Electronics > Power/Renewable Energy/EV's

Solar Cell - Equivalent Circuit Question

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fourfathom:
So here is a common equivalent circuit for a solar cell:

My question: in a real solar cell is power being dissipated when there is no external load?  We will measure VOC of about 0.6V (or a bit more), and according to the model the cell-generated current IL is passing through the internal diode and through RSH.

But does this current really flow in an actual solar cell?  I'm curious about internal power dissipation and panel self-heating when the panel is open-circuit.  I'm not worried, since I know this isn't a problem in practice, I'm merely curious as to how well the model describes the actual cell's inner workings.

TimFox:
In that model, with no external load connected, when you apply light flux the photocurrent flows through the internal resistance (which is not linear) until the forward-bias on the internal diode is sufficient for substantial current through that diode.  Thereafter, the photocurrent (proportional to the light flux) flows through the forward-biased diode (at roughly 0.6 V drop), which dissipates power.
With a substantial load (low external resistance), the voltage does not reach the forward bias for substantial diode current, and almost all of the photocurrent flows into the load resistance at < 0.6 V.
(I find that analysis a good mnemonic reminder to determine the polarity of photocurrent in a given wiring diagram.)

fourfathom:

--- Quote from: TimFox on June 23, 2022, 04:31:38 pm ---In that model, with no external load connected, when you apply light flux the photocurrent flows through the internal resistance (which is not linear) until the forward-bias on the internal diode is sufficient for substantial current through that diode.  Thereafter, the photocurrent (proportional to the light flux) flows through the forward-biased diode (at roughly 0.6 V drop), which dissipates power.
With a substantial load (low external resistance), the voltage does not reach the forward bias for substantial diode current, and almost all of the photocurrent flows into the load resistance at < 0.6 V.
(I find that analysis a good mnemonic reminder to determine the polarity of photocurrent in a given wiring diagram.)

--- End quote ---

Thanks Tim, but I know how the model works.  I've simulated it, and also done many load-line tests on actual panels (I use them on my boat and have set up solar/battery rigs for remote power).  The model is quite good at mimicking the behavior of an actual solar cell.

What I am trying to find out is if this model photocurrent that flows in the open-circuit case is a real thing, causing physical heating in a real cell, or is it just an artifact of the model?  (I do not understand the physics of photocurrent generation beyond a hand-waving model level)

Siwastaja:
Yes, as far as I have understood, panels do heat up more when disconnected from any load.

floobydust:
Studies are basically saying PV cells always absorbs a fixed percentage (~85%) of the incident solar energy. Whether or not some is converted and going out (electrically) say 13% depends on the electrical load.
With no load, the cells run that much hotter and apparently can degrade a bit due to the higher temps and thermal cycling.

"A study has declared that only about 13% of the total incident solar energy is converted into electricity and little of it is reflected by the cell surface, thus >85% of the incident energy must be dissipated as heat by the cell [5]. In this condition, the solar cell operates at a relatively high temperature; the situation is even more serious if the module is left in open-circuit."
"... amorphous silicon (a-Si: H) solar cells operating under open circuit conditions can degrade more when compared to similar cells operating under maximum power conditions after 13 days of field exposure." {in the desert}

I would think Spice model is correct then, in that there is a shunt load on the photo-current.