What hardware for 3phase +pv?


i have a 3 phase connection and 2 solar inverters i was thinking of iotawatt but is that possible with this configuration / 3 voltage sensors ?

i have a raspberry pi 3 leing around for the emoncms


solar inverters


The number of three-phase IoTaWatt installations is growing. I have no hard statistics, but from the forum inquiries, it appears that the Derived Method IoTaWatt can use (one voltage reference) produces reasonably accurate measurements. Anecdotal evidence is in the 1% range.

There are users with three phase inverters, and they are reporting success measuring the output. (Not sure if you have single or three-phase inverters, both are possible).

IoTaWatt is very flexible. You would need to use three of the 14 inputs for the mains. A single phase inverter would need one input and a three-phase inverter would require three. So worst case of two three-phase inverters would require using 9 of the 14 inputs for the mains and inverters, leaving 5 for monitoring other circuits.

There are some techniques for combining circuits on the same phase, and suffice to say that if you might be able to combine the two inverters into three inputs and measure the combined output.

If you are intent on using three voltage references for three phase (direct reference) there is an adapter required that you must build it yourself (schematic available on github).


i guess i have single phase inverters cause the solar output meter has 2 black wires instead of 3
the digital meter in the top right corner.

and if this is the case isnt there a voltage difference that the reading will be a lot further off than 1% ?

if it will be only 1% off i am happy eneugh with it! :wink:


It could be.

Only two of the three phases are derived. If one or both of the inverters are on the same phase as the voltage reference, those measurements will be with actual voltage. The caveat is that when the inverter raises that voltage, the other two phases will also assume that voltage. All that said, users seem generally satisfied with the results they are getting for both single and three-phase.

But you don’t need to agonize over that possibility. You can install using derived reference and see how it goes. At any time you can convert to using direct reference. It’s also possible to use two direct reference sources and monitor the third phase with derived reference.

Much has been made of the potential variation in voltage from phase to phase, and the potential for phase shift from 120 degrees in Wye configurations. These are academic assertions and I’m sure based on sound physics. But I’ve seen no data that demonstrates the effects of these things under ordinary circumstances. To the contrary, I’m seeing that pragmatic folks don’t find them compelling reasons to undertake the complexity and cost of direct reference and are getting useful data with derived reference.


thanks now i have mush more confidence and order an Iotawatt immediately !