What is solar shading loss?
Solar shading loss is the reduction in electricity production when an obstruction blocks light reaching panels. Its electrical effect depends on the cell and string arrangement [S1]. For an assumed unshaded output of 10,000 kilowatt-hours, a modelled 5% loss means 500 kilowatt-hours less energy. This is an arithmetic illustration, not a forecast for your roof. Checked October 2026.
What does solar shading loss mean for your site?
Solar shading loss is electricity production lost because trees, buildings or roof equipment block light reaching solar panels. Uneven illumination can also create electrical mismatch between connected cells or panels [S1]. For your site, request a shade model before treating the roof’s panel capacity as a generation forecast.
A string is a series-connected group of panels. Its devices carry the same current, so the effect of partial shade can extend beyond the patch in shadow [S1]. A photograph of the shaded area alone cannot establish annual loss. Use the roof survey guide to prepare the site information.
What do bypass diodes and optimisers change?
A bypass diode provides an alternative current path around an affected group of cells. When it conducts, that group’s contribution is lost; it does not recreate the missing sunlight [S2]. An optimiser adjusts a panel’s electrical operation to reduce the impact of mismatch. Energy Saving Trust explains their role on shaded systems [S4]. Ask for a model with and without the proposed electronics, rather than assuming complete recovery.
How should a designer model the loss?
Request a drawing that includes parapets, ventilation equipment, nearby buildings and trees. SAM’s shade calculator models the sun’s position against three-dimensional objects and generates time-based shading losses [S3]. Ask the designer to explain how those light losses feed into the electrical string model.
Illustration only: assumed unshaded production of 10,000 kilowatt-hours (kWh), a measure of energy, with a 5% modelled reduction gives 10,000 × 0.05 = 500 kWh lost, leaving 9,500 kWh. Neither input is a site estimate.
Link the result to how commercial panels work and regional generation forecasts.
What should you do next?
Bring roof photographs to the site check and get matched with an installer that covers your area.
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Common questions
Can one shaded panel affect other panels?
Yes. Devices connected in a series string carry the same current, so uneven sunlight creates electrical mismatch [S1].
Is the percentage of shaded roof equal to the energy loss?
No. String current constraints mean electrical loss depends on the connection arrangement as well as blocked light [S1].
Do optimisers restore sunlight blocked by a tree?
No. They can reduce the impact of uneven panel output; the obstruction still removes incoming sunlight [S4].
Should roof equipment appear in the shade model?
Yes. SAM supports three-dimensional shading objects and calculates losses at different sun positions [S3].
Can a designer model shadows at different times of year?
Yes. SAM can produce hourly shading data for a year from the array location and surrounding objects [S3].
Ask about your site
Sources
- Mismatch losses, Sandia National Laboratories,Last checked 19 October 2026
- Photovoltaic performance modelling workshop report, Sandia National Laboratories,Last checked 19 October 2026
- Shading and layout, National Renewable Energy Laboratory,Last checked 19 October 2026
- Solar panels, Energy Saving Trust,Last checked 19 October 2026