18 Glossary
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18
Glossary
18.1
Azimuth (ß) and elevation (α)
For the optimal use of solar radiation the modules and collectors are arranged in a way that allows a preferably
large solar yield. In this context the incidence angle of the sun, but also the azimuth and the elevation of the
modules and collectors play a certain part. The azimuth angle specifys the angle between the orientation of the
modules or the collectors and the exact adjustment to the south. The elevation means the angle of the modules
from the horizontal. Studies have approved that PV plants with an azimuth of 0° and an elevation of about 30°
are aligned in the best possible way. Nevertheless small deviations are not implicitly problematic: with the
orientation to south-east or south-west still around 95% of the possible yield can be realised. Larger plants are,
to enhance the profit, tracked towards the sun by electric motors. (see also → tracking).
For measurements with the PVPM the accurate alignment of the irradiation sensor with the modules is very
important. The sensor has to 'see the same part of the sky' as the modules. At the same time it is to be taken in
account that by reflections from the environment (by house walls or other light surfaces) the incidence of light on
the modules and the sensor can be intensely influenced.
18.2
Slope
When planning a solar plant the question for the slope of the roof (e.g. on the internet) leads to wrong
conclusions, as it is not the slope of the roof - but the slope of the collectors that is important. Through an
appropriate elevation and mounting the collectors can be brought into a good position even if the slope or the
adjustment of the roof are disadvantageous.
For the optimum use of solar radiation the sun rays should fall on the collectors in a right angle. The optimum
elevation and angle of setting-up correspond to the geographical latitude of a location. (Freiburg is located on
the 48. degree of latitude; Lübeck on the 54. degree of latitude) Since the sun stands higher in the summer than
in the winter it depends on in which time of the year the solar equipment is predominantly being used.
Photovoltaic plants for example carry the highest yield on long summer days, while thermal solar plants are
taken to support heating installations in the winter. As a rule of thumb for the elevation of the collector you can
use latitude minus 10° in the summer and latitude plus10° in the winter is considered to be effective.
Not to be confused with the slope is the orientation (azimuth angle) to the south. In practice smaller deviations
from the optimum slope or orientation decrease the productivity insignificantly. A temporary shading of the
collectors impairs the effectiveness far more.
18.3
DC
Short form for direct current, as it is being produced by solar cells and modules and stored by a battery. If many
solar cells are connected in series to a module, the single voltages add.
18.4
Degradation characteristic
The degree of efficiency of amorphous solar cells declines at the beginning of the phase of irradiation rapidly
and first stabilises after a time between 3 weeks and 5 month. Besides this irreversible degradation, another
reversible degradation is taking place. That means that amorphous solar cells have a better degree of efficiency
in spring-/summer-time compared to autumn/winter.
18.5
Direct radiation/ diffuse radiation
Direct radiation (forces casting shadows) meets a surface without scattering through components of the earth'
atmosphere. Through scattering (fog, haze, clouds) diffuse/ indirect radiation develops.
18.6
Generator
Lat.: producer. Generators dissipate other forms of energy into current. In the photovoltaic the entirety of the
interconnected photovoltaic modules is characterised as generator or as solar power plant.
Operation manual for PVPM devices
PV-Engineering GmbH
