We have solar hot water I just got a larger one a few weeks ago the reason you need a pressure tank is because you have a pressure system for your house. I have a solar system for sale it is 12 tubes & 115 liter tank it is good for 3or 4 people I can show you the way we hooked ours up it is very easy & It is nice to cut out a lot of gas .The reason we changed to a large unit is more people come to see us in the winter months . there is nothing wrong with the older unit 7 I will sell it for $ 300.00 US, or whatever the peso is that day . the brand is thermos .call if you want to see the unit or just want to see & learn.7664973