Shading and solar panels: when a single tree really does matter
Shading is one of the few solar variables that can genuinely dominate results. Learn why small obstructions can cause big losses, why winter shade matters most in the UK, how to spot it in your monitoring, and what mitigation actually helps.
Shading and solar panels: when a single tree really does matter
Shading is one of the few solar topics where the scary-sounding version can be true.
A single chimney, a neighbour’s roofline, or a mature tree can take a system that looks great on paper and quietly blunt it in real life.
If you want a quick, postcode-level baseline for what “normal” output looks like where you live, start here: Find your postcode
This guide explains why shading can punch above its weight, how to spot it from your generation curve, and what practical fixes are worth paying for (and which ones are not).
If you are still choosing a layout, read this alongside the flagship guide in the same “roof geometry” cluster:
Quick answer: does shading matter?
- Shade is not a small “percentage loss” problem. It often shows up as sharp notches or early drop-offs in your curve.
- Winter is the danger zone. Low sun means long shadows. Many people only check shade in summer and get surprised later.
- Not all shade is equal. A brief morning shadow on one module is very different from a recurring 2–3 hour window across multiple modules.
- Mitigation exists. Layout choices, stringing choices, and (sometimes) optimisers or microinverters can localise the damage.
Assumptions and variability
- We assume a typical UK roof and a typical residential PV system where the roof has some near-field objects (chimneys, dormers, trees, neighbouring rooflines).
- We talk about output in kWh and system size in kWp (see Glossary).
- We assume “shade” is recurring shadow on panels, not temporary cloud. Cloud tends to flatten the whole curve rather than create sharp, repeatable notches.
- What varies most between real homes: the exact shade window (time of day), how many modules are affected, and whether the system design localises shade or lets it propagate.
- If you want the full modelling assumptions behind SolarByPostcode pages (yields, rates, and how we calculate savings), see: Data sources and methodology
What “shade” really means (and why it’s so predictable)
Most homeowners picture shade as “half the panels are in shadow”.
In reality, UK shading problems are usually smaller and more annoying:
- a chimney that clips one corner of the array for 45 minutes
- a tree that shades the lower row when the sun is low
- a neighbouring roofline that eats the first hour of generation in winter
Because the sun’s path is predictable, shade often produces a repeatable pattern in your monitoring.
If you live in a dense urban area like London, you often see shade patterns driven by nearby roofs and walls (try comparing curves across a few clear days, even just from a single outcode such as SE1 (Southwark)).
Why a little shade can cause a bigger loss than you expect
Solar modules are made of many cells wired together, and those modules are usually wired together in strings.
That wiring detail is why “one shaded bit” can sometimes pull down more than its share.
The exact behaviour depends on how the system is built.
Table 1: How shade propagates in different system setups
How to spot shading in your monitoring (without guessing)
Most people first notice shading because “the curve looks weird”.
The simplest mental model is:
- cloud makes the curve lower and smoother
- shade tends to create notches, steps, or repeatable cut-offs
If you are unsure, compare a few clear days, ideally in different months.
A roof with lots of chimneys and dormers (common in many older areas such as NR1 (Norwich)) often shows a repeating notch pattern that moves earlier or later through the year.
Table 2: What you see vs what it usually means
If you want to understand the “smooth vs notched” difference properly, this pairs well with:
Why winter shade is the silent killer in the UK
Most shade assessments (and most homeowner intuition) happen in spring and summer.
That is a problem, because UK winter has:
- a lower sun
- shorter days
- longer shadows
If you are in a northern region such as South Scotland and you compare curves from a clear day in EH1 (City of Edinburgh) between July and December, the sun’s angle changes enough that “a harmless tree” can start eating meaningful hours.
Table 3: Why the same obstruction matters more in winter
The most common UK shading culprits (and what actually helps)
1) Chimneys and dormers
Chimneys are classic because they produce a sharp, repeatable shade line that moves through the year.
In places with dense housing and varied roof geometry (for example SE1 (Southwark) or older mixed stock like NR1 (Norwich)), it is common to see a consistent notch rather than a general “low output” day.
What helps most:
- put modules where the chimney does not clip them
- group “at-risk” modules together (so you sacrifice fewer strings)
- consider module-level electronics only if the shade window is frequent and meaningful
2) Trees
Trees are the most emotionally loaded shading source, because they can feel “optional” but the shade is real.
This comes up a lot in leafier suburbs and mixed neighbourhoods. A postcode like B13 (Birmingham) is a good mental model: large street trees and back-garden trees are common, and the shade can be minor in July but meaningful in December.
Another useful reference point is NG1 (Nottingham), where the same “one tree near the roofline” story is common.
What helps most:
- measure the actual shade window (not just “it looks shady”)
- prioritise winter checks (or at least be conservative about winter impact)
- do not pay for complex hardware unless the shade repeats for meaningful hours
3) Neighbours and rooflines
Neighbour shading often looks like a clean cut-off: generation starts later than you expect, or stops earlier.
This is especially common in terraced and closely spaced housing. The regional hub for London is a useful way to compare a dense region baseline, but your outcode page is where you sanity-check your own numbers.
4) Terrain and horizon shading
This is less common than trees and chimneys, but it shows up in hilly areas where the local horizon blocks early or late sun.
A region like South Wales can have micro-areas where the surrounding terrain matters more than you expect, and an outcode like CF10 (Cardiff) is a good anchor for comparing “typical” urban vs more constrained sites nearby.
What to do about shade (the practical ladder)
Most shade outcomes improve the most from boring decisions:
1) Put panels where the shade is not.
This sounds obvious, but it is often cheaper than any electronics.
2) Design the array so shade is localised.
If some modules will be shaded, it is usually better that they are shaded together rather than sprinkled across the array.
3) Use electronics only when the shade window is meaningful.
Optimisers and microinverters can help, but you want to pay for them when the gains are steady and recurring, not when shade is occasional and small.
4) If the shade is “big and unavoidable”, consider layout changes.
In some homes, splitting across two roof faces is a better real-world outcome than cramming everything onto a partly shaded “best” face. This is where east-west can be a practical win:
And if you want a quick, numbers-first intuition for orientation trade-offs:
“Is it still worth it?” How to think clearly about the decision
Shade does not automatically make solar “not worth it”.
It changes which question matters:
- not “what is my perfect annual yield?”
- but “how much good generation do I still get in the hours I can use?”
A high-yield region like South West England often has more headroom. An outcode like EX1 (Exeter) is a reasonable example of “strong baseline solar”, where even a modest shade hit can still leave good outcomes.
By contrast, in places where the baseline yield is lower, losses bite harder. The region hub for North West England and an outcode like M1 (Manchester) are useful anchors for that mental model.
The fastest way to de-confuse this is:
1) check your baseline in your outcode page
2) then think about shade as a reduction in usable hours, not just annual percentage
FAQs
Do optimisers or microinverters “solve” shade?
They can reduce how far shade propagates, which often makes shade losses more local.
They do not turn shade into free energy. If half a module is in shadow, that module will still produce less.
If only one panel gets shade, is it still a problem?
Sometimes yes, sometimes no.
The key is whether the shading is:
- frequent and predictable (same daily window on clear days)
- long enough that it clips meaningful production hours
- affecting modules that are mixed into the same strings as unshaded modules
Does morning or late-afternoon shade matter less?
Not automatically.
Morning and late afternoon can be exactly when you want generation for self-use (kettle, breakfast, cooking), and winter shade can stretch those windows significantly.
How do I avoid overreacting to a “bad looking” day?
Compare multiple clear days, then compare different months.
If the notch is repeatable and time-specific, it is likely shade. If everything is just lower and smooth, it is usually cloud or haze.
Bottom line
- Shading is one of the few factors that can genuinely dominate real-world solar outcomes.
- Shade patterns are usually predictable, which means they are often designable around.
- Winter shade is the risk people miss.
- The best first step is to identify the shade window before paying for upgrades.
Next reads
- Solar monitoring: how to spot underperformance early (without obsessing)
- Inverters explained (UK): what they do, what can go wrong, and what “clipping” really means
- East-west vs south-facing solar in the UK: yield, self-use, and the real trade-offs
- Roof direction penalty (east and west vs south)
- Solar system sizing in the UK: choosing the right kWp without wasting money