Solar panel cost calculator — UK new builds (2026)
Work out how many solar panels you need and what they cost in 30 seconds. Enter your ground floor area and we calculate system kWp, panel count, install cost at 2026 MCS-benchmarked pricing, annual generation and savings.
Sizing inputs
All required by Part L 2026 — units are SI / metric.
Typical 3-bed semi: 40–50 m² · 4-bed detached: 55–75 m² · 5-bed exec: 80–110 m²
Your FHS-compliant system
Live calculation as you change inputs.
Solar panel cost per kWp — UK 2026
These are the 2026 benchmark install prices the calculator uses, by route. New-build in-roof is the cheapest way to buy solar in the UK because the panels go on while the scaffold is already up and displace the roof tiles they replace.
| Route | 2026 cost per kWp |
|---|---|
| New-build in-roof (build stage, panels replace tiles) | ~£1,200 ex VAT & scaffold — source: Spirit Energy roof-integrated solar KB |
| Retrofit on-roof — UK MCS average | £1,565–£1,686 — source: MCS Installation Database via GOV.UK (published 28 May 2026) |
| Retrofit on-roof — DESNZ median typical domestic | £1,800–£1,900 |
| Retrofit 3–4 kWp system total | ~£7,349 (MCS England, March 2026; typical 3-bed £7,505) |
| New-build delta | ~20–30% cheaper than retrofit — £1,200 vs £1,565–£1,686/kWp works out at 23–29% lower |
Why the gap: no separate scaffold hire (the site scaffold is already up), in-roof panels offset the tile cost at design stage, and labour mobilisation is shared with the main build programme.
How many solar panels do I need? By bedroom count
| Bedrooms | Usage-based | Panels (~430W) | FHS minimum (40% GFA rule) |
|---|---|---|---|
| 1–2 bed | 2–3 kW (~1,800 kWh/yr) | 4–8 | ~2.5–3.0 kWp |
| 3 bed | 3.5–5 kW (~2,700 kWh/yr) | 8–12 | 3.74 kWp reference (42.5 m² GFA) |
| 4 bed | 4–5 kW (~4,100 kWh/yr) | 10–12 | 5.2 kWp (65 m² GFA) |
| 5+ bed | 5–6+ kW | 13–16 | 7.6 kWp (95 m² GFA) |
Methodology: annual consumption anchors follow Ofgem's Typical Domestic Consumption Values; the FHS column applies this page's 40%-of-ground-floor-area sizing methodology; usage-based system sizes and panel counts follow The Eco Experts.
Quick-answer solar calculator FAQs
How many solar panels do I need? Calculator
Number of panels = reference kWp ÷ panel rating, rounded up. The reference kWp comes from Approved Document L 2026, equation 5.1: ground floor area × 0.40 × 0.22 kWp/m². For a 3-bed semi with a 42.5 m² ground floor: 42.5 × 0.40 × 0.22 = 3.74 kWp, or 9 panels of 425 W. A 4-bed detached at 65 m²: 5.72 kWp, 14 panels of 425 W. A 5-bed at 95 m²: 8.36 kWp, 20 panels of 425 W. Use the calculator above for your specific plot.
Solar kW calculator — what size system?
Reference kWp = ground floor area × 0.40 × 0.22. Approved Document L 2026 uses 0.22 kWp per m² of panel, which it notes is 1 kWp for every 4.5 m². Reference arrays: 42.5 m² ground floor, 3.74 kWp; 50 m², 4.40 kWp; 65 m², 5.72 kWp; 95 m², 8.36 kWp. The requirement is an annual output at least equal to that reference array (south-east to south-west, 45° pitch, not overshaded), so an east-west or shaded roof needs a larger array to match. Larger arrays also improve payback.
Solar panel and battery calculator — combined sizing
For a combined PV + battery system on a UK new build, size the battery at roughly 2.5× the PV array kWp value. Example: 4.0 kWp PV → 10 kWh battery. 5.2 kWp PV → 13 kWh battery. 7.6 kWp PV → 16-20 kWh battery. This ratio captures roughly 78% of self-consumption potential — enough to take typical evening household loads from stored solar without grid import. See our battery storage guide.
Flat roof solar panel calculator
Flat roofs use ballasted east-west split arrays rather than south-facing pitched arrays. The panel area requirement under FHS is the same (40% of ground floor area), but east-west splits generate roughly 8-12% less per kWp than south-facing pitched arrays. To match a south-facing pitched array\'s annual generation, size flat-roof installations roughly 12% larger. Annual generation: a 4.0 kWp flat-roof east-west split produces ~3,300 kWh/yr vs ~3,750 kWh/yr for the equivalent south-facing pitched.
Install cost by house type (2026)
Fitting solar at build stage runs roughly 20–30% cheaper than a retrofit of the same system. The table below prices the Approved Document L reference array (0.22 kWp/m² over 40% of the ground floor area) for three example houses at ~£1,200/kWp new-build in-roof against the £1,565–£1,686/kWp MCS retrofit on-roof average:
| House type | Reference array | New-build in-roof (~£1,200/kWp) | Retrofit on-roof (£1,565–£1,686/kWp) |
|---|---|---|---|
| 3-bed semi (42.5 m² ground floor) | 3.74 kWp | ~£4,490 | £5,850–£6,310 |
| 4-bed detached (65 m² ground floor) | 5.72 kWp | ~£6,860 | £8,950–£9,640 |
| 5-bed executive (95 m² ground floor) | 8.36 kWp | ~£10,030 | £13,080–£14,090 |
New-build prices are ex VAT and scaffold; retrofit ranges use the MCS Installation Database UK average. For payback and lifetime returns see the full ROI breakdown →. For the cost detail by bedroom count see our 3-bed, 4-bed and 5-bed cost guides.
Solar panel cost calculator FAQs
How much do solar panels cost in the UK in 2026?
How many solar panels do I need for a 3-bed house?
Are solar panels cheaper on a new build than a retrofit?
Is in-roof solar cheaper than on-roof?
How accurate is a solar panel cost calculator?
Get a quote for FHS-compliant solar
Share your plot details and a solar installer can price a system sized to the Part L 2026 notional dwelling, with PV area equal to 40% of the ground floor area. There is no obligation to go ahead.
- ✓ Sized to the 40% ground-floor-area rule
- ✓ For developer programmes and one-off self-builds
- ✓ Check any installer against the MCS register before you sign
Request a quote
A few details about the plot help an installer price it accurately.