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Producing PV Import / Export statistics over time

Question: How do I produce a record over time of what I Export to the grid?
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  • I have x1 emonPi (Solar Bundle version) in a barn (no PV on this circuit)
  • I have x3 emonTx c/w ESP8266, (house, loft & garage), & this circuit does have PV panels & an Export meter.

These units are all in separate buildings, & all communicate to emonCMS via WLAN, & I have created a variety of Inputs & Feeds on emonCMS.

Merely subtracting the generation feed (G) from the usage feed (U) won’t work, because (in an extreme to highlight my point) if 90% of generation happens during the day but 90% usage happens at night, then U minus G will not give me the export (E) or import (I) values that I am looking for.

Am I missing something here?

When one version of the emonPi is described in the shop as the “Solar PV version”, what does that actually mean? Do I need to have an emonPi Solar PV version on the circuit with the PV panels? The reason I don’t is that I need the additional inputs that the emonTx’s give me.

TIA

Julian

Hello @haffle

If your usage feed is 500W for a given 10s period (default data rate) and solar feed is 2000W then U - G = -1500W export. Alternatively if U is 500W and solar is 100W: U - G = +400W import.

By calculating at a regular interval e.g balance in a 10s period and then recording the cumulative import you can get the totals for the day.

Does that make sense?