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Good planning is half the battle – tips & tricks for the roof-top solar plant

Erecting photovoltaic plants can be tricky – but it doesn’t have to be. Below you will find a description of the most important steps in building a roof-top solar plant as well as tips and tricks for efficient planning.

For any solar installation, the initial consultation is crucial, enabling the EPC or installation partner to lay the foundation for a successful project. Ideally, this first meeting should take place at the intended installation site, because checking the general suitability of the building structure for installing a solar plant is a basic prerequisite. Good preparation of this site visit is paramount. It will save time, prevent planning errors or miscalculations.

Tip: Don’t forget checklists, camera, compass and tape measure

Tip: Any peculiarities? Grid-connect point? Type of grid?


Good planning makes for easier installation subsequently

The next step involves planning the plant based on the relevant calculations. Not such a simple task. To ensure that the solar power plant will last more than 20 years and deliver a consistently high yield, all parameters must match and be coordinated. Once again: the more careful and detailed the planning the simpler and more straightforward the installation and operation will be later on.

To ensure the best possible yield, the solar plant should be adapted to the site and the given circumstances. The greater the amount of shade the lesser the yield. To avoid the modules being shaded, the surrounding area should be checked for any obstacles that might block out sunlight, such as trees, satellite aerials, skylights or other rooftop structures.

Tip: Are there any obstacles blocking out sunlight? If so, adapt the module location accordingly.


The plant size is a further important key figure in the calculations and can be determined on the basis of the available space, the desired energy yield and, if applicable, the amount of investment available.

The alignment and inclination of the solar modules also affect the plant’s energy yield. However, compared to the detrimental effect of shade, they play a less critical role than is often assumed.

There are two basic methods of placing photovoltaic plants onto roofs: mounting on top of the existing roofing by means of metal frames (“on-roof”) or integration of the solar generators into the installation surface, for instance by replacing conventional roofing and facade elements (“in-roof”). For both these versions and for all the different types of roof and roofing, there are numerous suitably designed and optimised mounting systems available to choose from. As a rule, the general condition and the weather resistance of the installation surface should already be examined closely during the initial site visit.

Tip: Does the roof require remedial work?

 Tip: Fragile roofing: When carrying out the planning, allow for the possibility of effecting roof repairs without having to dismantle the entire installation.


Next come the selection and sizing of the mounting system, taking into account the specific building and roof statics. The structural analysis of the roof loads is predominantly concerned with static loads, such as the weight of the solar plant itself.

Tip: Higher wind loads close to roof edges and corners: avoid these areas or increase the number of securing elements.


Spoilt for choice – criteria for product selection

Once the general conditions at the installation site have been clarified, you get to the actual core of the plant: the selection, coordination and wiring of the components.

The solar modules are the most important components and still represent the most costly items of expenditure. The inverter feeds the power produced by the modules into the grid and therefore forms the heart and brain of the solar plant, so to speak. The interaction between solar modules and inverter is comparable to that between engine and gearbox in a car. While the solar modules act as the “engine” generating the power, the inverter “gearbox” ensures that as much of this “engine power” as possible gets onto the road or, respectively, into the grid. Optimum coordination and high quality are therefore essential in this area.

When choosing the products, the decisive criteria – apart from price – are above all product manufacturing quality, performance and guarantees. But considering quality above price usually pays off in the end, considering that you are looking at a return over 20 years and more.

Good quality starts with the manufacturer and its suppliers. A certified manufacturer has committed itself to a strict quality management and guarantees that its products are subject to strict quality control and testing, from the raw material to the finished product.

There are mandatory test certificates for modules as well as inverters, such as the IEC standard for modules, which every manufacturer must obtain. Additional tests and certificates from independent and respected institutes such as TÜV Rheinland provide a good indication about the extra value provided by a component in terms of quality.

Tip on module selection Technology: crystalline modules offer substantially more output per square metre


Quality checks relating to equipment properties: torsion-resistant, cavity-free aluminium frame; micro-structured solar glass; a min. load-bearing capacity of 600 kg/m2; encapsulated connection box; soldered connections – low-cost is not always cost-effective in the long term                     

Extra options: special certification of ammonia or corrosion resistance for installation in challenging environments

The two critical characteristics affecting the performance of a solar module are efficiency and nominal output (peak output in watts). The behaviour in low light conditions or at elevated solar cell temperatures also plays an important role.

When choosing the appropriate inverter, it is first and foremost its efficiency that counts. The faster the so-called MPP tracking (MPP: Maximum Power Point), the better the adjustment to the prevailing insolation conditions – and the higher the solar plant yield. A wide MPP input voltage range further allows the installer to choose the optimum layout for the installation, reducing both wiring costs and cable losses.

Aside from the solar module and inverter, to ensure the best possible reliability and quality, care must be taken to select special-purpose TÜV or VDE-certified cables as these are the most suitable ones for this type of application.

But even given the best quality of components, a solar system owner is only completely safe if the right protection is put in place in the event of a defect or damage. Today, most manufacturers offer guarantees for their products that go far beyond the statutory warranty period. So it is important to not just consider the length of the guarantee period but also its precise contents. Be sure to read the small print i.e. the guarantee services and conditions, very closely, because they often reveal customer-unfriendly pitfalls. In many cases, the plant operator is solely responsible for the costs involved in testing, assembly, exchange and transport. Also check the replacement options. In this area, manufacturers’ promises vary greatly, from reimbursement of the residual value to replacement by a module of identical type.

Tip: Product warranty period: preferably 10 years and longer

Tip: Module performance guarantee: linear performance guarantee more customer-friendly than tiered guarantee