Solar Energy and Solar Devices

Solar Energy

The energy emitted by the sun in the form of heat and light is known as solar energy. The hot air rises up and the cold air from the surrounding rushes to occupy its space. This is how the air moves. Moving air possesses kinetic energy which is also termed as the wind.

Sunlight makes photosynthesis possible through which plants prepare their food. The solar energy evaporates the water oceans, lakes and ponds. The evaporated water forms cloud. These clouds on cooling give rain. The rainwater is collected in the reservoir having potential energy. Finally, potential energy is converted into kinetic energy by letting water flow in higher speed. Kinetic energy rotates the turbine which is connected with the huge magnet. Current is induced by the magnet.

Even the energy of fossil fuels like coal, petroleum and natural gas also comes from solar energy. Due to high pressure, the biomass of dead animals and plants are converted into the fossil fuels like coal petroleum and natural gases.

The sun contains mainly light elements like hydrogen and helium. When the atoms of these elements fuse together at an extremely high temperature in the interior of the sun, a large amount of energy is radiated in the form of heat.

Solar Constant

The solar constant is defined as the energy received from the sun in one second by the unit square meter area of the outer edge of earth’s atmosphere exposed perpendicularly to the radiation of the sun at average distance between the earth and the sun. The upper part of the earth receives solar energy equal to 1.4-kilo joule per second per square meter (1.4 kJ/s m²). The amount is known as solar constant.

Thus, solar constant = 1.4 kJ/s m² or 1.4 kW/m²

Application of Solar Energy

1. It is used by green plants during photosynthesis.
2. The solar energy powers the flow of wind.
3. The solar energy causes rainfall by evaporating water on the earth’s surface.
4. It is used to produce electricity from the solar cells.
5. It is used for drying clothes and food grains.
6. It is used for transportation.
7. The solar energy sustains all lives on the earth.
8. It is used for heating water using the solar heater and various other purposes.

Solar Devices

The devices which convert solar energy into other forms of energy are called solar devices. Examples: solar cooker, solar furnace, solar water heater etc.

Solar Cookers

Construction:

It consists of a wooden box in which a metallic box painted black is fitted. The space between the wooden box and the metallic box is filled with an insulating material which minimizes the heat loss by conduction and radiance. The metallic box is covered by a thick glass sheet. A plane mirror is used to reflect the sun rays into the box shown in the figure. The uncooked food placed in the black container is put inside the box.

Working:

The plane mirror reflector is adjusted in such a way that maximum sunlight falls on it. The light reflected by the plane mirror falls on the thick glass sheet cover. The heat radiation coming from the sun and have a short wavelength and high energy pass through the glass sheet and is absorbed by the black container or any other object placed in the box and black surface of the box. The temperature inside the box is between 100 ^oC to 140 ^o C.

Advantages

1. The cost of cooking food in the solar cooker is very small as money is only spent upon solar cooker.
2. It can cook two or three dishes at a time.
3. It saves the costly fuel like wood, gas, kerosene oil etc.
4. Nutrition value of the food is preserved as there is no burning of fuel.
5. It can cook multiple dishes at a time.

Reference

Manu Kumar Khatry, Manoj Kumar Thapa, Bhesha Raj Adhikari, Arjun Kumar Gautam, Parashu Ram Poudel.Principle of Physics. Kathmandu: Ayam publication PVT LTD, 2010.

S.K. Gautam, J.M. Pradhan. A text Book of Physics. Kathmandu: Surya Publication, 2003.