What happens to electricity generated in solar panel when no load is connected? How does it get dissipated?
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3\$\begingroup\$ Counter question that might help: What happens to the electricity generated in an alkaline battery when there is no load connected? \$\endgroup\$– JustmeCommented Jan 30, 2021 at 10:37
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\$\begingroup\$ Solar controllers usually require the batteries to be connected first, then others loads and finally panels... that should give you an idea. Or check the controller instructions. \$\endgroup\$– Solar MikeCommented Jan 30, 2021 at 10:42
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\$\begingroup\$ It doesn't just build up voltage. The solar cell is a forward biassed diode; the forward bias voltage increases until the diode current = the generated current, so the power is dissipated in the cell itself. That's why Voc is slightly higher than Vmpp. \$\endgroup\$– user16324Commented Jan 30, 2021 at 11:13
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There is no "electricity" produced when the panel is disconnected from a load. For it to be actual electricity there must be both voltage and current. With the load disconnected you have voltage (i.e. potential) but no current. Since the charge carriers liberated by the incoming light energy have nowhere to go, an equilibrium is developed in the panel.
So where does the energy go? It becomes heat energy in the panel which is ultimately radiated or conducted away. If you were to take two identical panels, one connected to a load and the other one not and place them next to each other, the disconnected panel would be hotter than the connected one. Likewise, if you checked the temperature of the loaded panel and then disconnected the load, you'd see its temperature rise until a thermal equilibrium is reached.
When loaded, some percentage of the light energy is converted into an electric field which then is able to flow through the load. Since we have an ongoing conservation of energy here, there will be a corresponding reduction of heat energy for the amount of electrical energy produced by the panel.
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\$\begingroup\$ "... the disconnected panel would be hotter than the connected one." I think that can be explained by the solar cell electrical model's internal shunt resistance which is where the "electricity" goes. \$\endgroup\$ Commented Jan 30, 2021 at 11:38
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\$\begingroup\$ Not really in my opinion. The value of Rs is going to be quite high and is not going to significantly contribute to the heating of the panel. Of course you are right in that there is shunt resistance and some current does flow, even when the load is connected but PV panels are designed to minimize Rs because this path will interfere with the panel's efficiency. \$\endgroup\$– jwh20Commented Jan 30, 2021 at 11:43
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\$\begingroup\$ Yes, where does the energy go was my doubt :) \$\endgroup\$ Commented Jan 30, 2021 at 13:37
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\$\begingroup\$ Conservation of energy could be satisfied (theoretically, at least) in other ways. The unloaded panel might become more reflective or transmissive so that the absorbed energy is lower. In that case the temperature could stay the same. Of course this is not what happens. I am just pointing out that conservation of energy alone does not dictate a temperature rise in the unloaded panel. \$\endgroup\$ Commented Jan 30, 2021 at 20:16
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\$\begingroup\$ I was not attempting to provide an exhaustive explanation here. Just a basic answer. There are entire texts on this behavior and analysis of PVs. As with so many things in engineering, the vast majority of use cases will be explained by the relatively basic ideas above. \$\endgroup\$– jwh20Commented Jan 31, 2021 at 11:42