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@jerzone@techhub.socialFor those following the solar hot water project it got assembled this morning, flushed with water, checked for leaks, emptied, and then pumped full of a glycol/water mix. The motor purrs like a kitten as it circulates the liquid through rooftop collector and heat exchanger at bottom of 120gal storage tank.
The solar controller is checking bottom of the tank and comparing it to collector. When I plugged it in:
top of tank: 120° (heated by electric earlier)
solar collector: 102°
bottom of tank: 57°
In last twenty minutes the bottom of tank has risen to 70° and collector is up to 115°.
#SolarHotWater #electronics #homerepair
@jerzone Congrats!
In my days I made the controller with a PIC16F84. Since 2017 it runs on an STM8 with STM8-eForth.
@tg9541 I haven't cracked open the old solar controller to see what kind of brains it has. From the 70’s/80's time period it might be pretty simple. Then again it has been doing its job for over 40 years while my little ESP32 circuit to send temperature to home assistant just broke a wire because I don't have it in a case and it's still on a breadboard! “:^)
@jerzone solar heating controllers are indeed very simple and the can be made with a quad op-amp (when you're generous). Using a µC, however, can do linearization, electrical failure detection, overheating protection (boiling!), or gravity-temperature inversion detection. It can also support monitoring, e.g., through an ESP32.
I would build something simple and robust, a reliable, low risk approach, with "wireless" loosely attached.
My code, in Yoda-Speak is here: https://gist.github.com/TG9541/47ded721f209c48f3aee7562ee18b9db
@tg9541 Thanks for the link, also checked out your hackaday post. It would be nice to tie into the day’s forecast to decide if the electric heating should be enabled or not. Right now my computer desk is close enough to tank that I can hear electric kick in and go flip off the breaker if it's a sunny day. ":^)
@jerzone Yes, knowing the weather forecast would be useful. For the general probability of sunshine, date and time might be sufficient.
Loose coupling to external services is key. It should still work when the web service silently dies.
My last house had glycol solar hot water, with the panel consisting of those evacuated glass tubes with coated metal strips inside, and I dearly miss it. I was able to turn the propane water heater off, completely, from ~ April 15 until Nov 1st or so.
@Geojoek That’s typically the range I turn the electric portion of tank off, with a few exceptions for long stormy weeks. I've had my eye on those glass tubes, but the existing panels just keep working.
Nothing wrong with working with what you got! My landlord / old house had a very similar set up to yours, with an overflow tank for excess heat. He had that circulate into radiant floor heating loops running through the concrete slab in the basement, to keep it above dewpoint in the summer and combat condensation. Ingenious setup, and, as a whole, used almost negligible electric compared to my current barn, I mean, house.
@Geojoek I probably should have some method to vent excess heat from the system in the summer. Our storage tank can get really hot and shut off the pump at some point, which means the glycol is just cooking in the panels, which probably shortens its life (a guess). If I had a vat of phase change salts (waves hands in air dismissively at details/reality) the heat could be stored for winter. Failing that maybe preheat water for distilling or something.