OH4: Sum two ModBus register values to an ITEM

Hi All

I am looking for some advise/best practice.

I have a solar setup with two MPPT strings for the solar input.

These are accessible via two ModBus registers which I am able to read. I will be linking these to ITEMS to carry the values for the two strings of panels

I however would also like to get the TOTAL Solar Generation - which would be the sum of the two registers. I would like to populate this to an ITEM as well.

What is the BEST way to achieve this?

  • Run a rule for every change on the two ITEMS and calculate the sum?
  • Have a transformation to calculate the third item? How to access the individual register data for the two ?
  • Some other more clever/efficient way?

Any advise would be appreciated - this is my first delve into ModBus etc.


If you a two items that carry a value, I’d create a group that shows the sum of those items (Aggregation Function: sum).

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