PLC Programmable Logic Control and Dumping Solar Power

[myles]

Hey For all those have ventured down this road before. I know that once my solar is done charging my batteries (off grid) all the extra power that it is producing is useless. i'd like to make a PLC circuit that can tell when the batteries are in float charge state, so that it can turn on another loads panel that will power an electric water heater and an inline heater element for my floor heat.

two things, i am not new to programming or automation, but have others used a PLC in this way before? If so which one and what components did you use to sense the voltage to the PLC and use it to switch on a relay that will feed power to the other loads panel?

This is intriguing to me as I just learnt the power of the PLC today by talking to a subtrade that was working on our house. This seems the best way to control the no waste from the sun mentality i'm going for.

 

[Shimmy]

You don't need a PLC to make this happen, but it is a valid option (as would a microcontroller like an ESP32 or a device with GPIOs like a Raspberry Pi).

Your starting point needs to be to explain your system in detail-- how do you know currently that the batteries are in float state? Do you actively monitor state-of-charge? Can you interface via modbus or some other high-level protocol, or do you need to directly sense the state via current and voltage measurements?

pinging @GXMnow as he has experience on the PLC side for PV. @400bird has used a Raspberry Pi for a similar solution.

 

[myles]

Awesome I have way more experience with rpi and esp32 (especially particle firmware) I think I'll stick on my own field.

My system is 15kw solar into 3 growatt 5000es-us. 4 banks of 280AH lifepo4 48v controlled by chargery and TE kilovac contactors.

I have also an 8.5kw propane backup generator hooked up to a separate growatt 5000es-us. I use the dry contacts in this case to trigger when the battery reaches low state of charge to auto start the generator and let it run to charge the batteries.

I figure we could use the dry contacts on the growatts to determine when batteries are full

 

[Shimmy]

You will have a much more elegant solution if you get analog inputs rather than binary... and that will be much easier to do if you can do it via serial communications.

Knowing that as you approach 90% SOC at a specific time of day that you will have enough energy for the night... as well as hot water... is kind of liberating.

 

[myles]

You will have a much more elegant solution if you get analog inputs rather than binary... and that will be much easier to do if you can do it via serial communications.

Knowing that as you approach 90% SOC at a specific time of day that you will have enough energy for the night... as well as hot water... is kind of liberating.

I'll have to check out the rs232 and BMS outputs on the growatts and see if that language can be used.

 

[meaCulpa]

U could buy a cheap MakeSkyBlue CC and install my hack and go from there..MSB already has a 'load' output available for doing exactly what u want.. divert PV to a load when battery is full..
here's my mod.. attached..I used Adaruit QT Py micro--

 

[timselectric]

A Victron smart shunt with relay (i don't remember the model number, maybe 712) is a simple solution. And what I will be using.

 

[myles]

Thank you all for the input i'll be exploring all the options and report what I end up doing! :D