Environmental Engineering Reference
In-Depth Information
Figure 2.24
Dimensions of Solar Energy Systems and Support Structure Rows
Optimum distance of solar energy system support
structures
Photovoltaic and solar thermal systems are often installed on the ground or on
flat roofs. Support racks are used to mount the solar energy systems. Usually
these are tilted to get higher annual irradiances, as explained in the section on
irradiance on tilted surfaces (see p60).
Furthermore, horizontally installed solar energy systems have relatively
high losses due to soiling, for example, through deposition of air pollutants,
bird excrement or other dirt deposits on the surface of the collector. Rain or
snow can clean tilted surface more easily. As a general rule, the lower the tilt
angle the lower is the cleaning effect of rain and snow. In central European
climates, average soiling losses in the range of 2-10 per cent can be expected
for surfaces tilted at 30° if these are never cleaned manually. These losses can
increase significantly for lower surface tilt angles. In other climatic regions
with long periods without rain these losses can also increase significantly.
The disadvantage of rows of support structures is that they can cause self-
shading. Optimization of the distance between the rows can decrease the
shading losses. A way to estimate the optimum distance and tilt angle is
described as follows.
The distance
d
between the rows and the length
l
of the solar energy
system as shown in Figure 2.24 define the
degree of ground utilization
:
(2.44)
Shading will affect different positions on the tilted solar energy system surface
differently. Shading has the highest occurrence at point
P
0
. If the utilization
u
increases, the shading losses will also rise.
