Photovoltaic cells – The most useful way of harnessing solar energy is by directly converting it into electricity by means of solar photo-voltaic cells.When sun shine is incident on solar cells,they generate DC electricity without the involvement of any mechanical generators , i.e, in this system of energy conversion there is direct conversion of solar radiation into electricity .The photo-voltaic effect is defined as the generation of an electromotive force as a result of absorption of inoizing radiation.Energy conversion devices which are used to convert sun light to electricity by the use of photovoltaic effect are called solar cells.
To obtain the energy,large number of solar cells are connected in series parallel combination.These solar cells whwn exposed to solar radiation give direct current (DC) which can be converted into alternatin current (AC) ,using inverters .The silicon solar cells consist of n-type and p-type silicon semiconductors.The p-type silicon conducts positive charges n-type conducts negative charges.
Electromagnetic radiation – Electromagnetic radiation is a self propagting wave.It consist of the energy in terms of photons.Photons can have different frequencies.The energy associated with a particular radiation depends upon its wave length.
Types of radiation –
(A) Alpha particles has a positive electric charge.They have a large specific ionization values.These particles can cause health hazard through inhalation because they can not penetrate outer layers of skin.
(B) Betaparticles are light in weight ,and are penetrative.These cause internal or external health hazard due to ionization radiation.
(C) X-rays and Gamma rays are very penetrating compared to alpha and beta particles.They constitute the chief health hazard
Hydro Electric energy – It is a renewable energy source,which is used to generate electricity.Hydro power is obtained from water flow or falling water from height.Water stored behind dam and at a height have a lot of potential energy which is converted into mechanical and electrical energy.The water is released gradually and is allowed to fall under the gravitational force and drive hydraulic turbines which rotate,and the generators produces the electricity.
Limitations – The generation of electricity by hydro electric power plants result in pollution and ecological disturbance like flooding ,situation and adverse effects on flora and fauna.Smaller dams and reservoirs cause less damage.
Advantage – Hydro power does not pollute the water or the air ,during operation ,no waste product is formed.