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What OEM gear to buy for my scenario?

I am hoping for a few pointers on what OpenEnergyMonitor (OEM) devices to get to cover my set-up.

The property (all single phase) has a 2x6kWh PV array (KACO inverters), running into the switchboard of the house.
The 240V cable then runs form the house into the shed.
Here it is connected to an inverter/charger that has a 20kWh battery connected to it.
This inverter/charger (a Selectronic SP PRO GO) is connected to the grid. (In fact the only thing connected to the grid; it feeds all consumers on the property, and limits the export to 5kW/h).

I’d like to measure in real-time what energy is generated, imported and consumed.

I reckon I need

  1. two CTs, one per inverter to record generation (connected to what OEM hardware? or, do I measure what goes inot the house, which is the generation = one location less to physically monitor.)
  2. one CT for house consumption (and as per the point above, comes from the PV array)
  3. one CT to measure the grid (import and export; positive or negative values?!)
  4. one CT to measure what goes in/out of the battery (this is DC up to 200A at 56V)
  5. one CT to measure what goes into the the shed

Writing this down, and I figured I have two physical locations to measure it all.
That is house for PV in, House to shed, house consumption (=3 CTs)
And shed for grid import/export, battery in/out, shed consumption

If the DC part for the battery requires “more effort” in gear and cost, I already capture the battery in/out (as in V and A) via a battery monitor connected to opeHAB (which I heavily use for automation; ATM more for pump, tank and irrigation automation than for home automation. Sensors are all based on Arduino UNO with Ethernet shield and MQTT).

I would like to connect the emonTX(s) or emonPi(s) via wired Ethernet (otherwise wireless; not 433MHz due to distances/obstacles to cover). There is Ethernet wired everywhere on the the property.

What are you using to measure individual 240V consumers? emonXXX? sOnOff/Tasmota/MQTT.

In essence: what OEM to buy for my set-up?
Or building my own? (which I could, but I am time-poor)

As for geography: the PV is 40m from one side of the house, the shed is 40m from the other side of the house, the grid is 40m from the shed (all lined up like a string of pearls). A significant green house is planned, which could connect to the PV system switchboard. (I would opt for another “OEM sensor” to measure what goes into the greenhouse when the time comes).

Thanks in advance for reading this far, and even better for providing some input.

Hi Max, welcome.

Photos of your setup are useful, I’ve bumped your trust level so you should be able to post some.

Do you mean appliances?

Yes, appliances, such as pumps and heaters.

To answer this one bit, OEM kit is not really suitable for appliance consumption monitoring as it needs a single Live or Neutral (Terminology correct?) wire to clip the CT onto.

For appliances I’d suggest one of the Tuya plug clones (do you have those?) or Sonoff kit that can be wired in series. A bit of fiddling with the way the data is returned, and you can pull the consumption data into EmonCMS or another database as required.

Line or Neutral. Both are live conductors.

To answer some of the rest:

Why 3? House consumption = what’s left when you take the shed off the PV in.

C.T’s don’t work on d.c. You need to measure the a.c. side of the inverter, or assume that the inverter power is the difference between Grid and the feed to the house.

The nearest we can do to wired Ethernet for the emonTx would be an Arduino with Ethernet plus an emonTx Shield. But the emonTx can have the ESP8266 WiFi module attached, and the emonPi can do both wired Ethernet and Wi-Fi. Would WiFi mean extra access points?

I take it you mean 2 × 6 kW? kWh is a measure of energy, not power.

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I knew I’d got something wrong there :grinning:

PV generation can be captured, but maybe I capture it at the source location (as the future greenhouse may get its power from there.
Meaning, I can get away with one CT to measure house consumption.

Thanks, understood; silly me :slight_smile:
We can drop the battery measurement, as I already have that through the BMS.
The inverter charger sits between grid and the rest of the property; With its 20kW battery, it acts as a UPS for the whole property.
(Grid goes first to shed, then out to other place in a star config. One string is shed to house to PV (and later PV to greenhouse).

Wired Ethernet is a design decision. I have underground Ethernet and power all over the property.
I am not a fan of Wireless for various reasons (coverage/distance is one).
I basically put all three services (water, power, Ethernet) in, wherever I need one of them.

Yes, thanks, I should know better. :slight_smile:


So, what does this set-up come down to?
From what I gather I need three emonTX shields (PV, house, shed) with Ethernet board (but I can’t find the latter in the shop).


… plus a few CTs, and the power supply.
The emonTX would run Shield_CT1234_SerialOnly firmware.
In case the “green” Ethernet board is not available, use a another Arduino with Ethernetshield to read the emonTX serial, and send ‘home’ as I please?!

emonTx seems right as I can add CTs as required (even if I use only one ATM).
One in each location provides more precise energy calculations.

Three sounds about right, assuming all the cables come reasonably close together at each location. Extending the c.t. cables isn’t difficult, and should be problem-free provided that you don’t use an off-the shelf headphone extension cable. (If you do need to extend one, see the ‘Learn’ section.)

The Shop only sells the emonTx Shield. I’m not an Arduino expert, the Shield and its software are designed for the Arduino Uno, so I’d imagine that most Arduinos that have Ethernet and are Uno-compatible will be usable - but note the warning in the Wiki about compatibility.

If you’re using an Ethernet Shield, bear in mind the emonTx Shield only stacks as the top one. And make sure you solder the connectors on the correct side of the p.c.b.

:+1: Empty ducts are quite good too.

Thanks for your feedback :slight_smile:

Yes, CTs will be close, due to clamping them in the switchboard…
Did further reading; it seems I can stack Uno, Ethernetshield, emonTX…

Empty ducts… yes, but if you do not know what to put in them it is difficult to space them properly. In AU 240V and data has to be 400mm apart, with data at least 300mm deep; meaning that power needs to be 700mm deep (otherwise 600mm). Water just goes in with data. I had a cheap trench digger, hence, “trenched” the heck out of it. :slight_smile:

(Now I am going to check out what emonCMS can do…)