I have a non-pressurized (gravity driven) open solar thermosyphon hot water system on my roof installed like this:
Cold water is fed through a float on the top, dropping the level opens the valve. Hot water is sucked in somewhere in the lower 1/3 of the 220l tank.
Here is my situation: At the end of a cloudy day I have roughly only 45C degrees temperature of the water and if I am not to cut off the cold water filler, it will soon become too cold for a shower. Therefore I turn it off and use 45 degrees C of water until the tank is empty. I'd like to have knowledge though how much water I have in the tank left.
I was thinking of attaching a water pressure sensor at the hot water pipe, but these seem a bit expensive. I have access to the tank (it is open) from the top, where the cold water filler is, so I can insert a wet probe there too.
I am looking for reasonably priced sensor to read the water level in the tank, any advice is welcome.