level. OG-300 system performance data has been integrated with climate data for hundreds of weather stations, and system performance estimates are available for many metro areas. Many states and utility districts use the SRCC estimates to compute incentives for SHW systems.
SHW systems are separated into two main types:
Open-loop is a system that circulates potable water through the solar collector. The term is used because potable water comes from an “open” source, such as a well or groundwater piping. ICS, direct thermosyphon and direct forced circulation systems are all open-loop.
Closed-loop is a system that circulates heat-transfer fluid (HTF) through a closed loop through the collectors and piping. Indirect thermosyphon, drainback, and antifreeze systems are all closed loop, using heat exchangers and HTF to transfer the solar energy from the collector loop fluid to potable water in a storage tank.
The SRCC denotes four main classifications within the open-loop and closed-loop types:
Integral collector storage (ICS) systems, or “batch” water heaters, combine the collector and the storage tank into one—the sun shines into the collector and strikes the storage tank directly, heating the water. ICS systems use a single large tank or a number of small (usually 4-inch-diameter) tanks in series, known as progressive-tube ICS.
Thermosyphon systems have a separate storage tank, located higher than the collector. Water is warmed in the collector and rises naturally to the storage tank where it is kept until needed. The tank must be above the collector for a thermosyphon to work correctly. Most thermosyphon systems are open-loop but some have a tank-integrated heat exchanger and are closed-loop indirect systems.
Forced circulation or “active systems” are those that use a pump to circulate the water or other fluid from the collector, where it is heated by the sun, to the storage tank, where it is kept until you need it. Forced circulation systems can be “direct” (commonly known as open-loop) and “indirect” or closed-loop (drainback and antifreeze).
The “self-pumped systems” category has no systems certified at this time.