I have a solar inverter (Fronius Symo 15.0-3-M) and a pool heater (AstralPool Heat II). I want the heating to turn on when there is excess power from the solar power station so that the excess electricity don't go back to the grid. So to achieve desired outcome I think I need to find other devices to connect the two together. They are about 200 meters apart so long electric cords are out of the question, but they can both be connected to the same Wi-Fi and/or ethernet at their different locations.

There seems to be a few possible routes here. I am not sure which is the best way to go. Inverter has JSON API. Inverter also has HTTP POST (XML or JSON). Inverter can also send a 12V electric signal. Inverter has ModBus. Heater has ModBus.

Am I looking for a JSON to modbus device of some sort? When JSON hook sent a smart relay turns on the 3phase switch in the electric box powering the heater?

In the future there will probably be more devices using the excess power, this is why I want to set it up smart in the first place.

I have found a world of smart sensors but feel unsure of which kind of devices can perform this task. Most solutions seem like an overkill.

I own a Moxa NPort Express DE-311 which seems capable of receiving a signal and communicating with modbus, would that be a good idea?

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    Without knowing a lot more information about all the equipment involved we can't possibly answer this. Please edit the question to add details
    – hardillb
    Dec 5 '18 at 14:54
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    There isn't really a question here, what you're describing is basically 'obvious' in the state of the art, and might be found under 'demand management' if you want to do more research. Dec 6 '18 at 14:28
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    Hi, and welcome to the site. Thanks for clarifying your question. I think it still needs a bit of tweaking, however - it's still quite broad. It sounds like you are looking for some kind of relay, but we'll need some info on what voltage is coming its way from the solar panel, as well as exactly what you're trying to control with it. There are literally thousands of relays available, so we'll need a bit more detail. Thanks!
    – anonymous2
    Dec 7 '18 at 2:16
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    Hi Dani, can you add which kind solar power station and what kind of pool system you have? Another question, are both already in the same Wi-Fi, e.g. your roof and your garden within range of the same Wi-Fi?
    – Helmar
    Dec 7 '18 at 17:48
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    Although what you're asking is fairly straight forward, it is more of an electronics question than an IoT application that you're describing. WiFi may come into the signalling part, but the interfacing is your real challenge. There is nothing 'complete' as an off the shelf solution, and some concern about unattended power electronics. Many more people will have done something similar with an immersion heater and their domestic hot water. Dec 10 '18 at 16:49

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