SCIENCE PPT ON

SOLAR ENERGY

By: Charan S Devaraj 10th A AMRIT VIDYALAYAM

WHAT IS SOLAR ENERGY?

Solar energy Originates with the thermonuclear fusion reactions occurring in the sun.

Represents the entire electromagnetic radiation. This energy consists of radiant light and heat

energy from the sun. Out of all energy emitted by sun only a small

fraction of energy is absorbed by the earth. Just this tiny fraction of the sun’s energy is

enough to meet all our power needs.

How much solar energy is obtained

The surface receives about 47% of the total solar energy that reaches the Earth. Only this amount is usable.

• Using present solar techniques some of the solar energy reaching the earth is utilized for generating heat, electricity etc….

• Even then the energy demand met by using solar energy is very less.

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Bio-fuels

Hydro-based

SOLAR(0.8%)

Windmills

Fossils

Nuclear

WHY SOLAR ENERGY?

• The fossil fuels are non renewable sources so we can not depend on them forever.

• Though nuclear energy is a clean and green energy ,as said by Dr.A.P.J Abdul Kalam, there are always some problems associated with it.

• So the only option we have is solar energy because it is a nonpolluting and silent source of electricity and also low maintenance and long lasting energy.

How solar energy is used.

Solar Thermal Energy Solar cooker Electricity Generation Using Solar Concentrators Solar street lights or home lights Solar water pumps etc..

SOLAR THERMAL ENERGY Solar thermal technologies involve harvesting energy from

the sun for heating water or producing electrical power. Solar collectors are used for this purpose. Three Types: Flat-plate collectors Evacuated-tube collectors Integral collector-storage systems(Batch or Bread Box)

A solar cooker is a device which uses the energy of direct sunlight to heat, cook or pasteurize food or drink. Many solar cookers presently in use are relatively inexpensive, low-tech devices, although some are as powerful or as expensive as traditional stoves, and advanced, large-scale solar cookers can cook for hundreds of people.

SOLAR COOKER

Because they use no fuel and cost nothing to operate, many nonprofit organizations are promoting their use worldwide in order to help reduce fuel costs (for low-income people) and air pollution, and to slow down the deforestation and desertification caused by gathering firewood for cooking. Solar cooking is a form of outdoor cooking and is often used in situations where minimal fuel consumption is important, or the danger of accidental fires is high, and the health and environmental consequences of alternatives are severe.

SOLAR COOKER

Concentrated solar power (CSP) systems use mirrors or lenses to concentrate a large area of sunlight, or solar thermal energy, onto a small area. Electrical power is produced when the concentrated light is converted to heat, which drives a heat engine (usually a steam turbine) connected to an electrical power generator or powers a thermo chemical reaction.

Electricity Generation Using Solar Concentrators

Solar street lights are raised light sources which are powered by photovoltaic panels generally mounted on the lighting structure. The photovoltaic panels charge a rechargeable battery, which powers a fluorescent or LED lamp during the night.

Solar street lights

A solar-powered pump is a pump running on electricity generated by photovoltaic panels or the thermal energy available from collected sunlight as opposed to grid electricity or diesel run water pumps. The operation of solar powered pumps is more economical mainly due to the lower operation and maintenance costs and has less environmental impact than pumps powered by an internal combustion engine(ICE). Solar pumps are useful where grid electricity is unavailable and alternative sources (in particular wind) do not provide sufficient energy.

Solar water pumps

Photovoltaics

• Converting solar energy directly into electrical energy.

• Devices used are called solar panels.

• Solar cells work on the principle of photoelectric effect.

Then what is solar panel?

Solar panel is a group of solar cells.

Solar cell A typical solar cell is a multi-layered unit consisting of a: Cover - a clear glass or plastic layer that provides outer

protection from the elements. Transparent Adhesive - holds the glass to the rest of the solar cell.

Anti-reflective Coating - this substance is designed to prevent the light that strikes the cell from bouncing off so that the maximum energy is absorbed into the cell.

Front Contact - transmits the electric current. N-Type Semiconductor Layer - This is a thin layer of

silicon which has been mixed (process called doping) with phosphorous.

P-Type Semiconductor Layer - This is a thin layer of silicon which has been mixed or doped with boron.

Back Contact - transmits the electric current.

WORKING OF A SOLAR CELL

• Photoelectric effect

When a light of certain frequency falls on the surface of a metal

Electrons will absorb the energy If incident light energy is greater than the work

function (minimum energy required to remove the loosely bound valence electrons) of the metal

Then the photo electrons will be emitted and The excess energy is converted to the kinetic

energy of electron.

• When solar panels are placed in the sunlight , photons will strike the surface and emits electrons.

• As a result electron hole pair is created in the solar cell.

• When external circuit is connected to the solar cell , electrons flow in the circuit and the current is generated.

Advantages of solar energy

1. Solar energy is free although there is a cost in the building of ‘collectors’ and other equipment required to convert solar energy into electricity or hot water.2. Solar energy does not cause pollution. However, solar collectors and other associated equipment / machines are manufactured in factories that in turn cause some pollution.3. Solar energy can be used in remote areas where it is too expensive to extend the electricity power grid.4. Many everyday items such as calculators and other low power consuming devices can be powered by solar energy effectively.5. It is estimated that the worlds oil reserves will last for 30 to 40 years. On the other hand, solar energy is infinite (forever).

Disadvantages of solar energy

1. Solar energy can only be harnessed when it is daytime and sunny.2. Solar collectors, panels and cells are relatively expensive to manufacture although prices are falling rapidly.3. Solar power stations can be built but they do not match the power output of similar sized conventional power stations. They are also very expensive.4. In countries such as the UK, the unreliable climate means that solar energy is also unreliable as a source of energy. Cloudy skies reduce its effectiveness.5. Large areas of land are required to capture the suns energy. Collectors are usually arranged together especially when electricity is to be produced and used in the same location.6. Solar power is used to charge batteries so that solar powered devices can be used at night. However, the batteries are large and heavy and need storage space. They also need replacing from time to time.

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