Hi,
I am planning to supplement my solar PV with battery. After that i hope to heat a hot water tank depending on available energy within the battery. To do that I am looking for an off the shelf switch to trigger the water heater. Ideally i would like to avoid flashing with custom firmware and have a solutjon which i can integrate with openhab easily from an oem perapective. Can you please offer any suggestions ?
Not really because this forum is not meant to give advice on general HA question.
Essentially you can choose from all technologies that OH supports. You’ll probably want to deploy an actuator from a system you already have in use (like KNX or ZWave for example or whatever you already run). What’s an “OEM perspective” ?
This is a z-wave switch relay 2.5KWh
http://store.zwavecenter.com/index.php?route=product/product&path=59&product_id=355
I´m not sure a 3KWh is avialable anywhere.
Thanks for the useful feedback.
Markus what I mean by OEM is something which will work with an interface to Openhab as intended by the original manufacturer. Looks like the item posted by Kim is promising.
Remember, it requires you have a z-wave gateway to your openhab.
When you got that part running, you can switch on/off you´re heater from a rule by openhab.
Okay looks like this shpuld do the job as a gateway Aeotec Z-Stick Gen5, Z-Wave Plus USB to create gateway, White https://www.amazon.co.uk/dp/B00YETCNOE/ref=cm_sw_r_cp_apa_i_-OgvDb0NJ2MXF
Also be aware that z-wave devices are region-specific due to different frequencies used.
Be sure you get what is appropriate for our region.
Correct…
Nice catch! Forgot all about that part 
Out of curiosity…
How do you plan to control that part?.. Can you monitor your Solar system and Battery?
(I can with my SMA solar setup and LG Chem Resu 10H battery).
Amazon is selling EU compliant devices. I’ve ordered one and will attempt the i integration with pi 4 as deacribed here …
Here is a page from the binding developer.
https://www.cd-jackson.com/index.php/openhab/habmin/10-habmin-zwave-binding-initialisation
For completeness, here are the official docs.
Thanks really appreciate the guidance. Only problem is there is a supply issue with the LG Chem battery and interface to my Solaredge Inverter. Hopefully that will be solved soon 
You will need a battery inverter to run the LG chem battery, (unless your main inverter is ready for battery). And you need something to monitor the production of the solar system as well as the energy in the battery. Thats the tricky part… You inverter may have modbus, and then you´ll need a modbus interface to openhab as well.
My SMA solar system consist of a main inverter TPL6000 which is connected to the solar panels.
Then I have a SMA SunnyBoy Storage 2.5 (thats the battery inverter).
Battery Lg chem Resu10H connected to the battery inverter.
Last I have the SMA Energy Meter. Thats the device which monitors everything. This devices is connected to openhab as well, where I can moitor all production from the panels, as well as what i receive from the Grid.
Unfortunaly I do not have an electric water heater. If I had, I could use the solar system to heat the water when the solar system is producing power above a specific value, simply by the use of a short rule in openhab. I believe this is where you´re going?
In have an existing solaredge system. An additional interface (storedge) and the resu10 battery will be added. At the moment I can use the Solaredge binding to access date via the API. I expect to be able to obtain battery stats when the interface and battery are added.
Thats the way I am going. When the battery is charged I intend to heat water in the morning.
Ahh okay, then you should be good to go
I explain how I have it in my case, they gave me a 500-liter thermos, which had 3 electrical resistors of 1000w, replaced them with 500w resistors, and depending on the energy left over from the plates, activated the necessary resistors to consume the leftover and not consume the external power grid.
That makes sense. That is the way I would have had it as well, if I had an electrical heater.
Small tip!
If you can control the 3 500W electrical resistors individually, then getting a 6 channel 2KW switch relay could be a better option like this one:
http://store.zwavecenter.com/index.php?route=product/product&path=59&product_id=362
Then you can switch on/off each resistor depending of temperature inside the water tank, or perhaps even from use, (ie if you need much hot water, like a shower or something like that), then turn on all three resistors. Else only turn on one resistor…
You just need a temperature sensor inside the tank, and perhaps a water measuring sensor (measuring the cold water entering the tank).
Things like these can be optimized alot, if or when you have the opputunity to control each device individually.
I would love to have this way. Unfortunatly I have a gas heater in our house, and I have no easy way to add a electrical water tank. I have thought about adding a heatpump (air to water) though. But its a rather high investment, which has to be calculated from its savings.
I use 3 sonoff, from the outlet of the thermos the water is redirected to the thermos of the diesel boiler, if it needs more temperature the boiler starts up (normally in winter), if the temperature is sufficient, it continues its route towards the services used at home
Hi,
I have returned the Aeotec device as there are lots of reports that there is an issue with the USB interface and RPi4, looks like an issue with Aeotec.
The device from zwave.me has arrived and ive managed to configure it with no issues. The zwave.me UZB device is also less expensive.
Hi - if you are going to switch heaters which draw 3kW you are talking about serious electrical currents; domestic smart switches (like Aeotec) are max 10A so they are totally unsuitable.
I have a working OpenHAB solution controlling 6x 2.4kW heaters. The configuration uses OpenHAB on a RaspberryPi, mysensors NRF24L01 to an Arduino which controls 6x relays (via two Arduino 4-relay board - with two spares) but these Arduino controlled relays just switch a 12V low current out to a serious set of relays that my electrician installed (30A mechanical relays that he normally uses for industrial air conditioning systems) that in turn control the heaters. Also between the relays and the heaters are circuit breakers.
By utilizing this design it means I can play with all the fun bits (12V RPi and Arduino) and my electrician controls all the deadly bits (high voltage, high current).