Hybrid solar


Sorry if this has been answered before.

I currently have emonTX monitoring my house (with 4kw solar system) and love emonTX.

I’m about to start significantly upgrading the system but I haven’t decided on any particular inverter or battery hardware, my only requirements are:

  • I will be installing 3 phase
  • I should have power when the grid is down
  • The batteries should be ~2.5KWH rackmount (like the BYD 2.5KWH)
  • Domotics integration (like Home Assistant)

I would love to take emontx on my journey, how do I do it?

Ideally at the end of the journey I will be able to make decisions based on my “state”, for example my pool pump uses a lot of power and it would be good to have “rules”, for example:

  • Only turn it on when the system is exporting over 1.5 KW to the grid
  • Make sure it runs for 4 hours a day
  • Don’t use batteries to run the pool pump, use grid

Would I be interfacing emonTX directly to the batteries, it uses a CAN bus I believe?

Hopefully that makes sense, there is a bit of buzz around products like Reposit but it just looks like an emonTX that can talk to the battery.

So in a nutshell can I use emonTX and domotics as a backbone in my future system?


Hi Richard
I’m also on the journey to PV+battery+grid (on/off) with OEM, and have been inquiring about options. A couple of things to note:

  1. The pool pump is easy to setup if you are happy to use the Node-red platform and/or the wifi mqtt-relay. I have this set up to heat a second hot water tank when there is excess PV. The mqtt relay has a scheduler that you can use to turn a control relay on/off. I think you could monitor export with emonTx and setup a rule in Node-Red to run the pump.

  2. Many of the commercial battery chargers/inverters will not allow you to connect to their modbus/Canbus. Some do - I have connected to my Fronius Primo, but it doesn’t have battery control capability. I’m on the verge of buying the Selectronic SP Pro which seems the most flexible.

  3. Having power when the grid is down is also system dependent. The Selectronic SP Pro has this option (transfer switch).

I’m sure the “veterans” on the forum will have more great advice!



If find in the end you can not get emontx to work for you - you could try instead of emontx you use an emontx shield and wemos r3 ( though I never tried with 3 phase )… and send data to both domoticz and emoncms

use this to install domoticz on your emon PI or whatever you are using

sudo curl -L install.domoticz.com | bash

I’ve done pretty much all that you want too… but using openwrt on a opesource router platform ( BPI-r1) as my base has pretty much everything I want on there for me as an all in one device

wemos r3 uno
emontx shield
opensource router platforms


Thanks Tony & Stephen!

From memory, motors have an inrush current and the amperage that your relays support needs to be 5-10x your normal amperage, my pump is 1100w so I guess that is 5A (1100[w] ÷ 220[v]) so if it was an SSR it should be able to handle 25-50A for a short period of time, I could be wrong but I think that’s right, or you have a small relay that energises a larger relay?

for me depending on what i want to do
for energy diversion I use SSR I usually use 80 amp or bigger driven by wemos di mini or mini pro depending on distance using custom code or espeasy

for big draw contacts I tend to maintain the electromagetic relays that they normally use then using either wemos d1 mini shield or an arduino relay shield using wemos D1 to drive it - on espeasy firmware

the reason I like contact version for big draw if overloads then the most you have to do is polish the contacts and it good again where SSR tend to burn out and you have to buy a new one

I prefer using the larger arduino shield as in gives you more options and such manual control and on board sensors ( the price is about the same) – say such as my greenhouse controller- it controlled by domoticz but also manually on/off and automatically --ie it gets to hot or soil to dry it automatically turn on ventilation/ irrigation if max thresh holds have being reached ( in case domoticz failed to do it for some reason)

also for my battery control i also make work automatically controlled for things that i deem essential , then there are secondary controller for less then primary usage that domoticz controls … you should not only rely on computer control – build in a bit of primitive redundancy for safety reasons

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Beware relays that don’t mention a contact rating for inductive loads, i.e. there is only a “resistive” rating mentioned, or the rating is not specific. It’s likely they are completely unsuitable for switching something like a pump motor - or any motor, or fluorescent lighting.

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