Basics of Solar Water Heating
The drain-back system is another common cold climate system. With this system, the water in the collectors and exposed piping drains into an insulated drain-back reservoir tank each time the pump shuts off. Removing all water from the collectors and piping when the system is not collecting heat provides a fail-safe method of ensuring that collectors and the collector loop piping never freeze. In warmer climates, direct systems are more commonly used. The direct system circulates potable water directly through the solar collector into the storage tank. In other words, the water that is used in the house is the same water that has circulated through the solar collector. These systems incorporate various strategies to control the operation of the circulating pump, which can include photovoltaic or differential controllers. Passive direct systems are also used in warmer climates. The unique characteristic of these systems is that they do not use pumps or other electrical components, thereby providing a simple and reliable system. The most common passive systems are the thermosiphon and integral collector storage systems. Indirect thermosiphon systems could also be used in colder climates. With regular inspection, the system will operate for 20 to 30 years with minimal maintenance and costs.