1. Principles of Panel Mounting
Installing solar panels is one of the most visible parts of the installation, yet it's where most mechanical errors can occur. A panel is not just "glass on the roof"; it's a multi-layered structure sensitive to stress. Incorrect mounting doesn't necessarily cause immediate breakage; it more commonly leads to a gradual decrease in performance over several years.
The goal of panel mounting is not to "hold it tightly," but to dissipate loads through the frame to the rail system in a manner specified by the manufacturer.
Mechanical Behavior of the Panel
A solar panel consists of an aluminum frame, tempered glass, and the cell structure located behind it. The central part of the panel tends to bend under load, while the frame resists this bending at the mounting points. This means that the load is not evenly distributed. Critical stress points always develop around the clamping areas.
If the panel:
- is not placed on a flat surface,
- the rails are not aligned,
- or the mounting point is not in the correct position,
then internal stress will build up in the frame and the glass. This often results in micro-cracks in the cells, which are not visible to the naked eye but cause long-term power loss.
Important principle:
the panel should never be "forced" onto the support structure.
The structure must be precise; the panel should not have to adapt to an error.
Manufacturer's Mounting Zones
Each solar panel comes with manufacturer-specified mounting instructions. These define which section of the frame the panel can be clamped.
These zones are typically:
- located on the longitudinal sides,
- at a specified distance from the corners,
- and determined based on the panel's structural calculations.
Portrait and Landscape Orientation
Panels can be installed in portrait or landscape orientation. From an electrical perspective, this is often irrelevant, but not from a mechanical one.
In portrait orientation
- the longer side is vertical,
- the mounting points are closer to each other,
- generally more favorable in terms of frame bending.
In landscape orientation
- the longer side is horizontal,
- the mounting points can be further apart,
- panel deflection can be greater if rail spacing is incorrect.
There is no universally better solution. The choice is always determined by the roof geometry, wind loads, and panel size.
Row and Column Spacing
The distance between panels is not an aesthetic matter. The spacing must ensure:
- the possibility of thermal expansion,
- drainage of water and contaminants,
- ease of installation and maintenance.
If spacing is too tight, panels can press against each other during thermal expansion. If the gap is too large, the surface exposed to wind increases. For larger arrays, it's particularly important that replacing one panel doesn't require dismantling the entire row. This is decided during the design phase.
2. Mid and End Clamps
Mid and end clamps provide the direct connection between the panel and the rail. Although small in size, their role is critical: they mechanically secure the solar panel, determine the clamping force, and in many cases participate in the electrical connection. If the clamp is not properly selected or installed, it can lead not only to mechanical instability but also to earthing or corrosion problems.
The Role of Clamps in the System
The task of clamps seems simple: they secure the panel frame to the rail. In reality, however, there's more to it. The clamping force must be large enough to prevent the panel from moving due to wind or snow, but not so great as to deform the frame or cause stress in the glass.
End clamps are located at the edges of the panel array, providing single-sided support.
Mid clamps, on the other hand, secure two adjacent panels simultaneously. Here, the force distribution is particularly important, as both panels must receive the same amount of clamping.
Role of Electrical Earthing
In many systems, clamps serve not only a mechanical but also an electrical function. Panel frames are made of anodized aluminum. The anodized layer acts as an electrical insulator. This means that simply having two aluminum components touch each other does not guarantee a good electrical connection.
Therefore, some clamps:
- have serrated washers,
- ribbed contact surfaces,
- or special contact designs
- to break through the anodized layer and create a secure metallic connection.
If the clamp is not suitable for this, or not properly tightened, then equipotential bonding between the panels is not ensured. This can pose earthing and lightning protection risks.
Risk of Galvanic Corrosion
In the vicinity of clamps, different metals often meet: aluminum panel frame, aluminum rail, stainless steel or galvanized steel screw. If these come into contact in the presence of moisture, galvanic corrosion can begin. In such cases, one of the metals with different electrochemical potentials corrodes faster.
The risk can be reduced by appropriate material selection. This is why anodized aluminum profiles, stainless steel fasteners, and mutually compatible system components are used. Combining different metals "haphazardly" might work in the short term but can cause serious problems over years.
3. Thermal Expansion and Wind Load
Solar energy systems are not static structures. They operate outdoors for decades, continuously exposed to temperature changes, wind, and precipitation. There are two physical phenomena that cannot be resolved by "clever installation" – only by correct design: thermal expansion and wind load.
Ignoring these rarely causes immediate failure. The problem typically develops slowly, over years.
Thermal Expansion of Aluminum
The frames of panels and most of the support structure are made of aluminum. Aluminum expands and contracts relatively significantly with temperature changes.
In the case of a solar energy system, the temperature range can be extreme:
- down to –15 °C in winter,
- 70–80 °C on sun-exposed surfaces in summer.
This is a difference of several tens of degrees, which can cause longitudinal changes of millimeter magnitude for long rails and large panel arrays. If the system cannot "dissipate" this movement, the stress does not disappear but is transferred.
Role of Fixed and Sliding Points
Managing thermal expansion does not mean leaving the fixings loose. On the contrary: it must be consciously decided where the system should be fixed and where it should be allowed to move.
Fixed points:
- determine the geometric position of the system,
- provide a rigid connection to the support structure.
Sliding points:
- allow longitudinal movement,
- while still transferring the load.
If all points are rigidly fixed, then the movement resulting from thermal expansion manifests within the panel. In such cases, the frame and the glass begin to stress, which can lead to micro-cracks and performance degradation.
Wind Uplift Forces
Wind does not simply act on the system as lateral pressure. The air flowing above and below the panels creates an uplift force that tries to lift the panels upwards.
This effect is particularly critical because:
- the suction effect of wind can often be greater than the system's own weight,
- mounting points receive tensile loads,
- screws and hooks are subjected to extreme stress.
Tensile load is much more dangerous than pure pressure or shear, as it literally tries to "tear" the structure off the roof.
Edge Zones and End Panels
Wind load is not uniform across the entire panel array. Eddies form at the edges and corners of the roof and at the perimeter of the panel array, significantly increasing the suction effect. Therefore, end panels always experience greater stress than those in the interior of the array.
Common solutions in such cases include:
- denser mounting spacing in the edge zone,
- greater clamping force,
- or using a stronger rail profile at the edges.
If the mounting of the end panels is undersized, the system will not fail overnight. First, micro-movements appear, then the load is transferred to the inner panels as well. This can lead to gradual, chain-reaction-like failure.
