Energy Resources (DP IB Physics: SL)

• Energy resources are large stores of energy that can be transferred from one form into electrical energy that can be used by society
• Generating energy reliably requires the use of a range of different energy resources

• A renewable energy resource is defined as

An energy source that is replenished at a faster rate than the rate at which it is being used

• As a result of this, renewable energy resources cannot run out
• Renewable resources include:
  • Solar energy
  • Wind
  • Bio-fuel
  • Hydroelectricity
  • Geothermal
  • Tidal
  • Bio-fuels

• Non-renewable energy resources are those that cannot replenish faster than they are used
• Non-renewable resources include:
  • Petrol (gasoline)
  • Diesel
  • Coal
  • Natural gas
  • Nuclear fission

Energy Resources Table

Uses of Energy Resources

• The three main uses of energy resources include:
  • Transport
  • Electricity generation
  • Heating

Types of energy resources

Transport

• The majority of vehicles in the world are powered by petroleum products such as petrol, diesel and kerosene
  • These resources all originate from crude oil, which is a fossil fuel

• A growing number of vehicles are now being powered by electricity
  • The advantage of this is that while the vehicle is being driven, it produces zero carbon emissions
  • The disadvantage is that when the vehicle is being charged, it is connected to the National Grid, which currently uses a combination of renewable and non-renewable energy sources

• Vehicles can also be powered by biofuel
  • The advantage of biofuel is that it is a renewable resource
  • However, the claim that biofuels are carbon-neutral is largely controversial

Electricity Generation

• Electricity plays a bigger role in people's lives than ever before
• With almost 8 billion people in the world, this means the demand for electricity is extremely high
• To keep up with this demand, a combination of all the energy resources available is needed
• On the downside, the majority (84%) of the world's energy is still produced by non-renewable, carbon-emitting sources
  • This has an enormous negative impact on the environment
  • Currently, scientists are working hard to develop more and more efficient ways to produce electricity using more carbon-neutral energy resources

Pie chart of global energy consumption

Heating

• Most homes in cold countries are fitted with central heating systems
• These utilize natural gas in order to heat up water which can be pumped around radiators throughout the home
  • Unfortunately, gas is a non-renewable energy resource

• In geologically active countries, such as Iceland, they are fortunate to be able to heat their homes using geothermal energy

Solar Heating Panels

• Solar heating panels are used to heat tap water (for washing and showers) using the thermal energy of the Sun
• Solar heating panels can contain a water or glycol-water mixture which is pumped around to heat cold water from the main water supply
• The pumped fluid becomes hot within the solar panel and transfers this heat within a hot water storage cylinder
• A solar panel heating system is usually combined with a boiler to produce hot water at all times

A solar heating panel system in a home

Photovoltaic Cells

• Photovoltaic (PV) cells are able to convert light from the Sun directly into electricity
• PV cells contain a single crystal of semiconductor that has been doped to have one side be a p-type semiconductor and the opposite side is an n-type semiconductor
• p-type and n-type relate their names to the majority of charge carriers within them
  • negative electrons for the n-type semiconductor
  • positive 'holes' which is the absence of electrons in the p-type semiconductor

• Photovoltaic cells generate electricity as follows:
  • Light from the sun incident on the PV cell creates a photoelectric effect on the electrode at the surface
  • The reflect-proof film prevents the light from being reflected back into the air
  • Typically, the charge carriers in the semiconductor are in equilibrium, but when radiation is incident upon the PV cell, it enables electrons to move from the n-type layer to the p-type layer
  • The movement of the electrons generates an electrical current

A simple diagram of a PV cell

• A solar panel system is made up of many PV cells in series and parallel within the panel to increase electrical generation
• Typical efficiencies of commercially available PV cell-based solar panels are around 20%

Advantages and disadvantages

• Advantages of using solar power include:
  • Unlimited supply of energy
  • Clean to produce the electricity
  • Freely available everywhere
  • Cheap maintenance
  • No fuel is required for energy

• Disadvantages of using solar power include:
  • Impacted by poor weather
  • Limited efficiency
  • Only available during the day
  • Requires large investment upfront
  • Needs large areas

Step 1: List known values

• • Solar panel area = 103 m²
  • Average intensity of the Sun = 1.36 × 10³ W m^-2
  • Solar panel efficiency = 23%
  • Time = 1 hour = 3600 s

Step 2: Identify the relationship needed

• • The final answer required is energy, in Joules
  • So we must first find power, in Watts
  • Therefore the quantities must be multiplied together as follows:

Power = Area × Average Intensity × Efficiency

Step 3: Calculate the power output of the panels

Power = 103 × (1.36 × 10³) × 0.23 = 3.2 × 10⁴ W

Step 4: Calculate the energy output in 1 hour

• • Energy output = power × time
  • Energy output in 1 hour = (3.2 × 10⁴) × 3600 = 1.15 × 10⁸ J