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Materials For Solar Energy Applications Question Paper
Materials For Solar Energy Applications
Course:Bachelor Of Education Science
Institution: Kenyatta University question papers
Exam Year:2009
KENYATTA UNIVERSITY
UNIVERSITY EXAMINATIONS 2009/2010
FIRST SEMESTER EXAMINATION FOR THE DEGREE OF
BACHELOR SCIENCE AND BACHELOR OF EDUCATION
SPH 470: MATERIALS FOR SOLAR ENERGY APPLICATIONS
DATE: Wednesday 30th December 2009
TIME:
2.00pm – 4.00pm
INSTRUCTIONS
Answer question ONE and an other TWO
Q1.
a)
Define the term semiconductors? [2marks]
b)
Name two materials commonly used as semiconductor. Materials in the fabrication of integrated circuits. [2marks]
c)
Name the three types of solids and state how they differ from one another. [6marks]
d)
Distinguish between the valence band and the conduction bund. [4marks]
e)
What are the Intrinsic and extrinsic semiconductors? [3marks]
f)
Define the following terms:
i)
Solar cell/photovoltaic cell
ii)
Photovoltaic effect [3marks]
g)
What is meant by quantum efficiency (QE) of a solar cell? [3marks]
h)
Consider a single solar cell whose terminal voltage is 0.6 volts. Show how you can connect 20 of this cells to provide a total of 12 volts. [4marks]
i)
Solar cells behave like diodes. Explain this statement. [3marks]
2.
a)
What is the advantage of a single crystal over other materials as a semiconductor? [3marks]
b)
What mostly affects the properties of semiconductor? [3marks]
c)
What does Pauli’s exclusion principle state? [2marks]
d)
Clearly differentiate between the metals, semiconductors and insulators in terms of their electrical behaviour. [6marks]
e)
Define clearly and in detail the following terms;
i)
P-type and n-type Semiconductors
ii)
A p-n junction [6marks]
3.
a)
Provide diagrams showing:
i)
Unbiased p-n junction
ii)
A forward based p-n junction
iii)
A reverse based p-n junction [6marks]
b)
A p-n junction is forwarded biased through an external voltage V. Using the symbols derive the rectifier equation for the diode. [6marks]
c)
Usually, a single solar cell does not provide sufficient current and voltage for any practical use. As such, cells without module are integrated with bypasses and blocking diodes. Draw a diagram showing such kind of an arrangement. What is the purpose of the diode in this case? [6marks]
d)
When light is absorbed by matter, electrons are usually exited higher energy states within the material but the excited electrons quickly relax back toothier ground state. What prevent this relaxation is a photovoltaic device? [2marks]
4.
a)
Give a three major differences between a photovoltaic cell and a battery. [6marks]
b)
A photovoltaic cell is illuminated with light of sufficient energy such that a photocurrent is generated. Write the equation of the resulting short circuit current density in terms of the quantum efficiency (QE), the incident photon flux density bs (E) and the electronic charge q. [3marks]
c)
Name three factors that affects the quantum efficiency of a photovoltaic cell. [3marks
d)
Define the term dark current and provide an equation for the corresponding dark current density Jdark. Give the meaning of the symbols used. [4marks]
e)
Provide a sketch showing the variation of bias voltage and the current density J. [4marks]
5.
a)
A solar collector is designed such that it has a duct through which air can be pumped from one end to exit on the other end. Provide a simple diagram that depicts this system. [4marks]
b)
State two assumptions made when designing such a solar collector in (a) above. [4marks]
c)
Name three energy fluxes with respect to the absorber. [3marks]
d)
The rate of absorption of energy is commonly given as a fraction of the insulation. If the irradiance of the absorber is G, the surface area A, and the transmission-absorption factor of the absorber ista , write the equation governing this rate absorption energy. [3marks]
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