5.2.1 Energy Resources (Cambridge International AS Environmental Management)

Renewable Energy Sources

Spec point — 5.2.1

What Are Renewable Energy Sources?

• Renewable energy comes from energy sources that will not run out and includes:

  • Biofuels (biomass including wood, bioethanol and biogas)
  • Geothermal energy
  • Hydroelectric dams
  • Tidal energy
  • Wave energy
  • Solar energy
  • Wind energy

• Once in place, these renewable energy sources do not produce any greenhouse gas emissions (with the exception of biomass):

  • However, it is important to note that greenhouse gases may be emitted in the production, construction and transport of the equipment required for the above renewable energy sources

Renewable Energy Sources Examples

Biofuels

• Biofuels (also known as biomass fuels) are renewable fuels derived from organic materials, such as plants and animal waste, that can be used as an alternative to fossil fuels:

  • However, they have only half the energy density of fossil fuels

• The three main biofuels are:

  • Biodiesel - made by refining renewable fats and oils (e.g. vegetable oils, animal fats or recycled cooking oil)
  • Bioethanol - made by fermentation (of crops rich in sugars or starches, such as corn or sugarcane)
  • Biogas - released when organic waste products decompose

Advantages

• Biofuel is a renewable resource - uses waste or bioproducts that can be regrown
• Some vehicles can be powered by biofuel rather than using fossil fuels
• Biofuel is considered to be carbon neutral
• No sulfur dioxide is produced

Disadvantages

• Crops of biofuel producing plants must be grown, which takes time
• Growing the crops takes a lot of land, and takes resources needed for food production
• Burning biofuels releases carbon dioxide into the atmosphere (however, it is considered carbon neutral because plants take in carbon dioxide when they photosynthesise)

Plants take in carbon dioxide during photosynthesis, but carbon dioxide is released back into the atmosphere when biofuels are burned

Geothermal Energy

• Geothermal energy is caused by the heat that is generated from within the Earth:

  • The Earth's interior is extremely hot, partly due to radioactive elements deep in the Earth that release energy as they decay

• This geothermal energy heats up rocks in the Earth's crust, sometimes to an extremely high temperature:

  • Water can be poured into shafts below the Earth's surface
  • The water is heated and returned via another shaft as steam or hot water
  • Steam can be used to turn a turbine and generate electricity, and the hot water can also be used to heat homes

Advantages

• Renewable resource
• Reliable source of energy
• Geothermal power stations are usually small compared to nuclear or fossil fuel power stations

Disadvantages

• Few suitable locations on Earth, so only viable for small scale electricity production in many countries
• Can result in the release of greenhouse gases from underground
• Expensive to build and maintain

Cold water is heated by natural geothermal energy underground, and then returned as hot water or steam, which can be used to generate electricity

Hydroelectric Dams

• When water is stored above ground level it has gravitational potential energy
• This energy can be transferred to kinetic energy if the water is allowed to flow down the slope
• Flowing water turns the turbine to generate electricity

Advantages

• Can respond to demand quickly so is reliable and available
• Can generate large-scale amounts of electricity in a short period of time
• Often in sparsely populated areas

Disadvantages

• Expensive to build and maintain
• Creating reservoirs sometimes results in the need to flood valleys, which destroys habitats, towns and villages
• The pumping systems (used if water needs to be pumped up to the reservoir) often rely on fossil fuels, releasing large amounts of greenhouse gases
• Dam traps sediment which can affect ecosystems downstream
• Visual pollution
• Can prevent fish movement and migration upstream

A hydroelectric dam transfers the gravitational potential energy of the water to kinetic energy in order to generate electricity

Wave & Tidal Energy

• The rise and fall of waves or the tide can be used to turn a turbine and generate electricity

Advantages

• No pollution
• Reliable and can produce a large amount of electricity at short notice
• Renewable energy resource
• Small systems are being developed to provide electricity for small islands

Disadvantages

• Expensive to build and maintain
• Damages fragile habitats
• Very few suitable locations
• The technology is not advanced enough for large-scale electricity production

Underwater turbines generate electricity from the movement of waves

Tidal barrages can generate electricity from the movement of water, both as the tide comes in and as it goes out again

Solar Energy

• 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 roughly 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 is expensive (due to the equipment required) and inefficient

Solar PV panels

• Solar photovoltaic (PV) panels transfer energy from sunlight electrically producing a current and therefore generating electrical power:

  • Solar cells, sometimes called photovoltaic cells, are made of semiconducting materials
  • A number of photovoltaic cells or panels connected together can supply electricity to homes, small-scale businesses, communication devices and satellites
  • Energy generated can be stored in batteries for later use

Advantages

• 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 farms produce no greenhouse gases or pollution
• Solar energy can be generated in remote places where they don't have electricity (e.g. to power solar street signs in rural areas)
• Can be small- or large-scale
• Can be incorporated into building design
• Technology is improving and reducing the cost

Disadvantages

• Solar farms need to be large-scale to produce large amounts of electricity, which is expensive to set up
• Uses large areas of land
• People often don't like the appearance of large solar farms; this is known as visual pollution
• 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 PV panels use energy from sunlight to produce electricity

Wind Energy

• Wind energy is a renewable form of energy that harnesses the power of the wind to generate electricity
• It involves the use of wind turbines, which have large blades that spin when the wind blows
• The rotating blades transfer kinetic energy to a generator, which converts it into electrical energy

Advantages

• Wind is an abundant resource that will never run out, making wind energy a sustainable and renewable source of power
• Wind energy produces no greenhouse gas emissions or air pollutants during operation, helping to reduce the negative impact on climate change and air quality
• Wind energy reduces dependence on fossil fuels and foreign energy sources, promoting energy independence and security
• The wind energy industry creates jobs in manufacturing, installation, operation and maintenance of wind turbines
• Can be small- or large-scale
• Can be on land or offshore
• Cheap to run

Disadvantages

• Wind is not constant, and the availability of wind energy fluctuates
• Electricity generation from wind turbines depends on wind speed and consistency
• Wind turbines can be visually intrusive, especially when installed in large numbers
• Some people may find the noise generated by wind turbines to be disruptive
• Wind farms require large areas of land, which can have an impact on agricultural or natural landscapes
• Birds and bats may occasionally collide with wind turbines, causing some impact on local wildlife populations

A wind farm in Austria - some people think wind turbines are an eye-sore, especially when installed in large numbers (Photo by Zbynek Burival on Unsplash)

Non-renewable Energy Sources

Spec point — 5.2.1

• Non-renewable energy comes from energy sources that will eventually run out, including:

  • Fossil fuels
  • Nuclear energy (using uranium as a fuel)

What Are Fossil Fuels?

• Fossil fuels include:

  • Coal
  • Natural gas (mostly methane) which is used in domestic boilers and cookers
  • Crude oil, which is refined into petrol, diesel and other fuels

• Fossil fuels are formed from the remains of plants and animals:

  • Chemical energy stored in fossil fuels originally came from sunlight
  • Energy from the sun was transferred to chemical energy stores within plants through photosynthesis (plants use energy from sunlight to make food)
  • Animals ate the plants and the energy was then transferred to their chemical store

Fossil fuels include coal, oil and natural gas

Advantages

• The current systems of transport and electricity generation used by human societies rely heavily on fossil fuels, which are generally readily available on a daily basis
• In the past fossil fuels have been reliable for large-scale energy production (although this is changing as supplies deplete and prices rise)
• Efficient - fossil fuels typically have a high energy density (they produce a large amount of energy per kilogram)

Disadvantages

• It takes millions of years for fossil fuels to form:

  • This is why they are considered to be a non-renewable energy resource

• The increasing demand for a decreasing supply causes prices to increase:

  • Fossil fuels are predicted to completely run out within the next 200 years

• Burning fossil fuels pollutes the atmosphere with harmful gases such as:

  • Carbon dioxide, which contributes to the greenhouse effect
  • Sulphur dioxide, which produces acid rain
  • Both carbon and sulphur can be captured upon burning, preventing them from being released into the atmosphere, but this is expensive to do

• Oil spills can occur during transport of fossil fuels, which damage the environment and wildlife over very large areas

• Prices fluctuate rapidly

• Supplies can be affected by conflict and political disagreements (e.g. the war in Ukraine)

Global energy sources used in 2019

Uses of Fossil Fuels

• Fossil fuels are mainly used for:

  • Transport
  • Generating electricity
  • Heating

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

Electricity generation

• Fossil fuels, such as coal and oil, are used to produce energy on-demand when energy is needed:

  • This is done by burning the materials when the energy is required
  • When coal is burned, it produces thermal energy

• This is used to boil water creating steam

• Steam is forced around the system and this turns a turbine

• The turbine turns coils in a magnetic field in the generator:

  • This generates electricity

• The electricity is transferred through a step-up transformer and is carried out of the system by electrical lines

• The steam within the turbine will cool and condense and then be pumped back into the boiler to repeat the process

Electricity generation using a coal-fired power station

Energy Demand

• The demand for energy across the globe is rising

• Population growth and development are the two main causes of the increase in energy demand:

  • The higher demand for food leads to more intensive farming, which requires more energy for machines, light and heat
  • Increasing industry requires energy for heating, lighting and machinery
  • There is more transport, all of which requires energy in the form of petrol, diesel or electricity
  • Urbanisation increases with the development increasing domestic appliances, heating and lighting
  • Increased wealth means people buy more appliances and technology, which require energy

World energy demand

Nuclear Energy

• Energy stored in the nucleus of atoms can be released when the nucleus is broken in two:

  • This is known as nuclear fission

• Nuclear power stations use fission reactions to create steam to turn turbines to generate electricity

• Nuclear power is a low carbon, low-emission, non-renewable resource but is controversial due to the radioactive waste it produces and the potential scale of any accident

Advantages

• No pollution released into atmosphere
• Nuclear reactors are perfectly safe as long as they are functioning properly (rigorous safety checks must be routinely carried out and rigorous safety procedures followed)
• Nuclear power stations can generate electricity reliably on a large scale to be available as needed
• Small amounts of uranium are needed, and large reserves are available
• Reduces reliance on fossil fuels
• Increases energy security

Disadvantages

• Uranium ore found in the ground is used for fission reactions and since there is a finite supply, nuclear power is a non-renewable resource
• Nuclear fuels produce radioactive waste, which needs to be stored for thousands of years
• Safe ways of storing radioactive waste are very expensive
• If an accident occurs at a nuclear reactor, radioactive waste can leak out and spread over large areas
• Cost of decommissioning (shutting down) nuclear power plants is very high

Nuclear fission occurs when a large nucleus is broken into two smaller nuclei, releasing large amounts of energy

• Nuclear energy is often used in countries who do not have their own supplies of fossil fuels, such as France

• In 2019 approximately 4% of the global primary energy supply was from nuclear power

• There are 439 active nuclear reactors across the world. Most of these are in just five countries:

  • USA (92)
  • France (56)
  • China (54)
  • Russia (37)
  • Japan (33)

Share of electricity production from nuclear power plants