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Solar Heating feeding a Gas Geyser

Peter Topp

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My system consits of 20 vacuum tubes heating a small reservoir. The reservoir feeds a standard 150L geyser.

The feed is done with a 12v pump which only feeds when the difference in temp is above 4 degrees. A geyser wise kit will do the job.

My geyser feeds a 20L variable force feed gas geyser which does need electricity to work.

I do it this way to save on gas as the gas geyser can regulate the temperature and use less gas when the geyser is hot and also have a constant temperature.

I also have a 2kw heater installed in the geyser and have wired it so that if all fails I can still use the element to heat the water.

I do have grid tied inverters and a generator so I do not have any problems during a power failure.

I had to modify my geyser so that I do not have cold water circulation problems when the pump is circulating.

This mod is done with a heatpump kit that adresses this problem.


At the moment I am only using the gas geyser as lightning has damaged my solar controll X2.

I will be changing the solar controll to a geyser wise on the 5th of January through my insurance.

The system can also bypass the geyser and only use the cold water supply.

Attached are photos  and electrical circuit of the system.

20L Atlas Force Feed Gas Geyser.jpg


Solar Panels2.jpg

Solar Gas and Electrical Heating Electrical Diagram.jpg

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Water Flow Diagram and explanation of Solar feed to Gas Geyser


I have eventuaty drawn out the water flow diagram for the system and is now posted .

How does it work?

The solar controller allows the pump to to circulate the hot water to the standard 150L geyser when there is a 4 degree hotter difference in water temp on the roof.

This system does not allow the water to circulate all the time. 

The pump will also switch on if the roof temp water is below 4 degrees to allow hot water in the pipes so that they do not freeze up.

There is also a timer in the control box that can be set to heat the water with the element when there no sun or at night.

I have put a switch in this circuit near the gas geyser and only use the element if I run out of gas or there is a gas geyser problem.

They system is designed is such a way that I can use any of the systems individualy or combined.

Because I have a 20L force feed variable gas geyser (Atlas) you can remotely set the temperature of the heated water.

If the water is warm  before it can be heated the gas geyser the gas geyser will use less gas and the temperature will be constant.

Threre are gas geysers that are specifically made to allow solar geyser input. 

The 20L Atlas gas geyser I have does not state that it can handle hot water from solar, however it does do the job well and is less expensive.


The mod I  spoke about in the post is only for when you use the solar geyser without gas.

What would happen is when you are showering and cold water intermitently would spoil a hot shower.

This is caused by the circulation pump switching on during the shower.

The circulation inlet and hot water outlet in the 150L geyser are close together and the cold water in the pipe from standing would go staight to the outlet.

The fix for this is to allow the circulated water to enter  only in the middle of the 150l geyser. This done by changing the position of the safety valve and hotwater outlet around and fitting a pipe that reaches to the center of the geyser. This mod is also used for heat pumps.

There are a number of things that might influance the system.

If the feed water is too hot it can switch off the gas geyser as it has a sensor to protect it.

My solar system is not efficiant enough to reach above 75 degrees at best on a sunny summers day and does sometimes switch off the gas geyser.

This does not cause any problems.

Hot water systems are also not made to withstand boiling water.

I hope I have supplied enough information.



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Working with Solar Vacuum Tubes

I have a interesting story to write on about during the installation of the solar heating system.

When the vacuum tubes were installed on the roof they are individual pushed into the reservoir.

One of the 20 vacuum tubes tip was accidenty  damaged and it was not found during installation.

The following day at about 11am there was a huge bang and it sounded like a gunshot. I later had neighbours asking what had happened.


Well what had happened is that the vacuum tube that was damaged at the tip had lost its vaccuum and had filled with air.

When it was installed the tip was now sealed off.

When the sun heated the tube without vacuum and the air and other material inside started to expanded and eventually caused the tube to explode.

I found pieces of glass 10 meters away.

So beware when you install  solar vacuum tubes to check for any damage.

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  • 2 weeks later...
  • 3 years later...

Hi Peter - I have the same setup, and get an itermittent "En" - Yes - not E1 or E2, but En (E with a little n) error on the Atlas display. Any ideas ?

I have a Geyserwise to circulate the water between geyser and roof-top tubes, but find it is actually quite noisy - It's in the roof above my bedroom - I don't normally hear it unless I'm having a Sunday nap 🙂

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  • 1 month later...

Hi Guys


I am deciding on the following :

Option 1 : Replace my Electric Geyser with a 26l Paloma

Option 2 : Removing the Element from the Electric Geyser and adding a Heat Pump


My Current Geyser Setup :

1 x 200l Solar Geyser with Tubes, Feeding into 1 x 150l Electric Geyser which feeds the house,


My Solar Setup :

2 x 5.5kw Sunsynk Inverters

2 x 3.6kw Pylontech Batteries

18 x 330 Solar Panels

I plan to add 1 more Battery and Maybe a Wind Turbine(A Whole new Topic).

The Idea is to go off grid or as close to off grid as possible and not to depend on Eskom.


My problem :

My Electricity Bill is currently 3k per month. Family of 6 + 2 Domestics, Everyone showers at different times, Hot water is being used for Mopping floors, Washing clothes, Dishwater, etc (its out of my control) Every time someone opens the hot water tap the geyser element kicks in, Unfortunately I cannot change the habits of how they use hot water, 


I should also mention that i have a Gas Hob and Gas Fireplace.


My Solution :

Option 1 : Let the Solar Geyser feed the Gas Geyser.

Pros - Hot Water on Demand, Hot water during Load Shedding, Saving on my bill,

Cons - High Gas Bill??? and??


Option 2 : Let the Solar Geyser Feed the Electric Geyser, Remove Element on Electric Geyser and replace with Heat Pump,

Pros - Saving on my Electricity Bill 

Cons - No Hot water during Load Shedding or Power Outages, Unless its connected to my Solar System but Will Probably drain my Batteries during the Evenings. Also it still uses some Electricity.


Please note - the Element on the Solar Geyser is Switched off.


Looking forward to the feedback.

Edited by Rehaan
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