How to compare solar options
When weighing up solar choices, most people fixate on one number — usually payback. But the full picture needs all five:
- Cost — what you pay upfront.
- Annual generation — how much electricity the system produces.
- Annual savings — what that generation is worth against your bills.
- Payback — how many years to recover the cost.
- 25-year profit & ROI — the total money you keep over the system's life.
The most common comparison is battery vs no battery. A battery adds roughly £4,000 to the cost but lifts self-consumption from ~45% to ~75% — meaning you use more of what you generate instead of exporting it. Whether it's worth it depends on your usage pattern and region — our home battery ROI guide works through that maths (short answer: it only pays on a time-of-use tariff).
How we calculate
generation = system kW × sun hours
savings = (self-consumed × import rate) + (exported × SEG rate)
self-consumption = 45% (no battery) or 75% (with battery)
25-year profit = Σ savings (0.5% degradation + 3% rate inflation) − cost
Where the data comes from
- Electricity rate — Ofgem price cap, 26.32p/kWh (Q4 2026).
- SEG rate — 6p/kWh typical.
- Sun hours — PVGIS 5.2 regional averages (European Commission).
- System cost — ~£1,600/kW, 0% VAT until 31 March 2027.
- Battery — ~£4,000 for a typical 5 kWh home battery.