15.3
one would expect from ideally matched and interconnected solar cells. This loss in
performance translates to a lower efficiency at module level. If the illumination across the
module is not constant or if the module heats up non-uniformly, the module performance
reduces even further. Often, differences between cell and module performance are
mentioned in datasheets that are provided by the module manufacturers. For example, the
datasheet of a Sanyo HIT-N240SE10 module gives a cell level efficiency of 21.6%, but a
module level efficiency of only 19%.
Bypass diodes
PV modules have so-called bypass diodes integrated. These diodes are necessary, because
in real-life conditions, PV modules can be partially shaded, as illustrated in Figure 15.4
(a). The shade can be from an object nearby, like a tree, a chimney or a neighbouring
building. It also can be caused by a leaf that has fallen onto the module. Partial shading
can have significant consequences for the output of the solar module. To understand this,
we consider the situation in which one solar cell in the module is shaded. For simplicity,
we assume that all six cells are connected in series. This means that the current generated
in the shaded cell is significantly reduced. In a series connection the current is limited by
the cell that generates the lowest current; this cell thus dictates the maximum current
flowing through the module.
one would expect from ideally matched and interconnected solar cells. This loss in
performance translates to a lower efficiency at module level. If the illumination across the
module is not constant or if the module heats up non-uniformly, the module performance
reduces even further. Often, differences between cell and module performance are
mentioned in datasheets that are provided by the module manufacturers. For example, the
datasheet of a Sanyo HIT-N240SE10 module gives a cell level efficiency of 21.6%, but a
module level efficiency of only 19%.
Bypass diodes
PV modules have so-called bypass diodes integrated. These diodes are necessary, because
in real-life conditions, PV modules can be partially shaded, as illustrated in Figure 15.4
(a). The shade can be from an object nearby, like a tree, a chimney or a neighbouring
building. It also can be caused by a leaf that has fallen onto the module. Partial shading
can have significant consequences for the output of the solar module. To understand this,
we consider the situation in which one solar cell in the module is shaded. For simplicity,
we assume that all six cells are connected in series. This means that the current generated
in the shaded cell is significantly reduced. In a series connection the current is limited by
the cell that generates the lowest current; this cell thus dictates the maximum current
flowing through the module.