Solar energy:
It is otherwise known as radiant energy of sun, it is useful to us in both passive and active form.
Passive form:warms up earths atmosphere.
People in temperate regions are spending more money for room heating, because availability of radiant energy is not as much intensive as in tropics.Hence by designing their houses in a manner that suns rays are better trapped through wall made of glass (special type) and facing north.All the heated up air is circulated to rest of the rooms using exhaust fans. The Above technique conserve lots of money which otherwise spent for room heating.
Active form solar energy:
Solar energy can be collected, concentrated with the help of some devises. They are:
1. Collectors
2. Concentrators
3. Photovoltaic cell(s)

Collectors are used to collect the radiant energy of the sun and convert it into thermal energy and store the energy in energy storage system (water).
Example:
Solar water heaters
Solar cookers
Concentrators:
These are the devices, used for concentrating the radiant energy of the Sun at one point with the help of parabolic mirrors or concave lenses.They will have a sun tracking mechanism.Hence their energy out put does not get easily affected.
Photovoltaic system:
These devises are used for converting solar radiant energy to electrical energy using semiconductors.Semiconductors are materials which act both as conductor as well as insulators.Silica is normally used as semi conductor in PV-cell, since their availability is enormous in our Earth.It behaves as a semiconductor, if it is added with some impurities(other minerals rich/ poor in electrons).Such process is called doping.
Components of PVC:
N-type conductor:

1. -posses a negative charge (Rich in electrons)
2. -always kept as top layer
3. -also known as absorbing layer/absorber
   

Electron barrier:

1. Allows only the electrons of higher energy level

P type conductor:

1. -posses a positive charge
2. -number of electrons are less (called normally as holes)
3. -it is kept at the bottom of the membrane barrier(ion selective membrane)
   

Working mechanism:

When the absorber layer is exposed to the suns radiant energy, electrons absorbs photons and become excited and jump through membrane towards electron deficit p-type conductor and occupy the holes in it.after most of the holes are filled up the charge become negative and because of electron lose the n-type now quires positive charge and since both the conductors are connected through proper circuit, these fast moving electrons are channelized and go on moving from n-type to p-type and vise verse.Electricity is developed because of electron movement and voltage difference between the two conductors.The nature of electricity generated by the above process is DC.It can be stored in batteries or directly used and if needed, can be converted to A/C by using an inverter.