Shading analysis is one of the most essential steps in phase of solar energy system
design or analysis. In photovoltaics it is important to analyse shading caused by
surrounding objects and/or vegetation. In special cases like analysis or design of
BIPV systems, exact analysis of "shadow-voltaic" systems (overhangs, vertical
shading fins, awnings etc.) is also very important. Similar analysis is also part
of passive house or solar house design - overhangs must also be planned very
carefully in such case. Basic calculations can be done by some simple equations -
formulas for some typical simple cases you may find below. Some graphical tools
like solar path calculator (pilkington) are also available. For analysis of
complex objects several computer tools are available. Some of them offer even
3D simulation. Shading is especially important in photovoltaics. It should be
eliminated as much as possible. Even small obstacles like chimneys, telephone
poles etc. shouldn't be neglected. To minimise influence of photovoltaic array
shading (if shading can not be avoided) different system optimisation techniques
can be used. Detailed explanation of such cases you may
find on this page below.
Shading devices, general
For different simple cases it is in general not difficult to calculate shadows for
particular day and time. Below you will find some formulae's end equations which
may help you to calculate shadows for most common particular cases in engineering
Horizontal shading device, overhang, side view (left)
vertical shading device, vertical fin, top view (right)
h, D - geometry of horizontal shading device (overhang dimension, see picture above)
α - sun height,
Φ - solar azimuth,
Ψ - plane azimuth
w, D - geometry of vertical shading device (vertical fin, see picture above)
Φ - solar azimuth, Ψ - plane azimuth
γ = vertical shadow angle (VSA)
w, D - geometry of vertical shading device (see picture above)
Φ - solar azimuth, Ψ - plane azimuth
Solar-Fabrik, modules used as shading devices and as part of a facade
(courtesy: Solar-Fabrik AG, Freiburg)
SHADING AND PV SYSTEM OPTIMIZATION
Shading of strings
Shading losses of photovoltaic systems can not be avoided (if shading occurs),
but at least portion of them can be minimised. Right time to consider this issue
is the system plannings phase, later it is usually too late.
Shading of strings - if crystalline modules are mounted on the roof like on the
picture below, they should be always mounted horizontaly (like on the picture)
and never vertically. Reason is quite simple: each crystalline module usually
includes two bypass diodes which are active if shading occur. When modules are
mounted horizontally the module still operates with some amount of power
(50 0% or less) if the bottom row is shaded, because only one bypass diod is active.
But if modules are mounted vertically and if lower row is shaded partially or
completel both bypass diodes are active and amount of output power is close to zero.
Strings on the roof, modules oriented horizontaly, souce SSES
Preffered orientation of modules in strings on the roof (courtesy SSES).
String configuration - modules that are shaded more often than other parts of
array should be connected into separate string(s) if possible. This will prevent
losses of the whole system because of partial shading of only one part of array.
Inverter configuration - some inverter offer several inputs, for each string its
own input - in case of shading of one string, other inputs will still operate in
Amorphous modules - in cases where shading can not be avoided use of amorphous
modules should be considered. Amorphous modules are far less sensitive on partial
shading (in comparison with crystalline modules) so that even in case of partial
shading they produce significant amount of power.
Array shape - In some cases, like example of the church roof on the picture - you
can also prevent shading losse with carefully array design. Array on the picture
has shape of trapezoid, because of shading of church's bell tower.
Church's roof covered with photovoltaic roof tiles, optimised array shape
(courtesy: Pfleiderer Dachziegel)
Solar Pathfinder - The Solar Pathfinder has been the standard in the solar
industry for solar site analysis for decades. Its panoramic reflection of the site
instantly provides a full year of accurate solar/shade data, making it the
instrument of choice.
SunEye™ - The Solmetric SunEye™ (patent pending) is a hand held electronic device
that allows users to instantly assess total potential solar energy given the
shading of a particular site. Identifying the shading pattern early in the process
reduces the expense of system and home design and improves the efficiency of the
final system or house.
Solmetric iPV - is an iPhone® based site evaluation tool, providing full solar
site analysis in an affordable hand held package.
HORIcatcher - HORIcatcher is an easy and fast tool to take outdoor pictures of the
horizon. The pictures can be used to determine the solar energy input, sunshine
duration and sun exposure reduced by obstacles like trees, houses or mountains.
HORIcatcher is supplied with a digital camera.
Pilkington Sun Angle Calculator - This handy tool provides a relatively simple
method of determining solar geometry variables for architectural design, such as
designing shading devices or locating the position of the sun relative to a
particular latitude and time.
Sonnenbahn Indikator Pro - is a simple tool for site evaluation.
Autodesk ECOTECT Analysis -
is an industry leading building analysis program that allows designers to work easily in 3D and apply
all the tools neccesary for an energy efficient and sustainable future.
Global Meteorological Database for Solar Energy and Applied Meteorology.
METEONORM is a comprehensive climatological database for solar energy applications:
a meteorological database containing comprehensive climatological data for
solar engineering applications at all points of the globe between the polar
circles; a computer program for climatological calculations;
a data source for engineering design programs in the passive, active and
photovoltaic application of solar energy with comprehensive data interfaces; a
standardization tool permitting developers and users of engineering design
programs access to a comprehensive, uniform data basis.
Shadow Analyser -
Shadow Analyzer is an advanced parametric CAD tool
for professionals in the area of Solar Energy Engineering and Architecture.
Shadows is a program used to design sundials and astrolabes and it is very
useful also in solar energy engineering. Supports plane sundials with polar
style of any orientation and reclination, analemmatic sundials, cylindrical and
bifilar sundials. Simulates, displays and animates the shadow of the style and
offers complete ephemeris of the Sun and draws the Solar Diagram.
Amethyst ShadowFX -
Amethyst ShadowFX is a sun and shadow modeling program for architects and town planners.
Amethyst ShadowFX enables you to easily generate shadow profiles cast by buildings and
other objects for any latitude, longitude and time of year.
A PC-tool to calculate shadows on arbitrarily oriented surfaces.
For both, active use of solar energy (domestic hot water, photovoitaics)
as well as for passive solar architecture, shading or lighting of
planes plays an important role Sombrero provides quantitative results for
the shading of collectors or windows by buildings, trees, overhangs or the horizon.
Web site available in:
Panorama master -
with "Panorama master" you can make exact matched set of photos - base for panorama picture.
software simulates sun path diagrams for arbitrary latitude.
Mit dem städtebaulichen Simulationsprogramm GOSOL können städtebauliche
Planungen solar+energetisch schnell und zielsicher verglichen, bewertet und
Web site available in:
Sustainble by design - Sustainable By Design provides a suite of shareware design tools on sustainable energy topics.
SOURCES AND ADDITIONAL INFORMATION
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Olgyay, V.: Design with climate, Van Nostrand Reinhold, New York 1992,
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Architectural Press, 2010, ISBN 978-0-7506-8704-1.
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Scofield, S.H., Moore, F.: Climatological sundial, Proc. 6th National passive Solar Energy Conference, Portland, OR, September 8-12, 1981, ASME, p.382.
Sharp, K.: Calculation of monthly average insolation on a
shaded surface at any tilt and azimuth;
Solar Energy, Volume 28, Issue 6, 1982, Pages 531-538.
Sharp, K.: Analytical integration of the insolation on a shaded surface of
any tilt and azimuth, Proc. 5th National Passive Solar Energy Conference, Amherst, MA,
October 19-26, 1980, ASME , p.166.
Yanda, R.F., Jones, R.E.:
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Quaschning, V., Hanitsch, R.: Der Einfluss von Abschatungen auf Photovoltaikanlagen in der Landwirtschaft; 19.Konferenz CIGR Sektion IV, Stuttgart, 25.-28.9.1995.
Quaschning, V.: Höhere Flächenausbeute durch Optimierung bei aufgeständerten Modulen; 13. Symposium Photovoltaische Solarenergie · Staffelstein · 11.-13. März 1998.