Energy savings
AlphaESS inverter joined to Octopus half-hourly meter reads and tariff prices.
Solar & battery installed by Heatable
£150 off solar £75 off a battery £50 off your Octopus bill referral
Where the benefit came from, by day
Solar and battery are separated by costing three worlds for every half hour — no panels and no battery, panels alone, then what actually happened — and taking the differences. A negative battery day is one that spent more storing energy than it gave back; it returns when the battery discharges. Export earnings sit inside the solar bar rather than beside it: the panels-alone world already sells its surplus, so that income is part of what solar is worth.
View as table
| Day | Solar | Battery | Total | of which export | Solar kWh | Imported | Exported |
|---|---|---|---|---|---|---|---|
| Mon 31 Aug | £0.00 | £0.00 | £0.00 | £0.00 | 0.0 | 0.1 | 0.0 |
| Sun 30 Aug | £4.85 | −£0.74 | £4.10 | £1.38 | 30.1 | 0.8 | 11.5 |
| Sat 29 Aug | £2.36 | £0.36 | £2.73 | £0.17 | 12.3 | 1.1 | 1.4 |
| Fri 28 Aug | £5.95 | £0.28 | £6.23 | £3.79 | 40.1 | 1.3 | 31.6 |
| Thu 27 Aug | £4.32 | £0.21 | £4.52 | £2.22 | 28.1 | 1.3 | 18.5 |
| Wed 26 Aug | £6.81 | £0.14 | £6.95 | £3.58 | 43.8 | 1.0 | 29.8 |
| Tue 25 Aug | £7.18 | £0.46 | £7.64 | £4.55 | 50.4 | 1.0 | 37.9 |
Cumulative benefit
Running total across the selected window.
Monday 31 August 2026, half by half
Energy arriving above the line, energy leaving below it, and the price you were paying on the same timeline. Charging through a cheap window and discharging through an expensive one is the shape to look for.
Inverter versus meter
The two measure at different points in the circuit and will never agree exactly. A few percent of drift is normal; a consistent double-digit gap means one feed is wrong and the solar/battery split should be treated with suspicion. The headline figures come from the meter either way.
| Day | Meter import | Inverter import | Drift | Meter export | Inverter export | Drift |
|---|---|---|---|---|---|---|
| Mon 31 Aug | 0.06 | 0.59 | 883.3% | 0.00 | 20.58 | — |
| Sun 30 Aug | 0.84 | 0.60 | -28.5% | 11.50 | 18.30 | 59.1% |
| Sat 29 Aug | 1.11 | 0.92 | -16.8% | 1.41 | 2.61 | 85.4% |
| Fri 28 Aug | 1.34 | 0.98 | -26.8% | 31.59 | 31.49 | -0.3% |
| Thu 27 Aug | 1.26 | 0.94 | -25.6% | 18.50 | 18.42 | -0.4% |
| Wed 26 Aug | 1.03 | 0.78 | -24.0% | 29.84 | 29.77 | -0.2% |
| Tue 25 Aug | 1.04 | 0.69 | -33.3% | 37.91 | 37.78 | -0.3% |
Return on investment
Measured across everything on record (7 Apr 2025 to 31 Aug 2026), not the range selected above — annualising a fortnight of summer would roughly double the apparent return. The yearly figure comes from the trailing twelve months, so it covers a full seasonal cycle.