Solar panels continue generating electricity when part of the roof is shaded, but their output will be lower. In some circumstances, the reduction can be considerably greater than the visible area covered by the shadow.
The effect depends on:
- What is casting the shadow
- Which panels and cells it covers
- How long the shade lasts
- The time of day and season
- How the panels are connected
- The inverter and number of MPPT inputs
- The panels’ internal bypass diodes
- Whether power optimisers or microinverters are fitted
The most important distinction is between the sunlight blocked from reaching a panel and the additional electrical loss created when shaded and unshaded panels operate differently.
Optimisers, microinverters and inverter shade-management software may reduce the additional mismatch loss. They cannot recover solar energy that never reaches the panel.
Good solar design should therefore:
- Avoid the worst shade where possible.
- Position and connect the panels appropriately.
- Use additional electronics where there is a defined benefit.
- Include the remaining loss honestly in the generation forecast.
Shading is only one part of assessing a property. See Is Your Home Suitable for Solar Panels? for the complete roof assessment.
How much does shading affect solar panels?
There is no universal percentage.
A small shadow can sometimes have a disproportionate effect, while a larger shadow at a time of low solar production may have a relatively modest impact on annual generation.
The result depends on both the physical shadow and the electrical design of the array.
| Shading situation | Likely concern |
|---|---|
| Short early-morning shadow | May have a limited annual effect |
| Chimney shadow moving across panels | Requires layout and electrical assessment |
| Large tree directly south of the roof | Potentially significant and seasonally variable |
| Distant hill or building | Restricts the available solar horizon |
| Parapet shading the bottom panel row | Layout issue that should be addressed |
| Leaves or bird fouling | Maintenance problem rather than permanent shade |
| Most of the array shaded around midday | Potentially poor solar location |
Shading can sometimes matter more than roof direction. An unshaded east- or west-facing roof may produce more useful electricity than a south-facing roof affected by significant shade.
This is why a photograph taken at one time of day is not enough to assess a roof. The installer needs to consider how the shadow moves across the proposed array throughout the day and year.
The two different losses caused by shading
Solar-panel shading creates two related but different problems.
Sunlight is blocked from the panel
The first loss is straightforward: a tree, chimney or building prevents some sunlight from reaching the solar cells.
The panel has less solar energy available to convert into electricity.
No inverter, optimiser or microinverter can replace this missing sunlight. Panel-level electronics may manage the consequences more effectively, but the shaded panel will still generate less.
Shaded and unshaded panels operate differently
The second problem is electrical mismatch.
Solar cells and panels are connected together. When one section receives less light, it may operate at a different current or voltage from the sections around it.
This mismatch can create an additional loss beyond the solar energy directly blocked by the shadow.
| Type of loss | Cause | Can electronics reduce it? |
|---|---|---|
| Missing sunlight | A physical obstruction blocks solar energy | No |
| Cell or panel mismatch | Parts of the array operate differently | Sometimes |
| String-design loss | Differently performing panels are connected unsuitably | Often reduced through better design |
| Row self-shading | Tilted rows are positioned too closely | Better solved through layout |
| Soiling loss | Dirt, leaves or bird fouling cover cells | Requires inspection or cleaning |
This distinction matters when an installer recommends optimisers or microinverters.
The relevant question is not simply whether there is shade. It is whether the proposed equipment will recover enough additional electricity to justify its cost.
What can shade solar panels?
Solar shading can come from the roof itself, neighbouring property, vegetation or the surrounding landscape.
Chimneys, dormers and roof equipment
Common roof-level obstructions include:
- Chimneys
- Dormer windows
- Aerials
- Satellite dishes
- Flues
- Roof vents
- Soil pipes
- Rooflights
- Adjacent roof slopes
These objects can cast well-defined shadows that move across individual panels as the sun changes position.
A relatively narrow chimney or aerial shadow may cross several internal cell sections. Its effect cannot be judged solely by the percentage of the panel that appears shaded.
Trees and vegetation
Trees can create some of the most complicated shade patterns.
Their effect changes with:
- The season
- Whether the tree is deciduous or evergreen
- The density of its canopy
- Wind movement
- Annual growth
- Pruning
- Falling leaves and sap
A survey completed during winter may underestimate the effect of a deciduous tree once it is in full leaf. Conversely, a bare branch visible in winter may cast less shade during high-generation summer periods than its appearance suggests.
The installer should explain how seasonal foliage has been treated in the forecast.
Nearby buildings and the horizon
Neighbouring buildings, woodland, hills and elevated ground can block part of the solar horizon.
These obstructions may affect the entire array rather than one individual panel. If the sunlight is blocked equally from every panel, module-level electronics may offer little or no additional benefit because there is little mismatch to correct.
The principal loss is the solar energy that the roof never receives.
Flat-roof parapets and panel rows
On a flat roof, panels can be shaded by:
- Parapet walls
- Rooflights
- Ventilation equipment
- Taller sections of the building
- Other rows of solar panels
Row-to-row shading should be considered during the layout design. Increasing the panel tilt produces a longer shadow and may require greater separation between rows.
A lower-angle or east–west arrangement can sometimes fit more panels while reducing self-shading. Read South vs East–West Solar Panel Layouts on Flat Roofs.
Leaves, dirt and bird fouling
Leaves, dirt, lichen and bird fouling are more accurately described as soiling, but they can cover individual cells and create a similar mismatch problem.
Unlike permanent building shade, this loss may be addressed through maintenance. The underlying cause should be identified before assuming that different inverter equipment is needed.
Different types of solar-panel shade
| Type | Example | Main response |
|---|---|---|
| Permanent solid shade | Building or wall | Avoid the affected area where practical |
| Moving hard shadow | Chimney, aerial or flue | Review panel position and electrical design |
| Dappled shade | Tree branches and foliage | Model seasonally and allow for growth |
| Horizon shade | Hills or distant buildings | Include in the annual solar estimate |
| Temporary coverage | Leaves, snow or bird fouling | Monitor and maintain |
| Self-shading | Adjacent panel rows | Change the spacing, angle or layout |
The correct solution depends on which type of shade is present. Adding optimisers to every shaded installation is not a substitute for understanding the cause.
Why can a small shadow create a larger loss?
A solar module contains many individual cells connected electrically. A shaded cell cannot provide the same current as a cell receiving full sunlight.
The result is not always proportional to the area covered. A narrow shadow crossing several cell groups may have a greater effect than shade concentrated over one part of the module.
The precise response depends on:
- The panel’s cell arrangement
- The number and position of bypass diodes
- Whether the panel uses a half-cut design
- The shape and direction of the shadow
- Portrait or landscape mounting
- How the panel is connected to the rest of the array
- The inverter’s MPPT behaviour
This is why percentage area alone is a poor way to estimate shading loss.
What do bypass diodes do?
Most modern solar panels contain bypass diodes. These divide the panel into electrically protected cell sections.
When shading restricts one section, its bypass diode may provide an alternative route for the current. The shaded cell section contributes little or no power, but current from the operating sections can continue around it.
When a bypass diode activates:
- The affected cell section loses output.
- The panel’s voltage falls.
- Other sections of the panel can continue generating.
- The complete array does not necessarily stop operating.
Bypass diodes reduce the wider effect of shade, but they do not restore the electricity that the shaded cells could have generated.
They also make the claim that one shaded cell always switches off the complete array inaccurate. A shaded cell can cause a significant loss, but the actual result depends on the module and system design.
How does shading affect a string inverter?
In a conventional string-inverter system, several solar panels are connected in series. The inverter manages the combined electrical output of that string.
If one panel is shaded, its operating conditions differ from the unshaded panels. The inverter must find the best available power point for the combined arrangement.
Bypass diodes may allow current around affected cell sections, while modern inverter software may search for alternative maximum-power points created by partial shade.
A string inverter is therefore not automatically unsuitable for every roof with a chimney or short period of shade.
Good string design can include:
- Grouping panels with similar directions and conditions
- Keeping strongly shaded and unshaded panels separate
- Connecting different roof sections to separate MPPT inputs
- Selecting an inverter with suitable shade-management functions
- Keeping every string within the inverter’s required voltage range
- Modelling the actual panel and inverter combination
Poor string design can increase losses. A well-designed string system may perform better than a poorly planned system containing additional electronics.
For a detailed comparison, see String Inverters vs Microinverters.
Why does the time of the shade matter?
The same shadow can have a different annual effect depending on when it occurs.
- Morning shade
- Particularly relevant to east-facing panels. Its annual effect may be limited if it clears before the array's strongest generation period, but it may reduce electricity available for early household demand.
- Midday shade
- A shadow crossing a south-facing array around midday can remove generation during one of its strongest periods. This may reduce direct household solar use, battery charging, export and peak system output.
- Afternoon shade
- Has a greater effect on west-facing panels and can reduce generation when occupants return home and electricity demand rises.
- Winter shade
- The winter sun remains lower in the sky, producing longer shadows. Hills, buildings and trees that have little effect during summer can block a high proportion of the available winter sunlight. However, winter represents a smaller part of total annual solar generation, so a high percentage winter loss is not necessarily the same as a high annual loss.
- Seasonal vegetation
- Trees may cast different shadows depending on leaf coverage. A generation estimate should consider the full annual cycle rather than conditions on the day of the survey.
Why annual shading loss does not tell the whole story
Two arrays can lose the same annual number of kilowatt-hours but experience different effects on household energy use.
For example:
- Morning loss may reduce direct use before occupants leave for work.
- Midday loss may reduce battery charging or export.
- Afternoon loss may increase grid imports during evening demand.
- Winter loss may affect periods when electricity prices and household consumption are higher.
An annual shade factor is essential, but it does not show when the lost electricity would have been generated.
Where shading is material, ask the installer for monthly or hourly modelling in addition to the standard annual figure. This is especially valuable for homes with batteries, heat pumps, EV charging or time-of-use tariffs.
How is solar-panel shading assessed?
A proper shading assessment should consider:
- The direction and pitch of each array
- The precise panel positions
- The direction and height of obstructions
- Nearby roof objects
- Trees and seasonal growth
- The distant horizon
- Flat-roof parapets and adjacent panel rows
- The proposed strings and MPPT connections
- The time and duration of shadows
The UK MCS shade-analysis procedure distinguishes between nearby and distant objects. Objects within 10 metres of the centre of the proposed array are treated differently because their apparent size and effect across individual panels can be greater.
An installer may use the MCS sun-path method or suitable modelling software capable of providing an equivalent or better assessment.
What is an MCS shade factor?
The MCS performance estimate uses a shade factor, normally shown as SF.
The shade factor represents the proportion of otherwise expected generation remaining after the estimated shading loss has been applied.
| Shade factor | Estimated annual shading loss |
|---|---|
| 1.00 | No shading loss applied |
| 0.98 | 2% |
| 0.95 | 5% |
| 0.90 | 10% |
| 0.80 | 20% |
| 0.70 | 30% |
The basic relationship is:
Shade factor = 1 − estimated shading loss
For example, an estimated loss of 11% gives a shade factor of 1 − 0.11, so 0.89 is used in the forecast.
The shade factor is then incorporated into the annual generation calculation.
Example calculation
Suppose the property's unshaded generation forecast is 4,000kWh a year.
With a shade factor of 0.90: 4,000kWh × 0.90 = 3,600kWh.
The estimated annual shading loss is therefore 400kWh.
This is an estimate rather than a guarantee. Annual weather and real operating conditions will still affect the final result.
The current MCS Solar PV Installation Standard explains how the shade factor is included in the performance estimate.
What is a sun-path diagram?
A sun-path diagram represents the position of the sun at different times of day and year.
The installer plots the direction and height of objects that could obstruct the proposed array. The areas where those objects overlap the sun’s path contribute to the estimated shading loss.
On a typical diagram:
- The horizontal position represents direction.
- The vertical position represents height above the horizon.
- Curved paths show the sun’s seasonal movement.
- Obstructions are marked over the parts of the sky they block.
- Nearby objects receive additional treatment under the MCS method.
You do not need to calculate the shade factor yourself. The diagram should, however, bear a recognisable relationship to the property.
Check whether it includes:
- The main chimney
- Significant trees
- Neighbouring buildings
- Dormers or taller roof sections
- The correct obstruction directions
- Summer foliage where relevant
- The final proposed panel position
Where an MCS shade factor below 1.00 has been calculated using the MCS method, the customer documentation should include the sun-path diagram used.
Can shading be assessed remotely?
Aerial images and three-dimensional roof software can support the early design, but a remote assessment may miss:
- Small chimneys and vents
- Aerials
- Parapets
- Tree branches
- Recent construction
- The exact height of nearby objects
- Shadows from adjoining roof sections
- Seasonal vegetation
- Items hidden by the image angle
PVGIS can account for the surrounding terrain, but its standard horizon data cannot identify every nearby house, tree or roof obstruction.
Where orientation, inclination or shading has been estimated remotely, the proposal should make this clear. The final assumptions should be checked against the actual property before installation.
What can be done about solar-panel shading?
The solutions should be considered in a sensible order.
Avoid the shaded area
The simplest solution is often to change the panel layout: moving panels farther from a chimney, using a different roof plane, changing between portrait and landscape positioning, leaving out a heavily shaded panel, increasing the spacing between flat-roof rows, or changing the tilt or direction of a flat-roof array. Avoiding the shadow removes both the missing-sunlight loss and the mismatch it could create.
Reduce or relocate the obstruction
Depending on the obstruction, it may be possible to relocate an aerial or satellite dish, reposition a planned roof vent, prune vegetation with the necessary permission, remove accumulated leaves, or address avoidable bird nesting beneath the array. Any change must be safe, legal and practical to maintain.
Improve the electrical design
If shade cannot be avoided, the panels may be grouped and connected more effectively: separating shaded and unshaded panels, using different strings, using separate MPPT inputs, selecting an inverter with effective shade management, and checking the inverter's minimum and maximum string voltages. The design needs to work electrically throughout the expected range of conditions.
Consider panel-level electronics
Power optimisers or microinverters may reduce the additional mismatch loss where individual panels experience different shading. Their predicted benefit should be quantified rather than assumed.
Include the remaining loss
Some shading may be unavoidable without making the installation unviable. The remaining loss should be incorporated into annual generation, expected self-consumption, battery charging, grid imports, export payments and financial payback.
Do power optimisers solve solar-panel shading?
Power optimisers can help individual panels operate more independently while retaining a central inverter.
Potential benefits include:
- Panel-level maximum-power-point tracking
- Reduced mismatch between differently performing panels
- Panel-level monitoring
- Greater flexibility for irregular roof layouts
- Easier identification of an underperforming panel
However, an optimiser cannot recover sunlight blocked by a solid object.
If a tree prevents a panel from receiving 200Wh of solar energy, the optimiser cannot recreate that energy. It may only prevent the shaded panel from causing additional avoidable loss elsewhere in the array.
Other considerations include:
- Equipment and installation cost
- Compatibility with the inverter
- Whether every panel needs an optimiser
- Minimum string-voltage requirements
- Extra electronics installed on the roof
- Warranty arrangements
- Future access if a device fails
Read Solar Optimisers Explained before accepting a blanket recommendation.
Do microinverters perform better in shade?
A microinverter is normally fitted to each panel. It converts that panel’s DC electricity into AC independently from the others.
This means one shaded panel does not determine the operating point of all the other microinverter-equipped panels.
Microinverters can be useful where:
- Shadows move between individual panels
- The roof has several directions
- Panels have different pitches
- The layout is irregular
- Panel-level monitoring is valuable
The shaded panel still loses the sunlight blocked from it. Microinverters reduce the wider mismatch effect rather than eliminate the underlying shade.
They may also:
- Cost more than a conventional string inverter
- Place more electronic devices on the roof
- Require roof access if a unit needs attention
- Need to be considered alongside the battery arrangement
The appropriate choice depends on the layout, predicted recovery, equipment compatibility and lifetime cost.
Are optimisers or microinverters worth the extra cost?
Ask for two generation forecasts:
- The proposed array using the standard inverter arrangement
- The same array using the recommended panel-level electronics
The installer should identify:
- Additional annual generation expected
- Additional installed cost
- Warranty period
- Monitoring benefits
- Compatibility with the inverter and battery
- Potential roof-access requirements
- Whether the equipment is needed on every panel
The value of the recovered electricity depends on what happens to it.
Electricity used in the home can avoid the full import price. Electricity exported is worth the applicable export rate. These amounts may be very different.
A basic comparison is:
Annual value recovered = additional self-used electricity × import value + additional exported electricity × export rate
Do not assume that a higher technical output automatically delivers a good financial return.
Panel-level monitoring may still be valuable for fault identification, but that benefit should be considered separately from claims about shading recovery.
Should trees be cut back for solar panels?
Important
Pruning a tree can improve solar exposure, but it should not be treated as a permanent solution without further checks.
Consider: Who owns the tree? Is permission required? Is it protected? Will pruning damage it? How quickly will it regrow? Can the work be repeated safely? Has summer foliage been included in the forecast? Is the proposed generation dependent on regular pruning?
Do not accept a generation estimate based on removing or reducing a tree unless that work is permitted, practical and genuinely planned.
Trees can also grow substantially during the operating life of a solar installation. The survey should consider future growth rather than only the shadow visible on the installation date.
Is a larger partly shaded array better than a smaller unshaded one?
Not necessarily — but a shaded panel should not automatically be excluded either.
The correct comparison may include:
- A smaller array using only the clearest roof area
- A larger array containing partly shaded panels
- An alternative roof plane
- A different portrait or landscape layout
- Additional panels connected separately
- Power optimisers or microinverters
A partly shaded extra panel may still make a useful annual contribution, particularly when scaffolding and installation overheads are already being paid.
Conversely, a heavily shaded panel may add equipment and design complexity for very little useful electricity.
Ask for side-by-side forecasts showing:
- Installed capacity
- Annual generation
- Shading loss
- Additional system cost
- Self-consumed electricity
- Export
- Expected financial value
The best design is the one that uses the complete roof and household energy profile effectively, not necessarily the layout with the lowest shading percentage.
How can you identify shading on an existing system?
Shading can sometimes be recognised in production monitoring.
Possible indicators include:
- A recurring dip at approximately the same solar time
- A dip that moves gradually as the seasons change
- One panel consistently underperforming in panel-level monitoring
- Lower generation following tree or hedge growth
- A sudden reduction after leaves or bird fouling appear
- Repeated underperformance associated with a chimney shadow
Compare several clear days rather than drawing conclusions from one graph.
A production dip could also be caused by:
- Passing cloud
- Inverter clipping
- An export limit
- Battery charging or control behaviour
- High panel temperature
- A panel or inverter fault
- Monitoring or communications problems
A shadow usually creates a pattern linked to the sun’s position. An electrical fault may appear at unrelated times or produce a more persistent reduction.
Contact the installer if the loss is unexplained or the system is performing significantly below its forecast.
Solar shading quotation checklist
Before accepting a proposal, check that it shows:
- The final panel layout
- Roof pitch and direction
- Shade factor
- Annual generation with shading included
- Sun-path diagram where applicable
- Relevant trees, chimneys and buildings
- Whether the assessment was remote or completed on site
- Assumptions about pruning or removing obstructions
- String and MPPT arrangement
- Reason for recommending optimisers or microinverters
- Additional generation expected from that equipment
- Separate forecasts for materially different layouts
If two installers provide significantly different shade factors for the same roof and panel layout, ask both to explain their obstruction measurements and modelling assumptions.
Frequently asked questions
Do solar panels work in the shade?
Yes. Solar panels can generate from diffuse daylight and partial sunlight, but their output will be lower when shade blocks solar energy from reaching the cells.
Can one shaded panel reduce the whole array's output?
It can affect other panels connected to the same string, but the result depends on bypass diodes, string design, MPPT behaviour and inverter technology. One shaded panel does not always switch off the complete array.
Do solar optimisers eliminate shading losses?
No. They can reduce additional mismatch losses between panels, but they cannot recover sunlight physically blocked from the shaded panel.
Are microinverters always better on a shaded roof?
No. They can be valuable when individual panels experience different conditions, but moving panels, separating strings or using suitable inverter shade management may provide a simpler solution.
What is a good MCS shade factor?
A factor closer to 1.00 represents a lower estimated annual loss. Whether a lower factor is acceptable depends on the system’s capacity, cost and resulting generation.
Should my solar quotation include a sun-path diagram?
Where an MCS shade factor below 1.00 has been calculated using the MCS method, the customer documentation should include the sun-path diagram used.
Can an installer assess shade using satellite images?
Remote tools can support an initial design, but they may miss small or recent obstructions. Estimated values should be identified and verified before the final system is installed.
Is morning shade a serious problem?
It depends on the duration, array direction and household demand. A short morning shadow may have a limited annual effect, while persistent shade on an east-facing array can be more significant.
Should a shaded panel be removed from the design?
Not automatically. Compare the generation and cost of the larger and smaller layouts. A partly shaded panel can still increase total annual output.
Can trees affect solar panels after installation?
Yes. Trees and hedges can grow significantly during the life of the system. Future growth and realistic maintenance should be considered in the forecast.
Avoid shade first and optimise second
Solar-panel shading should be addressed in a clear order:
- Establish where and when the shade occurs.
- Move panels away from the worst areas where practical.
- Group and connect the panels appropriately.
- Use optimisers or microinverters where they solve a defined mismatch problem.
- Include the remaining loss in the annual forecast.
- Consider when the lost electricity would otherwise have been generated.
The strongest system is not necessarily completely shade-free. It is the one where the available roof, panel layout, electrical design and generation forecast work together honestly.
Check the complete solar potential of your roof
Shading is only one part of solar suitability. Roof direction, pitch, available area and structural condition should be assessed together before choosing a system.