Solar mounting structures
Solar Row Spacing And Shadow Calculator
Row spacing is where rooftop solar quietly loses output. Pack the rows close and you fit more panels; the front row then shades the back row every winter morning, and the whole string underperforms for months. Space them properly and you fit fewer panels that all work.
- Free, no sign-up
- Runs in your browser
- Built for Islamabad & Rawalpindi
This free calculator runs in your browser and needs JavaScript. If it does not load, call or WhatsApp us on +92 304 2435577 and we will do the calculation for you.
This explorer does the geometry. Enter your latitude, the design month and time, the panel length and the tilt, and it works out the sun altitude and the gap needed to keep the next row clear, with a side-view drawing of the result.
What This Tool Does
It calculates the solar declination and sun altitude for your latitude, date and time, then the shadow length cast by a tilted panel row and the row gap and pitch that keep the following row unshaded. It also works out the shadow from an obstacle of a given height.
Who It Is For
- Solar installers and structure fabricators setting out rows on a flat roof.
- Homeowners checking whether a proposed layout leaves enough space between rows.
- Anyone with a tall parapet, mumty or tank wanting to know how far its winter shadow reaches.
How To Use It
- Enter your latitude. Islamabad is about 33.7 degrees north and Rawalpindi about 33.6.
- Choose the design month. December is the usual choice because it gives the worst shadows of the year.
- Choose the time of day. Rows are commonly spaced to be clear from about nine in the morning to three in the afternoon.
- Enter the panel length along the tilt, and the tilt angle your installer proposes.
- Optionally enter an obstacle height to see how far its shadow reaches.
Inputs And Units Explained
- Latitude — in degrees north. The further north, the lower the winter sun and the longer the shadows.
- Design month — December gives the worst case; June the best.
- Time of day — in solar time. Earlier and later means a lower sun and wider spacing.
- Panel length and tilt — the panel dimension along the slope, and the angle it is tilted at.
- Obstacle height — optional, for a wall, mumty or tank.
How The Calculation Works
Solar declination uses Cooper’s equation, 23.45 degrees times the sine of 360 times (284 plus the day number) divided by 365. Sun altitude then comes from the standard relationship: the sine of the altitude equals sine of latitude times sine of declination, plus cosine of latitude times cosine of declination times cosine of the hour angle. These are textbook formulas from solar engineering, not approximations invented here.
The back edge of a tilted panel rises by the panel length times the sine of the tilt. The shadow that height casts is the height divided by the tangent of the sun altitude, which is the row gap needed. Row pitch is that gap plus the panel’s horizontal run, the panel length times the cosine of the tilt.
This is illustrative design geometry. It is not an energy yield model, and it assumes the sun is along the row line, which is the worst case rather than the average.
Worked Example
Islamabad at 33.69 degrees north, December, nine in the morning, a 2,278 mm panel at 25 degrees tilt.
| Input or result | Value |
|---|---|
| Sun altitude | About 20 degrees at that date and time |
| Panel back edge height | Panel length times sine of 25 degrees |
| Row gap | That height divided by the tangent of the sun altitude |
| Row pitch | Gap plus the panel horizontal run |
The gap at nine in the morning in December is substantially larger than most people assume, which is exactly why winter is the design case. Use the resulting pitch in the rooftop layout planner to see how many panels genuinely fit.
Features And Benefits
- Real solar geometry rather than a rule of thumb.
- A side-view drawing that makes the relationship between tilt, height and gap obvious.
- Obstacle shadows calculated from the same altitude figure.
- Feeds straight into the rooftop layout planner.
Assumptions And Accuracy Limits
- Geometry only. It is not an energy yield or shading-loss model.
- It assumes the sun lies along the row direction, which is the worst case, not the average.
- Panel tilt and row orientation are design decisions made by your installer.
- Real roofs also shade from parapets, cables and neighbouring buildings.
Common Mistakes To Avoid
- Designing for June. The summer sun is high and forgiving; December is when the spacing is tested.
- Using a single rule of thumb for every tilt. Gap scales with the sine of the tilt angle, so a steeper array needs noticeably more room.
- Forgetting the walkway. The shadow gap and the cleaning access are not necessarily the same number; take the larger.
Solar Row Spacing: Avoiding Shade Between Panels
When panels are tilted and installed in rows, the back row can be shaded by the front one in the morning and evening, and more so in winter when the sun is low. Too little spacing wastes energy, while too much wastes roof area.
Enter the panel height, the tilt and the lowest sun angle you want to design for, and the tool shows the row gap and a simple shadow diagram.
Frequently Asked Questions
What tilt angle is best for solar panels in Pakistan?
Tilts in the range of roughly fifteen to thirty five degrees are commonly used for fixed arrays at Pakistani latitudes, with the choice trading winter output against wind load and row spacing. Your installer picks it; this tool shows what each choice does to the spacing.
How far apart should solar rows be?
Far enough that the back edge of one row does not shade the next during the hours that matter in winter. That depends on latitude, tilt, panel length and the time window you design for, which is precisely what this calculator works out.
Why design for 9 am rather than noon?
At solar noon the sun is at its highest and shadows are shortest, so spacing designed for noon shades badly all morning. Nine in the morning to three in the afternoon is a common design window that keeps the array clear for most of the useful day.
How far apart should solar panel rows be?
It depends on the tilt and the sun angle at the time of year you want to protect. The tool calculates the gap for the values you enter.
Does shade on one solar panel affect the others?
It can, especially when panels are wired in series, so keeping shade off the panels at key hours is important.
Related Free Tools
- Rooftop Solar Layout & Obstacle StudioDraw your roof, add the mumty, tank and walkways, and see how many panels genuinely fit.
- Solar Mounting Frame Material & Budget EstimatorBuild a member-by-member frame takeoff with theoretical steel weight and your own rates.
- Solar Rooftop Survey & Maintenance Checklist BuilderBuild a printable rooftop survey and maintenance log so the installer visit is not wasted.
Get A Measured Quotation
Once the spacing is settled, the structure has to be built to hold it on your particular roof. Ramzan Steel Works fabricates solar mounting frames to a measured layout rather than a standard pattern.