Solar Energy: Alternate Sources of Energy

Introduction:

Solar energy is the radiation from the Sun capable of producing heat, causing chemical reactions, or generating electricity. The total amount of solar energy received on Earth is vastly more than the world’s current and anticipated energy requirements. In this session, we are going to learn about solar energy and how it is harnessed by different devices.

Explanation:

Solar Energy:

The energy produced by the Sun in the form of heat and light energy is called as solar energy.

Principles of the utilization of Solar Energy: Solar energy is utilized by the involvement of two main principles:

1. In the appliances requiring a moderate temperature, the incident sun rays are reflected by a plane mirror on a black container which absorbs solar energy and gets heated.
2. In the appliances requiring a high temperature, the incident sun rays are reflected and concentrated by using a large concave reflector which focuses all the sun rays at a single point called focus, and any object kept at the focus gets strongly heated.

Harnessing or Utilization of Solar Energy:

The Sun is the ultimate source of energy, having a remarkable capacity to produce energy in the form of heat and light. The energy produced by the Sun in one day is about 50,000 times more than the energy consumed in the whole world in one year. However solar energy has certain limitations, which do not facilitate its large-scale utilization. However, solar energy can be put to use in two different ways, viz.,

1. Direct utilization: – Solar energy can be used directly either by collecting it as heat energy or by converting it into electricity.
2. Indirect utilization: – Indirectly, solar energy can be utilized by converting it into chemical energy like biomass or by utilizing the energy obtained from wind, sea waves, tides, etc.

Solar Heating Devices:

A device that gets heated by absorbing solar energy radiated by the Sun in the form of heat and light energy is called a solar heating device. E.g., solar cookers, solar water heaters, solar furnaces, and solar cells are solar heating devices.

Solar Cooker:

A solar cooker is a device that utilizes solar energy for cooking food material.

It consists of an insulated wooden box (B) painted black from the inner side. The lid of the box is provided with a plane mirror reflector (R) and a glass sheet (G). The food to be cooked is placed in a metal container (C) painted black from the outer side and kept in the box. The container is covered with glass sheets. The box is then kept in direct sunlight, and its reflector is adjusted in such a way that a strong beam of sunlight falls over it.

Working: When the solar cooker is kept in direct sunlight, the reflector (R) reflects both visible and infrared rays of the sunlight onto the top of the box in the form of a strong beam of light. The black surface of the box and the vessel absorb it. When the inner black surface becomes quite hot, it also starts radiating heat energy in the form of infrared rays, but the upper glass sheet (G) does not allow these rays to pass through it and go outside the box.

As a result, these infrared rays get absorbed in the box, which increases its internal temperature up to about 1000C.

This high temperature cooks the food material kept in the metallic container inside the box.

Limitations of Solar Cooker:

1. It cannot be used during the night.
2. On a cloudy day, it cannot be used.
3. The direction of the reflector has to be adjusted according to the position of the Sun.
4. It cannot be used for making ‘chapatis.’
5. It cannot be used for frying.

Solar Cell:

A solar cell is a device that converts solar energy (light energy) directly into electricity.

It is made of semiconducting materials like silicon, germanium, selenium, or gallium. A modern solar cell is made from wafers of semi-conducting materials containing impurities in such a way that a potential difference gets generated when light falls on them.

A 4 cm 2 solar cell produces a potential difference of about 0.4-0.5 volts and generates about 60 milliamperes of current.

To generate a large amount of current a number of solar cells are arranged together in a definite pattern in a solar panel.

The energy (electric current) generated in a solar panel is stored in a battery connected to it and can be used for various purposes.

Uses of a Solar Cell:

Solar cells are used effectively in various fields, but some of their important uses are:

1. Solar cells are used for the production of electricity for lighting, houses, streets, etc.
2. Solar cells are used for the production of electricity to run electronic appliances like televisions, radios, watches, calculators, toys, toy games, etc.
3. Solar cells are used to develop electricity for offshore oil drilling platforms, etc.
4. Solar cells are used to generate electricity in artificial satellites, rockets, space vehicles, etc.

Questions and Answers

Question 1: A black surface absorbs more heat radiation as compared to a white or
reflecting surface under identical conditions. List two solar devices that make use of this property in their design.
Answer: Solar cooker, solar water heater.

Question 2: Name any two elements that are used in fabricating solar cells.
Answer. Germanium, Silicon.

Question 3: Why is a solar cooker painted black from the outside?
Answer: A black surface absorbs more heat as compared to a white or reflecting surface under identical conditions.

Question 4: Mariyam made a solar cooker on her own. She used a white metal box with a lid. She put the food in the solar cooker for heating and closed the lid. But she did not get good results. She then consulted her teacher to find out her mistakes. Her teacher pointed out her mistakes, which she later rectified.

1. According to you, which two mistakes were made by Mariyam and what did she do to rectify them?
2. Which qualities of Mariyam are rectified in her action?

Answer:

1. The possible mistakes made by Mariyam are:
2.  The outer and interior of the solar cooker might not have been blackened.
3. Instead of using a glass lid, she might have been using a plastic cover.
4.  The solar cooker might not have been insulated properly.
5.  The cooker utensil used for cooking might not have been blackened.
6. Gaining practical knowledge of what she has learned in theory. She wanted to adopt an eco-friendly lifestyle.

Question 5: Aditya suggests his family install a solar water heater at their residence. But
Some of the family members were in favor of installing an electric geyser.
Ultimately the family got a water heater installed.

1. Which, according to you, was correct? Give two reasons in support of your answer.
2. Mention two possible changes in the thinking of the family members
   because of the arguments Given by Aditya.

Answer:

1. The decision to install the solar water heater was correct; this is due to
2. Their system uses solar energy, which is a renewable source of energy and free.
3. It will reduce our dependence on fossil fuels, improve our energy security, and reduce the country’s import bill for fuel.
4. Two possible changes in the thinking of the family members because of the arguments given by Aditya are:
5. We should conserve non-renewable fuels for application for which renewable source of energy is not easily available.
6. Solar water heating is a good investment and cost-effective. It is one of the safest and most efficient ways to deliver hot water free of cost.

Summary

• The energy produced by the sun in the form of heat and light energy is called solar energy.
• Direct utilization
• Indirect utilization
• A device that gets heated by absorbing solar energy radiated by the sun in the form of heat and light energy is called a solar heating device.
• A solar cooker is a device that utilizes solar energy for cooking food materials.
• A solar cell is a device that converts solar energy (light energy) directly into electricity.