Interactive estimate
The solar savings calculator
Slide, toggle and see the arithmetic for your home — generation, bill savings, export income, payback and your 25-year position. Built on the same public figures we cite everywhere else on this site.
Do the sums first
What could solar actually save you?
Move the sliders and watch the arithmetic — same public figures we cite across this site, no hidden optimism. It's an illustration, not a quote: the real answer comes from a survey.
Set up your home
Three sliders, two switches — that's it.
Quick-pick a system
2 kWp8 kWp
£60£400
Roof direction
Estimated annual benefit
£0
bill savings + export payments
Pays for itself in
0 yrs
at today's flat prices
25-year net position
£0
after paying for the system
CO₂ avoided over 25 yrs
0 t
vs the same power from the grid
from your roof
Your 25-year position
Cumulative benefit minus the system cost — the line crossing zero is your payback point.
Same 25 years, two ways
estimated difference £0
Every assumption behind these numbers
- Electricity unit rate: 26.11p/kWh — the Ofgem average rate we cite across this site. Flat for 25 years (conservative: no price-rise assumptions).
- Standing charge: ~£220 a year comes off your bill before we work out usage — solar can't remove it, so it stays in the "stay on the grid" comparison on both sides.
- Coverage is capped at 50% of your usage without a battery (generation peaks at midday, usage peaks in the evening) and 90% with one. A calculator that lets solar cover your night-time kettle is lying to you.
- The EV switch means adding an EV — it puts ~1,800 kWh of home charging on top of the usage implied by your current bill. If your bill already includes an EV, leave it off.
- Export rate: 13p/kWh — the average SEG earning in 2024–25; the market spans a few pence to 15p+.
- Generation: ~857 kWh per kWp per year south-facing (a typical 3.5 kWp UK system makes about 3,000 kWh); we scale SE/SW roofs at 95% and east–west at 85%.
- System cost: scaled from £6,100 installed for 3.5 kWp (Energy Saving Trust guide price, 0% VAT until 31 March 2027); battery adds a typical £4,600 (Energy Saving Trust, ~5 kWh).
- Self-use scales with your usage. The more electricity you use relative to what you generate, the more of your solar you use directly — the model is calibrated so a typical home on a 3.5 kWp system self-uses about 40% (our blog's worked example), rising towards a ceiling of 48% without a battery and 85% with one. That's why the bill slider moves the savings, not just the coverage ring.
- Panel output declines 0.5% a year in the 25-year projection — in line with typical manufacturer performance warranties. That's the gentle flattening you can see in the chart.
- CO₂: 0.207 kg per kWh — the UK Government 2024 grid-electricity conversion factor, applied to the declining output.
This is an illustration, not a quote or a promise. Real numbers depend on your roof, shading, usage pattern and tariff — that's what the free survey is for.
How this calculator works — and where it can't help you
The model is simple on purpose. Your monthly bill tells us roughly how much electricity you use at the Ofgem average rate. The system size, roof direction and typical UK yields tell us what your panels would generate. The overlap between the two — the solar power you actually use — replaces electricity at around 26p a unit, and whatever's left over is exported under the Smart Export Guarantee at around 13p. Set that annual benefit against the Energy Saving Trust's guide costs for the hardware, and you get a payback year and a 25-year position.
What no web calculator can see: your shading, your roof's pitch and real usable area, how your household actually uses power through the day, and the tariff you're on. Those change the answer — sometimes a lot, in either direction. That's the job of the free survey: we look at the real roof and the real bills, then give you numbers we're prepared to stand behind. If solar genuinely wouldn't pay its way on your home, we'll tell you that too.
Calculator questions, answered straight
How accurate is this calculator?
It is an honest illustration, not a quote. Every assumption is a cited public figure — the Ofgem average unit rate of 26.11p/kWh, the 13p/kWh average SEG export earning, typical UK generation of about 3,000kWh a year from a 3.5kWp system, and Energy Saving Trust guide costs. What it cannot know is your actual roof, shading, usage pattern or tariff — which is why the free survey exists. Treat the output as the right order of magnitude, not a promise.
Why does adding a battery change the numbers so much?
Because of the gap between what electricity costs you and what exports earn you. Every unit you use yourself is worth around 26p; every unit you export earns around 13p. Without a battery a typical home only manages to use about 40% of its solar power, because generation peaks at midday while usage peaks in the evening. A battery shifts that midday power into the evening, lifting self-use to around 70% in our model — so more of your generation earns the 26p rate instead of the 13p one.
Does the calculator include finance or monthly payments?
No, deliberately. It models the cash position only: what a system costs, what it returns each year, and when it pays for itself. If you want to spread the cost, we can introduce you to finance options through an FCA-authorised partner as part of a real quote — but credit figures belong in a regulated illustration, not a web calculator.
Why are the savings flat rather than rising each year?
We hold electricity prices flat for the whole 25 years, which is deliberately conservative. If energy prices rise over the next 25 years — as they have over the last 25 — a solar system pays back faster and the long-term position improves. We would rather the calculator undersells than oversells.