Solar Panel Installer St Helens (solar for St Helens homes) / Shade
St Helens shade checker: what will shade your panels, and when?
Describe one thing that stands to the south of your roof: a stack on the next house, the houses across the road, a tree. The checker follows the sun over St Helens through the year, marks when that object hides it from your panels, and tells you how much of the direct sunshine it costs.
Sources read on 3 November 2026. Published by SEO Dons, which runs this St Helens site.
Change any number to see the result.
sun on the panels hidden by the obstacle sun down (clock time; summer time April to October)
Three examples
| Obstacle | Whole year | Worst month |
|---|---|---|
| Chimney stack due south, 4 m away, 1.5 m higher, 1.2 m wide | 2.6% | Dec, 28% |
| Two-storey house across the street, due south, 16 m away, 3.5 m higher, 12 m wide | 0.9% | Dec, 29% |
| Garden tree to the south-south-west, 14 m away, 7 m higher, 6 m wide | 5.9% | Dec, 29% |
Our calculation: sun positions from the NOAA solar equations for St Helens on the 21st of each month; direct sunshine weighted with a clear-sky model. Read as a comparison between obstacles, not as kWh.
How it works
For each quarter-hour of the 21st of each month, the checker places the sun over St Helens (53.45° N, 2.74° W) using the standard solar position equations, on clock time with British Summer Time from April to October. It then asks two questions. Is the sun in the slice of sky the obstacle covers, judged by its width and distance? And is the sun lower than the obstacle's top, judged by its height and distance? If both are true, that quarter-hour is shaded.
The "share of direct sunshine" weights each quarter-hour by how strongly a clear-sky sun would strike a panel facing your way at your pitch, so an hour of shade at noon in June counts for far more than an hour on a December morning. Cloud, and the diffuse light that still reaches a shaded panel, are not modelled, which is why the result is a comparison, not an energy figure.
What the results mean
- Under about 2%: a winter-only obstacle. It will barely show in a year's output, though it can matter on a December afternoon.
- About 2 to 10%: worth designing around. Keep the bottom row of panels clear of the shadow, or use optimisers on the panels it reaches.
- Over 10%: a real cost. Check whether another roof face is clearer, and ask the installer to show its own shade assessment.
The result applies to the panels nearest the obstacle, measured from the bottom of the array. Panels further up the roof see less of it, because the obstacle's top is lower relative to them.
How this compares with an installer's shade factor
MCS-certified installers must allow for shade when they predict a system's yearly output: the figure is the system size times a regional yield factor times a shade factor. Where there is shade, they must give you the sun-path diagram they used. MCS's guidance method draws the outline of every obstacle on a chart of 84 sky segments, each worth 0.01, and takes 0.01 off the shade factor for each segment the obstacles touch.
For objects within 10 m of the array, such as a chimney or a vent pipe, the MCS method is deliberately cautious: it draws a "shade circle" around the object with a radius equal to its height and counts every segment the circle touches. In MCS's own worked example a near object takes the shade factor from 0.89 to 0.6. So for a close stack, expect the installer's figure to look worse than this checker's share of direct sun. Both are right about different things: this checker shows when the sun is actually hidden; the MCS method builds in a margin because close shadows are large and move across the array.
Ask to see the installer's sun-path diagram. If a stack or a tree you know about is missing from it, the predicted output is too high. MCS's guidance also says systems should not be sold where shade would have a severe effect.
Related pages
References
Questions about shade
How do I know if my roof is too shaded for solar panels?
Work out, for each obstacle to the south of the roof, how much higher its top is than the bottom of where the panels would go, how far away it is and how wide it is. The shade checker turns those into the months and hours it blocks the sun. An obstacle that only matters in the winter months costs far less than one that blocks the summer sun.
Does a chimney stop me having solar panels?
Rarely. A stack on your own ridge throws its winter shadow north, off a south-facing slope. In our example, a stack 4 m due south of the panels that stands 1.5 m above the bottom of the panels takes about 2.6% of the year's direct sunshine off the nearest panels, nearly all of it between November and January. The bigger effect is electrical, on the other panels wired with the shaded one, which optimisers or careful layout can limit.
Why does winter shade matter less?
Because there is little winter sunshine to lose. At midday on 21 December the sun in St Helens is only about 13 degrees above the horizon, against about 60 degrees in June, and a south roof here makes only around 3% of its year in December.
Get a solar quote for your St Helens roof, shade and all
Tell us what you would like a quote for, with your St Helens postcode and what stands to the south of the roof: a stack, the houses opposite or a tree. Your details go to SEO-DONS LTD, publisher of Solar Panel Installer St Helens, and we reply by email.
What happens next
- Send the form: it reaches SEO-DONS LTD, and a full postcode tells us which part of the borough you are in.
- We read it and reply by email, with the figures and sources that apply to you.
- Asking for a quote costs nothing, and whether and with whom you go ahead is your decision.