Solar Panel Calculator
Size photovoltaic systems and calculate generation, costs, and payback for UK installations
Solar Panel Calculator
Size a photovoltaic system for your UK property
How Many Solar Panels Do I Need? Quick Answer
A typical UK home needs 10-12 solar panels (4kW system) costing £6,000-8,000 installed with 0% VAT. This generates 3,400 kWh per year, saving £550-750 annually on electricity bills at the Q2 2026 Ofgem cap of 24.67p/kWh. The payback period is 9-13 years with 25-year returns of £7,500-14,000+. MCS certification is required for Smart Export Guarantee (SEG) eligibility.
Solar Panel System Size Guide (UK)
| Home Size | System Size | Panels Needed | Cost (Inc. Install) | Annual Saving | Payback |
|---|---|---|---|---|---|
| 1-2 bed flat | 2-3 kW | 6-8 | £4,000-6,500 | £350-500 | 10-13 years |
| 3-bed semi | 4 kW | 10-12 | £6,000-8,000 | £600-800 | 9-12 years |
| 4+ bed detached | 5-7 kW | 14-20 | £7,000-10,500 | £800-1,200 | 8-10 years |
| Large home + EV | 7-10 kW | 20-30 | £10,000-13,000 | £1,000-1,400 | 8-9 years |
Based on 350-450W panels, south-facing roof, UK average irradiance of 850-1,000 kWh/kWp/year. Costs include MCS-certified installation at 0% VAT (domestic, valid until March 2027).
UK Energy Prices & Solar Savings Context
Understanding current UK energy prices is essential for calculating solar panel savings and payback periods. The Q2 2026 Ofgem price cap fell 10.9% from Q1, lowering import rates — which slightly extends solar payback periods compared to the 2024-2025 highs but preserves the underlying economics for typical installations.
Current UK Energy Prices (Q2 2026, Ofgem Cap)
Electricity Import Costs:
- Unit rate (Ofgem Q2 2026 cap): 24.67p per kWh (£0.2467/kWh)
- Standing charge: £0.35-0.60 per day (varies by region)
- Average annual bill: £1,100-1,700 for typical home (3,000kWh usage)
- Trend: Q2 2026 cap -10.9% vs Q1 2026; future caps quarterly
Smart Export Guarantee (SEG) Export Rates (Q2 2026):
- Basic fixed tariffs: £0.033-0.05 per kWh
- Octopus Outgoing (fixed): £0.12 per kWh (reduced from £0.15 in March 2026)
- OVO Energy (fixed): £0.12 per kWh
- Octopus Flux (time-of-use): Up to £0.24 per kWh at peak export (16:00-19:00)
Key Insight: Every kWh you generate and use yourself saves £0.2467 (not bought from grid). Every kWh exported earns £0.033-0.24 depending on tariff. This is why maximising self-consumption — through battery storage, solar diverters, or shifting appliance use to daytime — is critical for ROI.
Typical UK Household Energy Usage
| Home Type | Annual Usage | Annual Cost @ 24.67p/kWh | Recommended Solar |
|---|---|---|---|
| Small flat/1-2 bed | 1,800-2,400 kWh | £444-592 | 2-3 kW (8-10 panels) |
| Medium house/2-3 bed | 2,700-3,500 kWh | £666-863 | 3-4 kW (10-14 panels) |
| Large house/4+ bed | 4,000-6,000 kWh | £987-1,480 | 5-7 kW (16-22 panels) |
| Large house + EV | 6,000-10,000 kWh | £1,480-2,467 | 7-10 kW (22-32 panels) |
Usage includes heating, hot water, appliances, lighting, and EV charging where applicable. Ofgem cap resets quarterly — actual rate varies by supplier and tariff.
Solar Panel Roof Angle & Orientation UK
The optimal angle for solar panels in the UK is 35°-40° from horizontal, facing due south. Most UK pitched roofs (30°-45°) are within 99% of optimal. Orientation matters more than pitch: a south-east or south-west facing roof still delivers 95% of south-facing output, while east or west-facing roofs deliver 76%-78%. North-facing roofs reach only 49% and are generally not recommended for solar installation. MCS-accredited installers use SAP 2012 / MCS Solar Irradiance Datasets to apply these correction factors to your postcode.
Roof Pitch Correction Factor (vs 40° optimal)
Multiply your system's baseline generation by the factor below if your roof pitch differs from the 40° optimum. Applies to south-facing roofs in Southern England; other latitudes shift the optimum slightly (Scotland optimum is closer to 42°).
| Roof Pitch | Annual Output vs Optimal | Typical UK Example |
|---|---|---|
| 0° (flat) | ~88% (needs mounting frame) | Flat-roof extension or garage |
| 15°-25° | ~95%-97% | Low-pitch bungalow or modern flat roof |
| 30° | 98% | Typical post-1980 housing |
| 35° | 99% | Common UK residential pitch |
| 40° (optimal) | 100% (baseline) | Ideal UK south pitch |
| 45° | ~99% | Pre-1950 traditional housing |
| 60° | 95% | Victorian gable or dormer |
| 75° | 85% | Steep Victorian or church roof |
| 90° (vertical) | 73% | Wall-mounted (BIPV / facade) |
Roof Orientation Correction Factor (at 35°-40° pitch)
Orientation impact is larger than pitch for most UK roofs. Values below are for typical domestic pitched roofs at 35°-40° using MCS irradiance datasets for England & Wales.
| Roof Orientation | Azimuth | Output vs South | Notes |
|---|---|---|---|
| South | 180° | 100% (optimal) | Peak generation at solar noon |
| South-east / South-west | 135° / 225° | ~95% | SE peaks earlier, SW peaks later |
| East | 90° | ~78% | Morning peak — good for EV home-charging before work |
| West | 270° | ~76% | Afternoon peak — matches evening return-home usage |
| North | 0° | ~49% | Not MCS-recommended; rarely payback-positive |
East-west split arrays ("E-W" config) sacrifice ~10% peak output vs south-only but deliver a wider, flatter generation curve — often preferred when a battery or solar diverter can absorb mid-day production.
Combined Correction — Worked Example
A 4kW array on a south-east facing roof (azimuth 135°) at 30° pitch:
- Baseline generation at UK average 850 kWh/kWp/year: 4 × 850 = 3,400 kWh/year
- Pitch correction (30°): × 0.98
- Orientation correction (SE): × 0.95
- Combined: 3,400 × 0.98 × 0.95 = 3,165 kWh/year (93% of optimal)
Bottom line: Most UK roofs that aren't north-facing deliver 90%-100% of optimal. Shading from chimneys, neighbouring trees, or dormers usually has a larger impact than small deviations from 40° south — consider panel-level optimisers or micro-inverters if shading is a factor.
UK Solar Generation by City (kWh per kWp installed)
Annual solar generation in the UK varies by ~25% from the sunniest southern cities to the cloudiest northern ones. Use the table below to get a location-specific baseline for a south-facing 35°-40° pitched array, then apply roof pitch and orientation corrections.
Annual Solar Yield by UK City (south-facing, optimal pitch)
| City / Region | kWh per kWp per year | 4kW system (annual) | Annual bill saving @ 24.67p/kWh, 50% self-consumption |
|---|---|---|---|
| Plymouth / Cornwall | 1,050-1,100 | 4,200-4,400 kWh | £518-543 |
| Brighton / South Coast | 1,020-1,060 | 4,080-4,240 kWh | £503-523 |
| London | 1,010-1,040 | 4,040-4,160 kWh | £498-513 |
| Bristol / Cardiff | 980-1,010 | 3,920-4,040 kWh | £484-498 |
| Birmingham / Midlands | 930-970 | 3,720-3,880 kWh | £459-478 |
| Leeds / Sheffield | 890-920 | 3,560-3,680 kWh | £439-454 |
| Manchester / Liverpool | 880-910 | 3,520-3,640 kWh | £434-449 |
| Newcastle / North East | 850-880 | 3,400-3,520 kWh | £419-434 |
| Edinburgh / Glasgow | 820-860 | 3,280-3,440 kWh | £404-424 |
| Inverness / NW Scotland | 780-820 | 3,120-3,280 kWh | £385-404 |
| Belfast / Northern Ireland | 850-890 | 3,400-3,560 kWh | £419-439 |
Figures assume 450W mono panels at MCS irradiance baselines. For specific postcode yields use the Energy Saving Trust postcode calculator. Scottish Highland winters are ~3-5× worse than summer peaks; a 30%/70% winter/summer split is typical across the UK.
How the UK compares globally
UK average of ~900 kWh/kWp/year is lower than Southern Europe (Italy ~1,400, Spain ~1,600) but higher than Northern Germany (~950) and comparable to the Netherlands (~900). Combined with UK retail electricity prices being among the highest in Europe, the payback economics of UK solar remain competitive with Mediterranean countries despite lower irradiance.
Solar Battery Sizing — What Size Do I Need?
Most UK homes with a 4-5kWp solar system need a 5-10kWh battery. The optimum size is roughly two-thirds of your average daily electricity consumption— so a 3-bed house using 2,900 kWh/year (~8 kWh/day) needs ~5.3 kWh of usable battery capacity. Sizing a battery larger than your daily generation wastes capacity in winter when panels produce 3-4 kWh/day; sizing smaller than a third of daily use leaves most evening load on the grid. Battery cost ranges £2,500-£8,000 depending on capacity and brand.
Battery Size Guide by Solar System + Usage
| Solar Size | Annual Usage | Daily Avg Use | Recommended Battery | Typical Cost |
|---|---|---|---|---|
| 2-3 kWp | 1,800-2,400 kWh | 5-7 kWh | 3-5 kWh | £2,500-3,500 |
| 4 kWp (typical) | 2,700-3,500 kWh | 7-10 kWh | 5-7 kWh | £3,500-5,000 |
| 5-6 kWp | 4,000-5,500 kWh | 11-15 kWh | 8-10 kWh | £5,000-7,000 |
| 7-10 kWp + EV | 6,000-10,000 kWh | 16-27 kWh | 10-15 kWh | £6,500-8,500 |
Usable capacity shown (depth of discharge 80%-95% depending on chemistry). Lithium iron phosphate (LFP) batteries last 6,000+ cycles (~15 years); older NMC chemistry is now rare on UK domestic installs.
Does a Battery Improve Solar Payback?
Self-consumption jumps from ~30% without battery to 60%-80% with battery, which means you buy less from the grid. But batteries also delay payback because they add £3,000-£8,000 upfront. Whether they pay back depends on the import-export rate spread (currently 24.67p import vs 12p export = 12.67p gap per shifted kWh).
Typical comparison, 4kW system in UK:
| Config | Cost | Self-Cons. | Annual Saving | Payback | 25-yr Return |
|---|---|---|---|---|---|
| 4kW no battery | £7,000 | ~30% | ~£590 | 11.9 yrs | +£7,750 |
| 4kW + 5kWh battery | £11,500 | ~65% | ~£730 | 15.8 yrs | +£6,750 |
| 4kW + 10kWh battery | £13,500 | ~75% | ~£780 | 17.3 yrs | +£6,000 |
Verdict at Q2 2026 rates: Batteries add comfort and grid resilience but modestly reduce 25-year total returns because the import-export spread is narrow. If Ofgem caps rise back toward 30p/kWh, battery payback improves significantly. A battery is easier to justify on a time-of-use tariff (charge at 7p off-peak, discharge during 30p+ peak) than on flat-rate SEG.
Hybrid Inverter vs Retrofit Battery
If you're not installing a battery immediately, spec a hybrid inverter(SolarEdge, GivEnergy, Solis, Sofar, Growatt) rather than a plain string inverter — this adds DC battery-ready terminals for future upgrade without replacing the inverter. Cost premium is typically only £200-£500 over a string inverter.
Retrofit-only battery systems (AC-coupled) use a separate battery inverter and cost £500-£1,500 more than DC-coupled battery systems added to a hybrid inverter from the start.
Solar Panel Installation Costs UK
UK solar panel installation costs have decreased significantly since 2010 while panel efficiency has improved. Current Q2 2026 market prices below include MCS-certified installation and 0% VAT (domestic, valid until March 2027).
Installation Cost by System Size (Q2 2026)
| System Size | Panels Needed | Total Cost | Cost per kW | Annual Generation |
|---|---|---|---|---|
| 2 kW | 5-6 panels | £4,000-5,000 | £2,000-2,500 | 1,700-2,000 kWh |
| 3 kW | 8-10 panels | £5,000-6,500 | £1,667-2,167 | 2,550-3,000 kWh |
| 4 kW | 10-13 panels | £6,000-8,000 | £1,500-2,000 | 3,400-4,000 kWh |
| 5 kW | 13-16 panels | £7,000-9,500 | £1,400-1,900 | 4,250-5,000 kWh |
| 6 kW | 15-18 panels | £8,000-10,500 | £1,333-1,750 | 5,100-6,000 kWh |
| 8 kW | 20-24 panels | £10,000-13,000 | £1,250-1,625 | 6,800-8,000 kWh |
Prices include MCS-certified installation, scaffolding, electr ical work, and VAT at 0% (domestic only)
What's Included in the Price?
Equipment (60-70% of cost):
- Solar panels (£150-300 each)
- Inverter (£800-2,000)
- Mounting system & rails
- DC cables & connectors
- Generation meter
- Isolators (DC & AC)
Installation (30-40% of cost):
- Scaffolding hire
- Labour (1-3 days)
- Electrical work & consumer unit updates
- DNO application (G98/G99 grid connection)
- MCS certification
- Commissioning & testing
Additional Costs to Consider
- Battery storage: Add £3,000-8,000 (5-13.5 kWh capacity)
- Roof repairs: £500-2,000 if needed before installation — use a free roofing calculator to estimate materials
- Bird protection mesh: £300-600
- Optimizers/micro-inverters: Add 10-20% to system cost
- EV charger integration: £500-1,200
💰 VAT Savings: No VAT on solar panel installations for domestic properties (0% VAT until March 2027). This saves 20% compared to commercial rates. Combined with 2026 panel price reductions driven by global manufacturing oversupply, real installed costs are at 10-year lows.
Real-World Solar ROI Examples (UK Prices)
These worked examples use representative UK energy prices and installation costs to show accurate payback periods and 25-year returns. Examples assume a 27p/kWh import rate (average of the 2024 Ofgem cap peak and the current Q2 2026 cap of 24.67p); at the current 24.67p rate, annual savings are roughly 8% lower and payback periods 8%-10% longer.
1Semi-Detached House, 4kW System
Scenario:
- Property: 3-bedroom semi-detached, south-facing roof
- Annual usage: 3,200 kWh (£864 @ £0.27/kWh)
- System: 4kW (12 panels, 400W each)
- Installation cost: £7,000
- Location: Southeast England
Annual Generation:
4 kW × 850 kWh/kW = 3,400 kWh/year
Self-Consumption Analysis:
Assuming 40% self-consumption (typical without battery):
• Self-consumed: 3,400 × 40% = 1,360 kWh @ £0.27 = £367 saved
• Exported: 3,400 × 60% = 2,040 kWh @ £0.12 SEG = £245 earned
Total annual benefit: £612
Payback Calculation:
Installation cost: £7,000
Annual savings: £612
Payback period: 11.4 years
25-Year Return:
Annual savings: £612 × 25 years = £15,300
Minus installation: £15,300 - £7,000 = £8,300 profit
Assuming 0.5% annual degradation and flat energy prices (conservative)
✓ Result: 11.4-year payback, £8,300 profit over 25 years (119% ROI)
24kW System + 5kWh Battery Storage
Scenario:
- Same 4kW system as Example 1
- Plus 5kWh battery storage (£4,000 additional cost)
- Total investment: £11,000
- Battery increases self-consumption to 65%
With Battery Storage:
• Self-consumed: 3,400 × 65% = 2,210 kWh @ £0.27 = £597 saved
• Exported: 3,400 × 35% = 1,190 kWh @ £0.12 SEG = £143 earned
Total annual benefit: £740
Payback vs Without Battery:
With battery: £11,000 ÷ £740 = 14.9 years
Without battery: £7,000 ÷ £612 = 11.4 years
Battery adds 3.5 years to payback but increases long-term returns
25-Year Comparison:
With battery: (£740 × 25) - £11,000 = £7,500 profit
Without battery: (£612 × 25) - £7,000 = £8,300 profit
Note: Battery may need replacement after 10-15 years (£2,000-3,000 cost)
⚡ Verdict: Battery adds comfort (power during evening) but slower ROI unless energy prices rise significantly
37kW System for Home with Electric Vehicle
Scenario:
- Property: Large 4-bed detached
- Annual usage: 5,000 kWh home + 3,000 kWh EV = 8,000 kWh total (£2,160 @ £0.27/kWh)
- System: 7kW (20 panels, 350W each)
- Installation cost: £10,000
Annual Generation:
7 kW × 850 kWh/kW = 5,950 kWh/year
With Smart EV Charging (daytime):
EV charges during sunny hours (50% self-consumption possible):
• Self-consumed: 5,950 × 50% = 2,975 kWh @ £0.27 = £803 saved
• Exported: 5,950 × 50% = 2,975 kWh @ £0.12 SEG = £357 earned
Total annual benefit: £1,160
Excellent Payback:
Installation cost: £10,000
Annual savings: £1,160
Payback period: 8.6 years
25-Year Return:
(£1,160 × 25) - £10,000 = £19,000 profit (190% ROI)
✓ Best ROI: Larger systems with high daytime usage (especially EV charging) offer fastest payback
💡 Key Takeaways for UK Solar
- Payback periods: Typically 8-13 years depending on usage and self-consumption
- Best ROI: Large systems (6kW+) with high daytime usage or EV charging
- Battery storage: Adds comfort but extends payback by 2-4 years
- Energy price assumption: These calculations assume prices stay flat (conservative - likely to rise)
- Self-consumption is key: Use appliances during sunny hours to maximize savings
- 25-year returns: All systems show positive ROI with minimal maintenance costs
How Solar Panels Work in the UK
Solar photovoltaic (PV) panels convert sunlight into electricity. Even on cloudy days, UK solar panels generate power, making them a viable renewable energy solution across all regions.
Key Components of a Solar PV System
- Solar Panels: Convert sunlight to DC electricity (typically 350-450W per panel)
- Inverter: Converts DC to 230V AC for home use (97% efficient)
- Mounting System: Secures panels to roof with optimal angle
- Generation Meter: Records energy produced for SEG payments
- Battery Storage (Optional): Stores excess energy for evening use
UK Solar Generation by Region
Annual averages. Summer generation 3-5× winter generation.
Typical System Sizes
MCS Certification & Compliance
MCS (Microgeneration Certification Scheme) is essential for UK solar installations. It ensures quality, provides consumer protection, and is required for SEG payments.
What is MCS?
MCS is a quality assurance scheme for renewable energy installations. Only MCS-certified installers can install systems that qualify for SEG (Smart Export Guarantee) payments.
- Installer must be MCS-certified
- Products must meet MCS standards
- Installation must follow MCS guidelines
- System must be commissioned and tested
- Certificate issued within 2 weeks of completion
DNO Notification (G98/G99)
Planning Permission
Usually Permitted Development: Most domestic rooftop solar installations don't require planning permission.
- Listed building
- Building in conservation area
- Ground-mounted system in front of house
- Panels protrude more than 200mm from roof
- Installation on flat roof visible from street
Always check with your local planning authority before installation.
BS 7671 Electrical Compliance
Solar PV installations must comply with BS 7671 Section 712:
- DC isolators at array and inverter
- AC isolator at consumer unit
- Type B RCD required for solar inverters
- Proper earthing and bonding
- Solar-rated DC cables (EN 50618)
- Overvoltage protection
- Generation meter installation
SEG Export Tariffs Explained
The Smart Export Guarantee (SEG) requires electricity suppliers to pay for renewable energy exported to the grid. All MCS-certified systems are eligible.
How SEG Works
When your solar panels generate more electricity than you use, the excess is exported to the National Grid. Your energy supplier pays you for this exported energy.
- Basic fixed tariffs: £0.033-0.05/kWh
- Octopus Outgoing (fixed): £0.12/kWh (reduced from £0.15 in March 2026)
- OVO Energy (fixed): £0.12/kWh
- Octopus Flux time-of-use: up to £0.24/kWh at peak export (16:00-19:00)
Important: SEG rates vary by supplier. Shop around for best rates. Some tariffs track wholesale prices and can be higher during peak times.
Maximizing Export Income
- Compare tariffs: Different suppliers offer different rates
- Smart meters: Enable time-of-use tariffs with better peak rates
- Battery storage: Export during peak price times
- System sizing: Oversize slightly to maximize export revenue
- Monitor generation: Track export to optimize tariff choice
Self-Consumption vs Export
Key principle: Using solar energy yourself saves more than exporting it.
- 1 kWh self-consumed = £0.30 saved (not paid to supplier)
- 1 kWh exported = £0.15 earned (paid by supplier)
- Self-consumption is 2× more valuable
Strategy: Use appliances during sunny hours (dishwasher, washing machine, EV charging) to maximize self-consumption. Battery storage increases self-consumption from ~30% to ~70%.
Choosing Solar Panels & Equipment
Panel Types
- Efficiency: 19-22% (highest)
- Better performance in low light
- More expensive but best value long-term
- Black appearance, premium look
- Typical UK choice: 350-450W panels
- Efficiency: 15-17%
- Lower cost per panel
- Blue appearance
- Less common now, being phased out
- Efficiency: 10-12% (lowest)
- Flexible, lightweight
- Rarely used for UK domestic installations
Panel Specifications to Check
- Product warranty: 10-12 years minimum
- Performance warranty: 25 years (80-90% output guaranteed)
Inverter Selection
- One inverter for entire array
- Most cost-effective
- Good for unshaded roofs
- 97% efficiency typical
- Optimizer on each panel
- Better for partial shading
- Panel-level monitoring
- 10-15% more expensive
- One inverter per panel
- Best for complex roof layouts
- Most expensive option
- 25-year warranty typical
- Built-in battery compatibility
- Future-proof for battery addition
- Slightly more expensive
Top Brands (UK Market)
Always verify MCS certification for panels and inverters to qualify for SEG.
Frequently Asked Questions
Recommended Products
Affiliate links
Free: BS 7671 Quick Reference Card
Max Zs values, diversity factors, cable ratings, voltage drop — one printable page. Plus occasional emails with calculator updates and useful tips.
Was this calculation helpful?