Solar Panel Orientation Calculator (UK)
Free UK solar panel orientation calculator. Enter your latitude, roof azimuth and pitch — see the percentage of optimal yield versus due-south, MCS-style.
Solar Panel Orientation Calculator
Formula used
Production factor = cos(Δβ) × (1 − 0.3 × (1 − cos(Δγ)))
Δβ = panel tilt − optimal tilt (latitude × 0.76)
Δγ = panel azimuth − equator-facing azimuth (180° in N. Hemisphere, 0° in S.)
Calibrated against NREL PVWatts v6 sample runs. Within ±5% for tilts ≤ 45° and azimuth deviations ≤ 135°. For panels facing within 30° of the pole (e.g. due-north in N. Hemisphere) the model under-predicts diffuse-light gains; expect 5–10 percentage points more than shown.
How to use this calculator
Enter three numbers:
- Your latitude — right-click any UK location on Google Maps to get the coordinates. London is 51.5°N, Birmingham 52.5°N, Manchester 53.5°N, Edinburgh 55.9°N.
- Panel azimuth — the compass direction your roof face points, in degrees clockwise from true north (0° = north, 90° = east, 180° = south, 270° = west). Use the compass quick-pick buttons if you do not have a precise reading.
- Panel tilt — the roof pitch from horizontal. A flat roof is 0°, a typical UK pitched roof is 30°–45°.
The calculator returns a production factor — the percentage of the optimal yield you will capture — alongside the optimal orientation for your latitude and a verdict on whether the array is worth installing as-is.
How orientation affects UK solar output
Solar panels generate the most output when sunlight strikes them perpendicular to their surface. Two angles control how often that happens:
- Azimuth (compass direction) determines whether the sun is in front of, beside or behind the panel during the day. Due-south arrays in the UK capture the daily solar arc symmetrically.
- Tilt (angle from horizontal) determines whether the sun hits the panel head-on or at a glancing angle. The right tilt depends on your latitude — see the solar panel tilt calculator for the optimal value.
Get both right and a UK 4 kWp array produces roughly 3,400 kWh per year. Get one wrong and you lose 5%–20%. Get both wrong and the loss can stretch to 30%–50%.
How much each orientation produces in the UK
The table below shows approximate annual production factor relative to optimum for typical UK latitudes (50°–58°N). Values are derived from PV-GIS reference runs published by the European Commission’s Joint Research Centre and rounded to the nearest 5%.
| Roof faces | Tilt 0° (flat) | Tilt 15° | Tilt 30° | Tilt 45° |
|---|---|---|---|---|
| South (180°) | 86% | 95% | 100% | 97% |
| South-east (135°) | 86% | 92% | 94% | 91% |
| South-west (225°) | 86% | 92% | 94% | 91% |
| East (90°) | 86% | 83% | 80% | 75% |
| West (270°) | 86% | 83% | 80% | 75% |
| North-east (45°) | 86% | 73% | 65% | 58% |
| North-west (315°) | 86% | 73% | 65% | 58% |
| North (0°) | 86% | 68% | 58% | 48% |
Three things to notice:
- Flat panels lose the same regardless of compass direction. All orientations sit at 86% of an optimally-tilted south array — useful to remember when designing London flat-roof installations.
- East and west are nearly identical. Pick the side that matches your usage profile — west catches the late-afternoon peak that lifts self-consumption for households with electric cars, east catches the morning shoulder for early-rising families.
- North-facing roofs in the UK are workable but expensive per kWh. A 30° north-facing array produces only 58% of an equivalent south-facing one, so you need 72% more panels for the same annual generation.
The formula behind this calculator
The production factor uses a first-order approximation of projected solar irradiance integrated over a typical year:
factor = cos(Δβ) × (1 − 0.3 × (1 − cos(Δγ)))Where:
- Δβ = (panel tilt) − (optimal tilt). Optimal tilt is approximated as latitude × 0.76, weighting the long British summer day-length over the low-sun winter. This is the same rule used in the solar panel tilt calculator.
- Δγ = the angular distance between panel azimuth and equator-facing azimuth (180° in the UK). Wrapped so values stay in the 0°–180° range.
- The 0.3 coefficient in the azimuth term is fitted against PV-GIS UK output and accounts for the high diffuse-light fraction in British weather. Pure cosine over-penalises east/west under cloudy skies.
Limits of the model. It is a back-of-envelope estimator, not an hour-by-hour simulator. It assumes:
- Typical UK climate with diffuse irradiation fraction around 50%–60%
- Standard fixed-rack mounting (not single- or dual-axis tracking)
- Tilts ≤ 50° and azimuth deviations ≤ 135°
For unusual roofs (mansards, hipped, vertical wall installations) run a free PV-GIS hour-by-hour simulation rather than relying on this calculator.
When to install at sub-optimal orientation anyway
Solar production is one factor; cost is the other. A south-facing ground mount might be optimal but cost £4,000 more than tying into your existing east-facing roof. The MCS-installer rule of thumb:
- Above 90% of optimal: install as-is. The 5%–10% loss is dwarfed by the cost premium of re-orienting.
- 75%–90% of optimal: install if your roof is the only sensible option, but oversize the array by 10%–20%. Verify the kWh estimate against PV-GIS before signing.
- Below 75% of optimal: consider an alternative — east-west split on the same roof, garage roof, ground-mount in the garden, or a different pitch. Payback under SEG export rates of 5p–15p/kWh stretches uncomfortably long below this threshold.
For full system economics, use the solar panel charge time calculator for off-grid setups, or check the Energy Saving Trust solar PV calculator for grid-tied figures.
Common UK orientation mistakes
- Reading roof azimuth from a magnetic compass without correction. The 0°–4° UK declination rarely changes the verdict, but check with the British Geological Survey declination tool before signing off on a borderline north-east or north-west install.
- Confusing roof pitch quoted in degrees with rise:run ratios. A 6:12 American-style pitch is 26.6°, not 6° — UK builders are equally comfortable in either notation, so confirm units when reading drawings.
- Ignoring shading from chimneys, dormers and neighbouring trees. A perfectly oriented array under a sycamore will under-perform a poorly oriented array in full sun. Use a Solar Pathfinder or a free phone app like Sun Surveyor to map shading separately.
- Mixing east-facing and west-facing strings on a single string inverter. String inverters lose more than the calculator predicts when panels in the same string face different directions. Use micro-inverters or DC optimisers (SolarEdge, Tigo, Enphase) for east-west splits — the price premium of around £400–£600 per array pays back through the recovered yield.
What MCS and the Energy Saving Trust say
MCS Standard MIS 3002 gives reference performance bands by orientation and pitch. Within 30° east or west of due south at any pitch from 15° to 50°, the standard reference values exceed 95% of the maximum, which is why MCS-certified installers seldom go to the trouble of mounting tilt frames on an existing pitched roof. The Energy Saving Trust’s domestic solar guidance reaches the same conclusion using the same PV-GIS dataset.
For a borderline orientation, ask your MCS installer to share the PV-GIS PDF report for your postcode and orientation alongside their MCS performance estimate — both are free and take five minutes.
Related UK solar calculators
- Solar panel tilt calculator — optimal pitch by UK latitude
- Solar panel charge time calculator — off-grid battery sizing
- Solar panel voltage calculator — BS 7671 voltage drop
- Solar panel wire size calculator — DC and AC cable sizing for UK installs
For installation, always use an MCS-certified installer. MCS certification is required to access SEG export payments and the 0% VAT relief. Both the Energy Saving Trust and Which? publish current UK solar buying guides for early-stage research.