Test: Solar Cell - Electronics and Communication Engineering (ECE) MCQ

• The use of bypass diodes allows a series (called a string) of connected cells or panels to continue supplying power at a reduced voltage rather than no power at all.
• Bypass diodes are connected in reverse bias between solar cells (or panel) positive and negative output terminals and have no effect on its output. 
• The bypass diodes’ function is to eliminate the hot-spot phenomena which can damage the PV cells and even cause a fire if the light hitting the surface of the PV cells in a module is not uniform. 
• Thus it enables the PV modules to operate with high reliability throughout their lifetime.

The correct answer is Silicon.

Solar Energy:

• Under identical conditions, as compared to a white or a reflecting surface, a black surface absorbs more heat.
• Solar water heaters and solar cookers use this property to work and hence these devices are useful only at certain times during the day.
• Above limitation is overcome by the use of solar cells that convert solar energy into electricity.
• Silicon is used for making solar cells, it is abundant in nature but the availability of the special grade silicon is limited.

Solar cell:

The Sun is the major source of energy on Earth and has been producing energy for billions of years. Heat and light from the Sun, solar energy, is one of the cleanest and most abundant sources of renewable energy.

Solar Cell:

• Solar energy is an ideal renewable energy resource due to its abundance and inexhaustibility.
• Solar cells convert sunlight into electricity and are the most direct devices to use solar energy.
• Silicon is the most widely used material for solar cells due to its abundance in the earth’s crust. It is also a semiconductor with good stability, non-toxicity and well-established refining and processing technologies.
• silicon is obtained by melting silica in the furnace.
• Solar cells can be used for various purposes – lighting, rooftop panels, pumping etc.
• Crystalline silicon is widely used in fabricating solar cells.
• Silicon is treated with phosphorus and boron and then made shiny using usually titanium oxide (for anti-reflective properties) and then used as disks in solar cells.

Concept:

Calculation:

Solar Array:

• Combining several solar cells in a series of parallel creates an array.
• The size of your solar array depends on the position of the roof and the energy requirement.
• A solar array can be used for solar heating, electrical power generation, lighting of spaces, etc
• For maximum current rating, the solar array is grouped in parallel.
• For maximum voltage rating, the solar array is grouped into series.

Solar Cell:

A PN Junction diode with wider depletion width used for the conversion of photo to electrical signal. 
The current and voltage relation for a solar cell is given by,

For sun intensity of unit 'x'/

Putting the values in the equation, we get


subtracting equn (2) from (1)

V_oc = (Open circuit voltage) of a solar cell

Where η = 2 for Si p-n diode.
J_L = Photo current density
J_s = Saturation (Reverse) current density.

Calculation:
Given V_oc = 0.451 V
For J_L = 2.5 mA /cm², n = 2 and V_T2 = 25 mV.

Solving, we get J_s = 3.024 × 10^-7
If the intensity of the incident light is increased by 20 times, JL (Photocurrent density) also increases by 20 times

Putting values, we get

Concept:

The fill factor of a solar cell is defined as:

Efficiency is the ratio of the output power to the input power, i.e.,

Also, the optical generation rate (G_L) will be:

Calculation:
Given η = 0.25, FF = 0.8, V_oc = 0.7 and thickness = 200 μm.

The optical generation rate (using equation (2)) will be:

Concept:
The open-circuit voltage for a solar cell is given as:

V_T = Thermal voltage
I_sc = Short circuit current
I₀ = Reverse saturation current

Calculation:
Given I_sc = 20 mA, V_oc = 0.65 volt V_T = 26 mV
Here η = 1, i.e.