Understanding How Thermal Home Solar Power Systems Work

Thermal home solar power systems work by amplifying heat from the sun and then transferring it to air, water, or a solution. There are a number of different thermal solar designs, however, each system is either active or passive and either direct or indirect.

The terms active and passive refer to how the home solar power systems circulate water throughout the system. An active system uses pumps to circulate water or a glycol solution through thermal collectors while passive systems rely on thermodynamics and do not use any pumps or controls. Passive systems are used most often in regions where there is an absence of extensive below freezing temperatures.

Direct or indirect refers to how the water in the home solar power systems is heated. When using a direct system, also known as the open loop, water is heated directly by the sun without the use of any antifreeze. Direct systems have controllers and thermometers that determine when it is time to heat the water. When the solar collector is warm enough, it starts a pump, which moves cold water into the collector and heat it. After the water is heated, it is stored in a hot water tank until used. Even though this thermal system circulates pure potable water, it must go through an outdoor collector, which may become a problem in many climates where there is not an ample amount of sunlight or those that are prone to freezing weather. In this case, it may be necessary to supplement solar power with electricity or gas.

When using indirect systems, also known as closed loop, water is heated by way of a pump moving a glycol solution through a loop in the solar collector, and then through the collectors piping, and eventually out of the solar collector. At this point, the glycol solution has been warmed by the sun and moves into a heat transfer unit where it warms the water. After the water is heated, it is stored in a hot water tank until used. The glycol solution will then go back to the pump and back into the solar collector. As opposed to direct home solar power systems, indirect systems can stand up against harsher climates and are encouraged for areas of frequent freezing weather.