Negative solar (battery) and Usage accounting?


#1

I have an AC coupled energy storage system (ESS), aka a battery, that can charge from mains/grid power. It appears Sense does not account for the charging (negative “Solar”) within mains “Usage”. It does correctly debit and credit within “Solar” usage, but then it’s not correctly reflected within the main “Usage”. Which results in significantly incorrect “Usage” data.

An example of a typical ESS charge event (12:00AM) with solar CT disabled:

ESS charge event (12:00AM) with solar CT enabled which is not captured in “Usage”:

Solar usage correctly reports charging @ -7.5 kWh, but not sure how to read -217 cents:

Later in the day the ESS discharges a couple of times and Solar usage is credited correctly, but it doesn’t appear Usage was debited:

Realtime ESS charge:

Realtime ESS discharge:

Any hints, tips, or suggestions?

Thanks,
Lael


#2

Not clear from your message - do you have solar and a battery, or just the battery ? Does your battery charge/discharge backfeed run through the solar CTs ?


#3

Just the battery for now, solar panels are disconnected. And yes, the battery charges/discharges through the solar CTs. For now the battery only charges from the grid, but does not discharge to the grid, it matches current behind the meter (BTM) load (household load).


#4

If you are seeing negative Solar and negative $ in this configuration, I suspect that you either have your solar CTs backward or Sense calibrated the solar incorrectly for your usage. With a correct solar setup, both will be positive.


#5

Thanks for your reply; I believe the Sense and solar CTs are configured and oriented correctly. When the battery discharges to the house/grid power via Solar CTs it’s positive and when it charges from grid it’s negative. Similar to positive output from the solar panels and the negative inverter power consumption without sun.


#6

Now that I think about it, the behavior you see (as I understand it) is exactly as expected. Usage represents all usage inside your house, battery charging excluded (the battery is like solar - an external source/sink). Solar / battery production must be added to main power entering the house to compute total usage. Battery charging must be subtracted from the main power to compute usage solely in the house.


#7

I would agree for a DC coupled solar/battery system, where the battery can only charge from solar. However for an AC coupled system, the battery can charge independently from the grid. In that case the battery or any other load on the solar side, such as a very large low frequency grid tie inverter(standby about 200w), should be accounted for in “Usage”. Before solar CTs, “Usage” would mirror my Utility power bill. However after solar CTs, it appears “Usage” does not correctly account for load/sinks on the Solar side of the CTs. Maybe someone from Sense can chime in?


#8

I think you mistake what “correct” operation is. The correct interpretation of Usage is the total usage of your house, not your mains as monitored by both your utility meter and the Sense mains CTs. Your house usage will differ from what is seen at the mains by the negative and positive contributions of the battery (in Solar, 99.9% by the positive contribution of solar production). Sense house Usage shouldn’t be exactly what is seen by your utility via the mains, but rather a time shifted version of usage depending on usage of the battery.

To put it differently battery charging power is subtracted from the mains power (when charging), and battery discharge is added to the mains power, to compute the just the power flowing into your house wiring and associated lights/HVAC/appliances/etc…