We have a pool, 20 m3 of nice cold water. I want the water even nicer and warmer so I need a heater. I am Dutch and a cheap ass so I am not going to invest in a fancy electric heater or something similar. Because of the size of the pool solutions with woodburners etc. seem tricky. The sun is free, and with thin walled PE tubes you can get pretty decent temperatures. Pump the water through a tube and we have warm water. There are plenty examples here and elsewhere on the interwebs. I made a prototype with a 25 meter roll of thickwalled PE tube I had in the shed, and the result was promising. Lets make things better then!

Supplies

100 meter thin walled PE tube, the type used for driplines. € 17,00 Amazon

T-joints and straight angles About € 20,00 Local hardware store

A submersible pump, online from about € 30,00 If you hook the system to the pools filterpump you don't need this, I had one so I use it.

Hose to pump cold water into the heater and warm water back to the pool. I used 22 mm garden hose I had laying around.

Step 1: Preparations

I want 2 heaters with 10 tubes so I cut the 100 meter roll in 4,5 meter pieces

I also cut small pieces to connect the joints

Step 2: Connect

Connect the pieces. I advise you to use gloves since you need a lot of force to shove the tube all the way up over the barbs. This is important since you do not want leakages.

Hook everything up. First the top parts and finally the long 4,5 meter long tubes

Step 3: Action!

Connect one part to the hose coming from the pump and connect a hosw on the other side that goes back to the pool.

Succes!!! The system works perfecty. On a normal sunny day the pool gains 3 degrees celcius per day. Seems like a bit, but in 4 days I went from 14 celcius to 26 celcius, Sweet!!!!

Next steps, maybe:

Make a structure to hold the subes at an angle for optimal result. Maybe even a casing....

control the pump with an Arduino and a relay. Switch on if there is enough sunlight and when the water temperature is below a certain threshold and switch off when there is no of not enough sun to prevent the heater becoming a radiator leaking the heat and start acting as a cooler. Should be simple enough...