What one Hampshire roof has actually saved
22 panels and a 15 kWh battery, measured every night against the installer's proposal. On day 147, it's on course to pay back in 7.9 years, not the 5.4 quoted.
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
75%of its projected pace
Like for like
96%of the pace, counting only income open to us now
At this rate
7.9yrvs 5.4 quoted
Latest day
The nightly upload is late, so these figures are days old. They'll catch up when Home Assistant next reports in.
Generated
2.4kWhExported
0.0kWhnothing earned
Imported
8.2kWhDay's saving
£2.89vs a no-solar baseline
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.
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.
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.
The configs
The apps.yaml, automations and helpers that run this Sigenergy and Predbat
setup, with secrets removed and comments added. Free to copy.
The tariff and the VPP
VPP earnings · grid events
£122.30 paid for 21 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.