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Solar thermal alignment

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The optimal alignment of a solar thermal system

Large solar thermal power plants usually have one or two-axis tracking technology. The situation is different with statically mounted systems in the area of ​​one and two-family houses. The most common installation method here is in the form of on-roof installation of the collectors. In order for a domestic solar thermal system to achieve the desired efficiency, the ideal alignment of the collectors is one of the most important factors when installing the system.

The alignment of the solar thermal system

In most cases, solar thermal systems are installed on pitched roofs. While the orientation and inclination can still be freely selected in the case of new buildings, the position of the house and the roof in the existing building determine the options for collector orientation. In order for the system to bring the greatest possible yield, an optimal alignment is desirable. Even the highest quality solar thermal system cannot achieve top performance with an unfavorable collector alignment.

With a collector surface facing south, the optimum yield can be achieved with the solar thermal system if the incline is appropriate. Structurally, however, this optimum cannot always be achieved; not every roof surface faces south. A circumstance that is no longer tragic, because even a deviation of 30 percent to the east or west only reduces the yield of the system by around 5 percent. South-west or south-east roofs are therefore also suitable for the efficient operation of a solar thermal system, whereby the yields with a western orientation can be slightly higher than those of the eastern orientation. However, roofs facing north are currently not yet suitable for practical operation.

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Roof pitch offers a lot of leeway

In addition to the orientation, the collector inclination also plays an important role for the yield of a solar thermal system. The right angle forms the optimum of solar radiation on the collector surface, but the angle of radiation changes with the time of day and the season. However, since not only direct, but also diffuse solar radiation can be used to operate a solar thermal system, and a high proportion of this radiation is available in this country, efficient operation of the solar thermal system can be expected even if the roof pitch deviates from the optimum.

Depending on which solar thermal system is used, the optimal angle of inclination also differs. For solar drinking water heating, which is mostly used in summer, the high position of the sun can be used well at this time of the year with an inclination angle of 20 to 50 degrees. For the heating support, which is used in the transitional months when the sun is even lower in the sky, an angle of inclination of 45 to 70 degrees is favorable. A facade installation (90 ° inclination) can also be useful.

In principle, a correspondingly large collector surface can partially compensate for a lower yield, but operating a solar thermal system is not suitable for roofs with an inclination angle of less than 10 degrees, as the self-cleaning effect due to rain is missing. It is advisable to mount the collectors here. Orientation and inclination can be freely selected on flat roofs. As an alternative to an elevation, vacuum tube collectors with direct flow can also be installed parallel to the roof. This enables a significantly slimmer substructure and is less noticeable.

Tip: An unfavorable roof pitch can be compensated for by elevating the solar thermal system. The optimal roof pitch depends on the chosen system. A lower roof pitch is possible for DHW heating than for heating support.

Check the roof's condition and statics

Depending on the type of collector selected, the roof has to bear a not inconsiderable additional load. It has to withstand this additional load not only under normal circumstances, but also in winter when the additional load from snow presses on the roof.

Before installation, it is therefore necessary to check whether the roof can withstand at least an additional load of 300 Newtons per square meter of roof area. In addition, the rafters also have to be connected to one another in such a stable manner that the collectors installed later can neither slide off due to the snow load nor be levered out by the wind. The minimum distance between the roof cladding and the collector is 6 cm. This type of installation is a bit more noticeable than an in-roof solution, which is out of the question for vacuum tube collectors.

The even distribution of the load by the collectors is also of great importance, as excessive, punctual loading of individual roof tiles can cause the system to slip. The integrity of the roof is also of great importance - not only for the pipe system lying directly under the roof membrane, but also for the durability of the roof itself. Leaking or damaged roof areas must always be present both before and during the operation of the solar thermal system repaired to prevent moisture penetration and damage resulting from it.

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Sun, shade and regional weather data

Solar radiation is not the same everywhere in Germany. Basically there is a north-south increase with a difference of about 20%. Regional peculiarities such as valley location or low mountain range, proximity to the coast, etc. can lead to a deviation from the regional mean. How it behaves with the solar radiation in the respective region can be found out from the German Weather Service. But it is not just the regional differences in solar radiation that determine the future yield of the planned solar thermal system.

Possible shading by trees, chimneys, neighboring houses or satellite dishes can also lead to a loss of performance. The placement of the collectors must therefore be determined before installation, taking possible shading into account. If the conditions are difficult to assess, a shading analysis can help.

Tip: If the roof does not bear the additional load of a solar thermal system, this can quickly mean the end of the planned solar project. Shading also leads to a loss of performance. The roof should therefore be checked carefully in advance.

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Tags:Alignment, solar thermal installation