Solar Panel Savings Estimator
Estimate how much solar panels could generate and save you, based on your roof and location.
How this is calculated
Annual generation is roof area × panel efficiency × your country's average daily peak sun hours × 365. Half of that generation is assumed self-consumed (valued at your import tariff and capped by your current bill) and half exported (valued at your export tariff). Payback period divides an estimated installation cost of £1,200 per kWp by your total annual benefit.
Roof area is really a stand-in for system size — a rough conversion is that every 1 kWp of panels needs about 5–7m² of usable, unshaded roof space at typical panel efficiencies, so this calculator's default 30m² roof corresponds to a system size in the 4–6 kWp range for most homes. Panel efficiency, orientation, and shading all affect how much of that theoretical generation you actually capture — a south-facing roof at the stated efficiency will outperform a similarly sized east/west-facing or partially shaded one. For your baseline electricity costs before panels, see the Home Electricity Cost calculator and the Electricity Cost by Country calculator.
Frequently asked questions
- What are "peak sun hours"?
- A way of expressing total daily solar energy as if the sun shone at its maximum intensity (1 kW/m²) for that many hours. It's not the same as daylight hours — a location with long but hazy days can have fewer peak sun hours than a location with shorter, more intense sunshine.
- Why is my bill saving capped?
- You can't save more than you were already spending — if your system generates more self-consumed value than your current annual bill, the saving is capped at your bill amount, with any further surplus counted as export earnings instead.
- What is the self-consumption assumption?
- This assumes roughly 50% of your generation is used directly in your home (valued at your import tariff) and 50% is exported to the grid (valued at your export tariff) — a common rule of thumb for a home without battery storage. Adding a battery would let you self-consume more.
- How is payback period calculated?
- Installed cost is estimated at £1,200 per kWp of system size, divided by your total annual benefit (bill saving plus export earnings) — a simple payback period that ignores financing costs, electricity price changes, and panel degradation over time.
- Can I use this in my own app?
- Yes — every calculator on Stupidly Clever has a matching REST API and MCP tool that runs the same underlying logic.
- What solar panel capacity do I need for my home?
- A rough guide: multiply your annual kWh consumption by 0.25–0.30 to get a system size in kWp. A typical UK home uses ~3,500 kWh/year, suggesting a 3–4 kWp system. The calculator works backwards from system size, so adjust the capacity input until the annual generation matches your target.
- How does the feed-in tariff (or Smart Export Guarantee) affect savings?
- If your grid has an export tariff (the UK's Smart Export Guarantee pays 4–15p/kWh), exported surplus increases your total financial return beyond just the bill saving. The calculator's bill-saving figure is the floor; the actual return will be higher once export payments are added.