60 days of data · 4 Jun 2026 → 2 Aug 2026
The numbers
Every figure below is pushed automatically from Home Assistant at 00:15 each night. The kWh come from the Sigenergy inverter's own meters and the costs from Predbat's daily tracking, including its estimate of what each day would have cost with no solar or battery. None of it is typed in by hand. How the pipeline works →
Running totals
Until the final installation certification comes through we earn nothing for export, but the inverter still pushes surplus to the grid once the battery is full. This is what that donated energy would have earned at the 12p rate. The certification story →
Daily generation vs consumption
Grid flows · export ↑ / import ↓
Battery throughput · charged ↑ / discharged ↓
Daily net cost vs no-solar baseline
Cumulative savings → £11,999 payback
Monthly ledger
| Month | Days | Gen kWh | Export kWh | Import kWh | Net cost £ | Axle £ | Saved £ |
|---|---|---|---|---|---|---|---|
| August 2026 | 2 | 98.2 | 56.1 | 0.0 | 0.88 | — | 9.40 |
| July 2026 | 31 | 1,616.6 | 1,096.0 | 0.5 | 13.70 | — | 107.49 |
| June 2026 | 27 | 1,195.0 | 805.4 | 1.1 | 7.90 | £4.27 | 79.25 |
| All time | 60 | 2,909.7 | 1,957.5 | 1.6 | 22.48 | £4.27 | 196.14 |
A day's saving comes from Predbat's no-solar comparison: what the day's usage would have cost if it were all imported at the actual half-hourly Agile rates, minus what it actually cost. Predbat also credits energy banked into the battery during the day (priced at the rate it later displaces), and debits energy drawn down, so a day that fills the battery scores higher than a pure avoided-import view. Over a run of days the battery starts and ends at a similar charge and it evens out. Standing charges hit both sides equally, so they cancel.
Axle £ is the VPP grid-event income (battery exported at £1/kWh during demand events), measured from our own meter. It is already part of the Saved figure — Predbat prices the event export into the day's net cost — so it counts toward payback too; the column just breaks out how much of the saving came from VPP events. Don't add it to Saved.