Energy from the Sun (CIE IGCSE Physics: Co-ordinated Sciences (Double Award))

Extended tier only

• The Sun transfers energy to Earth by electromagnetic radiation
• Most of our energy resources on Earth come indirectly from the Sun:
  • The Sun heats up the atmosphere, creating wind and producing waves
  • Water evaporated by the Sun falls as rain, filling up reservoirs
  • Plants grown using sunlight form the basis for fuels – both biofuels and fossil fuels

• Some energy resources, however, do not come from the Sun
• These include:
  • Geothermal – this comes from heat produced in the Earth’s core
  • Nuclear – this comes from elements which make up a small proportion of the Earth’s crust
  • Tidal – this comes (mainly) from the gravitational attraction of the Moon

The Sun

Energy from the Sun is the source of the energy stored in many of Earth's energy resources

 

• The energy from the Sun that falls on the Earth is transferred by radiation 
  • Mostly visible light and infrared radiation
• The amount of energy transferred from the Sun to the Earth each hour is equal to the energy use of the world for one year!
• Therefore, scientists are working hard to find methods of harnessing this energy
  • Solar energy has a low energy density, which means large collecting devices are required 
  • Collecting solar energy has been expensive (due to the equipment required) and inefficient
  • Although improved technology has improved efficiency, greater demand has lowered costs

• Solar cells transfer energy from sunlight and produce a current, therefore generating electricity 
  • Solar cells, sometimes called photovoltaic cells, are made of semiconducting materials
  • A number of cells connected together can supply electricity to homes, small-scale businesses, communication devices and satellites
  • Energy generated from solar cells can be stored in batteries for later use

Solar cells

Solar cells use energy from sunlight to produce electricity

Advantages of solar cells

• Solar energy is a renewable resource
  • A renewable resource is one which can be replenished at the same rate as it is used
• In many places on Earth sunlight is a reliable energy resource (this means that the sun shines most of the time)
• Solar farms produce no greenhouse gases or pollution
• Solar energy can be generated in remote places where they don't have electricity
  • For example to power solar street signs in rural areas
• Solar cells are readily available
• Solar farms are relatively quick and cheap to build, and inexpensive to run compared to power stations 
• Solar cells can be placed on top of buildings

Disadvantages of solar cells

• Solar farms need to be large scale to produce large amounts of electricity
• In many places on Earth, sunlight is not a reliable energy resource (there are not enough sunshine-hours to justify the set-up costs)
• Solar cells remain fairly expensive for households to install and maintain (they must be kept clean to work at full capacity)
• Each solar cell only produces a small amount of electricity so solar farms are needed to produce large amounts of electricity 
• Solar cells are relatively inefficient (around 20% - 40%)

• Useful energy may be obtained from infrared and other electromagnetic waves from the Sun using solar panels
• Solar panels transfer energy from sunlight to the thermal store of the solar panels which is used to heat water in the pipes 
  • Solar panels can be used to warm domestic water supplies 
    • This can reduce the cost of producing hot water since it is heated partially by the solar panels
  • Solar furnaces consist of large curved mirrors that focus the sun's rays on to a small area
    • These can be used to boil water, generating enough steam to turn turbines and generate electricity in a power station

Solar panel

Solar panels use energy from sunlight to heat water

 

• Water is stored in a water tank and pumped through small pipes running through the solar panel
• Infrared radiation from the Sun heats the water in the pipes as it flows through them
• The water returns to the tank at a higher temperature
• Water may still need to be heated further to reach the desired temperature (eg. for a shower)

Advantages of solar panels

• Solar energy is a renewable resource
• In many places on Earth, sunlight is a reliable energy resource (this means that the sun shines most of the time)
• Solar panels produce no greenhouse gases or pollution once they are operating
• Solar panels can cut the cost of energy bills for households
• Solar panels can be placed on the roofs of buildings

Disadvantages of solar panels

• Solar furnaces need to be large scale to produce high temperatures
• Energy is still needed to heat water to a higher temperature in domestic households
• In many places on Earth, sunlight is not a reliable energy resource (the sun doesn't shine regularly enough to justify the set-up costs)

• Energy from the wind can be used to generate electricity
• The wind turns a turbine, which turns a generator, which generates electricity
• Energy from the kinetic store of the wind is transferred
  • mechanically to the kinetic store of the turbine
  • which is transferred mechanically to the kinetic store of the generator
  • which is transferred electrically to the National Grid

Wind turbines

Wind turbines use energy from the wind to generate electricity

Advantages of wind power

• Wind is a renewable resource
• Wind turbines produce no greenhouse gases or pollution
• Wind farms are relatively inexpensive to build and cheap to run
• Wind turbines have a relatively high efficiency of 50%
• The land used for wind farms can still be used for farming
• Off-shore wind farms can be built in coastal areas
• Wind turbines do not use fuel, so there are no fuel costs

Disadvantages of wind power

• Wind power is not reliable because the wind does not blow constantly
• Turbines are built facing a specific direction so they only work when the wind is blowing in that specific direction
• Some people consider wind farms to be visual pollution , so there can be local opposition to the construction of wind farms in some towns and cities
• Each turbine only produces a small amount of electricity, so wind farms are needed for large scale electricity generation
• High-voltage power lines are required to transmit the electricity to the National Grid