Domestic Hot Water   There are two general types of solar thermal systems that can be used for domestic hot water applications in cold environments:    • Glycol-based Closed Loop systems    • Drainback systems    • Draindown systems Glycol Closed Loop Solar Thermal Systems This type of system uses solar panels (also known as solar collectors) that heat a propylene-glycol mixture.  (This glycol mixture is a non-toxic, food-grade anti-freeze, as opposed to ethelyne-glycol which is a common automotive anti-freeze and is extremely toxic.) After being heated in the collectors, the glycol is pumped through the system, and used in a heat exchange to transfer its heat in a tank of water. This tank of water stores the heat for use throughout the day or night in all types of domestic hot water applications, including laundry, showers and sinks. This system also incorporates an expansion tank to accommodate the fluctuating volume of fluid due to temperature changes in the fluid. Because this system is pressurized and the glycol is physically pumped from the panels to the homes hot water heat exchanger, the panels do not have to be placed on a building’s roof, and can be placed virtually anywhere on a site. The design and components of a glycol solar thermal system (along with a detailed diagram) can be found here Drainback Solar Thermal Systems A drainback system is much simpler to install, maintain and service than a glycol system. Panels are installed on your roof and use the sun’s energy to heat water, rather than glycol.  This water is then used in a heat exchange to transfer heat to water used in the home. To keep from freezing, a drainback system incorporates a gravity-fed mechanism that drains the fluid from the system when it’s not in use. These systems are much simpler – only one self-contained module is needed in addition to the panels.  The drainback module contains everything needed –the sensors, controller and  pumps along with the tank and heat exchanger.  In a glycol system these components may vary depending on system design. The Solar Rating and Certification Corporation (SRCC) – an independent third-party certification entity that sets equipment standards and is recognized by the government and the solar industry – recommends these systems due to their simplicity and long life. The design and components of a drainback solar thermal system (along with a detailed diagram) can be found here Draindown Solar Thermal Systems A draindown solar thermal system operates using many of the same principles of a drainback system. However, they use mechanical components rather than a simple gravity-fed mechanism. This design has proven over time to be more failure prone, and is not a recommended solution. Allow us to help you determine which solar system might be best for your situation. You can reach Sun King Solar at 505-285-5300 or 505-290-7850.