Overshadowing of a neighbour's solar panels
Loss of PV output can be a material consideration but usually carries limited weight. What the modelling shows, and how to settle it before objections land.
An extension overshadowing solar panels next door is a real problem with a weak planning answer. There is no right to sunlight for a photovoltaic array in English law, no numerical test in the standard daylight guidance, and no policy in most local plans that protects generation. Loss of output can be raised as a material consideration, and where it has been considered on appeal it has generally attracted limited weight.
That is an uncomfortable answer for the neighbour and an unreliable one for the applicant, because limited weight is not no weight.
Whether loss of generation is a planning consideration
Start with what the planning system does protect. Loss of daylight and sunlight to habitable rooms and to garden amenity space are established considerations, assessed against the BRE guidance on site layout planning for daylight and sunlight, which sets out the vertical sky component, no-sky line and annual probable sunlight hours tests, plus the two hour test for amenity areas on 21 March.
None of those tests measures energy generation. They measure light reaching windows and sun reaching gardens.
Loss of PV output is capable of being material, because material considerations are not a closed list and anything relating to the use and development of land can qualify. Planning inspectors have considered the point in individual appeals. Those decisions turn on their own facts and are indicative rather than binding, so treat any summary of them, including this one, as a description of how the issue has been approached rather than a rule.
The separate civil law of rights to light does not help either. An easement of light can be acquired for a window over time. There is no equivalent easement for collecting solar energy.
How shading of an array is modelled
Shading analysis is a well developed part of PV design, so the modelling is straightforward even though the planning weight is not.
The method used by installers combines a sun path for the site latitude with a horizon profile of the obstructions, then calculates the proportion of annual irradiation lost. A proposed extension is added to the obstruction model as a solid, using its ridge height, depth and distance from the array.
The output that matters is the annual energy loss expressed as a percentage, broken down by month.
One technical point changes the numbers enormously. Panels wired in series behave badly under partial shading, because current through the string is limited by the worst panel, so shading one panel can cut the output of the whole string. Where the array uses optimisers or microinverters, the same shadow costs far less. A shading claim that ignores the inverter architecture is not complete.
The dates and times that matter for generation
Intuition is misleading here, and both sides get it wrong.
| Period | Sun position | Generation significance |
|---|---|---|
| Midwinter | Very low, long shadows | Shadows are worst, output is lowest anyway |
| Equinox | Intermediate | The standard assessment date for amenity |
| Midsummer | High, short shadows | Output highest, shadows usually least |
| Morning and evening | Low sun, long shadows | Modest share of daily yield |
| 10am to 4pm | Higher sun | Most of the daily yield |
A two storey extension to the south of an array will cast its longest shadows in December, when the array was generating little in any case. The same extension may barely touch the array in June. That is why an objection framed around a winter shadow diagram usually overstates the annual loss, and why the applicant's answer should be an annual figure rather than a rebuttal about one day.
The exception is a tall obstruction close to the array on the southern side, which can shade through the middle of the day year round. That is the case where the loss is material in substance and not just in principle.
Evidence a neighbour needs to make the point
Objecting effectively requires more than a statement that panels will be shaded.
What carries weight:
- The array specification: number of panels, orientation, tilt, and whether the system uses a string inverter, optimisers or microinverters.
- A shading study using the proposed extension's dimensions taken from the submitted drawings, not estimated.
- Annual and monthly energy loss figures, with the modelling assumptions stated.
- Sun path or shadow diagrams at the equinox and both solstices, at three or four times of day.
- Historic generation data from the inverter, establishing the baseline.
Point five is the one that turns an argument into evidence. Most modern inverters log output, and a year of monthly data is a far stronger starting point than a manufacturer's estimate.
Get the dimensions right. An objection built on an assumed ridge height that turns out to be 600mm lower than proposed loses credibility on everything else.
Design changes that reduce shading
For an applicant, the least costly response is usually geometric rather than legal.
Reduce the ridge height, or hip the roof on the side facing the neighbour, which removes the top corner of the shadow-casting mass. Move the bulk northward within the plot. Set the first floor back from the boundary. Use a flat or shallow mono-pitch roof on the section closest to the array. Reduce the depth of the two storey element and take the extra space at ground floor, where the shadow reach is much shorter.
Each of those is a change a designer can test in an afternoon, and any of them may reduce the modelled annual loss from a number worth arguing about to one that is not.
Where an Overshadowing Study or a fuller Daylight and Sunlight Assessment is being prepared for the amenity case anyway, adding the array as a receptor costs very little and takes the sting out of the objection before it is made.
How officers have weighed the issue
The pattern, described generally rather than as a rule: officers acknowledge the point, note the absence of a policy test and of a right to sunlight, consider whether the loss is substantial, and weigh it in the overall balance alongside the more familiar amenity considerations.
Where the extension also fails the 45 degree test or the two hour amenity test, the solar point adds to a case that already exists. The related tests are set out in our notes on the two hour test on 21 March and the 45 degree rule in plan and section.
Where the extension is otherwise policy compliant, the solar point rarely carries the decision on its own. Being candid about that is more useful to both neighbours than pretending otherwise.
Practical resolution between neighbours
Most of these disputes are better solved with a conversation than with an objection letter.
Options that have worked between reasonable neighbours: relocating a few panels to an unshaded part of the roof at the applicant's cost, fitting optimisers so partial shading stops disabling a whole string, a modest design change agreed before submission, or a contribution towards the difference in yield.
None of that can be secured through a planning condition, because a condition must relate to the development and be enforceable, and a payment to a neighbour is neither. It sits in a private agreement.
Start it early. Once an objection is on the council's website, positions harden and the same conversation becomes much harder to have.
This is general guidance, not legal advice; check the position with your local planning authority or a qualified professional before relying on it.
PlanScope provides AI-assisted draft reports for planning applications. Reports should be reviewed before submission. We do not guarantee planning approval. Enter your postcode to see which reports an extension at your property is likely to need.
Frequently asked questions
Can I object to an extension because it shades my solar panels?
You can raise it. Loss of generation is capable of being a material consideration, since material considerations are not a closed list, but there is no right to sunlight for an array and no policy test in most local plans. Where the point has been considered on appeal it has generally attracted limited weight.
Do I have a legal right to sunlight for my panels?
No. An easement of light can be acquired for a window over time under the law of rights to light, and there is no equivalent easement for collecting solar energy. That is a civil law position separate from planning, and it means the planning objection is the only avenue in most cases.
How much output would actually be lost?
It depends on geometry and on the inverter architecture. Panels wired in series through a single inverter suffer disproportionately, because current is limited by the worst-shaded panel. With optimisers or microinverters the same shadow costs far less. A shading study should state annual and monthly losses and the assumptions behind them.
Is a winter shadow diagram good evidence?
On its own, no. Shadows are longest in midwinter, when the array generates least anyway, so a December diagram overstates the annual effect. Present shadow studies at the equinox and both solstices, and give the annual energy loss as a percentage with monthly figures behind it.
Can the council condition a payment or panel relocation?
No. A condition must relate to the development and be enforceable, and a payment to a neighbour or works to their roof is neither. Those arrangements sit in a private agreement between the parties. They are far easier to reach before an objection is published than afterwards.
Sources and further reading
This article is general guidance about the planning system in England and, where stated, the rest of the UK. It is not legal or professional advice. Check your local planning authority’s validation requirements and take professional advice for your specific site.