Well, I have now been monitoring my solar geyser and water temp for some time, and note there is a large drop in water temp during the night.

Now my geyser is mounted outside on the roof, and horizontal as the supplier recommended.

 

To understand this problem a bit better, we need to look at what is happening with the water inside the geyser.

Basically hot water moves to the top and cold water settles to the bottom. Between the top and bottom, we have water ranging from hot to cold.

This is basically the principle on how thermosypen solar water heating works to create water flow without a pump.

 

In my opinion, the horizontal tank have more surface area where this mixing can happen, so when cold water comes into the geyser, it cools down way quicker than with a vertical geyser.

Should a normal vertical geyser not be more economical than a horizontal one???

 

 

 

I resolved my water mixing issue by having 2 smaller solar geysers connected in series. Having the 2nd geyser feeding the house, only receiving hot water from the 1st, thus no cold water mixing with hot water when using 1 big solar geyser.