Solar Basics

What Is The Optimal Size For Your Solar Panel System?

What Is The Optimal Size For Your Solar Panel System? 1
3d illustration of house with solar panel, and blueprints roll

What Is The Optimal Size For Your Solar Panel System?


Photovoltaics is not only the best renewable Energy Source (read this article), but the best solar energy technology too (read this article).

This article explains you how to size your solar panel system in order to optimally use your roof and to cover your electricity needs.

An essential point in the planning of the solar panel system concerns its size or rather its output. The aim is in the end to optimize the self-consumption: so much solar power should be produced so that with a solar battery extension, a higher degree of self-sufficiency can be attained.

Roof area

The available roof area determines how many solar panels can be mounted, and which power can be installed.

Thus, the first step is examination und measuring of the roof surface and the analysis as to whether the roof is suitable for a solar PV system. This concerns roof orientation, roof pitch, and especially the possible shadowing.

The size, the shape of the roof and the position of the chimney, antennas and any satellite dishes must also be taken into consideration because they determine the available mounting surface.

Calculation of the roof surface


What Is The Optimal Size For Your Solar Panel System? 3

If you are lucky, there are construction plans with the exact dimensions of the roof.

Construction plans are not always exact, especially in old buildings, where things could have changed, for example, roof renovations, new windows, etc.

If there are no longer any construction plans or these are no longer valid, one can determine the size by counting the roof tiles.

In the case of flat roofs, there is another option: Google Earth, here you can calculate the surface with the help of a ruler.

Attainable power

If the roof surface has been established, then, for the pitched roofs can easily be calculated, how many solar modules of a certain size and power fit on the roof. Solar panels can be mounted vertically or horizontally. Thus, the number of installed modules can vary considerably.

Tip: Larger solar modules need fewer installation points and are cheaper to mount, but they have fewer possibilities of variation by the arrangement.

When planning it is also important that certain distances between the solar modules and from the edge of the roof must be kept.

We can approximately say that depending on the module type for one-kilowatt peak between eight (monocrystalline solar panels) to sixteen square meters (thin film modules) roof surface (pitched roof) are required.

On a flat roof, as a result of row spacings, a much higher space requirement must be expected (at least twice).

Thus, you can calculate the maximal installable power on a pitched roof with the following information:

  • the size of the available mounting surface
  • the number of solar modules, and
  • the power of the modules

For a flat roof, because of mutual shading of the modules rows, a reduction of at least 50 %  must be expected.

Choosing suitable solar panels

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Choosing suitable solar panels depends on how much power should be installed on the available roof surface. Here, in some circumstances, the roof area can be optimally exploited with smaller solar modules.

Monocrystalline und polycrystalline solar panels have the highest efficiency. If the available roof surface is small, then this solar cell technology is recommended. The monocrystalline solar panels need ca. 8 m2 per kWp and the polycrystalline ca. 10 m2/kWp.

Generally, you obtain a proposal from a solar specialist company in connection with the quotation, for the roof layout with the offered solar modules and their resultant total power.


Checklist: The Most Important Preconditions For the Installation Of a Solar PV System

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