O Level Revision : Integrated Science - Science in Energy Uses - Solar Energy

Solar energy refers to energy from sun. Solar energy has three main components; visible light, infrared radiation and ultraviolet radiation. Visible light enables us to see, ultraviolet radiation enables the skin to produce vitamin D while infrared (radiant heat) warms up objects and heats up any object which absorbs it. Solar energy absorbed by plants enables them to manufacture food through the process of photosynthesis. When solar energy strikes an object, it is either reflected if surface is polished, e.g. a mirror or it is absorbed.

May 3, 2021 - 11:19
0 177

 

Transmission of radiant heat

  • There are three ways through which radiant heat can be transmitted i.e. conduction, convection and radiation.
  • Convection and conduction require a medium since heat is carried by atoms and molecules while radiation does not require a medium since heat waves pass through a vacuum.

Conduction

  • Heat is passed from atom to atom in a material until the whole material gets hot.
  • This increases as the source of heat continues to supply heat.
  • The atoms vibrate more as heat is supplied thus they gain kinetic energy.
  • The ability to conduct heat differs from one material to another, but metals are generally good conductors of heat while non-metals like plastic, cork, wood and glass are poor conductors hence they are used as insulators. Atoms of insulators do not pass heat to the next atoms when heated.

Convections in liquids and gases

  • The liquid and gas particles move and carry heat with them.
  • When a liquid is heated from the bottom of the container, the particle at the bottom get hot and become less dense and rise while cool particles move to the bottom. This sets up convention currents.
  • Convection is explained by the kinetic theory in terms of particles.
  • Particles at the heat source gain more kinetic energy and move further apart from one another and this makes the liquid less dense.

 

  • Radiant heat from the sun travels through space since heat waves travel through a vacuum.
  • When radiant heat falls on an object some of the energy is absorbed and transmitted while some is reflected.
  • The absorbed energy raises the temperature of the object. Dull/black surfaces absorb heat while shiny or polished surfaces reflect it.
  • The concept of radiation is applied by people warming themselves using a fire place or roasting maize.

Solar cooker

Radiation

  • The concept of reflection can be applied in a solar cooker

Solar cooker

  • Heat is reflected by a curved surface to a point. The temperature at this point (focus) is enough to raise the temperature of water to boiling point.
  • This enables cooking to be done using radiant heat.

Solar water heater

  • This is used to heat water for domestic use or for clinics and schools.
  • It consists of a blackened copper plate, copper pipe, glass wool, and air space .

Solar water heater

  • Below is a description of the functions of each component of the solar water heater.

Blackened copper plate

  1. Black enables it to absorb heat since black surfaces are good absorber of heat.
  2. The plate quickly conducts heat to pipe since copper is a good heat.

Copper pipe                                               Glass wool

1.    Quickly conducts heat to water.

1.

Poor conductor of heat.

2.    It has low thermal capacity.

2.

Reduces heat loss.

 

3.

Traps air reducing convection.

Air space

  1. Allows radiant heat in.
  2. Traps heat/reduces heat loss to the surrounding.

 

The best location for a solar water heater is at the roof top facing the sun for more hours of heating.

 

Topics: