22 panels · 15 kWh battery · Hampshire
Payback so far
Saved compared with what the same usage would have cost with no solar and no battery. Worked out every night from the inverter's readings.
Vs proposal
69%of its projected pace
Like for like
95%excluding income we can't get yet
At this rate
8.6yrvs 5.4 quoted
Yesterday
Generated
26.8kWhExported
21.2kWhearned £2.54 at 12p
Imported
21.0kWhDay's saving
£6.71vs a no-solar baseline
VPP earnings · grid events
£69.39 paid for 12 grid-balancing events at £1/kWh, plus £13.12 topping quiet months up to the £10 minimum. These figures come from Axle's own statement, which doesn't always match our meter.
£25 referral Got a battery? We both get £25.
Tariff · Intelligent Octopus Go
8p overnightWe left the 24.5p flat fix on 14 September, five months early (reasons here). Intelligent Octopus Go gives us 7 hours at 8p every night, in time for the heat pump. Export started paying 12p on 22 September. Before that, £299 worth of surplus went to the grid unpaid.
£50 referral Switching? We both get £50.
What each decision is worth
This section is modelled. Everything else on this page is measured from the inverter. These figures describe the finished house: heat pump installed, gas gone, on an 8p overnight tariff and paid for export. The tariff and export are live now; the heat pump goes in this December. We'll swap in measured numbers once it's been running a while.
Without any of it
£5,003/yr£1,754 electricity, £1,427 gas, £1,822 petrol and diesel.
With all of it
£341/yr£591 of electricity, less £250 of VPP earnings. No gas bill, no fuel bill.
These don't add up to the total. The three figures add up to £5,528, but the real total is £4,662. Each change is worth more when the others are in place, because every new load gives the battery and the cheap overnight window more to do. Each figure is fine on its own, but they can't be added together. The combined figure is £4,662 a year.
One roof, every number published
An ordinary UK house that spent £12k on solar and a battery. We wanted to know whether the installer's payback estimate was right, so the real figures go up every night, including the cloudy days. It's all run with Home Assistant and Predbat, and the config files are public too, in case they save someone else the faff.
Hardware
The system
22 Aiko 475W panels on an east/west roof, a Sigenergy hybrid inverter and 15.06 kWh of battery. £11,999 fully installed.
Software
The software
Home Assistant on a £50 second-hand Dell, running Predbat, which replans every half hour using the tariff prices and a Solcast forecast.
Copy them
The configs
The apps.yaml, automations and helpers that run this Sigenergy and Predbat
setup, with secrets removed and comments added. Free to copy.