What does a Solar water heating system do?

Solar water heating systems use the free and inexhaustible energy streaming down from the sun to provide your home with hot water.  Providing renewable free energy, solar water heating contributes to reducing the carbon footprint.

How long has solar water heating been in use?

These solar water heating ‘thermal’ systems are available and have been in use in many countries world-wide for many decades now. In some of the Mediterranean countries  the law requires all new buildings to have solar heating.

Is solar water heating different from solar photovoltaic panels?

The two systems work in completely different ways and achieve different goals.

  • Solar hot water systems use the direct heat of the sun to produce hot water. The system then stores the water in a tank for your household needs.
  • Solar power systems use the light from the sun to provide the power you need to run your home. Photovoltaic (PVC) panels convert the sunlight falling on them into electricity. This electric current then feeds directly into your home grid and supplies the power to run your lights and appliances.

Solar water heating system designs

While there are a number of different systems available, all use a minimum of three basic components:

  • The sun’s direct energy.
  • A heat collector.
  • A storage system

How does the system work?

A typical solar hot water system is fairly straight forward in design.

  1. The system first uses a solar panel collector to capture the energy streaming down from the sun in the form of heat. This collector contains a solar heating fluid which the sun’s energy heats as it falls on it.
  2. When the system senses that there is enough heat available in the collector, a controller automatically starts a pumping system.
  3. The hot solar fluid then circulates from the collector through a heat exchanger which transfers its heat to the water in your home storage tank.
  4. The solar fluid then circulates back to the collector which reheats it again.
  5. The circulation loop continues as long as there is sufficient heat in the collector.
  6. At night, or during very cloudy weather, an automatic backup heating system activates to provide a continuous supply of hot water.

Types of Solar Water Heating (SWH) systems

Active Direct solar water heating (SWH) collector systems
See image (a) diagram below

These systems are suitable in warmer climates where freezing temperatures are uncommon. In a solar water heating system of this type, household water circulates directly through the solar collector into the storage tank without the need for solar heating fluid.

Various systems are used to pump the water supply through the collector into the storage tank as it is required.

Active Indirect solar water heating (SWH) collector systems
See image (b) diagram below

For colder climates where freezing is common, the most popular solar collector is the indirect flat panel design. A flat panel collector is an insulated weatherproofed panel with a high-strength transparent glazed cover. Inside the panel is an absorber plate and flow tubes. The solar energy passes through the transparent cover into the absorber which in turn heats the solar fluid circulating through the flow tubes.

The hot solar fluid is then circulated by a pumped system through the household storage tank, heating the water in the tank. Antifreeze liquid, usually a non-toxic propylene glycol-water antifreeze mixture is used in the flow tubes. This prevents the collector piping system from freezing while allowing for the maximum transfer of heat from the solar collector to the storage tank.

Passive Solar Water Heating System

The simplest type of SWH is a passive system whereby hot water circulates passively from the collector to the house supply tank without the use of an active pumping system. These systems work best in warm climates where freezing temperatures are rare.

Image source: Researchgate.Net

Where is Solar water heating used most widely?

While China dominates when it comes to Solar water heating, having over 85% of the world capacity, many countries are increasingly utilizing the technology.

In Israel, where solar water heaters became popular in the 1950’s, 90% of all homes have solar heating. A law was enacted requiring their installation in all new buildings, and in 2005 Spain adopted a similar law.

Israel skyline dominated by Solar water heaters

How efficient is solar water heating?

Solar thermal panels used in SWH systems are extremely efficient at converting the sun’s energy into heat. A good system should be able to supply a large percentage of the daily household needs over a year and is very cost effective.

In the hot Mediterranean climates, solar water heating, is an extremely popular choice. Even in the colder parts of the United States it can still be an effective and viable option.

The environmental advantages

While solar water heating is only a single-purpose use of the renewable energy that our sun provides, it continues to play an important economic role world-wide in many countries.

Considering the efficiency and the reasonable cost of solar water heating it is certainly an option you should consider.