Solar cell

MECH 487 Photovoltaic Cell and Solar Thermal Energy Conversion Systems

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[1](10 points) In the solar cell current equation (I=IL−I0[exp(qV/ nkT)−1]) recombination processes affect :

(a) n (b) IL (c) I0 (d) All Please elaborate how?

[2] (20 points) A poly-crystalline solar cell has two p-n junctions. Explain your approach to increase collection probability of light generated charge carriers. Comment on the relative thickness of n-Si and p-si.

Hint: In addition to what we discussed in the class you can also refer to the following link for better understanding http://pveducation.org/pvcdrom/design/current-losses-due-to-recombination

http://pveducation.org/pvcdrom/design/surface-recombination

http://pveducation.org/pvcdrom/design/light-trapping

http://pveducation.org/pvcdrom/design/material-thickness

[3] (20 points) Draw energy band diagrams for the following three scenarios.

(a) A Si solar cell with two p-n junctions

(b) A Si solar cell with two p-n junctions separated by an insulator with 4 eV band gap. (p/n-Insulator-p-n configuration)

[4] Describe how the energy band diagram help separating opposite charges in the solar cell. Make a drawing and indicate all the energy levels and Fermi level etc. clearly. If you make any assumption then write that clearly. (10)

[5] Derive the open circuit voltage expression in two ways (a) by using the Poisson equation and (b) by using the diode equation in light (hint http://pveducation.org/pvcdrom/iv-curve ) (20)

[6] Current – voltage study of a solar cell: (20)

(a) Draw the typical current-voltage profile of a p-n junction solar cell in the dark and light. For The current-voltage graph in light, mark the important points like Vo, short circuit current, Vmax and Imax.

(b) What equation governs the solar cell current-voltage profile? What is the equation for defining open circuit potential?

(c) From the experimental data above calculate, fill factor, maximum power, and efficiency if run radiation intensity is 500 W/m2 and solar cell area area is 2 cm2.

(d) What will happen to current–voltage graph if one increases the resistance of solar cell (series resistance (Rs))? Show by plotting current-voltage graph.

[7] Solar thermal panel.

(a) What is the difference between flat plate solar water heater and vacuum tube based solar heater?

(b) Describe how can calculate the efficiency of a solar thermal water heater?