Learn what each input means, where to find the right value, and how to read wind, snow, stress, deflection, and tracker torque results without getting lost in engineering notation.
Quick answer: Start by selecting the mounting system. Enter the module size, layout, site wind and snow data, then add the real section properties and analysis forces for your members. The calculator updates immediately. A green “Pass” means the entered demand is within the entered limit; “Review” means the demand exceeds that limit. Neither status is a construction approval.
What does the solar mounting structural load calculator check?
The LuminVolt Solar Mounting Structural Load Calculator is a preliminary engineering tool for two common PV support systems: a fixed-tilt table and a single-axis tracker. It converts the supplied engineering workbook into a browser-based form, so every dependent result changes as soon as you change an input.
For a fixed-tilt structure, the tool calculates basic wind pressure, design wind load, design snow load, distributed loads, combined member stress, utilization, and deflection limits. For a tracker, it calculates wind pressure in two operating cases, wind eccentric torque, gravity eccentric torque, unit torque along the torque tube, and a snow load value.
This calculator is for preliminary checks and engineering discussion. It does not select local design wind speeds, exposure categories, importance factors, load cases, connection capacities, foundation resistance, or code rules for you. Final design must be checked under the code adopted at the project location and signed off by a qualified structural engineer when required.
In the United States, ASCE/SEI 7-22 covers environmental loads and load combinations for structural design. ASCE also publishes worked guides for its wind and snow provisions. Projects in other countries may follow different national standards. Use the standard named in your project documents rather than assuming one method applies everywhere.
What should you prepare before opening the calculator?
You can explore the tool with its defaults, but a real project check needs verified inputs. Gather the following information first:
- PV module length, width, mass, and quantity
- Table layout, member spans, and torque-tube length
- Site design wind speed and air density
- Terrain or exposure data and the correct height coefficient
- Snow density, snow depth, roof or panel slope
- Member area, section modulus, and material design strength
- Analysis forces, bending moments, and actual deflections
- Applicable load combinations and project design standard
Module values normally come from the manufacturer’s datasheet. Section properties should come from the approved steel or aluminum profile drawing. Wind, snow, terrain, and load-combination values should come from the project’s design basis, local authority data, or an engineer’s calculation.
The fixed-tilt module and member lengths use millimetres, while snow depth uses metres. Tracker geometry uses metres. Section modulus is in cm³, area is in cm², moments are in N·m, stress is in MPa, and torque is in N·m or N·m/m. Read the unit printed beside every field before typing.
Step 1: choose fixed-tilt or single-axis tracker
| Mode | Choose it when | Main output |
|---|---|---|
| Fixed-tilt structure | The modules stay at one angle on purlins, rafters, posts, and braces. | Wind and snow loads, member stress utilization, and deflection checks. |
| Single-axis tracker | A row rotates around a torque tube and must be checked at different tracker angles. | Wind and gravity torque, unit torque, and the governing torque demand. |
If your project uses a conventional ground or roof table, begin with fixed-tilt. If it uses a rotating row like the systems described on our solar tracker page, choose tracker. The two tabs keep their own input values, so you can switch between them without mixing the models.
How to use the fixed-tilt calculator
Enter the module and table layout
Enter module length, module width, and module mass from the module datasheet. Then enter the number of layout rows and the number of modules in each row.
Total purlin length is the modelled length used to distribute module loads along the purlins. Rafter length is the relevant rafter span used by the workbook’s distributed-load calculation. Do not enter the overall project length unless it is the same modelled length.
Enter the wind inputs
The tool first calculates basic wind pressure using w = 0.5 × ρ × V². Here, ρ is air density and V is design wind speed.
The design wind load then applies the gust response factor βz, shape coefficient μs, and height factor μz. These coefficients are not universal constants. Select them from the project standard and design basis. The μz table lower on the calculator page reproduces the supplied workbook values for terrain categories A through D.
Enter the snow inputs
Enter the snow coefficient μr, snow density, and snow depth. The tool calculates basic snow pressure from density, gravity, and depth, then multiplies it by μr.
Use the mono-pitch table on the calculator to match μr to the slope angle α in the supplied workbook. For example, that table gives μr = 1.00 at slopes up to 25°, 0.85 at 30°, 0.70 at 35°, and 0 at 60° or more. Only use those values when they are valid for your project standard and loading condition.
Add the member section properties
Open Member section properties. For the purlin, rafter, and post, enter the net section modulus about each axis (Wnx and Wny), net area An, and the γ factors used by the workbook. Enter the brace design area and material design strength as well.
This is where beginners most often use the wrong data. Do not type the outside width or height of a profile into a section modulus field. Wnx and Wny are calculated geometric properties, usually listed in a profile table or engineering drawing.
Add forces, moments, and actual deflections
Open Member forces and moments. Enter axial force N and bending moments Mx and My for the load case being checked. Then enter the member lengths and actual deflections from your structural analysis.
The calculator does not generate a full frame analysis from the module layout. It checks the forces and deflections that you enter. This distinction matters: environmental inputs calculate load values, while member demand values still need to come from an appropriate structural model or verified workbook.
Read the fixed-tilt results
The top cards show design wind load, basic wind pressure, and design snow load. The distributed-load list shows how those loads are apportioned to the purlin, table, and rafter using the workbook formulas.
The strength table compares combined member stress with the entered design strength. Utilization is demand divided by capacity. The deflection table compares actual movement with the workbook limit for each member.
Worked fixed-tilt example using the default values
The default fixed-tilt model uses a 1,650 × 991 mm module weighing 16.5 kg, arranged as 2 rows by 11 modules. The wind speed is 26.84 m/s, air density is 1.25 kg/m³, βz is 1.00, μs is 1.30, and μz is 1.00. Snow density is 130 kg/m³, snow depth is 0.11 m, and μr is 0.85.
With those values, the calculator returns:
| Result | Default output | Plain-language meaning |
|---|---|---|
| Basic wind pressure | 450.24 Pa | Pressure from the entered air density and wind speed before the three wind coefficients. |
| Design wind load | 585.31 N/m² | Basic pressure after βz, μs, and μz are applied. |
| Design snow load | 121.55 N/m² | Snow pressure after the entered μr coefficient is applied. |
| Highest default strength use | Rafter: 80.4% | The rafter is the closest member to its entered design strength in this example. |
| Closest default deflection check | Purlin: 15.0 / 17.5 mm | Actual deflection is below the displayed limit, but it is closer than the other two checks. |
All default strength and deflection rows show “Pass,” but that only means the supplied workbook values are within the supplied limits. If you change the design strength, section properties, moments, forces, lengths, or actual deflections, the result may change immediately. A passing sample is not evidence that a different site or profile is adequate.
How to use the single-axis tracker calculator
Enter row and module geometry
Enter module length, module width, module mass, modules per row, torque-tube length, and module windward length. The tracker model uses metres, so do not paste millimetre values from the fixed-tilt tab.
Define the 0° wind case
Enter βz, μz, air density, wind speed, positive Cp, and negative Cp for the 0° position. The calculator uses the average of the two Cp values for displayed design wind load and their difference for eccentric wind torque.
Define the 45° wind case
Repeat the wind inputs for the 45° position. Do not assume the same wind speed or pressure coefficients automatically apply. Use the values stated in the tracker design basis or wind study.
Add gravity and snow values
Gravity eccentricity is the distance between the rotation axis and the relevant centre of mass. The tracker angle controls the gravity torque component. Enter μr, snow density, and snow depth for the snow output.
Read the governing unit torque
The results separate wind eccentric torque and gravity eccentric torque, then divide torque by the axis length to give N·m/m. The governing value is the larger absolute total from the two displayed tracker cases.
Tracker example using the defaults
The default tracker row has 56 modules, each 2.15 × 1.06 m and 30 kg, on a 60.7 m torque tube. The 0° wind case uses 25 m/s; the 45° case uses 15 m/s. The resulting governing unit torque is 176.58 N·m/m.
| Default tracker result | Value |
|---|---|
| Wind eccentric torque at 0° | 10,718.42 N·m |
| Wind unit torque at 0° | 176.58 N·m/m |
| Wind eccentric torque at 45° | 3,858.63 N·m |
| Gravity eccentric torque | 1,513.43 N·m |
| Total unit torque at 45° | 88.50 N·m/m |
| Design snow load | 0.175 kN/m² |
Use the governing unit torque as an input for the next engineering step, such as checking the torque tube, drive unit, bearings, dampers, and row response. The calculator does not confirm that these components are adequate.
How to use the three reference sections
Load combinations
The load-combination table lists 12 factors from the supplied workbook. Strength combinations include factored gravity, positive or negative wind, and snow. Deflection combinations use service-level factors. The table is a reference; it does not automatically create new member forces inside the browser tool. Apply the correct combination in your structural analysis, then enter the resulting forces and moments in the member fields.
Wind pressure height coefficient μz
Find the project height in the first column, then move across to terrain A, B, C, or D. The notes below the table describe the workbook’s terrain categories. If the height falls between two rows, follow the interpolation or selection rule in the applicable standard rather than choosing a value by eye.
Mono-pitch snow coefficient μr
The diagram separates the horizontal snow distribution from the sloped roof and shows α at the roof’s low edge. Select the μr value that matches the roof slope in the table. Do not read the long horizontal snow bar as the roof surface; it represents the uniform snow distribution shown in the source data.
What do “Pass,” “Review,” utilization, and deflection mean?
Stress is the calculated internal demand per area. Design strength is the allowable comparison value you entered. Utilization is stress divided by design strength. A value of 80% means the calculated demand is 80% of the entered strength; 105% means it is 5% above it.
The tool marks utilization at or below 100% as “Pass” and values above 100% as “Review.” For deflection, it marks the row “Pass” when actual deflection is at or below the displayed limit. These are numerical comparisons, not engineering approval.
A real design may also require checks for buckling, local buckling, lateral-torsional buckling, fatigue, connection strength, pull-out, bearing, foundation overturning, sliding, soil resistance, dynamic tracker response, erection conditions, corrosion loss, tolerances, and accidental cases. Ask the project engineer which checks govern.
Nine common input mistakes to avoid
- Mixing millimetres and metres. This can change a result by 1,000 times or more.
- Entering wind pressure as wind speed. Wind speed belongs in m/s; pressure is a calculated result in Pa.
- Using module dimensions for the whole table. Module size and structural member length are separate inputs.
- Guessing μz from height alone. Terrain category also changes the coefficient.
- Using the snow depth without confirming density. Equal depths can produce different loads when snow density differs.
- Typing profile dimensions into Wnx or Wny. Section modulus must come from a section-property calculation or table.
- Leaving workbook forces in place for a new project. Default moments and forces describe the sample, not your frame.
- Treating the reference combinations as automatic. The member demand fields still need correctly combined analysis results.
- Reading “Pass” as permit-ready. It only reports the comparison coded into the tool.
Save one set of verified inputs, change only one value at a time, and note which result changes. This makes unit errors and unexpected dependencies easier to spot. Use the Reset button whenever you want to return to the workbook defaults.
Frequently asked questions
Can I use the calculator without engineering experience?
You can use it to learn the relationships and prepare a preliminary comparison. For a project check, the coefficients, section properties, analysis forces, and acceptance criteria should be supplied or reviewed by someone qualified in structural design.
Where do I find the correct design wind speed?
Use the project design basis, the authority having jurisdiction, or the map and method required by the locally adopted standard. Do not copy the wind speed from a weather app or from another city.
Does the calculator automatically apply every load combination?
No. It displays the workbook’s combination table as a reference. Enter member forces and moments from the correct combined structural analysis case.
What should I do when a result says “Review”?
First check units and source data. If the inputs are correct, ask the structural engineer to review the section, span, bracing, load path, analysis model, and acceptance criteria. Do not solve an over-limit result by changing a coefficient without technical support.
Why does a small wind-speed increase change the pressure so much?
Basic wind pressure is proportional to wind speed squared. If speed rises by 10%, pressure rises by about 21% before other coefficients are applied.
Can this calculator size foundations or roof anchors?
No. It does not check soil, ballast, piles, anchor pull-out, roof capacity, or connection detailing. Use our separate wind and snow load calculator for another preliminary load view, then obtain project-specific foundation and connection checks.
Can I use it for both steel and aluminum members?
The stress comparison accepts editable section properties and design strength, but the correct resistance checks differ by material and standard. Confirm the member model, factors, buckling rules, and strength values with the project engineer.
Why are the fixed-tilt and tracker units different?
The two modes reproduce different workbook models. Fixed-tilt geometry is mainly entered in millimetres, while tracker geometry is in metres because its main result is torque per metre of tube.
Ready to try your own project data?
Open the calculator in a second tab, keep this guide beside it, and replace the defaults only with verified values. For mounting-system support, send LuminVolt your module layout, site loads, and project drawings.