How Solar Hot Water Works

Solar thermal panels, also known as solar hot water collectors, transfer heat energy from the sun to water.Solar water heating systems are connected to an existing domestic water heating system. In the event that the solar storage tank cannot meet hot water demand, the existing hot water heater is used.

Pressurized Anti-Freeze System

  1.  In an active, indirect heat-exchange closed loop system, non-toxic polypropylene glycol or anti-freeze is used as a heat transfer fluid. An anti-freeze solution works well in climates with freezing temperatures.The heat transfer fluid circulates through solar collectors, capturing and storing solar heat energy when the solar collector is exposed to sunlight.
  2. A single pump moves the glycol through solar thermal collectors, allowing it to collect heat energy from the sun.
  3. After making its way through the collectors, the glycol continues through a heat exchanger, which transfers heat energy from the glycol to water in a storage tank.


Because the heat exchanger transfers heat from the glycol to potable water in the storage tank, these two liquid substances never mix.The circulating heat-collection fluid operates in a pressurized self-contained loop, with very little or no noise.This type of closed-loop system requires additional maintenance, as the polyproplene glycol must be changed every 3 to 5 years.

Drainback System

  1. In a drain back system, water is used as a fluid heat collection medium. Distilled water not only provides excellent heat transfer, but also does not allow for minerals to deposit. Water circulates through solar collectors, capturing and storing solar heat energy when the solar collector is exposed to sunlight.
  2. When the system is not actively collecting heat, the circulation water is drained out of the collectors and piping, into an insulated reservoir tank. This prevents the water from freezing in colder weather conditions.
  3. As the sun comes out and heats the collector panels again, a differentially-controlled pump engages. The pump moves the water out of the reservoir tank and back through the collectors, so that more solar heat can be collected.


The circulating heat-collection fluid in this system operates in a non-pressurized closed loop, only moving between the collectors and a heat exchanger. The heat exchanger transfers heat to potable water in the tank. Nominal operation noise is evident in non-pressurized systems. Drain-back systems require less maintenance compared to other closed-loop systems; because water is the heat transfer liquid, it does not require periodic changing.