Morning 250W Power Discrepancy in 7kW PV System With Emporia Monitoring and Microinverters

Hello all,

we have a 7kW PV system installed (15 solar panels, 8 micro inverters, 2 strings, 15m wire to breaker panel). In the panel we have an emporia system to monitor all circuits - which works fine with all loads accounted for - EXCEPT: each morning from 8:00 (when PV production starts) to around 9:30, the system reports an unaccounted power difference of around 250W (30%). When we switch off both PV strings, the balance drops to 0 (so everything is accounted for). After a while, with PV on, the balance drops to 0, and stays there for the rest of the day.

The emporia helpdesk can't help. We are running one wire from each PV string through one CT together. Perhaps this is causing issues. But, everything works fine after ~9:30. So my question is: what signal form generated by the PV system can possbily cause the power meter discrepancy? The inverters synchronize with the grid, so there shouldn't be any phase differences, I suppose. I speculated that there might be a software issue in the emporia monitor, but then again, the discrepancy goes away after 1:30h or so. Perhaps it's a temperature issue? The house cools down to 15C at night, and the furnace kicks in at 8:00. Does temperature difference affect CT readings that much?

Thanks for any ideas you might have on this issue.
Cheers

The discrepancy in your PV system's power readings during the morning hours could be attributed to various factors. One possible explanation is the initial startup phase of the solar panels. When the PV production begins at 8:00, there might be transient effects or fluctuations that cause a momentary imbalance in the power readings. This could be related to temperature changes affecting the Current Transformers (CT) readings. The temperature drop overnight to 15°C and the subsequent furnace kick-in at 8:00 could influence the CT readings, especially if there's a sudden change in electrical characteristics. It's worth investigating if the CTs are affected by temperature variations. Additionally, the wiring configuration, with both PV strings passing through one CT, might contribute to the issue during this specific timeframe. It would be advisable to consult with a solar system technician to assess the wiring setup and its impact on the CT readings during the morning startup period.

Thanks for your comments and your suggestions.

Over the summer I kept on checking, and the discrepancy was still present until ~9:30a, but overall it's not that bad, as the unaccounted energy balance over almost one year is about 1% on my system.

Checking right now (9:25a local time) it's actually bad: ~240W (reported) solar production, ~730W usage (including 240W unexplained balance), ~500W net usage. So, the solar production number seems to be off by 50%...

I think I'll leave it as it is, given that the overall effect is small.