Solar Panel Spacing Calculation: Row Formula and GCR

Last updated: November 2026

Rows set too close shade each other, and rows set too far apart waste land. Here is the formula, a pitch table for 7 latitudes and the shading cost of getting it wrong.

Rows of panels that sit too close shade each other. NREL’s simulation of a fixed-tilt array at 20° tilt found yearly beam shading loss of 1.5% at a ground cover ratio (GCR) of 0.64 and 5.7% at 0.80. GCR is the row length up the slope divided by the row pitch. The calculation takes minutes once you know the formula. Most mistakes come from one wrong input.

A good solar PV design tool can run this check as you place rows. Even so, know the math. It lets you defend every number in a client’s proposal.

This guide covers the solar panel spacing formula, ground cover ratio (GCR), a quick table for 7 latitudes, and advice for ground-mount, flat-roof, bifacial and east-west layouts. Bifacial panels collect light on both sides. For a full walk-through, read the bifacial solar panel design guide.

In this guide:

• A quick table of row pitch by latitude and tilt
• Why spacing errors cost money, using NREL shading loss data
• The spacing formula, step by step, with worked examples
• The 9 AM to 3 PM design window and why it changes the answer
• Ground cover ratio (GCR) and how to pick it
• Spacing for ground-mount, flat-roof and pitched-roof systems
• Portrait and landscape layouts, bifacial panels, and east-west racking
• Ten common spacing mistakes
• How design software handles spacing

Quick Answer: Row Pitch by Latitude and Tilt

This table shows the row pitch that keeps one portrait module row (2.0 m up the slope) clear of shade at solar noon on 21 December. The module is an example size of 2.0 m × 1.0 m. Rows face true south in the northern hemisphere. Every value comes from the formula in this guide.

These are shade-free values at solar noon only. Section “The 9 AM to 3 PM Design Window” shows how much larger they get for a longer shade-free day. Sun height uses the noon formula from PVEducation.

Read down the 20° column. The pitch goes from 2.99 m at 35°N to 4.18 m at 50°N, which is 1.40 times as much.

Why Spacing Errors Cost Money

NREL simulated a fixed-tilt array of 3-up landscape rows (three modules stacked up the slope) at 20° tilt, facing south, with Sacramento weather data. It also simulated 2-up portrait rows. The simulations are in the NREL report “Photovoltaic Shading Testbed for Module-Level Power Electronics: 2016 Performance Data Update” (NREL/TP-5J00-62471, September 2016), Table 7. The report used a 60-cell module of 1.65 m × 0.99 m. Its row spacing is measured from the front of one row to the front of the next.

Beam loss is the loss from hard shadows on the panels. Diffuse loss is the smaller loss from reduced view of the sky. NREL reports total yearly losses of 4% to 14% across these cases, with beam loss about half of the total. NREL says the values apply to the orientation and weather data it assumed.

Here is what that means in money. This is an example, not a forecast. Take a 100 kWp system. Assume 5.5 peak-sun-hours a day, which gives 100 kWp × 5.5 × 365 = 200,750 kWh a year before any other losses. NREL’s own Sacramento irradiance is 1,993 kWh/m² a year, so this baseline is close. Price the energy at $0.10 per kWh.

The gap is 4.2 percentage points, or $843 a year (1,144 − 301). Over 25 years with a flat price, that is 843 × 25 = $21,075 on a 100 kWp system. It ignores panel aging and price changes. On a 500 kWp system the gap is 4.2% × 1,003,750 kWh = 42,158 kWh, or $4,216 a year. Over 25 years at a 6% discount rate, that has a present value of about $53,900 (4,216 × 12.78). That figure covers beam loss only. It leaves out the diffuse loss in the table.

Wide spacing has its own cost: more land. Land use scales with 1 ÷ GCR. A system at GCR 0.40 needs 0.50 ÷ 0.40 = 1.25 times the land of the same system at GCR 0.50. That is 25% more land. For 100 kWp of 400 W modules of 2.0 m² each, the array area is 200 × 2.0 = 400 m². The ground area is then 400 ÷ 0.40 = 1,000 m² at GCR 0.40 and 400 ÷ 0.50 = 800 m² at GCR 0.50. The difference is 200 m², or about 0.05 acre. Multiply that by your own lease rate to get the yearly cost.

The ten mistakes later in this guide come down to two things: a wrong input in the formula, or a formula for one layout used on another. The formula itself is short.

The Solar Panel Spacing Formula, Step by Step

The calculation has three steps. Each step feeds the next. Do them in order.

Step 1: Find the Row Height (H)

Row height (H) is how much higher the top edge of a tilted row is than its bottom edge. It sets how long the shadow is.

H = L × sin(β)

Where:
  L = row length up the slope
      (module length for portrait, module width for landscape;
       multiply by the number of modules stacked up the slope)
  β = tilt angle in degrees from horizontal

Worked example 1: portrait. A module that is 2,000 mm × 1,000 mm. L = 2,000 mm (the long side faces up the slope), β = 20°.

H = 2,000 × sin(20°)
H = 2,000 × 0.342
H = 684 mm = 0.684 m

Worked example 2: landscape. The same module turned 90°. L = 1,000 mm, β = 20°.

H = 1,000 × sin(20°)
H = 1,000 × 0.342
H = 342 mm = 0.342 m

Landscape cuts row height in half at the same tilt. A shorter shadow needs a smaller gap, so landscape rows can sit closer together. The GCR for a shade-free layout does not change, as the portrait and landscape section below shows.

Step 2: Find the Winter Solstice Sun Height (α)

A common design rule is to be shade-free at solar noon on 21 December. That day has the lowest noon sun of the year in the northern hemisphere. If the rows clear each other then, they clear each other on every other day at noon.

α = 90° − Latitude − 23.45°

(sun height at solar noon on 21 December, rows facing true south,
 latitude above 23.45°N)

The 23.45° is the tilt of the Earth’s axis. The sun’s lowest noon angle is the latitude’s complement minus that tilt. PVEducation gives the noon elevation formula. Its declination page gives the 23.45° value.

Step 3: Find the Gap, Row Pitch and GCR

With H and α, the rest follows.

D   = H ÷ tan(α)       [gap: back edge of one row to front edge of the next]
P   = L × cos(β) + D   [row pitch: front of one row to front of the next]
GCR = L ÷ P            [ground cover ratio]

Where:
  D = gap between rows (m)
  H = row height from Step 1 (m)
  α = sun height from Step 2 (°)
  L × cos(β) = horizontal footprint of one row (m)
  P = row pitch (m)

The footprint uses the row length L (up the slope), not the module’s other side. Using the wrong side is a common slip. It gives a pitch that is too small.

Rows not facing true south. At solar noon, rotating the rows by an angle ε away from true east-west shrinks the gap you need to about D × cos(ε). This is a noon-only approximation. A 10° turn changes D by 1.5% (cos 10° = 0.985). A 20° turn changes it by 6% (cos 20° = 0.940). Use a shading simulation for a full-day answer.

Worked Example: 35°N, 20° Tilt

Scenario: a ground-mount at 35°N (Los Angeles), 20° tilt, facing south. Modules are 2,000 × 1,000 mm in portrait. The design rule is solar noon on 21 December.

GIVEN:
  Module: 2,000 mm (L, up the slope) × 1,000 mm
  Tilt (β): 20°
  Latitude: 35°N

STEP 1: Row height
  H = 2.000 × sin(20°) = 2.000 × 0.342 = 0.684 m

STEP 2: Sun height at winter solstice noon
  α = 90° − 35° − 23.45° = 31.55° ≈ 31.6°

STEP 3: Gap
  D = 0.684 ÷ tan(31.55°) = 0.684 ÷ 0.614 = 1.11 m

STEP 4: Row pitch
  P = L × cos(β) + D = 2.000 × 0.940 + 1.11 = 1.88 + 1.11 = 2.99 m

STEP 5: Ground cover ratio
  GCR = L ÷ P = 2.000 ÷ 2.99 = 0.67

RESULT: 2.99 m row pitch, GCR 0.67.

Now run the same module and tilt at four latitudes.

Pitch is the output of the formula. GCR is the number that links spacing to land, shading loss and revenue.

The 9 AM to 3 PM Design Window

A noon-only rule is the least strict one. Many designers also want shade-free time in the morning and afternoon. The sun is lower then, and it is off to the side, so the shadow stretches.

To compute it, use the sun height and sun direction at 9 AM solar time on 21 December. The north-south part of the shadow is H × cos(azimuth offset) ÷ tan(sun height). Solar position follows the standard equations on the PVEducation elevation and azimuth pages, with a declination of −23.45°. The table uses H = 0.684 m (the 20° portrait example).

The 9 AM gap is 41% to 129% larger than the noon gap in this range. The further north you go, the faster it grows. Agree the shade-free window with your client before you set the pitch, and run a shading simulation to confirm it.

Ground Cover Ratio (GCR)

GCR turns a spacing choice into a money choice. A high GCR puts more kW on each acre. It also adds shading loss. A low GCR cuts shading loss and needs more land.

What GCR Means

GCR = row length up the slope ÷ row pitch

This is the definition used in the NREL shading report: array area divided by ground area. Check it against the NREL numbers: 3 modules of 0.99 m is 2.97 m, and 2.97 ÷ 4.6 m = 0.65, close to the stated 0.64. A GCR of 0.5 means panels cover half the ground.

NREL Shading Loss by GCR

The NREL table above is the best sourced reference here. It covers one site (Sacramento, about 38°N), one tilt (20°) and two layouts. Do not carry the loss percentages to a very different latitude. At higher latitudes the sun is lower in winter, so shade reaches further for the same GCR. NREL says its values depend on the orientation and weather data it assumed.

Pick the GCR with Three Scenarios

Do not guess the GCR. Compare options with your own numbers:

1. Pick three GCR values, for example 0.35, 0.45 and 0.55.
2. For each one, compute the pitch: P = L ÷ GCR. For a 2.0 m row, that is 5.71 m, 4.44 m and 3.64 m.
3. Compute the ground area: for 100 kWp of 2.0 m² modules (400 m² of panels), that is 1,143 m², 889 m² and 727 m².
4. Run a shading and yield simulation for each pitch on your site.
5. Compare the value of the lost energy with the cost of the land. Pick the GCR where the total is lowest.

Fixed Tilt and Trackers

NREL’s PVWatts paper (Dobos, Freeman and Blair) says that for silicon modules, row-to-row shade has a strong effect on a one-axis tracker as GCR rises. It also says backtracking can reduce the loss. Backtracking turns the panels flatter when the sun is low so the rows do not shade each other. The paper does not give one typical GCR. See also tracker vs fixed tilt and the solar land area calculator guide.

Spacing by Installation Type

Ground-Mounted Fixed Tilt

Ground-mounts give you the most freedom. A spacing error also costs the most there, because land and yield both move.

The shading rule is not the only limit. Workers need to reach the panels to clean and repair them. Vehicles may need a lane for mowing or cleaning. Ask the site operator and the racking maker for the clearances they need, then add them to the shade-free pitch. The ground-mount solar design guide covers the wider layout.

Try the three-scenario method above before you lock in a pitch. Keep in mind that the shade-free GCR falls as latitude rises (0.67 at 35°N, 0.48 at 50°N for a 20° tilt).

Standards such as NEC Article 690 cover electrical rules for PV systems in the US. Check which codes apply to your project with the permit authority. This guide does not cite a spacing rule from a standard.

Commercial Flat Roofs

On a flat roof the roof area is fixed. The goal is to fit the most capacity while keeping shade loss acceptable. Too much space between rows means fewer panels.

A Sandia and NREL project report, “Optimized Bifacial PV Systems”, states that most commercial rooftop systems are designed with modules in landscape orientation and one module per row (1-up). It adds that the pitch is usually set by a shading limit, the lowest sun height at which there is no inter-row shade. The report says it learned this from a PV racking company, so treat it as a typical practice, not a rule.

Racking makers publish their own spacing. For example, KB Racking’s EkonoRack 2.0 lists row spacing of 1.26 to 1.75 m (landscape) and 2.14 to 2.45 m (portrait). It offers 5°, 10°, 15° and 20° tilt in landscape, and 5° in portrait. Use the maker’s table for the racking you choose.

Tilt on a flat roof. A lower tilt gives a smaller H and a smaller pitch, but it costs yield. For a 2 m row at 40°N, a 10° tilt needs a pitch of 2.66 m. A 20° tilt needs 3.25 m. That is 18% less pitch at 10° (2.66 ÷ 3.25 = 0.82).

How much yield does the lower tilt cost? The EU’s PVGIS tool (version 5.3, south-facing, 1 kWp, 14% system loss), run on 28 October 2026 for three sites, shows that 10° tilt gives less yearly energy than 20°.

Whether the trade pays off depends on your roof. If the lower pitch lets you add rows, run both tilts in a simulation and compare the total yearly energy.

Residential Pitched Roofs

On a pitched roof, rows rarely shade each other, because the panels lie flat on the roof plane. The main limits are setbacks from edges and ridges for fire access. Local fire codes set those distances and they differ by place. Check your local code.

Row-to-row shade can matter when you stack rows on a long roof face or a carport. For that case, use the sun height at the first or last hour you want shade-free, not solar noon. See the solar carport design guide. For awkward roofs, see panel layout around dormer windows.

Portrait vs. Landscape

Orientation changes row height H, the gap D and the pitch P. It does not change the shade-free GCR.

Landscape halves H, D and P. Because the GCR is the same, one portrait row (pitch 2.99 m) covers the same roof depth as two landscape rows (2 × 1.50 m = 3.00 m). The shade-free layout does not fit more panels. The difference shows up in the electrical result when shade does fall on the panels.

NREL’s simulation gives a clear comparison. At the same GCR, beam loss for 2-up portrait rows was 51% to 53% higher than for 3-up landscape rows (2.3% vs 1.5%, 5.6% vs 3.7%, 8.6% vs 5.7%). The two layouts have different row heights, so read this as the result for those two NREL layouts and not as a rule for every module.

When to choose landscape: Roofs where you want to keep tight rows and lower beam loss when the rows do get shade. Sandia and NREL’s report says this is common on commercial roofs.

When to choose portrait: Layouts where your racking, string design or module size favors it. Check the datasheet and the racking guide.

Bifacial Panel Spacing

Bifacial panels collect light on both the front and the back. The back gets light that bounces off the ground, so the ground matters. Ground cover, row spacing and the height of the panel above the ground all change how much light reaches the back. The shade-free spacing check is the same formula: D = H ÷ tan(α). After that, run a bifacial simulation to check the rear gain for your clearance, GCR and ground.

Albedo of Common Surfaces

Albedo is the share of light a surface reflects. Sandia’s PV Performance Modeling Collaborative (PVPMC) lists these guide values from the PVsyst software:

Source: Sandia PVPMC, Albedo.

Sandia notes that going from dry concrete or asphalt (about 0.2) to fresh snow (about 0.8) can raise output by 5% to 10% when the array stays snow-free. That example is for a latitude-tilt array in Albuquerque, not a bifacial array. Treat it as a sign of how much ground reflection matters. See the albedo and bifacial solar panel glossary pages.

East-West Racking

In a south-facing layout, each row casts its shadow on the row behind it. In an east-west layout, modules face east and west at a low tilt. The south-facing spacing numbers do not carry over. Use the racking maker’s spacing and a shading simulation.

KB Racking’s AeroGrid East West system gives a feel for the numbers. Its listed tilt is 10°, in landscape, and its row spacing is “up to 5 in (peak-to-peak), up to 8 in (valley-to-valley)”, which is up to about 0.13 m and 0.20 m. The row height of a 0.99 m module at 10° is only 0.99 × sin 10° = 0.17 m. A low tilt means a short shadow.

This is KB Racking’s figure for one system. Other east-west systems may differ. This guide does not give a capacity or yield gain for east-west layouts, because no primary source for those numbers was found. Compare layouts with a simulation of your own roof.

Ten Common Spacing Mistakes

These errors show up often in spreadsheet-based spacing work.

1. Using solar noon when the client wants a longer shade-free day. The 9 AM gap is 41% to 129% larger than the noon gap between 35°N and 52°N (table above). A pitch set at noon leaves shade on winter mornings and afternoons.

2. Ignoring portrait vs. landscape in H. A row of 2.0 m has twice the height of a row of 1.0 m at the same tilt. Use L for the real row length up the slope.

3. Using the wrong module side for L. In portrait, L is the long side. In landscape, it is the short side. Swapping them can halve H.

4. Using the wrong side in the footprint. The footprint is L × cos(β), with L being the row length up the slope. Using the module’s width gives a pitch that is too small. For the 2 m example at 35°N, the correct pitch is 2.99 m, not 2.05 m.

5. Copying a GCR from a different latitude. NREL’s loss figures come from Sacramento at 20° tilt. The shade-free GCR for the same tilt is 0.67 at 35°N and 0.48 at 50°N. Recompute D for the real site.

6. Skipping maintenance access. The formula gives the least gap that avoids shade. It does not include space for people or vehicles. Add the access the site needs.

7. Not setting the ground surface in a bifacial design. Albedo changes the rear gain. Enter the real surface.

8. Using south-facing numbers for east-west racking. The two layouts work differently. Use the racking maker’s spacing.

9. Ignoring row rotation. At noon, a 20° rotation from true east-west changes D by about 6%. On a large ground-mount, run a full-day simulation.

10. Using module sizes from memory. Modules sold as “60-cell” or “72-cell” are not one fixed size. NREL’s report assumed a 60-cell module of 1.65 m × 0.99 m. KB Racking’s AeroGrid East West system lists a module fit of 990+ mm × 1,700+ mm. Use the datasheet for the module you will buy. If you swap modules later, redo the spacing. A module that is 40 mm longer up the slope raises H by 0.04 × sin 20° = 13.7 mm and D by about 22 mm at 35°N (0.0137 ÷ 0.614).

How Design Software Handles Spacing

A calculation like this one gives you a pitch for one row and one day. A design tool can check the whole layout. SurgePV’s scope covers 3D roof modeling, solar array layout, shading analysis, energy-yield modeling and financial modeling. In the guided demo, you can see how layout and shading analysis work on a project like yours.

When row pitch changes, a yield model shows the result in kWh. A financial model turns that into revenue. That is how you compare GCR options in the three-scenario method above. See shadow analysis and the generation and financial tool. Results depend on the input data, the assumptions, and the review by the responsible engineer. For more on layout, see the panel layout hub. Use the string sizing calculator to check the electrical side.

Frequently Asked Questions

How far apart should solar panel rows be?

It depends on tilt, row length and latitude. Row pitch = L × cos β + L × sin β ÷ tan α. For a 2 m module row at 20° tilt, the pitch is 2.99 m at 35°N, 3.25 m at 40°N and 4.18 m at 50°N. These values keep the rows free of shade at noon on 21 December. Racking makers list their own ranges. KB Racking lists 1.26 to 1.75 m (landscape) and 2.14 to 2.45 m (portrait) for its EkonoRack 2.0 flat-roof system.

How do I calculate inter-row distance for solar panels?

Use three steps. First, find the row height: H = L × sin β, where L is the row length up the slope and β is the tilt. Second, find the sun’s height at noon on 21 December: α = 90° − latitude − 23.45°. Third, find the gap: D = H ÷ tan α. Add the horizontal footprint of the row (L × cos β) to get the row pitch.

What is a good GCR for solar panels?

There is no single good value. GCR is the row length up the slope divided by the row pitch. NREL simulated 0.64, 0.74 and 0.80 for fixed-tilt rows at 20° tilt in Sacramento. In its simulation, yearly beam shading loss for 3-up landscape rows rose from 1.5% at 0.64 to 5.7% at 0.80. Pick the GCR by comparing yield loss with land cost on your site.

What GCR is typical for fixed tilt vs trackers?

No single typical value is published in the sources used here. For fixed tilt, NREL simulated 0.64 to 0.80 at 20° tilt. NREL’s PVWatts paper says row-to-row shade on a one-axis tracker is strong, and backtracking can reduce the loss. Run a shading simulation for your latitude and land cost.

How far apart should solar panels be on a flat roof?

KB Racking lists 1.26 to 1.75 m (landscape) and 2.14 to 2.45 m (portrait) for its EkonoRack 2.0 system, which offers 5°, 10°, 15° and 20° tilt in landscape and 5° in portrait. Other racking systems differ. Check the maker’s data sheet, then check the result with the formula for your latitude.

Does solar panel tilt angle affect spacing?

Yes. A steeper tilt makes the row taller (H = L × sin β), so the gap grows. For a 2 m row at 35°N, going from 20° to 30° tilt raises H from 0.68 m to 1.00 m. The gap D grows 46% (1.11 m to 1.63 m) and the pitch grows 12% (2.99 m to 3.36 m).

What is the solar panel spacing formula?

H = L × sin β is the row height. D = H ÷ tan α is the gap between rows, where α = 90° − latitude − 23.45° is the sun’s height at noon on 21 December. Row pitch P = L × cos β + D. GCR = L ÷ P.

Conclusion

Spacing is a short calculation with a 25-year effect. Three steps to take from this guide:

• Compute the pitch with the corrected formula (L is the row length up the slope), and set the shade-free window with your client.
• Compare three GCR values on your own site. Weigh the shading loss against land cost.
• Check racking spacing against the maker’s data sheet, and run a shading simulation before you lock the layout.

Next, the design has to become a client-ready document. Solar proposal software can build the proposal from the design output, and you can book a demo to see the full row-layout workflow.