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Solar savings estimator

A rough, first-year estimate of what solar panels could save you, using figures you can see and change. Every step of the sum is shown below the result. Not financial advice.

1 Your system
From your quote. Filled in: 4.5 kWp, which the Energy Saving Trust says is typical for a home.
kWh each kWp makes in a year on a south-facing 35° roof in your MCS zone. An MCS installer’s written estimate gives the figure for your own roof.
2 Your roof
100% = south-facing at 35°. Choose the direction and pitch above to fill it in, then take a few points off for any shading.
3 Your electricity
From your bills or your supplier’s app. Filled in: Ofgem’s typical medium home, 2,500 kWh.
Will you have a battery? Suggests a self-use share below
MCS example figures: 19% with no battery, 52% with about 5 kWh of usable battery (someone home half the day). Higher if you’re home all day, lower if you’re out all day.
4 Prices
Your unit rate, from your bill. Filled in: Ofgem price cap average, 26.32p, valid 1 October to 31 December 2026.
Your export tariff — e.g. Outgoing Octopus 12p, E.ON Next Export Exclusive 13p, EDF SEG Export Variable 3p (checked 9 October 2026). Northern Ireland has no Smart Export Guarantee.
Optional — your quote’s full installed price. Filled in: about £7,600, the Energy Saving Trust’s typical figure for a 4.5 kWp system.

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How we work it out

  1. Generation = system size × yield × roof factor (the MCS method is kWp × Kk × shade factor)
  2. Used in the building = generation × self-use share, but never more than you use in a year
  3. Exported = generation − used
  4. Bill saving = used × your unit rate
  5. Export income = exported × export rate
  6. Simple payback = installation cost ÷ (bill saving + export income)

Where the starting figures come from

Figures filled in for you come from the sources below, checked 9 October 2026. Your own bills and quotes are always better.

  • Yield: the MCS figure (Kk) for a south-facing roof at 35° in your MCS postcode zone, from the MCS Irradiance Datasets. MCS installers work out the same figure for your exact pitch and direction, and allow for shade — use theirs if you have it.
  • Roof factor: how a roof’s direction and pitch compare with south at 35°, worked out from the MCS data for zone 6 (Birmingham); other zones give almost the same ratios (within about 2 percentage points). Take a few points off for any shading.
  • Size and cost: the Energy Saving Trust says home systems are generally around 4.5 kWp and cost around £7,600 (October 2026). Use your own quote.
  • Electricity use: Ofgem’s typical medium household figure, 2,500 kWh a year (from 1 July 2026).
  • Unit rate: Ofgem price cap average for 1 October to 31 December 2026, 26.32p per kWh (Direct Debit, single rate, no VAT on electricity in Great Britain until 31 March 2027). Your own rate depends on your region, tariff and payment method.
  • Self-use: example figures from MCS guidance note MGD 003 for a home where someone is in half the day, using 2,500–2,999 kWh a year with 3,600–3,899 kWh of solar — 19% with no battery, 52% with about 5 kWh of usable battery.
  • Export rate: there is no single official rate — use your supplier’s tariff. On 9 October 2026, examples included Outgoing Octopus at 12p per kWh, E.ON Next Export Exclusive at 13p (E.ON Next customers) and EDF’s SEG Export Variable at 3p (open to anyone). Northern Ireland has no Smart Export Guarantee.

Sources

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