Solar Geysers
SWH - Solar Water Heater
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Glass Evacuated Tubes
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Flat Plate
Different Solar Geyser Types

There are two different basic types of Solar Geysers: the so-called ‘Flat Plate’ and the ‘Evacuated Tube’ type. Both work very well. The Flat Plate is the older technology, but slightly cheaper and is still very much preferred by most people.

Flat Plate Collectors

Flat Plate collectors are the most common solar collectors for use in solar water-heating systems in homes and solar space heating. A Flat Plate collector consists basically of an insulated metal box with a glass or plastic cover (the glazing) and a dark-colour absorber plate. Solar radiation is absorbed by the absorber plate and transferred to a fluid (water) that circulates through the collector in tubes.

Flat Plate collectors heat the circulating fluid to a temperature considerably less than that of the boiling point of water and are best suited to applications where the demand temperature is 30-70°C (86-158°F) and/or for applications that require heat during the winter months.
Evacuated Solar Tube Collectors
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Basically both technologies offer the same configurations

a) Thermosiphon
This is the most basic system. The geyser is placed higher that the heat exchanger. It works on the principle of warm water
rising and colder water going lower. This is an automatic process and as a result of this, the water is circulated between the heat exchanger and the geyser. No extra pumps, etc is required.

b) Split system
This configuration allows the geyser to be inside the roof or lower than the heat exchanger. However, this configuration needs to have a pump to circulate the water between the heat exchanger and the geyser. A control display is situated inside the house with the required information about water temperature, etc. It also allows switching to Eskom power with the press of a button, should this be necessary in extreme conditions, such as the entire family staying over for a weekend.

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Split System
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Control Display



Evacuated Tubes

c) Retrofit

If the existing geyser is less than 3 years old, a SWH system could be fitted using the old existing geyser.

Various other options are available, such as Pre-Feeder configuration, low pressure systems, etc.

It should be noted that the Eskom element can also be installed to serve as a backup, should unforeseen circumstances

require this, but over time it has been proven that this is very rarely required.


Power@Once can install both Flat Plate and Evacuated Tube SWH for you in any of these configurations.

Different configurations

  This is based on the evacuated tube SWH’s


No of

Hot Water Supply
(litres at
60°C per

Number of

100 10 120 1-2
150 10 120 3-4
200 20 240 5-6
250 20 240 6+
Guide to the size of geyser to choose

These look similar to Flat Plate collectors from the outside, but the panels contain a series of glass tubes which are evacuated and have very efficient heat conductors attached, trapping much more of the Sun's radiant heat. These are more expensive and involve a heat exchanger in the hot water tank to circulate water in the home.
Often, more than one panel is used in these systems. Thermostatic controls prevent hot water from being returned to the panels and so save energy by not pumping water unnecessarily.

Which is the best? : This is a personal decision, as both technologies have pros & cons. Evacuated Tubes reach higher temperatures and heat up faster, but are more fragile and have a lesser lifespan. Flat Plate collector panels are more durable and will last longer (with a bit of maintenance - the glycol needs to be replaced every few years), but reach lower temperatures.

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