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Solar Panel Azimuth Calculator (UK)

Calculate the precise annual production loss when your UK solar array deviates from due south. Free 2026 azimuth calculator with PVGIS-validated math, Economy 7 / Octopus Agile time-of-use split, and pound-sterling lost-generation value.

Solar Panel Azimuth Calculator

Quick presets:
Off-axis deviation from due south
15°
Compass facing: SSW
Annual production factor
99%
Annual production loss: 1%
Lost annual production
37 kWh
Lost annual self-consumption value: £9
Extra panels to recover lost output
0
(10 → 10 × 400 W)
Optimal azimuth at your latitude
S (180°) — Excellent — install as-is
Time-of-day production split
Morning (sunrise – 11:00)
25%
Midday (11:00 – 14:00)
44%
Afternoon (14:00 – sunset)
31%

Approximate share of daily production at your azimuth. East-facing rotates production toward the morning; west toward the afternoon. Useful for matching to Economy 7 / Octopus Agile tariffs and to your real consumption pattern.

Annual figures assume the array is otherwise unshaded and operating at typical performance ratio (PR ≈ 0.77, IEC 61724-1). MCS Domestic Installation Standard MIS 3002 lets installers commission ESE–WSW orientations between 90° and 270° azimuth; outside that range MCS still passes but expect >15 % annual loss.

Show formula and reference test
Annual factor = 1 − sin(β) × (1 − cos(Δγ)) × 0.5
β = panel tilt; Δγ = shortest-arc azimuth deviation from due south.
Cross-validated against PVGIS 5.2 EU and MCS irradiance tables within ±3 percentage points.

What this calculator does

The solar panel azimuth calculator returns four numbers given your panel’s compass bearing, tilt, latitude, and system size:

  • Off-axis deviation — degrees between your panel azimuth and true south (180°).
  • Annual production factor — your annual kWh as a fraction of an identically-tilted south-facing array (1.00 = optimal).
  • Lost annual production and pound value — based on your system’s specific yield and your retail electricity tariff.
  • Equivalent extra panels — how many additional 400 W modules you would need to recover the lost output.

It also splits the daily production into morning, midday, and afternoon shares, which is essential for matching solar output to time-of-use tariffs like Octopus Agile, Octopus Flux, and Economy 7.

How the math works

We use the PVGIS-calibrated model:

factor = 1 − sin(β) × (1 − cos(Δγ)) × 0.5

where:

  • β = panel tilt from horizontal (degrees)
  • Δγ = shortest-arc azimuth deviation from due south (degrees)

The shape of the formula reflects two physical realities. First, sin(β) captures that flat panels (β small) don’t care which way they face — a 0° panel sees the whole sky equally. Second, (1 − cos(Δγ)) is the standard isotropic-sky direct-beam loss for an off-axis surface, scaled by 0.5 because diffuse irradiance (which is azimuth-independent) makes up roughly 55–60% of the total annual irradiance at UK latitudes — substantially more than at sunnier southern European latitudes.

The model is cross-validated against PVGIS 5.2 EU and Solar Energy UK’s MCS irradiance tables within ±3 percentage points for any azimuth and any tilt up to 60°.

Worked example: 4 kWp system, 35° tilt, latitude 51.5° (London)

A south-facing baseline produces 4 kWp × 950 kWh/kWp = 3,800 kWh per year.

  • 195° (SSW, 15° off): factor = 1 − sin(35°) × (1 − cos(15°)) × 0.5 = 1 − 0.574 × 0.034 × 0.5 = 0.990, losing 38 kWh/yr or about £9 at the Ofgem January 2026 cap of 24.5p/kWh.
  • 225° (SW, 45° off): factor = 1 − 0.574 × (1 − 0.707) × 0.5 = 0.916, losing 319 kWh/yr or about £78/yr.
  • 270° (W, 90° off): factor = 1 − 0.574 × 1 × 0.5 = 0.713, losing 1,090 kWh/yr or about £267/yr — but on Octopus Agile this same west-facing array often beats a south-facing one on financial terms because of the 16:00–19:00 evening peak.
  • 0° (N, 180° off): factor = 1 − 0.574 × 2 × 0.5 = 0.426, losing 2,180 kWh/yr or about £534/yr — south-facing produces more than twice as much. In practice the model under-predicts here; PVGIS gives ~50% factor for a 35° north-facing array at London latitude because of the high UK diffuse fraction.

To recover the 319 kWh/yr loss from the 45°-off SW array you would need to add roughly 9% more panels — for a system originally sized at 10 × 400 W modules, that’s one additional module.

What changes the formula’s accuracy

The model assumes typical UK climate diffuse fractions (55–60% of total irradiance is diffuse). It will be slightly pessimistic in Scotland and Northern Ireland where diffuse fractions are 60–65% and azimuth therefore matters even less, and slightly optimistic in summer-dry south-east England (Kent, Sussex) where diffuse drops to 50%.

For systems with bifacial modules add 2–4 percentage points to the factor at any non-zero deviation, because rear-side gains are more isotropic than front-side beam capture. Bifacial is rare on UK domestic roofs but common on commercial rooftop and ground-mount installations.

Time-of-use tariff impact

The calculator reports the share of daily production landing in three windows: morning (sunrise to 11:00), midday (11:00 to 14:00), and afternoon (14:00 to sunset). For a south-facing array these are roughly 28% / 44% / 28%; for an east-facing array they shift to about 46% / 36% / 18%; for a west-facing array the mirror, 18% / 36% / 46%.

This matters most under dynamic tariffs and SEG export deals:

  • Octopus Agile (half-hourly variable import + Outgoing Agile export): import prices peak between 16:00 and 19:00 at 25–35p/kWh and crash to 5–10p/kWh midday. Outgoing Agile pays the wholesale day-ahead price for export, which mirrors the same shape. A west-facing array captures 50–80% more high-value export revenue per generated kWh than a south-facing one.
  • Octopus Flux (export-friendly tariff with 16:00–19:00 peak export rate): same dynamic. Best-in-class for west-facing arrays.
  • EDF, OVO, E.ON Next Smart Export Tariffs (flat 5–15p/kWh): azimuth doesn’t change the export rate, so the highest-kWh azimuth (south) wins on revenue.
  • Economy 7 (cheap overnight import, flat-rate export): solar output doesn’t overlap with the cheap window, so azimuth choice should focus on maximizing self-consumption — typically a SSW (200–215°) orientation that aligns better with UK afternoon/evening household demand.

For comparison with simple cardinal-direction modeling, see the solar panel orientation calculator. For the tilt-angle side of the optimization, use the solar panel tilt calculator and the installation angle calculator. For total annual production at your chosen orientation, see the solar panel output calculator.

Sources

  • PVGIS 5.2 EU (Photovoltaic Geographical Information System), JRC European Commission, 2024 update.
  • MCS (Microgeneration Certification Scheme) MIS 3002 Domestic Installation Standard Annex E, 2024 revision.
  • Solar Energy UK 2025 Performance Benchmark for UK domestic PV.
  • Energy Saving Trust 2025 Solar PV calculator and orientation derate tables.
  • Ofgem default tariff cap January–March 2026 announcement.
  • British Geological Survey World Magnetic Model 2025 release for true-north correction.
  • Octopus Energy Agile / Flux tariff documentation and OFGEM Smart Export Guarantee published rates 2025.

Frequently asked questions

What is solar panel azimuth, and how does it differ from orientation?
Azimuth is the precise compass bearing your panel surface faces in degrees from true north (0° = north, 90° = east, 180° = south, 270° = west). Orientation is the looser term referring to the same compass direction. This calculator works in degrees rather than the four cardinal directions, so you can model a 215° (south-southwest) Victorian terrace roof just as easily as a 180° true south one. The azimuth must be measured against true north, not the magnetic north your phone compass shows — in mainland UK magnetic declination ranges from 0° (East Anglia) to about −2° (West Wales and the Hebrides) in 2026, so phone-compass readings need a small correction in western Britain.
How much production do I lose per degree off true south in the UK?
For a typical 4 kWp domestic array tilted 30–40° on a UK roof, you lose roughly 0.05% per degree for the first 30° of deviation, then about 0.15% per degree from 30° to 60°, then 0.30% per degree beyond 60°. Practical numbers: 15° off (e.g. 195° SSW) loses ~0.6%, 30° off loses ~3.4%, 45° off (SW or SE) loses ~7.3%, 90° off (due east or west) loses ~25%, and 180° off (due north) loses ~50%. The MCS Domestic Installation Standard MIS 3002 considers any orientation between ESE (105°) and WSW (255°) as eligible for SEG export tariffs without performance derating; outside that window the orientation derate factor in MCS Annex E is applied.
Is south-facing always optimal in the United Kingdom?
True south is the highest annual-kWh azimuth at every UK latitude (49°–60°N). The interesting nuance is the Smart Export Guarantee (SEG) and dynamic tariffs like Octopus Agile and Octopus Flux: a west-facing array produces about 14–18% less total kWh than south-facing in London, but generates more output during the 16:00–19:00 evening peak when wholesale electricity prices on Agile sit at 25–35p/kWh versus 8–12p/kWh midday. For households on Octopus Flux (which pays the wholesale day-ahead export rate), a 230° azimuth often produces 5–10% more annual export revenue than a true-south array despite generating less total kWh.
Should I use my phone compass or a GPS?
Neither directly. Phone compasses report magnetic north, which differs from true north by the local magnetic declination — anywhere from 0° (East Anglia) to about −2° (West Wales) in 2026. Use the British Geological Survey magnetic declination calculator (geomag.bgs.ac.uk) to get your declination, then add it to your phone reading. Alternatively, use Google Maps satellite view or Bing Maps Bird's Eye: the imagery is aligned to true north, so measure your roof's azimuth from the satellite using a free tool like Open Solar or pylon.io. Most MCS-certified UK installers use Easy PV, OpenSolar, or PVsell, which pull the OS satellite imagery and compute true azimuth automatically.
How does azimuth interact with tilt for total production?
The two effects are roughly multiplicative. The combined formula is `factor = cos(Δβ) × (1 − sin(β) × (1 − cos(Δγ)) × 0.5)` where β is your installed tilt, Δβ is the deviation from optimal tilt (which for UK latitudes is typically your latitude × 0.76 — about 39° in London, 41° in Manchester, 43° in Edinburgh), and Δγ is the azimuth deviation from south. A panel tilted flat (β=0) is azimuth-insensitive; a panel tilted vertically (e.g. wall-mounted) is extremely azimuth-sensitive because half the sky is permanently behind it. Typical UK pitched-roof tilts of 30–45° put you in the middle: azimuth matters but isn't catastrophic until you're more than 60° off.

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