So I see that ITS has 2 VT collectors, ones a 12 tube and ones an 18 tube.

Whats the rule of thumb regarding how many tubes are required per litre of geyser capacity?

I was hoping to get away with a 12 tube collector on my 200 litre kwikot geyser.

They told me its 1 tube for every 15 l of water you want to heat. 

So that would work out to 13,3 tubes for a 200 litre geyser. Hopefully I can get away with a 12 tube VT setup instead of the 18. I have sent Sonpower a mail, lets see what they say.

Hello Noobie,

I found that installing a roof mounted outdoor geyser with glass evacuated tubes was my best solution. It heats the water directly into the geyser, so no heat loss. Also pop in a 2kw heating element as a backup and put in Geyserwise Max, so I have the ability to monitor the temp and can manually turn on the power if needed, and for winter can put a timer in play to ensure hot water at 5am

This works very well, and I found that I only used the timer for 2 hours 3-5am in July 2015, and it typically added 2kwh to per day for that month.

The only other time we hear electrically is when cold wet and overcast for 3 days

For the rest of the year it's for free.

My only other suggestion is try and get a solar geyser with

More capacity than you typically use, so you effectively store more

Hot water, and there is less risk of ending up with cold water when you have family over.

Here again I the solar max worked well as it has two sensors, one to decide what the water temp is and heat it, the other intended for a solar manifold / pump arrangement.

What I did was to put two 150l geysers in series, the first one could be electricaly assisted and the second one is purely solar, and used the second probe to monitor the 2nd geyser.

One of the family decided to go glass evacuated with existing geyser, and pump / panel to circulate, and this works well. The only consideration is the existing geyser is not designed with the same insulation as a solar geyser and so suffers with more heat loss, even with a solar blanket, compared to my outdoor version during winter months overnight.

If you are game to self install, let me know I can suggest a site or two where buy manifolds and solar geysers.

Enjoy the journey to solar

So I see that ITS has 2 VT collectors, ones a 12 tube and ones an 18 tube.

Whats the rule of thumb regarding how many tubes are required per litre of geyser capacity?

I was hoping to get away with a 12 tube collector on my 200 litre kwikot geyser.

From my calculations it appears to be 8.33 liters per tube, so 18 tubes for 150 liter, if you buy the geyser tank with correct insulation. If you use an existing geyser with the standard 24mm insulation vs 48mm solar geyser, your water will cool faster overnight, than the solar geyser which loses around 4-5 deg c overnight in winter.

Thanks Arandoza, I would like to do a solar geyser outside on the roof and make use of the thermosyphon effect but I think it would be far cheaper to use the existing geyser.

I am going to source a couple of quotes and take it from there