Updated for 2026: Your roof isn’t the “optimal” 40° south-facing angle most guides assume. Neither is mine. Neither are most UK homes. This guide shows you exactly what each roof type actually delivers in pounds and pence—because that’s what matters when you’re deciding where to put £5,000+ of solar panels.
The Earth’s axis is tilted 23.5°, causing the sun’s path to vary throughout the year. Your solar panel’s tilt angle determines how efficiently it captures that energy. But here’s what most guides don’t tell you: the difference between “optimal” and “your actual roof” is usually much smaller than you’d expect—and often not worth worrying about.
The Bottom Line: 10-Year ROI by Roof Type
Let’s cut to the chase. Here’s what a typical 4kW solar system generates annually based on roof type, and what that means for your wallet over 10 years. These figures use the current Ofgem price cap rates and real UK irradiance data.
| Roof Type | Typical Angle | Annual Generation (4kW) | 10-Year Savings* | Verdict |
|---|---|---|---|---|
| Flat Roof | 0-10° | 3,200 kWh | £7,100 | Best summer output, weak winter |
| Normal Pitched | 30-45° | 3,800 kWh | £8,400 | The UK sweet spot |
| Steep/Vertical | 60-90° | 2,800 kWh | £6,200 | Surprisingly good year-round consistency |
The “optimal” pitched roof generates about £1,300 more over 10 years compared to a flat roof—roughly £130/year difference. That’s significant, but not catastrophic if you’re stuck with a flat roof. And vertical installations? They shine in winter when you need energy most.
Solar Angle And Generation Calculator
Use this calculator to estimate your annual yield based on your location and panel direction. It uses optimal angles for UK latitudes and real irradiance data from the European Commission’s PVGIS database.
Flat Roof Installations: The Summer Champion
Flat roofs (0-10° angle) get a bad reputation in solar guides, but they’re far from useless. In summer, when the sun is high, flat panels capture excellent energy. The problem comes in winter when low sun angles dramatically reduce output.
Advantages: Easy installation, no tilting frames needed, excellent summer production, can install panels facing both East and West for wider generation curve. Ideal for battery owners who want to charge throughout the day rather than just at noon.
Disadvantages: 15-25% less annual generation than optimal pitch, poor winter output, panels below 10° don’t self-clean (rain can’t wash away dust), may require tilting frames for better performance.
My Experience With Nearly Flat Panels
In May 2024 I built a solar gazebo to expand my PV capacity. The location falls under height regulations from the local Building Regulations authority, so I had limited room on the roof angle. After aesthetic optimisation, I ended up with just a 6° angle—well below optimal.
The result? Rainwater cannot fully drain from the panels. Dust washed down by rain remains as residue and builds up. I now clean these panels every few months—a minor inconvenience for the extra capacity. The financial impact? Probably 5-10% generation loss when dirty, easily recovered with a quick hosing.
For detailed guidance on installation considerations, the Energy Saving Trust provides comprehensive solar advice including flat roof considerations.
Ballasting Requirements for Flat Roofs
If you’re using tilting frames on a flat roof, you’ll need ballast weight to prevent wind uplift. Here are illustrative requirements for different UK regions:
| Region | Average Wind Speed (m/s) | Recommended Ballast (kg) | Note |
|---|---|---|---|
| Southeast (London) | 4 – 6 | 40 – 50 | Urban windbreaks reduce requirements |
| Southwest (Bristol) | 5 – 7 | 50 – 60 | Coastal areas need more |
| Midlands (Birmingham) | 4 – 6 | 40 – 50 | Urban areas require less |
| Northwest (Manchester) | 5 – 8 | 50 – 65 | Hilly regions need more |
| Northeast (Newcastle) | 5 – 8 | 50 – 65 | Coastal exposure increases needs |
Normal Pitched Roofs (30-45°): The UK Sweet Spot
If you have a standard UK pitched roof between 30-45°, you’ve won the solar lottery. This range captures excellent energy year-round, balancing summer peaks with respectable winter output. According to research from Stanford University, the optimal angle for UK latitudes (51-56°N) is approximately 35-42°.
Why this works: UK latitude means the sun is never directly overhead, even in summer. A 35-40° tilt captures the winter sun efficiently while still performing well in summer when the sun is higher. You get the best of both worlds.
Direction Matters More Than You Think
For optimal energy production in the UK, panels need to point South. The next best directions are Southeast and Southwest with only ~5% efficiency loss. East and West lose about 15%—still very viable, especially if that’s what your roof offers.
| Estimated yearly generation for a single 430W panel | 40° (optimal) | 0° flat | 52.5° | 67.5° |
|---|---|---|---|---|
| South | 440.8 kWh | 336 kWh | 427 kWh | 398 kWh |
| East | 343 kWh | 336 kWh | 322 kWh | 289 kWh |
| West | 336 kWh | 336 kWh | 313 kWh | 281 kWh |
| North | 215 kWh | 336 kWh | 173 kWh | 133 kWh |
Update for 2026: The East-West Split Strategy
While South is best for total annual numbers, the rise of home battery storage has made the East-West split array increasingly popular. Instead of a massive spike at noon (which you might not use), you get a wider generation curve: East panels wake up early for breakfast, and West panels catch the late afternoon sun to top up your battery before evening peak rates.
Optimal Angles for UK Cities
| City | Summer Tilt | Winter Tilt | Year-Round Optimal |
|---|---|---|---|
| Southampton | 35.9° | 65.9° | 40° |
| London | 36.5° | 66.5° | 40° |
| Birmingham | 37.5° | 67.5° | 40° |
| Newcastle | 39.9° | 69.9° | 43° |
| Edinburgh | 40.9° | 70.9° | 42° |
| Aberdeen | 42.1° | 72.1° | 43° |
Steep or Vertical Installations: The Winter Champion
Wall-mounted panels at 60-90° look suboptimal on paper, but they have a surprising advantage: year-round consistency. While total annual output is lower, the generation curve is much flatter. You get respectable output in winter when electricity is most expensive and most needed.
My Experience: Garage Wall-Mounted Panel
When I ran out of roof space on my garage, I mounted one panel on the wall perpendicular to the roof. It’s practically vertical at 90°—textbook “wrong” according to most guides.
The result? That wall panel pulls its weight in winter when my roof panels are struggling. December through February, it often outperforms the flatter roof panels on cloudy days because the low winter sun hits it more directly. For my use case—maximising winter self-consumption to avoid peak rates—it’s been an excellent addition.
Can You Have Solar Panels at Different (Mixed) Angles?
Yes, and it’s increasingly common. You can have solar panels installed at different angles using a few strategies:
Microinverters or solar optimisers are the most effective approach. Each panel operates independently, maximising energy production regardless of the angle or orientation. This eliminates the “weakest panel drags down the string” problem.
Another option is exploring different connection configurations. You can wire in parallel or series to counteract performance differences from sub-optimal angles.
Having panels at different angles adds complexity to design, installation, and maintenance. If you’re unsure, consult a MCS certified installer who can optimise your system for maximum energy production.
Expert Tip: Bifacial Panels and Tilt
If you’re ground-mounting or using a flat-roof frame, consider bifacial panels. These collect light from both sides—direct sunlight on the front and reflected light (albedo) on the back. For bifacial panels, a steeper tilt (45° or even vertical) can be surprisingly powerful if you have a reflective surface underneath like white gravel or concrete.
This setup can boost total generation by 5-20% compared to standard monofacial panels—potentially recovering the “lost” efficiency from a non-optimal angle while providing better winter performance.
At What Angle Do Solar Panels Stop Working?
Solar panels don’t “stop working” at any angle—they just become less efficient. Even at 90° (vertical), panels still produce significant electricity as long as they receive some sunlight. The real question is whether the output justifies the cost.
At extreme angles, you lose efficiency but may gain other benefits: vertical panels shed snow instantly, never get dirty from dust settling, and provide excellent winter output. For some installations, these practical benefits outweigh the efficiency loss.
Conclusion: What Should You Do?
Stop worrying about the “optimal” 40° south-facing angle if you don’t have it. Here’s the decision framework:
Standard pitched roof (30-45°)? You’re in the sweet spot. Install panels and enjoy excellent year-round production. South is best, but East/West only loses ~15%.
Flat roof? Two options: install flat and accept 15-25% less annual output (still very viable), or add tilting frames with appropriate ballast. Consider East-West split if you have battery storage.
Limited roof space? Wall-mounting is a legitimate option, especially if you prioritise winter output or have exhausted roof capacity. The consistency can be valuable for battery owners.
The 10-year difference between “optimal” and “your roof” is typically £1,000-2,000—significant but not deal-breaking. What matters more is getting a quality installation from an MCS certified installer so you’re eligible for Smart Export Guarantee payments.
For general solar guidance, the Energy Saving Trust provides impartial advice. And if you want to explore how solar integrates with battery storage, check out our complete battery guide.
