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The list of 5 points for planning a grid-connected photovoltaic roof system

Partner contribution from Envaris GmbH, service provider for photovoltaic systems

Third contribution from Envaris, but after the mistakes we will now be constructive and show the planning process for photovoltaic systems in this article. When planning photovoltaic (PV) systems, many factors must be taken into account in order to ensure their long service life and optimum functionality.

In addition to high-quality photovoltaic components, the suitable location and the corresponding location analysis play a decisive role in the construction of the system.

This applies to both ground-mounted and rooftop systems. Nevertheless, there are considerable differences in the respective planning. The following procedure applies to the planning of grid-connected PV systems on roofs and was created by the engineers at ENVARIS GmbH:

1. Site analysis

Even before planning a PV system, the location must be analyzed in detail. The following points are the basic requirement for any system planning:

  • the Location and coordinates of the site are important for determining the climate data and the optimal inclination of the solar modules.
  • the orientation of the roof is decisive for the yield of the solar system. For Germany and all other countries in the northern hemisphere, the southern orientation of the roof is ideal. However, roof areas with larger deviations from this alignment can still be used sensibly for photovoltaics.
  • The area to be covered must be open possible shading eg be checked by buildings, masts and trees. At the same time, the lower position of the sun in winter and the growth of trees and other plants must be taken into account.
  • All important data about the roof must be recorded. This primarily includes the type and pitch of the roof, the type and condition of the roofing and at least one dimensioned sketch.
  • All roof structures such as dormers, light shafts, hatches, ventilation and smoke extraction systems and all other objects that could cast shadows or may not be built over must be specified. All objects are recorded with their dimensions and coordinates.
  • Should be a Lightning protection system be present, this must be noted. In this case, a lightning protection expert should be consulted for further planning. The protective effect of the existing lightning protection system must not be negatively influenced by the PV system.

2. Checking the roof statics

Based on static calculation it can be determined whether the system can be implemented at all on the selected roof area. This depends on the condition, quality of the roof covering and roof substructure. In the case of an old, unrenovated roof, it will either not be possible at all or only with great difficulty. This increased difficulty may come with a higher cost. Especially with such complicated roofs, an experienced structural engineer should always be consulted for the on-site inspection.The static analysis of a roof must not be neglected when planning or installing a PV system.

  • The existing ones inventory documents to the statics are checked to see whether they still match the actual condition of the building. If load reserves are available, these must be able to be planned for the PV system. If the statics allow the additional load to be applied by the PV system, further planning can begin.

3. Pre-planning

After the parameters already mentioned have been determined, a rough planning of the system is created.

The preliminary plan includes a drawing to scale the roof surface, all roof structures and solar modules in their appropriate inclination and orientation. Depending on whether it is a flat or pitched roof. With this preliminary planning, the possible system size can be determined and a simulation of the possible yields can be created.

  • With the Software simulation the probable yields can be calculated. All location information as well as the planned modules and inverters serve as the basis for calculation. The simulation result enables an initial assessment of the profitability.

4. Profitability calculation

The profitability of the system can be calculated using the investment costs, the annual yield of the system and the current feed-in tariff. Due to the EEG anchored in Germany, which sets a feed-in tariff for 20 years, the calculation can be made for a correspondingly long period. The investment costs, which depend on the size of the system and the selected components, can be divided into external and internal financing.

Calculating the profitability is an important factor for plant owners as it is a long-term investment that can generate high returns. Correct preliminary planning is a prerequisite for the profitability of the system.

5. Detailed planning

In this planning phase, the drawings of the solar system are completed and the number of all components is determined. The complete system for the substructure of the solar modules and the associated roof attachment is determined taking into account the static calculation. Finally, the electrical installation is designed. This includes the DC string cabling between the solar modules and inverters through to the AC connection of the inverters to the feed-in point and to the grid.

After the detailed planning, the installation of the PV system follows. The Berlin service company ENVARIS is the right contact for professional planning that takes these 5 points into account.

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