Questions we get asked
Mostly by neighbours. Cost, output, the Sigenergy and Predbat setup, the Octopus tariff, and how the data gets onto this site. Each answer links to a page with more detail and the numbers behind it.
What does a 10.45 kWp solar and battery system cost in the UK in 2026?
Ours cost £11,999 fully installed at 0% VAT. That covered 22× Aiko 475W panels (10.45 kWp), a Sigenergy EC 8.0 SP hybrid inverter and a 15.06 kWh SigenStor battery. That's about £1,148 per kWp including the battery. Before install, the modelling put year-one value at roughly £1,900–£2,060, with payback at around six and a half years. This site tracks how that's going.
What is the real-world output of Aiko 475W panels on an east/west UK roof?
On our 10.45 kWp east/west array in Hampshire, a clear June day does around 40–46 kWh and a dull one around 20 kWh. Estimated annual generation is about 7,500 kWh before losses, with roughly 11.5% annual shading loss per the survey. Each day's measured figure goes up on the stats page automatically.
Is an east/west split roof worth it compared with south-facing solar?
For a house with a battery and time-of-use pricing, yes. Peak output is lower than a south-facing array, but generation is spread across the day, with the east face catching the morning and the west face the evening. That lines up better with when the house uses power, and it clips less against the inverter limit. With a battery and a cheap overnight window it suits us well.
What is a Sigenergy inverter and does it work with Home Assistant and Predbat?
Sigenergy make the EC-series hybrid inverters and the stackable SigenStor batteries. Ours is a Sigenergy EC 8.0 SP (8 kW). It talks to Home Assistant entirely locally over Modbus TCP on port 502, using the community Sigenergy ESS integration from HACS, and exposes 250+ entities without going through the cloud. Predbat controls it through three small bridge automations that map Predbat's requested mode onto the Sigenergy EMS control registers.
What is Predbat and what does it do?
Predbat is free, open-source battery-planning software that runs inside Home Assistant. Every half hour it plans charging and discharging against your live half-hourly import and export rates, a Solcast solar forecast and learned household consumption. It decides when to charge from the grid, when to run the house off the battery, and when to export. There's no fixed schedule; the plan is recalculated from the rates each time. Ours runs on a £50 refurbished Dell OptiPlex 3050 Micro.
Is Octopus Agile worth it with a home battery?
We modelled it properly and went with something else. For a house with a battery, most of the value comes from cheap import: fill the battery in the cheapest hours and run the house off it through the evening peak. Agile prices change every half hour, while Intelligent Octopus Go gives a fixed block at 8p. On our own consumption, with a heat pump and an EV to schedule, IOG came out at 591 pounds a year and Agile at 946. Once the battery is big enough to fill in one go, a fixed cheap block beats Agile's average. Agile is still the better choice if your loads are flexible and you have no fixed overnight window to fill. Either way, avoiding peak-rate import is worth about as much per kWh as the old Flux export peak was.
What happened to Octopus Flux, and what should battery owners run instead?
Octopus Flux and Intelligent Octopus Flux closed to new customers in March 2026. We now run Intelligent Octopus Go for import with Outgoing Octopus flat 12p export. Losing Flux's 30p evening export peak only cost around 10% of the projected year-one return, because on a time-of-use import tariff the battery earns its keep by avoiding peak-rate import instead of exporting at a peak rate. We'd suggest not basing a multi-year payback on one tariff staying available, and modelling your second choice as well.
Can you earn money for exporting solar before installation certification clears?
Not at first. Export stays unpaid until the final installation certification is processed and an export MPAN is registered, and in the meantime the inverter exports surplus to the grid for nothing. Ours took from 4 June to 22 September: 2,487 kWh, about £299 at 12p, unpaid. Axle VPP was the exception. It settles directly through the smart meter, so its £1/kWh grid-balancing events paid out months before export certification cleared, and it was the first thing here to earn anything from export.
What is Axle VPP and how does "events-only" mode work with Predbat?
Axle is a virtual power plant that pays you to dispatch your home battery during grid-stress events. It pays £1/kWh with a £10/month minimum, and you typically get four to eight events a month. In events-only mode Predbat keeps full control of the battery the rest of the time. Predbat has built-in Axle support, so it pulls upcoming events into its plan and hands over control while one runs.
How can you publish Home Assistant energy data to a website automatically?
This site is fed directly from Home Assistant, with no spreadsheets or third-party service in between. Six daily utility_meter helpers wrap the Sigenergy cumulative energy sensors. At 00:15 an automation builds one JSON file for the previous day from those helpers plus Predbat's cost-tracking sensors, then pushes it to a GitHub repo with a single rest_command against the GitHub Contents API. GitHub Actions rebuilds the static site (Astro) and rsyncs it to the server. The commit history also works as an audit log.
For more, the install diary covers what happened, including what went wrong, the configs page has the actual files, and the stats page has every day's numbers.