this post was submitted on 22 Nov 2023
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Can confirm the solar water heating works great, if it's sunny you get 60°c water by noon.
My concern is legionella. If you don't get enough sun and the water temperature stay at ~45°C for extended amount of time, isn't the water tank became an ideal breeding ground for legionella?
Powered solar heat pumps sanitize themselves once a week if temperature doesn't reach 70C at least once. Same for heat pump boilers, they are usually set to 50C but goes up to 70C weekly.
On solar, there is always a downstream heater that can heat cold water to 60C+ and must be set at least that high for legionella. My setup is like that, unpowered solar tank for free heat if available, and gas boosts it up to safe temperature and does all the work in the winter.
Chlorine is also pretty effective at killing Legionella.
It is helpful to have backup heat when using solar is sunny days are not plentiful.
https://en.m.wikipedia.org/wiki/Legionella
The tanks can be set to bring the temp up to 60° specifically to prevent this.
That's great! Good to know. I remember staying at a hotel in rural Mexico where they had a cistern on the roof. Basically just a big metal tank, and even that thing heated enough that it was comfortable to shower when I'd come back from the beach in the afternoon. So it doesn't surprise me that a purpose-built water heater could do quite well.