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Dear "home improvers" I would like to create my own solar heating system for spa (intex 28456, pure spa jet & bubble octagon deluxe). This spa has its own heating system together with salt water chlorinator.

Because of I dont want to modify this system I thought about new system with the solar heater only.

I found some DIY projects and I inspired myself with them. But I do not know how "big" the solar system needs to be. Some projects has 120m, some of them 50. The intex spa has 1075l and "normal" temperature is around 25°C. I know I need increase the water temperature about 10°C. There are 2 possible solutions, have a "closed" water circulation system with some spiral at the end that will heat the water inside the spa, or "classical" solar system where one end will be intake for the water and second the output. I think the second solution will be better and quicker (but I am not sure). How much "panels" of what length should I use? (I would like to create them by my own, use PEX pipes, painted black with some glass in front of them - usual solution).

But the biggest problem for me is the pump. I would like to use some 12V pump, so I can use solar energy panels in future for it. The solar panel (for water) will be in 2m height, and they will be (depends on first question, how much panels of what length will i use), but for example I will have 100m of pipe in 2m height (in compare with water surface).

On aliexpress, there is plenty of 12V pumps with 800l/h and 5h head height. Those are specs only, in real, I guess that pump will have something around 300l/h (that is enough i think) and 1.5h head. That means, it will not be enough to pump the water inside the system. Do I need to count the length of the pipe that will lie on the floor "horizontaly" as well (it will lie on the floor in ~15° and its dimensions for 1 panel of 50-100m will be around 1.5x1.5m... Long story short, can anyone advice what pump should I use? And can anyone advice me how can I count (or estimate) the pipe length neccessary for the system?

Last but not least I would like to understand, someone is using "serial" connection of more panels. Someone is using parallel. What one is better and why?

How long will take the water to heat (inside the system)? for example temperature on the intake will be around 25°C, I would like to heat it on 50°C, air temperature will be around 30°C (sunny day). If I heat 50% of the water inside the spa on 50°C, the water will mix into something around 35°C (it will get cold a little bit with time). If I use for example 100m pipe (3/4"), the volume of this pipe will be around 0.11m3, so 110l. In this situation i need heat 500l, so 5x fully drain the system. But I have no idea how can I estime how long it will take to the water to heat inside the 100m pipe.

Thank you very much for advices (my first bigger and useful "diy" project)

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    One rule of thumb for a swimming pool is that the amount of solar panel is equal to the surface area of the pool but if you want to increase the temperature more then increase the amount of panel. There are software packages available to help if you search.
    – Solar Mike
    Jul 31 '19 at 10:48
  • @SolarMike ok, but how much will panel of this size heat that spa? Thank you very much Jul 31 '19 at 15:36
  • Maybe I missed it but what zone are you in (location). This has a bearing on the type and size of collector.
    – Ed Beal
    Aug 1 '19 at 16:24
  • @EdBeal I am located in Central Europe (Czech republic). Usual temperature in summer are around 20-30°C in the shad, on the sun it can go up to 40°C... We have those temperatures from the end of May till October or something so... I will use that heating system (and spa) only in the summer. Aug 2 '19 at 9:23

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