I have a 2000 liter cement (handbuilt) water tank that is located under my house but is above ground. It provides cool, refreshing water in the hot summer months. BUT, the water is rather cold in the winter. I'd like to use my south-facing roof to test out a thermosyphon system - only to warm the water in the tank, not make it hot.
I was thinking of painting some pvc pipe black and then run it from the bottom of the tank (coldest water) in a single line up to my south-facing roof and then directly back down to the top of the tank. The pipe would have to run about 35' to the top of my roof and then another 35' back to the tank. If anyone out there has any experience with this sort of thing, I'd be interested in picking your brain.
Thanks

Thermosyphon used to be used to cool down a water cooled car engine before water pumps were used,works on the priciple of rising heat,so as the engine got hot ,the water would rise via the top hose off the cyl head to the top of a radiator,then filter back down as it cooled,hence the large sized rads in early cars....You need to do the opposite you need a pump to send the cold water up and maybe send it through a couple of
Solar heating panels which will warm it as it returns to the tank...not particulary a cheap option for warming/heating water.
Personaly I'd buy an Instant Hot water heater. 3 or 4KW if you want to run a shower or 6KW if you fancy a bath

The other option might be to buy a stainless steel holding tank to put outside where it will heat up during the day,but I think the small electrical heater for showers is the cheapest way to go!