ar-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 an