Im doing research on temperature rise in solar cell during open circuit condition or partially loaded. Im sure that when solar cell is in open circuit the energy generated will be transferred as heat and the same will cause degradation of solar cells. Can you help me out with formula or methodology to find the rise in temperature when power generated in solar cells are unused? How long it will take to cool the developed temperature?
Dear Ramesh,
welcome,
This is an interesting question. As the energy balance or conservation one can write:
The absorbed radiation rate= dH/dt + Po
where H is the heat stored in the solar panel including solar cells
H = m cp dT , m is the mass, cp is the specific heat and dT is the temperature rise.
P0= the output power= Poe + Porad , with Poe is the output electrical power and Porad is the radiated output power from the surface of the panel and cells.
At steady state, the electrical power dissipated inside the solar cell will increase its temperature such that it will be instead radiated from the surface of the cells.
It follows that dPorad= epsilonr A K T0^3 (T-T0)= The assumed electric output power dissipated in the cell= Poe. Epsilonr is the relative emissivity, To is the initial temperature and T-T0 is the rise in temperature because of the electrical dissipation. A is the radiation area and K Stefan- Boltzmann constant.
This is a simplified energy balance model. You can elaborate it. For more very accurate model please follow our paper in the link:Article M.S. Farid, A Zekry, A.A. El-Shazly, and M.A. El-Koosy, “Eva...
Best wishes
As Prof Zekry states, an unloaded solar cell is just an inert solar absorber - like a flat rock. It's no more than that. So don't worry about where the energy goes. It all turns to heat - uncorrelated motion of all its atoms and molecules. Loading it allows the internal structure of the cell to deliver some otherwise uncoordinated energy as electricity - with all the usual thermodynamic and electrodynamic limitations.
Quantitatively significant amount of heat will not be generated in unloaded solar cell. It will be act like any other mineral/material placed in sun. Whatever small amount of heat generated due to solar radiation absorption due to absorbance of cell same will be emitted back at equilibrium condition. Surface area of cell is enough to release heat and maintain temperature.
Power balance equations are:
Psun=Pheat+Pelectric; Pelectric=Psun*Effeciency; Effeciency=13..17%.
So Pheat=Psun*(1-Effeciency)=Psun*(83..87)%.
Pheat=(Tpv-Tambient)/Rheat; Tpv-Tabient=20..35C.
dTpv=Tpv(OC)-Tpv(Pmax)=Tpv(OC)*(13..17)% =3..5C.
Rheat=1/(2*Spv*a). Spv - PV surface {m2}. For typical wind conditions a=20W/C/m2
V.I.Kubov, Y.Y.Dymytrov, D.D. Ziulieiev, R.M. Kubova. Thermoelectric Feedback Model of Photovoltaic Panels Hot Spots. //2017 IEEE 37th International Conference on Electronics and Nanotechnology (ELNANO), p.228-233.
Thanks for everyone who answered my question
Thanks Vladimir Kubov , I accept with your answer. With your formula I can calculate the temperature rise in solar cell due to solar radiation.
But this temperature rise will not happen in sudden moment. It will take some time to reach that temperature. If it is true then how long it will take to reach the calculated temperature on solar cell?
After reaching the temperature if I shutdown my system or no solar radiation available then how long the solar cell will take to restore to ambient temperature ?
I need the method to find the temperature of solar cell with respect to time (solar radiation available). If 800W/m2 radiation constantly hit my solar panel with 15% efficiency then what will be the temperature on solar panel with respect to time?
You needs to calculate PV-panel total thermal capacity Cpv=c*Mpv per 1m2 of PV-surface (protective glass and Si-element). Mpv=ro*Spv*h - Mass; ro - density; c - specific heat of glass and Si-element .
Then dTpv/dt=Pheat/Cpv - this is for temperature rising from Tabient to Tpv. And dTpv/dt=Pelectric/Cpv or temperature rising from Tpv(Pmax) to Tpv(OC).
So incrising time constant is tau=(Tpv(OC)-Tpv(Pmax))/(dTpv/dt).
I guess this time is about few minutes, more less then 5 minutes.
For more certain calculations You needs thermal model.
This task is similar to charging electrical capacitor with parallel resistor by current source.
The equations given by me are the same expressed by the the heat transfer equivalent circuit of the module given by Vladimir in his second comment. Also i gave an expression for heat transferred from the surface pf the panel mostly by radiation.
You can calculate the steady sate temperature of the module and you can also calculate the variation of the panel temperature with time.
The interesting thing here is that you can use the SPICE circuit simulator to solve for delta T of the module.
Best wishes
If the solar panel kept unloaded,then temperature rise will be more than loaded solar panel. Because electrical power and heat power together will cause temperature rise. This can lead to degradation of panel in lifetime. whether dummy load can solve this problem in unloaded condition?
The temperature rise of unloaded panel is negligible. The temperature rise of several shaded cells on loaded panel is more essential. The bypass diodes are used to prevent overhiating of shaded cells.
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