In discussions about "hot patches" and OC- SC-operation modes in
PV-batteries those participants said:
Ioannis john Tsanakas noticed:
It is known that when a PV module is short-circuited, its thermal image temporarily shows a pattern, with some cells apparently more warmer than others.
Anton Driesse explained:
Cells with a higher Isc.cell must operate at a positive voltage to
reduce their current, and cells with a lower Isc,cell must operate at a
negative voltage to increase their current. The sum of all the voltage
drops is zero, so no electrical power leaves the module. However the
individual cells with positive voltage drops will generate power that is
dissipated in those that have negative voltages.
Henri Cloetens explained:
This voltage distribution causes a net flow of energy from the cells
with positive voltages, to the cells with negative voltages. And that is
what you see.
I agree with these explanations. They help to explain the temperature
anomalies in electrically identical batteris.
My previouse qustion is:
Can anybody explain why the temperature are different on two identical
solar PV-batteries for SC- and OC-mode?
My next question is:
My experimental PV-batteries have 36 elements in serial, without any
blocking diode for reverse current. So in SC-conditions the 35 elements with positive voltage produce additional power for the single weakest element with negative offset. This will lead to non-realistic strong overheating of this single weakest element. But real thermal image consist of numerous (not single) hot patches with restrained overheating.
What factors limite overheating of single cell in PV-battery?
https://www.researchgate.net/post/PV_modules_present_a_so-called_patchwork_thermal_pattern_under_short-circuit_conditions_How_is_this_explained_in_a_physics_material_point_of_view2
https://www.researchgate.net/post/Can_anybody_explain_why_the_temperature_are_different_on_two_identical_solar_PV-batteries_for_SC-and_OC-mode2
There are no factors that limit overheating of a single cell beyond good fortune, which is why under uneven illumination the panels can burn out - the cell with the lowest Ic goes into reverse avalanche mode and is destroyed.
Please make sure you use bypass diodes in enough quantities to prevent any cell going into avalanche mode!
I want to concretize my question.
The numerical analysis of PV-battery (36 cells in series) circuit on Short Circuit mode leads to the paradoxical conclusion: The temperature overheating of weakest cell is 35 times higher relative to cooling of other cells. This result is independent of numeric value of photocurrent weakness.
But real experimental data donot demonstrate so big temperature difference
The detailed argumentation for numerical analysis is in link below.
Article PV-battery Power and Heat Balance
Let us think about what is happening here.
A PV panel is illuminated with solar energy, 80% of which is converted into heat and 20% into electricity. If there is a way for the electricity to exit the panel and deliver energy to an external load, it is the external load that gets hot instead of the panel.
If the external load is a short circuit or open circuit, the electrical energy does not exit the panel but remains in it and heats it up, just as if it had not been generated at all, that is, as if all the solar energy had been turned directly into heat.
The only difference is that under short circuit conditions the electricity can circulate inside the panel and heat the cells slightly unevenly depending on their electrical characteristics. The difference in electrical heating between different cells might be 1 or 2% of the total thermal energy dissipated in the panel.
It really isn't worth worrying about!
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