I used to have a solar water heater for my swimming pool, and it had a wax-actuated valve (!) When the water in the panels was hot enough to melt the wax, a paddle could start turning, and water could flow in the panels. If the water cooled, the wax would congeal and the paddle would "freeze" - blocking water flow - the pool circulating pump had a pressure regulating valve and relief valve, so when the panels on the roof were not accepting water, the pump would bypass them and deliver water straight to the pool without heating. I thought it was quite clever (the wax and paddle assembly were inside a sealed device - I never actually saw how it functioned, only recall the vendor explanation). I have not seen a comparable invention in several internet searches over the years.
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Do you by any chance mean this type of valve? https://en.wikipedia.org/wiki/Wax_thermostatic_element I must agree, it is quite ingeniously thought of
I am not sure if that is the same; the assembly on the solar panel was larger diameter than the rest of the piping system perhaps around the size of a two-inch PVC ball valve, where the rest of system was (if I recall right) about 1-inch or maybe 1.5? But I guess there could have been a component like this inside. I am familiar with these for automotive thermostats in cooling systems, but I never pictured that they might have meant this. Otoh, why not? It would do the job and maybe work for OP's project; especially if they are made for a range of different temperature conditions.
A way to switch to Celsius would be nice 😅
I guess the pond isn't deep enough for water stratification to effect the temperature at the bottom?
Yeah I'll definitely add Celsius! It's funny I'm using Kelvin and Celsius internally, but the people it's for are very Fahrenheit dependent.
As for water stratification, it's actually on the shore of a 30ft deep lake! It's just so close to the surface that it doesn't really matter here. I want to try and measure stratification, but I would need a long cable to get far enough out. Do you know of any temperature sensors that would work well over 100ft of cable?
Yeah, I only looked at the images after posting.
Sorry, no idea about these kind of sensors. But maybe someone else here has an idea.
Neat!
Nicely made! You have a small lithium or lead battery in there? Also can you read the voltage of the battery the whole year? I am interested in the survivability on the winterdays. I am living in Lithuania where the winter sun hours are very short and sometimes with days of overcast. But i would like to build solar powered tech that can survive in winter. Also interested in using capacitors instead of chemistrial (if thats a word) batteries.