thinking about switching to an IoTaWatt - can it do what i’d need?
european style 3-phase grid which i’ve been metering with an efergy (3 clamps after utility meter) up till now.
after installing a single-phase PV-inverter on the ‘far end’ of the house (so there are loads between PV and meter) i quickly realized that the ‘consumption’ efergy shows is going up when the sun is shining. it just doesn’t know (or show) the difference of ‘upstream’ or ‘downstream’ current (i think that’s what you are naming it round here).
getting a true grid consumption reading.
reading in the docs and forum it seems to me as if IoTaWatt can tell the difference, but not sure one can actually use it that way.
thinking about it - while out for a run - i realized that IoTaWatt by itself - or any meter after the utilty-meter - can’t know what is coming from the grid without knowing what the PV is feeding in. so i guess i’d need to bite the bullet anyways and run a line from the PV back to the utilitybox…
Disable auto reverse on the input CT then use the MIN 0 and MAX 0 calculations on the outputs based on that input to restrict the readings to one direction.
In your case it would just one of the phases that could flow in both directions (assuming there is no generation other than the single phase solar).
For export (negative) you would limit the output to a maximum of zero (if importing then report zero imported)
For import you capture the reading with a minimum of zero (if exporting record zero import)
This assumes that the CT is orientated so that export is negative. iotawatt allows you to switch it virtually if it is installed the wrong way round so you don’t have to access the panel again.
Note: You could have a third output from the same CT with the ‘natural’ reading if you wanted.
The iotawatt syntax of max/min is very specific - I have to double check the docs if I haven’t used it for a while.
Consumption = import (export) + solar so if you wanted accurate consumption you will need to capture your generation. If the efergy can report to influx db then shift the efergy to the solar, use the iotawatt on the mains and report using a graphing tool from your influx data.
If the efergy can’t report into influxdb then your options are taking the solar directly back to your distribution board (so you can capture with the same iotawatt as the mains) or potentially using a second iotawatt.
The advantage of a single iotawatt is that you can use it directly (with some limitations on sample time) for reporting. As soon as you have 2 units or other data sources you need influxdb to consolidate the data for reporting.
Not so. With CTs on all three mains, you would know both the magnitude and direction of energy flow through the meter, just as the meter no doubt knows.
In terms of billable grid energy, you should be able to replicate what the meter is measuring.
Now if you are also interested in the amount of PV energy produced, and the total consumption of the house regardless of whether it comes from PV or the grid, you would also need to put a CT on the inverter output. It’s not clear from your initial post whether that is near the mains. You can reasonably extend a CT lead up to about 10 meters, and farther with more effort.
With CTs on the mains and one on the inverter you would have:
where import + generation = export + consumption
This can be reported directly out of the IoTaWatt with Graph+, extracted with the Query API, uploaded to PVoutput or externally tracked with influx/grafana or emoncms.
still got another place to put the efergy to use anyways. currently i’m relying on the wattage the inverter is reporting (to homeassistant) but might better switch to something external or well - run a line back to the distribution box and a potential IoTaWatt…
it’s about 20 meters i’d estimate, but probably easier to just run the inverter output back to the distributionbox.
any estimates when the base unit might be back in stock?