Solar Panels, Heat Collectors and Solar Harnessing Devices for SS 1

Solar Harnessing Devices and Their Uses

Performance Objectives

By the end of the lesson, students should be able to:

1. explain the meaning of solar panel and its use;
2. explain the meaning of solar heat collector and its use;
3. describe how the solar panel and solar heat collector work;
4. construct a simple solar heater.

The Sun is a powerful source of energy that reaches the Earth in the form of sunlight and heat. This energy is clean, renewable, and abundant. Solar harnessing devices are technologies designed to capture and convert this solar energy into useful forms, such as electricity or heat, for various applications in homes, industries, and communities.

Solar Panels

Meaning of Solar Panel

A solar panel is a device that converts sunlight directly into electricity.

Solar panels are also known as photovoltaic (PV) panels. They are made up of many smaller units called solar cells, which are typically made from semiconductor materials like silicon. When sunlight strikes these cells, it creates an electric current.

Uses of Solar Panels

Solar panels are used for various purposes, primarily to generate electricity. Some common uses include:

1. Residential Power: Providing electricity for homes, reducing reliance on the national grid and lowering electricity bills.
2. Commercial and Industrial Power: Supplying power to businesses, factories, and offices.
3. Street Lighting: Powering streetlights, especially in areas without access to grid electricity.
4. Water Pumping: Operating pumps for irrigation in agriculture or for supplying water to remote communities.
5. Telecommunications: Powering remote communication towers and equipment.
6. Portable Devices: Charging small electronic devices like phones, laptops, and portable lamps.
7. Spacecraft: Providing power for satellites and space stations.

How Solar Panels Work

Solar panels work based on the photovoltaic effect. This effect describes how certain materials generate an electric current when exposed to light. The process involves the following steps:

1. Sunlight Absorption: When sunlight, which consists of tiny energy packets called photons, strikes the solar cells in a panel, the photons are absorbed by the semiconductor material (usually silicon).
2. Electron Excitation: The absorbed photons transfer their energy to electrons within the silicon atoms. This energy causes the electrons to become excited and break free from their atoms.
3. Electric Field Creation: Solar cells have a built-in electric field, created by doping different layers of silicon with impurities (one layer with a positive charge and another with a negative charge). This electric field acts like a one-way street, pushing the freed electrons in a specific direction.
4. Current Flow: The directed movement of these excited electrons creates an electric current. Metal contacts on the solar cell collect these electrons.
5. Electricity Generation: When the electrons flow through an external circuit, they generate direct current (DC) electricity. This DC electricity can then be used directly or converted into alternating current (AC) using an inverter for use in homes and businesses.

Solar Heat Collectors

Meaning of Solar Heat Collector

A solar heat collector is a device designed to absorb sunlight and convert it into heat, which is then transferred to a fluid (usually water or air).

These devices are primarily used for heating water or spaces. A common type is the flat-plate solar heat collector, which consists of a dark absorber plate, a transparent cover, and insulation.

Uses of Solar Heat Collectors

Solar heat collectors are used to provide heat for various applications. Some common uses include:

1. Water Heating: Heating water for domestic use (bathing, washing), commercial buildings, and swimming pools.
2. Space Heating: Providing warmth for homes and buildings, especially during colder periods.
3. Industrial Process Heat: Supplying heat for certain industrial processes that require moderate temperatures.
4. Crop Drying: Drying agricultural products like grains, fruits, and vegetables using solar-heated air.
5. Desalination: Using solar heat to evaporate saltwater, leaving behind fresh water.

How Solar Heat Collectors Work

Solar heat collectors operate on the principle of absorbing solar radiation and transferring that energy as heat to a working fluid. The process for a flat-plate collector typically involves these steps:

1. Sunlight Penetration: Sunlight passes through the transparent glass cover of the collector. The glass cover helps to trap heat inside the collector, similar to a greenhouse effect.
2. Absorption: The sunlight strikes a dark-coloured absorber plate, which is designed to absorb as much solar radiation as possible. The dark surface efficiently converts the light energy into thermal energy (heat).
3. Heat Transfer to Fluid: Tubes containing a heat-transfer fluid (such as water or a water-antifreeze mixture) are attached to or integrated within the absorber plate. As the absorber plate heats up, it transfers this heat to the fluid flowing through the tubes.
4. Circulation: The heated fluid then circulates out of the collector and into an insulated storage tank. In the tank, the heat is transferred to the water that will be used for domestic purposes.
5. Heat Retention: Insulation material placed behind and around the absorber plate minimises heat loss to the surroundings, ensuring that most of the absorbed heat is transferred to the fluid.

Constructing a Simple Solar Heater

Constructing a simple solar heater demonstrates the basic principles of solar energy absorption and heat transfer. This activity will help in understanding how solar heat collectors work.

Required Materials

The required materials are:

1. A wooden box or a sturdy cardboard box (as the wood base/casing)
2. A black copper tube or a black-painted metallic can (e.g., a soft drink can)
3. Insulating material (e.g., foam, old newspapers, sawdust)
4. A clear glass sheet or transparent plastic sheet (as the glass cover)
5. Insulated water container (e.g., a thermos flask or a plastic bottle wrapped in cloth)
6. Water
7. Thermometer
8. Adhesive tape or glue
9. Basic tools (e.g., scissors, knife, ruler)

Procedure for Construction

The procedure involves the following steps:

1. Prepare the Box: Obtain a wooden or sturdy cardboard box. This will serve as the outer casing of your solar heater. Ensure it has an open top.
2. Insulate the Box: Line the bottom and sides of the inside of the box with insulating material such as foam or crumpled newspapers. This helps to prevent heat loss from the sides and bottom of the heater.
3. Prepare the Absorber: If using a copper tube, coil it into a flat spiral or zigzag pattern that fits inside the box. If using a metallic can, paint it black. The black surface will absorb sunlight efficiently.
4. Position the Absorber: Place the black copper tube or black-painted can inside the insulated box. Ensure it is slightly raised from the bottom insulation to allow air circulation if needed, or directly on it if it’s a can.
5. Connect to Water Container (if using tube): If using a copper tube, connect one end to the bottom of the insulated water container and the other end to the top, creating a closed loop for water circulation. If using a can, simply place the can inside the box and fill it with water.
6. Add Water: Fill the insulated water container (or the black can) with water.
7. Cover the Box: Place the clear glass sheet or transparent plastic sheet over the open top of the box. Secure it with adhesive tape or glue to create a sealed cover. This cover allows sunlight to enter but traps the heat inside, creating a greenhouse effect.
8. Position the Heater: Place the assembled solar heater in a sunny location, tilting it towards the sun for maximum exposure.
9. Measure Temperature: Insert a thermometer into the water in the insulated container (or the can) to measure the initial temperature. After a few hours in the sun, measure the temperature again to observe the increase.

Safety Precautions

When constructing and using a simple solar heater, observe the following safety precautions:

1. Handle glass sheets carefully to avoid cuts. If possible, use thick transparent plastic.
2. Ensure the box is stable and will not tip over, especially if it contains water.
3. Do not touch the black absorber plate or the heated water directly after prolonged sun exposure, as they can become very hot.
4. Supervise children during construction and operation to prevent accidents.
5. Avoid using flammable materials near the heated parts of the collector.