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Solar Shading Calculator
Assess the impact of nearby obstructions on solar panel performance. Calculate shadow lengths, annual yield loss and financial impact for UK latitudes.
Height above ground
Height of panel centre
Horizontal distance
For yield loss calculation
UK range: ~49-59°N (52 = Midlands, 56 = central Scotland)
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How We Calculate This
This calculator assesses solar shading based on obstruction geometry and UK sun angles.
The formula
Shadow length = Height difference ÷ tan(sun altitude angle)
- Sun altitude at solar noon = 90° − latitude + solar declination
- December declination: −23.5° (lowest, longest shadows) — e.g. 14.5° at 52°N
- Equinox declination: 0°; June declination: +23.5° (highest, shortest shadows)
- Panels are shaded at noon when shadow length > distance to the obstruction
- Tree obstructions pass some light: a bare deciduous tree blocks far less in winter than a year-round evergreen canopy, so the loss is scaled accordingly
Scope of the estimate
The yield-loss figure is a simplified solar-noon indicator using a single midday shadow geometry for the selected month. It does not model time-of-day or east/west (azimuth) shading, which often dominate real-world losses, so treat it as an indicative guide rather than a certification figure. For an MCS-grade result, commission a full MCS MIS 3002 shading assessment with a measured horizon profile. Yield is based on a typical UK specific yield of ~950 kWh/kWp/year; the financial figure uses the Ofgem price-cap electricity unit rate of 26.11p/kWh (1 Jul–30 Sep 2026).
Frequently Asked Questions
Even partial shading can significantly reduce output. A single shaded panel in a string can reduce the entire string's output by 30-50% with conventional string inverters. Using microinverters or power optimisers limits the impact to just the shaded panel(s).
The minimum clear distance equals the shadow length at the worst case (solar-noon on the December solstice): clearance = height difference ÷ tan(sun altitude). At 52°N the noon sun is only ~14.5° high in December, so an obstruction 4m above the panels needs about 15.5m clearance (4 ÷ tan(14.5°) ≈ 15.5m) to be fully clear of its midday shadow. A loose "2-3× the height difference" rule of thumb is sometimes quoted for moderate-latitude inter-row spacing, but it under-states the worst-case winter-noon shadow at UK latitudes — use the calculator (or a full horizon assessment) rather than the rule of thumb for siting decisions.
Yes, deciduous trees lose their leaves in autumn/winter so they cause less shading in winter months when the sun is lowest. However, bare branches still block 20-40% of light. The main shading impact is actually in summer when trees are in full leaf but the sun is higher.
The sun's altitude at solar noon varies from about 15° in December to 62° in June at 52°N latitude (central England). At 56°N (central Scotland), it ranges from 11° to 58°. The low winter sun angle means shadows are longest in December.
Yes — MCS does not ban shaded installs, but MCS MIS 3002 requires the shading to be assessed and documented. Where the shade factor is below 1 (i.e. any measurable shading), the installer must record the shading data and reflect the reduced yield in the performance estimate; there is no published hard percentage that automatically fails certification. MCS certification is what makes a solar PV system eligible for SEG (Smart Export Guarantee) export payments. Power optimisers or microinverters can mitigate shading and recover much of the lost output. (Note: solar PV is not covered by the Boiler Upgrade Scheme, which only funds heat pumps and biomass boilers.)
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Last updated: June 2026
Verified against UK standards · estimates only, confirm with your supplier.