Installing photovoltaic panels on an industrial building is not simply a matter of choosing a structure compatible with the module and attaching it to the roof.
Solar roof structures must be sized taking into account the forces that may affect the system throughout its lifespan. These include wind, snow, and self-weight loads , as well as the characteristics of the roof itself, the fixing system, and, in certain solutions, the ballast required to ensure wind stability .
An incorrect calculation can cause displacements, deformations, damage to the waterproofing or even the failure of certain components of the installation.
Therefore, before installing a solar structure on an industrial building or commercial building, it is necessary to jointly analyze the structure, roof, loads and anchoring or ballast system .
Why is it important to calculate the loads on a solar roof?
An industrial roof may be subjected to different actions during its useful life.
The photovoltaic installation also introduces new loads and modifies the interaction of the roof with the wind.
The main factors that need to be analyzed include:
- Weight of photovoltaic modules.
- Weight of the structure.
- Weight of auxiliary elements.
- Wind loads.
- Snow loads.
- Maintenance actions.
- Geometry and slope of the roof.
- Building height.
- Geographical location.
- Exposure to wind.
- Roof type.
- Fixing system.
- Ballast distribution when using a ballasted solution.
The goal is not simply to ensure that the panels remain in place, but to guarantee that the assembly of the roof + structure + modules + fixings performs adequately under the expected conditions.
1. Wind loads on solar structures
Wind is one of the most important factors in the design of a rooftop photovoltaic installation.
Unlike the weight of the modules, which acts primarily as a gravitational load, the wind can generate pressures and suctions on the panels and the structure.
In certain situations, the suction may attempt to lift or displace the photovoltaic system.
What does wind load depend on?
Among other factors, the following should be considered:
- Building location.
- Basic wind speed.
- Roof height.
- Terrain roughness.
- Building exhibition.
- Roof geometry.
- Slope.
- Shape and arrangement of the panels.
- Distance of the modules to the edges.
- Row spacing.
- Presence of obstacles.
- Specific area of the roof.
This is especially relevant in the perimeter areas and corners of roofs, where wind forces can be more unfavorable.
Wind and edge effect
One of the most common mistakes is applying the same calculation criteria to the entire roof.
In reality, not all areas of a roof are necessarily subjected to the same actions .
Areas near edges and corners can present more demanding conditions. Therefore, the position of the modules and structures must be included in the analysis. How is the effect of wind calculated?
Maintenance in structures with ice
2. Snow loads on solar panels
Although Spain is not characterized by having high snow loads throughout its territory, there are areas where this factor can be decisive.
Snow represents an additional vertical load that must be considered in the design where appropriate.
The snow load depends, among other factors, on:
- Geographic area.
- Altitude.
- Climatic conditions.
- Roof geometry.
- Slope.
- Local accumulations.
- Panel configuration.
In addition, the photovoltaic installation can modify the way snow is distributed over certain areas.
Do we need to take snow into account even if the roof is flat?
Yes, when project conditions require it.
A flat roof does not mean that the snow load can be automatically ignored. The calculation must be performed according to the site and design conditions.
In certain configurations, localized accumulations can also occur , so it is not always sufficient to consider a uniform distribution.
3. What is ballast in a solar structure?
Ballast is an additional weight used to increase the stability of a photovoltaic installation, especially in systems that do not use a direct mechanical attachment to the roof.
The principle is simple:
more effective weight → greater resistance to displacement and lifting.
However, this does not mean that adding more ballast blocks is always a suitable solution.
The ballast must be sized according to the expected actions and the load-bearing capacity of the deck.
Ballast must be calculated, not estimated.
One of the common mistakes in photovoltaic installations is using an amount of ballast based solely on previous experience:
“We always put X kilos per panel on this roof.”
This approach may be incorrect.
Two decks located in different locations may require different amounts of ballast due to their wind conditions, height, geometry, and exposure.
Therefore, the ballast size must respond to the specific conditions of the project .
4. How is the necessary ballast calculated?
The calculation must consider the balance of the system against actions that may produce displacement or uplift.
In simplified terms, the following are involved:
Favorable actions:
- Weight of the modules.
- Weight of the structure.
- Ballast weight.
- Other permanent elements.
Unfavorable actions:
- Wind suction.
- Horizontal thrusts.
- Other actions applicable to the project.
The calculation must verify that the stability of the assembly is sufficient.
But there is a second fundamental issue:
The deck must also support the added weight.
A structure can be stable against the wind and yet generate an excessive load on the roof.
For this reason, the analysis must simultaneously check:
stability of the structure + resistant capacity of the cover.
This point is especially important in existing industrial roofs, where there may be load limitations or incomplete structural information.
5. Types and options of structures for rooftop solar panels
There is no single solution that works for all roofs.
Among the main options we find:
Mechanically fixed structures
The structure is connected to the roof or to resistant elements using suitable fixing systems.
It can be an interesting solution when the roof and its construction system allow for the corresponding fixings to be made.
Ballasted structures
They use the system’s own weight and ballast elements to ensure stability without necessarily relying on direct mechanical fixing.
They are particularly useful on certain flat roofs, but require a specific load and stability analysis. Learn more: Ballasted structures
Coplanar structures
They allow the modules to be installed following the geometry of a sloping roof.
The solution must be adapted to the type of roof, material, orientation, geometry and available fixing system.
6. Safety and risks in solar roofs
Structural dimensioning is only one part of the safety of a photovoltaic installation .
Risks associated with working on roofs must also be considered.
Among them:
- Falls from different levels.
- Falls through skylights.
- Falls due to fragile areas.
- Travel during maintenance.
- Risk of stepping on non-trafficable elements.
- Inadequate access to certain equipment.
- Lack of safe traffic areas.
Therefore, the project must consider not only where to place the modules, but also how to access, inspect and maintain the installation throughout its lifespan .
Here, the planning of technical corridors, lifelines, collective protections and other safety systems becomes especially important when necessary.
7. Common mistakes when installing solar structures on roofs
1. Not studying the existing roof
Before installing a structure, it is necessary to know, as far as possible, the composition and capacity of the roof.
A solution that works for one roof may not work for another that appears similar.
2. Use a standard ballast
The ballast weight should not be determined by a general rule independent of the location and characteristics of the project.
3. Ignore the effects of wind at the edges
The perimeter areas may present more unfavorable wind conditions.
4. Adding too much weight
More ballast does not automatically mean more safety.
Excess weight can unnecessarily increase the loads transmitted to the deck.
5. Failure to check the fixing points
In mechanically fixed systems, the strength of the anchors and the elements that receive the loads is fundamental.
6. Not considering maintenance and access
A photovoltaic installation must be able to be maintained safely.
The arrangement of rows, equipment, and routes should facilitate the necessary operations throughout the useful life.
7. Not differentiating between design and execution
A correctly calculated structure can present problems if during installation:
- the ballast distribution is modified;
- fixings are changed;
- the position of the modules is altered;
- elements are removed;
- The planned configuration is modified.
The assembly must comply with the project specifications.
Success story with Masnorte Renovables
8. Installation of fixed structures on the roof: what to check before assembly
Before starting a photovoltaic installation on an industrial building, it is advisable to check, at a minimum:
Roof
- Roof type.
- Slope.
- Material.
- State of conservation.
- Durable capacity.
- Unique elements.
- Skylights.
- Joints and vulnerable areas.
Solar structure
- Material.
- Fixing system.
- Module compatibility.
- Mounting configuration.
- Spacing between supports.
- Corrosion and surface protection.
Actions
- Wind.
- Snow.
- Self-weight.
- Ballast.
- Maintenance actions where applicable.
Security
- Access.
- Passable areas.
- Fall protection.
- Technical walkways.
- Future maintenance.
9. Regulations and technical criteria in Spain
The sizing of solar roof structures must be carried out within the regulatory framework applicable to the project and taking into account the specific characteristics of the building.
Among the technical references that may be involved in the analysis are the criteria of the Technical Building Code (CTE) , especially regarding actions in the building and structural safety.
Depending on the project, the following regulations may also be relevant:
- Wind actions.
- Snow actions.
- Steel structures.
- Fastening systems.
- Protection against corrosion.
- Safety of use and maintenance.
- Fall protection systems.
The applicable regulations must be determined for each project and do not replace the specific calculation of the installation.
10. How to reduce energy costs without compromising safety
Photovoltaic installations can significantly contribute to reducing energy costs in companies with solar roofs .
However, seeking the lowest possible initial cost should not lead to reducing essential design elements.
A properly sized structure can help to:
- Avoid unnecessary oversizing.
- Optimize material consumption.
- Reduce the added weight to the deck.
- Facilitate assembly.
- Reduce risks during operation.
- Simplify certain maintenance tasks .
Therefore, optimization must seek a balance between:
safety + cost + ease of installation + maintenance + lifespan.
{%CAPTION%}
11. Structures for industrial buildings and factories
The roofs of industrial buildings and factories have very different characteristics from each other.
Installing modules in:
- a deck-type roof
- a sheet metal roof
- a sloping roof
- a flat roof
- an old roof
- a roof with numerous skylights
- a roof with air conditioning equipment
- a roof with load limitations
Therefore, the selection of the structure should be made after analyzing the actual conditions of the roof .
For large industrial projects, it is also advisable to work from the early stages with engineering, structure manufacturers and EPC teams to avoid modifications during execution.
12. Checklist to verify a solar structure before installing it
Before assembly, the technical manager should be able to answer these questions affirmatively:
☑ Is the type and composition of the cover known?
☑ Has its resistance capacity been tested?
☑ Have wind loads been considered?
☑ Has the snow load been analyzed where applicable?
☑ Has the self-weight of the system been calculated?
☑ Has the ballast been sized where necessary?
☑ Have the perimeter areas and corners been considered?
☑ Has stability against sliding and lifting been verified?
☑ Are the anchors and fixings adequate?
☑ Is the solution compatible with the cover?
☑ Have maintenance needs been anticipated?
☑ Does the installation respect the configuration defined in the project?
If any of these issues are not resolved, it is advisable to review the design before starting assembly.
Alusín Solar and solar roofs
The correct sizing of solar roof structures requires much more than selecting a system compatible with photovoltaic panels.
Wind, snow, and ballast loads must be analyzed together with self-weight, installation geometry, roof characteristics, and fixing system.
Especially in industrial buildings and commercial buildings, each roof must be studied as a particular case .
A good design aims for a structure that is safe and stable, but also efficient in materials, easy to install, and compatible with the maintenance needs of the photovoltaic installation.
Structural safety should not be an added element at the end of the project: it should be part of the design from the beginning.
Frequently asked questions about solar roof loads
What loads need to be considered when installing solar panels on a roof?
Primarily the self-weight of modules and structure, wind and snow actions where applicable and, in ballasted systems, the additional weight required to ensure stability.
How much ballast does a solar structure need?
There is no universal amount. Ballast depends on factors such as location, wind, height, deck geometry, module configuration, and system characteristics.
Is a fixed or ballasted structure better?
It depends on the roof and the project conditions. A ballasted structure may be suitable for certain flat roofs, while other installations may require mechanical fastening systems.
Does snow affect photovoltaic structures?
Yes. In locations where snow load is relevant, it must be incorporated into the structural calculation and its distribution over the installation analyzed.
Why is wind so important in a rooftop solar installation?
Because it can generate pressures and suctions capable of causing displacements or lifting of modules and structures. Areas near edges and corners can be especially relevant.
Can a solar structure be installed on any industrial building?
No. Before installation, the compatibility of the solution with the roof, its load-bearing capacity, the expected loads, and the assembly and maintenance conditions must be checked.
