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Affect of Shading on a Photo
Voltaic (PV) Panel
PV Shading Types defined:
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Soft sources significantly
reduce the amount of light reaching some or all of the cell(s) of a photo
voltaic module. A tree branch, roof vent, chimney or other item shades the PV
panel from a distance, the shadow is diffuse or soft.
-
Hard sources are defined
as those that stop light from reaching the cell(s), such as a bird dropping,
tarpaulin, tree branch, directly on top of the glass. If even one full cell
is hard-shaded the voltage of that module will drop to half of its unshaded
value in order to protect itself. If sufficient cells are hard shaded, the
module will not convert any solar energy and will become a drain of energy on
the entire system.
Because all cells are connected in series, the weakest
cell will bring the others down to its reduced power level. For example, if ½ of
one cell is shaded, or ½ a row of cells are shaded the power decrease will be the
same and proportional to the percentage of area shaded, in this case 50%.
If a full cell is shaded, it can
become a consumer of energy produced by the remainder of the cells, and trigger
the PV module to protect itself. The module will route the power around that
string. If even one full cell in a series string is shaded, it will likely cause the module to reduce its power level to ½ of its
full available value. If a row of cells at the bottom of a module is fully
shaded, the power output may drop to zero. The best way to
avoid a drop in output power is to avoid shading whenever possible.
The following comes from
the Kyocera website their website is a good read and informative
www.kyocerasolar.com/learn/modules.html and explains shading very well
Shading:
PV modules are very sensitive to shading. Unlike a
solar thermal panel which can tolerate some shading, many brands of PV modules
cannot even be shaded by the branch of a leafless tree.
Shading obstructions can be defined as soft or hard sources. If a tree branch,
roof vent, chimney or other item is shading from a distance, the shadow is
diffuse or dispersed. These soft sources significantly reduce the amount of
light reaching the cell(s) of a module. Hard sources are defined as those that
stop light from reaching the cell(s), such as a blanket, tree branch, bird
dropping, or the like, sitting directly on top of the glass. If even one full
cell is hard shaded the voltage of that module will drop to half of its unshaded
value in order to protect itself. If enough cells are hard shaded, the module
will not convert any energy and will, in fact, become a tiny drain of energy on
the entire system.
Partial-shading even one cell of a 36-cell module, such as the KC120, will
reduce its power output. Because all cells are connected in a series string, the
weakest cell will bring the others down to its reduced power level.
Therefore, whether ½ of one cell is shaded, or ½ a row of cells is shaded as
shown above, the power decrease will be the same and proportional to the
percentage of area shaded, in this case 50%.
When a full cell is shaded, it can act as a consumer of energy produced by the
remainder of the cells, and trigger the module to protect itself. The
module will route the power around that series string. If even one full
cell in series string is shaded, as seen on the right, it will likely cause the
module to reduce its power level to ½ of its full available value. If a row of
cells at the he bottom of a module is fully shaded the power output may drop to
zero. The best way to avoid a drop in output power is to avoid shading whenever
possible.
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We use
a tool called a
Solar Pathfinder to determine Solar Panel
shading when establishing the site and capacity of a PV array
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