The use of unused commercial roofs for photovoltaic systems offers companies and the real estate industry the opportunity to achieve stable and favorable electricity prices in the long term, strengthen ESG compliance and generate attractive returns. 

However, before starting photovoltaic projects on commercial roofs, it is essential to check in advance whether the roof is suitable for photovoltaic systems at all. Does the building even meet the requirements for a PV system? Are special preparations necessary before installation? So here is our ultimate checklist for every commercial PV project:

The roof

1. roof refurbishment:
Before a photovoltaic system is installed, it must be ensured that the commercial roof can withstand the next 15 to 20 years without refurbishment. Prior roof refurbishment can avoid future safety risks and unnecessary costs that could arise from dismantling and rebuilding the system.

2. insulation compatibility:
The insulation of the roof, especially for flat roofs, must have a certain compressive strength in accordance with the VDE standard. Adequate insulation compatibility ensures the structural integrity of the roof under the load of the solar installation and improves the energy efficiency of the building. Particularly relevant here are: Line and point loads.

3. roof statics:
The roof must be able to bear additional loads from the photovoltaic system, including its own weight, wind load and snow load. It is essential to have the roof statics checked by experts.

4. roof orientation and inclination:
The optimum orientation for solar modules on pitched roofs is south-facing with an inclination of 30-40 degrees. However, west or east orientations can also be efficient and are increasingly common on flat roofs - these usually have a pitch of at least 10 degrees. While flat and low-pitched roofs often allow ballasted systems, steeper roofs require the solar installation to be firmly anchored.

5. public-law approvals:
Many buildings in the city have a green roof or are listed buildings (or are under monument protection). This coordination with the city planning office or the monument protection authority is often complex and time-consuming. However, with the introduction of the 2023 EEG amendment, renewable energies (including PV systems) were placed in the overriding public interest and therefore enjoy preferential consideration.

6. materials and condition:
The selection of the right materials and the condition of the roof are crucial. Materials such as metal, bitumen, plastic or gravel offer no obstacles, but combustible materials must be taken into account for insurance reasons.

7. roof size and PV system size:
The roof area must offer sufficient space for the required output of the PV system. If the area is too small, additional electricity can be obtained from the grid. In the case of surplus production, feeding into the grid or storage is an option. A particular "stumbling block": Distances to fire walls or smoke and heat extractors (SHEVs) can drastically reduce the maximum area that can be used. However, the use of glass/glass modules can reduce the required distances somewhat.

8. shading:
To achieve maximum yields, solar modules should be free of shading from chimneys, trees or neighboring buildings, for example. Even small shadows can affect the performance of the entire system. Shadows can also shift and change in size depending on the position of the sun. It is therefore essential to carry out a shade analysis on site. In this way, the system planning can be adapted to take account of the shading and yield losses can be reduced.

The reduction

1 Downpipe in the building

1.1 Sufficient space in inspection shafts: It is important that there is sufficient space in the existing inspection shafts to accommodate the cables (power cables, data cables and equipotential bonding) for the photovoltaic system. Bottlenecks can make installation difficult or impossible. Cable thicknesses depend on the PV output and cable path length and must be calculated individually.

1.2 Distance to other media: The cables must have sufficient distance to other media such as gas and water pipes in order to avoid safety risks and ensure compliance with regulations.

1.3 Fire bulkheads: Fire protection measures must be observed during installation. Fire barriers are required to prevent the spread of fire and smoke through cable ducts.

1.4 Short AC cable runs: To minimize losses and maximize efficiency, the AC cable runs should be kept as short as possible.

1.5 Strain relief for cables: The cables must be securely fastened and protected from mechanical loads. Strain relief prevents damage and increases the service life of the installation.

2. down conduction on the façade

2.1 Clarification of any architectural protection: When installing cables on the façade, it must be checked whether the building is under architectural protection. In such cases, special approvals may be required and the cables must then usually be routed in cable ducts painted in the RAL color of the façade.

2.2 Strain relief: As with the down conductor through the building, the cables must also be securely fastened and protected from mechanical stresses for the façade down conductor.

2.3 Compatibility of the façade: The façade must be suitable for the installation of the cables. The materials and construction of the façade must be taken into account to ensure a safe and durable installation.

The connection

1. checking the string diagram: It must be checked whether the photovoltaic system is to supply several tenants (multi-tenant) or individual consumers. This influences the design and the metering concept of the system.

2. maximum current of the busbar: The maximum current of the busbar indicates the maximum amount of current that can flow via the busbar. This is crucial for determining the self-consumption/direct consumption of the photovoltaic system. Sufficient dimensioning of the busbar is necessary to avoid overloads.

3. free disconnector slots: It must be checked whether free disconnectors are available at the appropriate fuse height for the direct connection of the photovoltaic system. If such disconnectors are missing, it may be necessary to extend the busbar.

‍Conclusion

The integration of photovoltaics on commercial roofs is an excellent way to increase a company's sustainability and reduce energy costs. A careful examination of the roof requirements, the downward slope and the connection are the first steps for a successful installation.

VOLTARO as a partner for photovoltaic projects

Comprehensive preparation and the selection of an experienced partner are essential. Our team at Voltaro brings the necessary expertise and experience to clarify all these open questions when implementing photovoltaics on commercial roofs and to dispel any concerns. We offer you transparent, well-founded and independent advice to help you make efficient and sustainable use of the benefits of solar energy. As your single point of contact, we guide you through the entire process - from the initial idea to the final implementation and beyond during operation. We ensure that you can concentrate fully on your core business while we take care of the details.

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