Energy from the Sun (Cambridge (CIE) IGCSE Physics): Revision Note

The Sun

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 thermal energy 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

Solar cells

• 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

  • Improved technology and large-scale manufacturing have made solar cells much cheaper and more efficient than they used to be

• 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

Advantages of solar cells

• Solar energy is a renewable resource since it relies on light from the Sun which will not run out

A renewable resource is one which can be replenished at the same rate as it is used

• Solar farms do not emit carbon dioxide or other greenhouse gases while operating, so they do not contribute to global warming

• Solar energy can be generated in remote places that are not connected to an electricity grid

  • For example, to power solar street signs in rural areas

• Solar farms have low running costs because there is no fuel to buy

Disadvantages of solar cells

• Solar cells provide an intermittent or unreliable supply of electricity because they depend entirely on the availability of sunlight

  • They cannot generate electrical power at night, and their power output is heavily dependent on weather conditions

• Solar farms need to be large-scale and contain vast numbers of solar cells to produce large amounts of electricity

• Each solar cell generally has a lower power output than a standard mains electrical supply

Solar panels

• 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 onto a small area

  • These can be used to boil water, generating enough steam to turn turbines and generate electricity in a power station

How solar panels work

• 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 (e.g. for a shower)

Advantages of solar panels

• Solar energy is a renewable resource since it relies on light from the Sun which will not run out

• Solar panels do not emit carbon dioxide or other greenhouse gases while operating, so they do not contribute to global warming

• While they may have an initial installation cost, they are cheap to run and require low maintenance

• Solar panels can be placed on the roofs of buildings, saving ground space

Disadvantages of solar panels

• Solar panels provide an intermittent or unreliable supply of electricity because they depend entirely on the availability of sunlight

• Solar furnaces need to be large-scale to produce high temperatures

• Solar panels have a much lower power output compared to a standard mains electrical supply

  • A solar panel will take longer to recharge a battery than a mains supply would

Wind energy

• 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 electricity grid

Advantages of wind power

• Wind is a renewable resource

• Wind turbines do not emit carbon dioxide or other greenhouse gases while operating, so they do not contribute to global warming

• Wind turbines do not produce sulfur dioxide or other acidic gases during operation, so they do not contribute to acid rain

• Offshore 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, and they cannot generate power if the wind is too weak or too strong

• Each turbine only produces a small amount of electricity, so wind farms are needed for large-scale electricity generation

• Wind turbines are often difficult to maintain, particularly if they are built offshore

• Offshore wind farms can disrupt shipping routes