Solar Cells work on the principle of Photovoltaic effect. Solar cells are made up of semiconductor material. The most commonly semiconductor material used is Silicon Crystal (other semiconductor material is selenium). Silicon Crystal arelaminated into n-type & p-type layers, stacked on top of each other. Light falling on the crystals induces Photovoltaic effect which generates electricity.
Working principle– N- type semiconductor material is having extra electron in it while p-type is having extra photon. A p-n junction is formed by placing p-type and n-type semiconductors next to one another. N-type semiconductor acts as a negative electrode & faces the sunlight & p-type acts as a positive electrode. The p-type, with one less electron, attracts the surplus electron from the n-type to stabilize itself. When sunlight (photon) hits n-type semiconductor, an electron gets excited & is attracted towards surface& this causes more negatives in the n-type semiconductor &a hole is created which carries positive charge so more positives in p-type which means flow of current with one positive terminal & one negative terminal. This is called photovoltaic effect.
IMPORTANT POINT TO REMEMBER –
- A Solar Cell produces voltage equal to – 0.6 Volt,
- Many Solar panels are wired to get 12V.
- In order to generate 12 V we need to connect 20 cells in series (0.6 V x 20 nos = 12 V).
- But practically more than 20 cells are wired to generate 14V or 16V to ensure to charge a battery properly. Secondly if the sun is low in the sky or cloudy we will still get same voltage from solar panels.
- Current from cell depends on the intensity of light, surface area of the cell & reflectivity of the device.
- Typically a small cell of 50mmx50mm might generate 0.6V at 100mA in full Sunlight.
- The efficiency of Solar cells varies with temperature. So it is not advisable to install Solar System in hot area even though there may be very good quality of Sunlight.
- To get maximum output from Solar Panels, these should be installed facing direction where sunlight falls on it for a longer period sosouth facing installation of solar panels is the best option in India.
FUNCTION OF CHARGE CONTROLLER/REGULATOR –
It serves two functions –
- It regulates the voltage from the solar cell so that even if the panel produces more voltage say 16V, the unit will pass 12V.
- it continually adjusts the power going to the battery to stop over-loading or over-charging.
DIFFERENCE BETWEEN SOLAR CELL & PHOTO CELL –
Solar cells convert light energy into electrical energy through photovoltaic effect (details are given in above section).
While photo cell is a type of resistor when light strikes the cell it allows more current to flow. It is better known as Light Dependent Resistor (LDR). Its resistance changes with light intensity, it means, on more light it offers less resistance & vice versa. It can be used as a light sensor which works in darkness. In darkness its resistance increases dramatically. Strictly speaking it is not a cell as it doesn’t generate electricity.