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Solar Water Heaters

Updated: Jan 16, 2021

The sun is the world's largest and most accessible source of energy. In any case, like other sources of energy, it has to be 'mined', 'extracted' or 'processed', otherwise, it is the freest source of energy.

The light from the sun can be used directly, as thermal power, or with the help of photo cells and other electrical systems. Thus, solar water heater or domestic water heating or 'hot water' systems can work in two ways: either with direct sunlight or as an appliance that uses a solar power system. In the later case, a water heater is merely connected to a solar power inverter system as an appliance as long as its capacity is within that of the inverter system. Such a system, otherwise an 'inverter water heater' can also be incorporated into an inverter form. Pictures of such inverter water heaters are shown below.

The water heater inverter aside, the most common type of technology used in making solar water heaters is the solar thermal energy. Solar thermal systems use energy directly from the sun to either heat water and any other liquid. In this set-up, the solar-panel and inverter system is replaced by a 'solar thermal collector'. The solar thermal collector is similar to a solar panel system but it is an entirely different equipment.

How Solar Water Heaters Work

Solar thermal water heaters are designed to

  1. Absorb sunlight

  2. Transfer heat from the absorbed sunlight into water

  3. Store the heated water in a tank, and

  4. Keep the tank warm using insulation. Thus, they are able to work at night.

  5. Also, they have measures to protect them from freezing and overheating.

Also Read: Solar Water Pumps


A solar water heating systems may be active or passive.

An active SWH will either: circulate heated water from the collector and into the homes or they may use a heat exchanger to heat a non-freezing fluid (water is a freezing fluid) and then circulate them into the home. The first type are meant for climates where it rarely freezes while the second type is meant for climates with freezing temperatures in the year.

A passive SWH, though less efficient but more reliable and with a longer lifespan, is usually designed in two forms: One, a collector is used and alongside a storage system for the heated water. Or two, a thermosiphon is integrated into the system. A thermosiphon, which works like a chimney and uses the natural ability of fluids to rise and flow when heated, removes the need for a mechanical pump. With a thermosiphon, water flows through the system when warm water rises as cooler water sinks. In this situation, the collector is usually installed below the storage tank so that warm water will rise into the tank.


The Solar Thermal Collector

A solar collector collects sunlight by absorption. They look very much like solar panels but are entirely different in operation. They are two main types of solar collectors and modifications.

1. The Flat Plate Collector They contain a dark absorber plate under one or more glass or polymer covers. They may be covered or left open.

A Flat Plate Solar Collector

2. Evacuated-tube solar collectors They feature parallel rows of transparent glass tubes with each tube containing a glass outer tube and a metal absorber tube attached to a fin. They are the most popular type of solar collectors though they are regarded as generally less efficient than flat-plate collectors.

An Evacuated-Tube Solar Collector

Storage Tank

Alongside the thermal collector, the second major component of solar water heaters is the storage tank. Most solar water heaters require a well-insulated storage tank. Solar storage tanks have an additional outlet and inlet connected to and from the collector.


Pumps serve to create the pressure that will circulate the heated water. Of course, a solar power system is often incorporated into the SWH to power the pump. Bubble and vacuum pumps are also incorporated into the systems as are thermosiphons. Thermosiphons remove the need for mechanical pumps. Most SWH use the thermosiphon.

A Thermosiphon Attached to a Collector

These components can also be used to heat air for ventilation purposes. They can be modified to serve as heliostats, that is devices that concentrate sunlight to solar panels and by so doing produce increase their production. But of course, this is in places where the sunlight is low. Also, they are used in the construction of swimming pools.

SWH are very important in Europe, Australia, Asia and America. For instance, from 2006, in Spain, every new residential building is required to install a SWH alongside a solar system. In Israel for instance, 85% of the total households use SWH. The reasons are obviously due to the lower temperatures in those areas. Since Nigeria receives a far higher amount of sunlight all year round than the countries where these SWH are manufactured, they are not a great consideration. But of course, in the case where they may be, for instance, in the construction of swimming pools, our engineers at SolarKobo will help you make the right choice.

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