how much energy to i actually have?

[powerwall88]

today my powerwall started at 100% and started discharging after midnight. it reached a low of 87% before it started recharging with solar. it received 5.8 kWh from solar to get it back to 100%, but it only discharged 4.1 kWh. i checked the API when the app said 88% of charge and it showed a nominal full pack energy of 42334 and nominal energy remaining of 37381 - the difference of these two numbers is 4953 (compared to the app's reported 4.1 kWh discharged) and the quotient is 88% which is consistent with the percentage reported by the app at that time.

if 4.1 kWh discharged represents 13% of the total available energy, that imputes a total available energy of 31.5 kWh, compared to what is supposedly 40.5 kWh for three powerwalls, and compared to the nominal full pack energy of 42334 reported by the API.

how to reconcile all these numbers which don't seem consistent, even if accounting for the supposed 10% roundtrip loss?

if i was really down to 87% after using 4.1 kWh of energy, how much totally energy would i actually have had available to use had the grid been down - 31.5 kWh? 42.3 kWh? something in between? is there any way of knowing?

 

[Redhill_qik]

With a nominal full pack of 42,334 Wh that means that you have 3 Powerwalls and they must be new. The Powerwalls consume internally about 200 Wh/day each that is not recorded as an export as it is used by the internal control circuits and cooling system, so for you that is ~600Wh/day. The reported percentages in the app are not the actual numbers and they are off by a sliding number where the real vs displayed is correct at 100%, but real is greater than displayed as it gets closer to 0%. Basically don't use this app percentage number for anything or than to know when you are fully charge or about to go offline.

The Powerwalls will stop powering the house loads at 5% as they need the energy reserve to be able to startup in the morning when solar comes online and the grid is not present. This limit is there regardless of the grid being present or not as it could go down at any time.

If you want to calculate your efficiency then use the REST API (http://#.#.#.#/api/meters/aggregates replacing #.#.#.# with your TEG IP address) to get the "energy_exported" and "energy_imported" values and log these on a daily basis after the Powerwalls have fully charged. Then you can use this formula to calculate your efficiency:

Eff% = (energy_exported_day2-energy_export_day1)/((energy_imported_day2-energy_exported_day2) - ((day2-day1)*200*3))