Solar Water Heaters and How They Function

Solar water heaters are equipment that emerged from the growth of solar energy technology. There are two kinds of solar water heaters: active and passive solar water heating systems. Active solar water heaters are more prevalent in countries with very cold climates.

This article will be discussing how these active solar heaters work and the types of active solar heaters.

How Active Solar Heaters Work?

These heating systems have solar collectors. They are typically installed on a roof. They use a heat-transfer liquid to absorb solar energy. This renewable energy is then converted into heat energy. This conversion is carried out when the heat transfer liquid is pumped via a heat exchanger, which transmits this heat energy to the water heating system.

The function of the heat exchanger is preheating the water flowing into the traditional water heater. This ensures that it lessens the energy required to heat it to the preferred temperature.

Types of Active Solar Heaters


The common types of active solar heaters are Drainback systems and Glycol systems.

Drainback Systems

These heaters utilize pumps to move water between the solar collectors and the conventional water heater in your house. The water instantly drains the solar collectors into a reserve tank when the collectors become cold, and the pumps are powered down.

drainback system
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Glycol Systems

These solar heaters trap and store heat energy in a closed-loop containing antifreeze (propylene glycol) solution. A heat exchanger transmits the heat energy to the incoming water.

Comparisons between Both Active Solar Heaters


The drain-back system is more efficient in heat transfer because it uses water instead of glycol.

Market Value

The drain-back may be more costly than the glycol system because it requires a reservoir tank. On the other hand, the glycol system may cost you less initially but periodically requires glycol replacement.


The drain-back system is harder to install. This is because a thorough installation needs to be carried out to ensure that the water automatically drains when required without hassle. On the other hand, glycol systems are easier to install because the positioning of pipes and collectors is not imperative to freeze protection.


The drain-back requires very little maintenance on an annual basis. It’s almost maintenance-free. On the other hand, the glycol system requires the replacement of the glycol at least every two years.

Solar Collectors

Solar collectors mainly come in two varieties. They are:

  • Evacuated tube collectors
  • Flat plate collectors

Evacuated Tube Collectors

This collector comprises several insulated glass tubes placed in parallel rows. Each of these rows contains a small absorber pipe. This receives solar energy and transmits the resulting heat energy to a glycol or water solution.

Flat Plate Collectors

This type is available in two varieties: glazed and unglazed.

The glazed versions are made up of solar heat absorbing plates placed within several copper tubes. These tubes are contained in a glazed insulator box. When solar energy heats the fluid in the tubes, the glazing lessens the volume of heat escaping while protecting the panels from humidity and other contaminants.

The unglazed versions absorb greater solar energy but allow more heat escape. As a result, they work best in seasonal conditions, such as heating an outdoor pool in the summer.