Renewable resources are parts of our natural environment and form our eco-system
SOLAR ENERGY
The energy that we get directly from the sun is called solar energy.
The nuclear fusion reactions occurring inside the sun release enormous amount of energy in the form of heat and light.
The solar energy received by the near earth space is approximately3.4 kJ/s/m2 known as solar constant.
Methods of Harvesting Solar Energy
1. Solar cells (or) photovoltaic cells (or) PV cells
Solar cells consist of a p-type semiconductor (such as Si doped with B) and n-type semi-conductor (Si doped with P).
They are in close contact with each other.
When the solar rays fall on the top layer of p-type semi-conductor, the electrons from the valence band get promoted to the conduction band and cross the p-n junction into n-type semi-conductor.
There by potential difference between two layers is created, which causes flow of electrons (ie.,an electric current)
cell Uses
Used in calculators, electronic watches. Street lights, water pumps to run radios and TVs.
Solar Battery
When a large number of solar cells are connected in series it form a solar battery.
Solar battery produce more electricity which is enough to run water pump, to run street-light, etc., They are used in remote areas where conventional electricity supply is a problem.
2. Solar heat collectors
Solar heat collectors consists of natural materials like stones, bricks, (or) materials like glass, which can absorb heat during the day time and release it slowly at night.
Uses
Used in cold places, where houses are kept in hot condition using solar heat collectors.
3. Solar water heater
It consists of
An insulated box inside of which is painted with black paint. Provided with a glass lid to receive and store solar heat.
Inside the box it has black painted copper coil, through which cold water is allowed to flow in, which gets heated up and flows out into a storage tank.
From the storage tank water is then supplied through pipes.
