How One UK Family Cut Their Energy Bill in Half — Then Got Paid by Their Solar

The video, in 60 seconds

Across the last 12 months KMM has filmed dozens of customer testimonials but one stands out — a UK family whose quarterly electricity bill went from a level they describe as "uncomfortable" to a quarterly position where their supplier owes them money. The video runs 54 seconds. The story behind it runs a bit longer.

The starting position

The family had a 4-bed detached home across the UK. Their pre-install consumption was around 5,800 kWh/year — slightly above the UK 4-bed average of around 4,200 kWh thanks to an electric water heater and the school-holiday gaming setup. Quarterly electricity bills sat around £540 on a fixed-rate domestic tariff. They had a south-east facing roof with no significant shading.

The KMM install

• System size: 5.6 kWp DC, 13 × 430W tier-1 panels
• Inverter: 5 kW SolaX X1 hybrid (G98 fast-track)
• Battery: 9.5 kWh LFP (GivEnergy)
• Tariff move: from a 28p flat-rate fixed contract to Octopus Outgoing Fixed (15p export) + Cosy time-of-use import
• Install timeline: contract → first generation in 4 weeks (3 weeks waiting for DNO notification, 2 days install)

The numbers after install

How the maths actually works

The bill flip isn't magic. Three things stack:

1. Solar covers 78% of consumption directly. With battery, almost all generation either powers the home in real time or charges the battery for evening use. Grid import drops by 70%.
2. The remaining grid import happens overnight at 7.5p. Cosy Octopus charges the battery during the cheap window; the battery powers the daytime gap when solar is low (typical UK winter).
3. Spilled solar is sold at 15p. Sunny days from April-September generate far more than the family needs. Octopus Outgoing Fixed pays 15p/kWh for every spilled kWh.

System cost and payback

• Install cost (VAT zero-rated): £11,650
• Year 1 saved + earned: £1,560 (£1,313 saved on grid + £247 SEG/cheap window)
• Simple payback: 7.5 years
• With 4% annual electricity inflation: payback closer to 6.5 years
• 25-year warranted system net benefit (at 4% inflation): around £52,000 in current prices

What this family did differently to most KMM domestic customers

Two things. First, they switched tariff before commissioning so the time-of-use rates kicked in from day one rather than 3 months later — most domestic customers leave their original supplier for 6 months out of inertia and miss the cheap import window. Second, they enabled battery cycling at the maximum allowed depth-of-discharge (95% rather than the default 80%) — this gives faster degradation but materially better payback.

How to replicate this

The setup isn't unusual but it does require a hybrid inverter (not a string-only) and active management of the tariff. KMM bundles tariff-switching support into every domestic install for exactly this reason. See the domestic solar page or book a fully funded survey if your bills sit anywhere near this family's starting position.