PHOTOVOLTSAIC CELL OR SOLAR CELL
Photovoltaic cell works on the principle of photovoltaic effect. The photovoltaic cell generates voltage proportional to the intensity of incident light.
Construction
· A photovoltaic cell is created when a positively charged (P-type) layer of silicon is placed against a negatively charged (N-type) layer of silicon to create a diode and this diode is connected in a circuit via metal conductors on the top and bottom of the silicon sandwich.
· An actual PV cell includes these elements with an anti-reflective coating to accept more sunlight into the silicon sandwich.
· The photovoltaic cell, a sandwich of two semiconductor materials. The cell reacts to solar energy and produces an electrical charge.
· Metal conductor strips that run along the top layer of silicon. These strips capture the electrons freed when solar energy hits the cell and concentrate them into a current. Another metal panel, attached to the bottom layer of silicon, feeds electrons back into the cell
· An anti-reflective coating placed on top of or directly adhered to the silicon sandwich. This sheet reduces the amount of sunlight reflected off the glass allowing more sunlight to hit the cell and increasing the panel's efficiency.
· The cell or multiple cells are the core of the photovoltaic panel
· A glass cover placed over the photovoltaic cell to protect it from the elements while allowing sunlight to pass through to the cell
· An additional plastic anti-reflective sheet is often used to enhance the effect of the glass cover and anti-reflective coating of the cell to block reflection.
A panel backing (typically plastic) and frame complete the photovoltaic panel, holding all the pieces together and protecting it from damage during installation.
Operation of Solar cell
· A solar cell is a p-n junction device with no voltage directly applied across the junction.
· It converts solar energy into electrical energy.
· When light hits the depletion region, electrons and holes are generated due to photons striking the valence electrons and imparting energy to them.
· The optically generated electron-hole pairs are quickly separated and swept outside the depletion region by the electric field.
· These electrons and holes flow to constitute the photocurrent across the load. Thus, it supplies power.
· A solar cell is a p-n junction device with no voltage directly applied across the junction.
· It converts solar energy into electrical energy.
· When light hits the depletion region, electrons and holes are generated due to photons striking the valence electrons and imparting energy to them.
· The optically generated electron-hole pairs are quickly separated and swept outside the depletion region by the electric field.
· These electrons and holes flow to constitute the photocurrent across the load. Thus, it supplies power.
Symbol
Output Characteristics
Equivalent circuit
Advantages
· Solar cells respond to a wide range of incident wavelength
· They require no external source
· They can produce large photocurrent
· They are robust and do not get damaged easily
Disadvantages
· Solar cells have a slow operation
· They are temperature sensitive
· The output voltage and current is very low
· Solar cells are expensive
· Conversion efficiency is low
Applications
· Electronic circuits and satellites
· Calculators and watches
· Solar cars and Space Technology
· Batteries
· Street lighting and rooftops of houses
· Solar cells respond to a wide range of incident wavelength
· They require no external source
· They can produce large photocurrent
· They are robust and do not get damaged easily
Disadvantages
· Solar cells have a slow operation
· They are temperature sensitive
· The output voltage and current is very low
· Solar cells are expensive
· Conversion efficiency is low
Applications
· Electronic circuits and satellites
· Calculators and watches
· Solar cars and Space Technology
· Batteries
· Street lighting and rooftops of houses
Heterojunction Solar cells
· Heterojunction is a junction formed between two different semiconductors with different band gap (Eg).
· They have better characteristics than homojunction solar cells.
· They have a wider band gap.
Amorphous Si Solar Cells
· Amorphous silicon material is used for solar cells for the applications that require larger areas and less cost.
· Their current gain is very high.
· When Si is deposited by CVD technique on any substrate below 6000C temperature, an amorphous Si layer gets formed.
· Amorphous Si solar cell is PIN device with thin p+ and n+ regions.
· Conversion efficiency is quite low and the cost is also very less.
· Heterojunction is a junction formed between two different semiconductors with different band gap (Eg).
· They have better characteristics than homojunction solar cells.
· They have a wider band gap.
Amorphous Si Solar Cells
· Amorphous silicon material is used for solar cells for the applications that require larger areas and less cost.
· Their current gain is very high.
· When Si is deposited by CVD technique on any substrate below 6000C temperature, an amorphous Si layer gets formed.
· Amorphous Si solar cell is PIN device with thin p+ and n+ regions.
· Conversion efficiency is quite low and the cost is also very less.