1. Roof orientation, pitch, shading
One of the most important parts of the on-site survey is examining the geometric and environmental characteristics of the roof. A solar panel system is not inherently "good" or "bad"; rather, it performs well or less well on a given roof, in a given environment.
Orientation, pitch, and shading collectively determine the expected energy production. These are not separate factors but interconnected parameters that influence both the annual yield and daily production profile of the system.
Effect of Cardinal Directions on Production
The instantaneous performance of solar panels depends on the angle at which sunlight strikes the panel surface. The closer the angle of incidence is to perpendicular, the greater the irradiance per unit area, and the higher the performance.
Due to Hungary's geographical location, the ideal orientation is south. On a south-facing roof surface, panels receive radiation at a favorable angle for most of the day, especially during midday hours when radiation is most intense.
In the case of east or west orientation, the daily production curve shifts. With an eastern orientation, the system produces more in the morning, while with a western orientation, it produces more in the afternoon and evening. The annual total production is typically lower than with a purely southern direction, but the difference is often moderate.
North-facing roof surfaces are generally not favorable for traditional installations. The angle of incidence is unfavorable for most of the day, and production is low and highly seasonal. In such cases, it is only worth considering with special mounting structure solutions or by involving other roof surfaces.
Optimal and Compromise Pitches
The pitch determines the angle of the panel relative to the horizontal. This affects not only summer but also winter production.
In Hungary, the optimal pitch for annual total production is typically 30–35°. In this range, the system performs balanced, and the annual yield is close to maximum.
For flat roofs, the pitch can be freely chosen, but a compromise must be made between production, wind load, and available surface area. A steeper pitch can improve winter performance, but it also increases mechanical stress and can reduce the number of panels that can be installed.
On steep roofs above 45°, summer production may decrease somewhat, while winter yield improves. This is not necessarily a problem, but the annual production curve will deviate from the optimal distribution in such cases.
In practice, most systems are designed with a compromise pitch, as the roof characteristics are given. A non-ideal pitch is rarely a disqualifying factor; rather, it is a yield-reducing factor that must be considered during planning.
Shade Types – Static and Dynamic Shading
Shading is one of the most critical issues for solar panel systems. Not just because it reduces production, but also because its effect is not linear.
Static shading refers to shadows originating from a constant source. Examples include chimneys, superstructures, or nearby walls. These can be well modeled and usually taken into account during planning.
In the case of dynamic shading, the source of the shadow changes over time. This could be a tree canopy or an adjacent building. These shadows appear differently depending on the time of day and season, making them harder to estimate.
Effect of Shading on Strings
Solar panels operate in series, meaning the current is the same throughout the entire string. If a panel (or even just a cell string) is shaded, it can limit the current of the entire string.
Therefore, the effect of shading is often not proportional to the covered area. Even a small shadow can cause a significant drop in performance. Although bypass diodes mitigate the loss, they do not completely eliminate it.
The goal of good design is to ensure that shaded and unshaded panels are not placed in the same string, or that a technical solution is developed to reduce the effect of shading.
2. Static analysis of the roof structure
The solar panel system is installed not on the roofing, but on the load-bearing roof structure. This is a fundamental difference that many overlook. Tiles, metal sheets, or bitumen roofing are just coverings – the loads are actually borne by the rafters, purlins, or slab structure.
The purpose of the static analysis is to determine whether the existing structure can safely bear the additional load of the solar panel system in the long term. A poorly chosen mounting point, an overloaded rafter, or an undersized connection can lead to structural damage, leaks, or even accidents.
Types of roof structures
The first step in a static analysis is to understand what structural system we are dealing with, as the path of the loads depends on this.
In family houses, the most common is the rafter roof structure. Here, the loads are transmitted through the rafters to the wall plate and the walls. For such roofs, key questions are:
- the cross-section of the rafters,
- their spacing,
- the condition of the timber.
The solar panel mounting must always connect to the rafter – it is not sufficient to attach it to the battens or boarding.
In older or larger span buildings, a purlin system is common, where the rafters rest on purlins. Here, the load is first transmitted to the purlin, and then through the supports to the load-bearing structure. It is important to understand that in such roofs, the load distribution is more complex, and not all elements behave in the same way.
For flat roofs, the static situation is completely different. Here, loads are typically borne by reinforced concrete slabs or steel trapezoidal sheets. The solar panel system can be fixed with penetrations or a ballasted design. In this case, not only the dead load but also concentrated point loads and the uplift force generated by the wind must be examined.
Loads: dead load, wind, snow
The impact of a solar panel system cannot be simplified solely to the weight of the panels. Three main types of loads must be considered, which can occur simultaneously.
1. Dead load
- the panels,
- the support structure,
- the rails,
- the mounting elements
total weight.
This is a constant load that represents continuous stress. Although not extreme in itself, it can have a long-term fatiguing effect on old or weaker structures.
2. Snow load
Snow load is seasonal but not negligible in Hungary. Solar panels alter the behavior of snow on the roof. In some cases, snow accumulates, while in others, it slides off and piles up.
This can cause locally greater loads than expected, especially near the eaves or next to penetrations.
3. Wind load
Wind load is one of the most frequently underestimated factors. Wind not only pushes the system down but also creates uplift. Particularly strong suction can develop at the edges and corners of the roof. Air entering under the panels can generate significant forces, so the fastenings must be dimensioned not only for compression but also for tension.
A solar panel system is not an aerodynamically neutral element.
Checking fastening points
One of the most important practical parts of the static survey is the checking of fastening points. This determines whether the system truly rests on the load-bearing structure.
During the on-site survey, it must be clarified:
- where the rafters or purlins run,
- what their material and condition are,
- what their spacing is.
The fastening element must always connect to a load-bearing element, with adequate penetration depth and appropriate screw quality. Drilling through the roofing itself is not a problem, but waterproofing and protecting the timber are critical issues.
For flat roofs, the situation is even more complex. For penetration-based fastening, the load-bearing capacity of the slab structure must be examined. For ballasted systems, it must be checked whether the roof can withstand the additional weight without permanent deformation or damage to the waterproofing.
When is a structural expert opinion required?
A structural expert opinion is justified when the load-bearing capacity of the structure is unclear based on the on-site inspection, or when the system presents unusual stress.
Typical cases:
- old or unknown condition of the roof structure,
- modified, reinforced, or extended roof,
- large-area solar panel array,
- ballasted system on a flat roof,
- industrial or large-span building.
The structural expert opinion is not an administrative formality, but a risk-reducing tool. The expert will confirm by calculation that the structure can safely bear the load, or, if necessary, make recommendations for reinforcement.
It is important to understand: a structural problem that emerges later cannot be easily rectified. A cracked rafter, a sagging roof, or a leak can have serious consequences – both technically and financially.
3. Electrical network survey
A solar panel system is not a standalone device; it works closely with the existing electrical network of the building. Therefore, during the on-site survey, it is not enough to only examine the roof and the placement of the panels – it is also necessary to accurately assess the condition of the network, what it can handle, and what limitations it imposes.
Many problematic installations are not due to faults in the solar panel or inverter, but because the existing network was not thoroughly inspected.
Phase count and connection capacity
The first step in the electrical survey is to determine whether the building has a single-phase or three-phase connection and what the available connection capacity is.
In a single-phase network, all consumers and solar power feedback occur on a single phase. This:
- limits the power of the inverter that can be installed,
- increases the risk of overloading the given phase,
- can make the system more sensitive to voltage fluctuations.
In a three-phase network, the load and feedback can be distributed among the three phases, allowing for more stable and higher power operation.
The connection capacity indicates the maximum power the network can provide or receive. This is a limitation not only from the consumption side but also from the solar power feedback side. If the planned system's performance exceeds this, a network upgrade may be necessary.
Condition of the metering point
The metering point is the primary connection between the solar panel system and the public grid. Its condition determines whether the system can be connected legally and safely.
During the survey, it must be checked whether the metering point:
- complies with current technical regulations,
- has adequate shock protection,
- is suitable for measuring bidirectional energy flow.
For older metering points, common problems include outdated design, inadequate protection, or non-standard execution. In such cases, the metering point must be modernized before the solar panel system can be installed.
It is important to understand that the metering point is not merely an administrative point, but also an electrical safety element.
Distribution board capacity
The distribution board is the center of the building's internal network. It houses the overcurrent protection devices, residual current devices, and from here, the various circuits originate.
In the case of old distribution boards, it is common for the design to no longer comply with current standards. In such cases, the solar panel system can only be installed safely in conjunction with the modernization of the distribution board.
Existence and quality of earthing
Earthing is one of the most important, yet often undervalued, elements of a solar panel system.
This is not just a matter of shock protection, but also a fundamental basis for the undisturbed operation of the system. The lack of proper earthing:
During the survey, it must be clarified:
- if an earthing system exists,
- if it is properly connected to the distribution board,
- if it is suitable for integrating the solar panel system.
The issue of earthing cannot be "added later" without affecting the safety of the system. Therefore, it must be clearly addressed during the on-site survey.
4. Typical errors during survey
The purpose of the on-site survey is not simply to "tick off" the necessary data. The real goal is to identify risks in time that could later lead to performance degradation, technical problems, or even legal and safety concerns.
Practice shows that the fate of most problematic solar panel systems is decided during the survey. Not necessarily due to spectacular errors, but due to small, neglected details.
Ignoring shade
One of the most typical and often most costly mistakes is underestimating shading.
This often happens because the survey is carried out at a specific time of day, and the light conditions experienced there are considered general. For example, if the on-site inspection takes place in full sunshine in the morning, it is easy to miss that in the afternoon, the shadow of an adjacent building already reaches the roof.
In reality, shade is a phenomenon that changes over time. The foliage of a tree, a chimney, or a nearby wall casts shadows in different places at different times of the day, at different angles throughout the seasons, and can be of different lengths.
Another common mistake is to examine shading only at the panel level, while the loss actually occurs at the string level. A single partially shaded panel can limit the current of the entire string, especially if the shading is regularly repeated.
Therefore, shading must always be interpreted in space and time; it is not enough to decide based on a single snapshot.
Underestimating the condition of the roof
Another common mistake is a superficial assessment of the roof's condition.
In many cases, the roof "looks fine," and the inspection is considered complete. However, the expected lifespan of a solar panel system is 25-30 years. If the roofing or the load-bearing structure remains operational for a shorter period, installing the system poses a long-term risk.
A later roof renovation may require partial or complete dismantling of the solar panel system. This not only means additional costs but also new risks of installation and waterproofing.
During the survey, things often remain hidden, such as:
- aged, cracked coverings,
- rotting timber,
- undocumented alterations,
- traces of previous leaks.
Underestimating the condition of the roof is not only a technical error but also an economic one. A conscious, preliminary renovation is often cheaper than a forced demolition later on.
Ignoring network limitations
The third typical error is ignoring the limitations of the existing electrical network. This usually stems from the survey focusing too heavily on the solar panel side and not sufficiently examining the connection point and the building's network.
For example, it may occur that:
- the planned inverter capacity exceeds the available connection capacity,
- the single-phase network is not suitable for the desired feed-in,
- the metering point does not comply with current technical regulations.
In such cases, the system could technically be installed, but legally or technically it cannot be connected to the grid.
Therefore, an on-site survey is not merely data collection. It is, in fact, a risk analysis, aiming to ensure that the system design is realistic, technically sound, and sustainable in the long term.
