Solar water heater boost control.

First, some background. My solar water heater boost element was initially connected to night-time tariff. This would be fine for anyone who uses most of the hot water in the morning but otherwise, the unit would be full of hot water and the next day’s sun’s rays would be wasted.

Being an electrician, I made my own timer setup – the idea being to boost as late as possible to maximise the sun’s input and be at full temperature by 7pm at which time we start using hot water.

The timing of the boost has been a bit of a guessing game and so the idea of micro-processor control was born.
My first attempts were with Arduino but it simply doesn’t have the capacity for all the required functions.

So, time to explore Raspberry Pi… and being an absolute newbie to Pi, Linux, Python etc, etc, any suggestions are welcome. I have ordered a Pi, a digital temp sensor and a relay.

Here goes with the framework:
The Pi will measure and record the water temperature at X minute intervals.
It will activate the relay for 10 seconds at a time to be determined.
It will determine and record the length of time of the boost.
It will have a 16x2 lcd to show current temperature (and boost status?)
It will act as a server so that the data is accessible on the LAN.

Once I have some data, I can begin to make an algorithm to start the boost at the optimum time.

I’m not looking to learning coding in a big way, simply finding what works for this project, so, again, any hints or tips will be most welcome.

Cheers, George

Hi George!

All of this is achievable with either an Arduino or Raspberry Pi! The bad news is that it will definitely take a lot of coding. We have workshops and tutorials that will guide you through all the steps you need to get it done:

To make the project easier on yourself I recommend searching around for similar projects and seeing if you can mix and match them a bit to get the results you want. I found this great Raspberry Pi project that is well documented that offers most of what you are looking to achieve and much more:

This one is simpler but still good:

Here is a similar project for arduino:

I hope that helps! Be sure to share your finished project on our project page! This is the sort of thing that many people could benefit from!

Wow, thank you very much, Stephen, for your time and effort to
put this reply together.

Now its time to start reading and trying to absorb it all!!

Cheers, George.

  Oh, and I will report in to the forum from time to time to share

how it is going.

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Hey George, any update about your project? I am looking for something similar with my solar water heater. Please share it when you are done.

Hey William,

Welcome to our forum!

Hopefully, George will still be able to access the information in order to provide an update about the project. Although, it’s worth noting that this forum post is more than two years old now. If there’s anything that we can help you with here please let us know. :slightly_smiling_face:

Core Electronics | Support

Hi everyone,
I’m so sorry I didn’t follow through with updates on the project - however, I found it to be quite specific in the way it needs to be wired and connected with the solar hot water service and in the switchboard… I wondered if anyone would ever go to such bother.
I am an electrician so I had no problem with that part but for someone else to get an electrician to do this work it could become expensive because initially the electrician won’t understand what she/he has been confronted with.
I am more than willing to explain it all and pass on my code but it does get a bit complex when hooking it all up. [In this country] we are dealing with 240v. Wiring and fitting contactors [relays] has to be done to the AS 3000 wiring rules. Because we are making a connection to the down-stream side of the water heater’s thermostat, that too has to be connected through a contactor to eliminate any possibility of applying power back directly to the boost element. Still with me?.. Now we need a power supply, 12v will do as long as it matches to coil voltage of the 2x pole contactor which will power the HWS, and a few more relays to hook it all up.
My rig has been up and running for a while now - it works a treat!! I have the thermostat set at 70 degrees and a target set for boost complete by 7pm. Is it usually very close to that time and only varies because of ambient conditions.
The rig sits on a small computer desk in my rumpus room and is very close to the switch board / meter box outside so my wiring is short. I wired the temperature probe into in the HWS with Cat6 cable, sharing the cores with the 3 of the probe which helped a bit to reduce voltage drop. Even so, it took a bit to get calibrated.
I hope that helps. William, if you want to go further, please give some details of what you want to achieve and I’ll do my best to help.
Cheers, George

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