Future Homes Standard PV calculator
Size a Part L 2026-compliant solar PV array in 30 seconds. Enter your house ground floor area and we calculate the minimum system kWp, panel count, expected annual generation and indicative system cost.
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.
Quick-answer solar calculator FAQs
How many solar panels do I need? Calculator
Number of solar panels needed = (Ground floor area × 0.40) ÷ 1.7 m². For a typical UK 3-bed semi at 42.5 m² ground floor: 42.5 × 0.40 ÷ 1.7 = 10 — round to 8-10 panels (3.4 kWp). 4-bed detached at 65 m²: 12-13 panels (5.2 kWp). 5-bed at 95 m²: 18 panels (7.6 kWp). Use the calculator above for your specific plot.
Solar kW calculator — what size system?
Required kWp = (Ground floor area × 0.40) ÷ 5. The divisor of 5 reflects that one square metre of panel area produces roughly 0.2 kWp at modern panel efficiency (425W on 2 m²). For FHS compliance from March 2027, the typical system sizes by house type are: 2-bed flat 2.5-3.0 kWp; 3-bed semi 3.4 kWp; 3-bed detached 4.0 kWp; 4-bed detached 5.2 kWp; 5-bed executive 7.6 kWp. Larger arrays exceed the FHS minimum and 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.
Solar panel ROI calculator UK — payback by house type
A solar panel ROI calculator works out how long the system takes to pay for itself from saved and exported electricity. For a UK new build the return on investment is strong because installation at build phase is 25-35% cheaper than retrofit. The table below shows typical ROI and payback at 2026 tariffs (22p import, 8p SEG export) for volume-developer pricing:
| House type | System | Install cost | Annual benefit | Payback | 25-yr ROI |
|---|---|---|---|---|---|
| 3-bed semi | 3.4 kWp | £3,380 | £420 | 8.0 yr | +210% |
| 4-bed detached | 5.2 kWp | £4,500 | £640 | 7.0 yr | +255% |
| 5-bed executive | 7.6 kWp | £6,270 | £940 | 6.7 yr | +275% |
25-year ROI assumes 0.5%/yr panel degradation and flat real tariffs. Adding a battery raises self-consumption (and total lifetime return) but extends simple payback by ~3 years. The interactive calculator above estimates payback for your exact plot from ground floor area and roof orientation. For the full cost breakdown by bedroom count see our 3-bed, 4-bed and 5-bed cost guides.
Get an FHS-compliant solar quote in 48 hours
Tell us your plot details — ground floor area, location and target start-on-site date. We return a fully-costed system sized to Part L 2026 (40% PV rule), with the SAP/HEM compliance pack included.