Free UK Solar Savings Estimator

Find out what solar
really saves you

Three honest scenarios. A personalised estimate you can keep. Built by the UK's largest solar installer so the numbers reflect what we actually see on real homes.*

⚡ Based on April 2026 Ofgem rates · 🇬🇧 UK-wide data · ✓ Updated quarterly · 🔒 Your details stay private

Your Home

Midlands average: ~900 kWh/kWp/yr

4 kWp
2 kWp 6 kWp 10 kWp
p/kWh
p/kWh
4%

Plain-English guide

What does it all mean?

Solar jargon decoded. Every term used in this calculator, explained clearly.

⚡

kWp (kilowatt-peak)

The rated maximum power output of your solar panel system in perfect conditions (bright sunshine, ideal angle). A 4 kWp system has four times the generating capacity of a 1 kWp system. Most 3-bed UK homes suit 3.5–5 kWp, typically 8–12 panels. It's the 'engine size' of your solar setup.

🏠

Self-consumption

The percentage of your solar generation that you actually use in your home, rather than exporting to the grid. If you generate 3,600 kWh/yr and use 1,800 kWh of it yourself, your self-consumption rate is 50%. Higher is better — using solar directly saves you the full unit rate (24p+), while exporting earns just 4–16p.

🔄

SEG (Smart Export Guarantee)

A UK government scheme that requires energy suppliers to pay you for every unit of electricity your solar panels send back to the grid. Every major supplier offers it, but rates vary enormously — from around 4p/kWh up to 16p/kWh. You choose which supplier pays you for exports; it doesn't have to be your current supplier (though some require you to switch).

🔋

Off-peak battery arbitrage

A strategy that uses a home battery and a time-of-use tariff to buy cheap electricity and use it when prices are high. For example: charge your battery overnight at 7–10p/kWh (off-peak), then use that stored energy during the day or evening instead of buying at 24–34p/kWh. The difference — the 'spread' — is your arbitrage profit. On tariffs like Octopus Flux, this alone can be worth £150–300/yr.

📊

Self-sufficiency

How much of your total annual electricity demand you meet from your own solar (and battery) generation, rather than the grid. A self-sufficiency of 60% means 60% of everything you use comes from your roof. With solar only, most homes reach 30–50%. Add a battery and this typically rises to 60–80%. This is distinct from self-consumption — one measures how much solar you use; the other measures how little grid power you need.

⏱️

Smart (time-of-use) tariffs

Electricity tariffs that charge different rates at different times of day — cheap overnight, expensive at peak times. Examples include Octopus Flux, Intelligent Octopus Go, and E.ON Drive. Paired with a home battery, you can time your energy use to always pay the lowest possible rate. Some smart tariffs also offer premium export rates during peak demand periods.

☀️

kWh/kWp (generation factor)

How many units of electricity a 1 kWp solar system generates in a year in your location. The UK average is around 900 kWh/kWp/yr. In the South West it can be 1,000+, in Scotland as low as 720. Multiply this by your system size to get your total annual generation: a 4 kWp system in the South West might generate 4,400 kWh/yr; the same system in Scotland, about 3,200 kWh/yr.

📉

Panel degradation

Solar panels gradually lose a small amount of efficiency each year — typically 0.5% per year. So in year 10 your panels produce around 95% of what they did in year 1, and by year 25 roughly 88%. This calculator builds this degradation into all long-term projections, so your 25-year totals are realistic rather than optimistic flat-line estimates.

Understanding your three scenarios

Each scenario builds on the last. See exactly where the extra value comes from.

Solar panels only

Your panels generate electricity during daylight hours. What you use directly saves you buying from the grid. What you don't use gets exported at your SEG rate. Simple — and profitable from day one.

  • ✓ Lowest upfront cost
  • ✓ Works without a battery
  • ⚡ You still buy from the grid in the evening

Solar + battery Most popular

A home battery stores surplus solar generation during the day and releases it in the evening. Instead of exporting cheap and buying expensive, you use your own electricity around the clock.

  • ✓ Use solar morning, noon, and night
  • ✓ Self-sufficiency typically rises to 60–80%
  • ✓ Protection from grid price spikes

Solar + battery + smart tariff

Time-of-use tariffs like Octopus Flux or Intelligent Octopus Go let you charge your battery from the grid overnight at 7–10p, then use that stored energy when rates rise to 24–34p. Combined with solar, this maximises every pound.

  • ✓ Extra £150–300/yr from rate arbitrage
  • ✓ Premium export rates up to 24p/kWh
  • ✓ Best long-term ROI

Choosing the right export tariff matters

The Smart Export Guarantee (SEG) pays you for every unit of electricity you export to the grid. Rates vary from 2p to 24p/kWh — choosing well can add hundreds of pounds per year to your savings.

SupplierRateCondition
Ecotricity16pMust switch supply too
British Gas15.1pMust switch supply too
E.ON Next13pSupply customer
Octopus Outgoing12pSupply customer
OVO Energy12pSupply customer
E.ON Next (standalone)6pNo conditions
Octopus SEG4.1pNo conditions

Rates correct as at April 2026. Full comparison at MoneySavingExpert →

Ready for the next step?

See what solar looks like for your home

These figures give you a clear picture of what solar could save. The next step is a no-obligation conversation with Project Solar UK — we'll look at your roof, your usage, and build a quote around the right system for your home.

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