Shadow-Free Area
Shadow-free area is the roof area that remains unshaded across the sun's daily and seasonal paths — after parapets, tanks, towers, trees and adjacent buildings cast their worst — and it, not gross roof area, dictates real plant capacity.
Why it matters on an MEPF project
Shading is nonlinear punishment: a shadow crossing one module can drag its whole string, so a "small" obstruction at the wrong hour costs disproportionate energy. Honest capacity therefore starts from a shadow study — worst-case winter sun angles, not the flattering June survey — and the array layout keeps rows and obstructions from shading each other across the year.
The number also arbitrates vendor promises: quotes sized on gross roof area inflate capacity that commissioning cannot deliver. Insisting proposals state the assumed shadow-free area (and simulate yield against it) converts sizing from salesmanship to engineering — and preserves roof for the walkways, spacing and service lanes a maintainable, fire-sane plant needs anyway.
How it's specified in practice
| Parameter | Typical / working position | Governing reference |
|---|---|---|
| Shadow study | Seasonal sun paths vs obstructions (worst-case months govern) | design analysis |
| Row spacing | Inter-row pitch preventing self-shading at design dates | layout design |
| Usable density | Roughly 9–10 m² per kWp within the shadow-free zone (working band) | practice band |
| Yield linkage | Simulation run against the shadow-mapped layout | yield report |
Common mistakes
- Sizing on gross roof area with obstructions hand-waved.
- June surveys deciding December shadows.
- Packing edge-to-edge, sacrificing walkways and fire lanes.
- Ignoring the neighbour's under-construction floor that will shade year three.
Related on this site
One of 68 working definitions in the MEPF & solar engineering glossary. The buying side of the same decisions is in the buyer's guides; the numbers are in the calculators.
Frequently asked
How much solar fits on my roof?
Map the shadow-free area, then apply the ~9–10 m²/kWp working band and layout realities. Our shadow-free-area calculator gives the first pass; the site survey and simulation give the commitment.
Does partial shading really matter that much?
Yes — string electricity makes one shaded module everyone's problem. Layout, string design and (where justified) electronics manage it, but avoiding it beats managing it.
Standards referenced: design practice; yield simulation reports