Energy resources Revision Notes

Fossil fuels such as coal, oil, and natural gas store chemical energy formed from ancient organic matter. When combusted, this chemical energy is released as heat energy.

Biofuels, derived from recently living organisms (e.g., plant material, animal waste), also store chemical energy that is released by combustion.

In power stations, the heat energy from burning fossil fuels or biofuels is used to heat water in a boiler, producing high-pressure steam. This steam drives a turbine connected to a generator, converting thermal energy into mechanical energy and then into electrical energy.

• Chemical energy in fuels is converted to heat by combustion.
• Boiler uses heat to produce steam from water.
• Steam drives turbine blades, converting heat energy to kinetic energy.
• Turbine shaft turns generator, producing electrical energy.

Water energy harnesses the kinetic and potential energy of moving water.

Wave energy captures the kinetic energy of surface water waves using floating devices that move with the waves, driving generators.

Tidal energy exploits the gravitational potential energy difference between high and low tides. Barrages or tidal lagoons trap water at high tide and release it through turbines at low tide to generate electricity, similar to hydroelectric dams but driven by tides rather than river flow or rainfall runoff.

• Wave energy converts kinetic energy of waves into mechanical energy.
• Tidal energy uses gravitational potential energy differences to drive turbines.
• Hydroelectric dams store water at height (gravitational potential energy).
• Water released flows through turbines, converting potential energy to kinetic energy and then electrical energy via generators.

Geothermal energy uses heat from within the Earth’s crust, originating from radioactive decay and residual heat from Earth's formation.

Hot water or steam from underground reservoirs is brought to the surface and used to drive turbines connected to generators.

This process converts thermal energy from the Earth into mechanical energy and then electrical energy.

• Earth’s internal heat produces steam or hot water.
• Steam drives turbines connected to generators.
• Thermal energy is converted to electrical energy without combustion.

Nuclear energy is released by nuclear fission, where heavy atomic nuclei (e.g., uranium-235) split into smaller nuclei, releasing large amounts of heat energy.

This heat energy is used to produce steam in a boiler, similar to fossil fuel power stations.

The steam drives turbines connected to generators, converting nuclear energy into electrical energy.

• Nuclear fission releases heat energy.
• Heat produces steam in a boiler.
• Steam drives turbine blades.
• Turbine turns generator to produce electricity.

Solar cells (photovoltaic cells) convert solar radiation directly into electrical energy by the photovoltaic effect, where light photons excite electrons to produce current.

Solar panels for heating water absorb solar radiation, converting it into thermal energy to heat water in pipes or tanks.

Solar heating systems do not involve turbines or generators; they transfer heat directly to water for domestic or industrial use.

• Solar cells convert light energy directly into electrical energy.
• Solar panels absorb sunlight to heat water.
• Solar heating uses thermal energy without mechanical conversion.

Wind energy harnesses the kinetic energy of moving air.

Wind turbines have blades that rotate when wind blows, converting kinetic energy into mechanical energy.

The turbine shaft is connected to a generator that converts mechanical energy into electrical energy.

• Wind’s kinetic energy turns turbine blades.
• Turbine shaft drives generator.
• Generator produces electrical energy.

Energy sources are classified as renewable or non-renewable based on whether they can be replenished naturally within a human timescale.

Renewable energy sources include solar, wind, hydroelectric, tidal, geothermal, and biofuels. These sources are sustainable because they are naturally replenished.

Non-renewable energy sources, such as fossil fuels (coal, oil, natural gas) and nuclear fuels (uranium), are finite and will eventually be depleted as they are consumed.

• Renewable sources: solar, wind, hydroelectric, tidal, geothermal, biofuels.
• Non-renewable sources: fossil fuels, nuclear fuels.
• Renewable sources have a lower risk of depletion.

Availability refers to whether the energy source is accessible at a given location and time.

Reliability refers to the consistency of energy supply from the source.

Fossil fuels and nuclear energy are generally available on demand and provide reliable, continuous power because fuel can be stored and used as needed, and power plants operate continuously (base load).

• Solar and wind energy depend on weather and time of day, causing variability and intermittency.
• Hydroelectric power is generally reliable but can be affected by seasonal water availability.
• Tidal energy is highly predictable due to regular tidal cycles but limited to coastal areas.
• Geothermal energy provides a stable and continuous supply where geothermal activity is accessible.
• Biofuels depend on agricultural production and can be variable but are generally more controllable than solar or wind.

The scale of energy production refers to the amount of energy that can be generated to meet demand.

Fossil fuel and nuclear power plants can generate large amounts of electricity suitable for national grids.

Renewable sources vary: hydroelectric dams can produce large-scale power, while solar panels and wind turbines are often modular and scalable from small to large installations.

• Fossil fuel plants: large-scale, high power output.
• Nuclear plants: large-scale, high power output with small fuel volume.
• Hydroelectric dams: large-scale but site-dependent.
• Solar and wind: scalable from small domestic to large farms.
• Tidal and geothermal: limited by location and resource size.

Environmental impact is a critical factor in evaluating energy sources.

Fossil fuels release greenhouse gases (CO₂, methane) causing climate change and air pollution.

Nuclear energy produces radioactive waste requiring careful long-term management but emits no greenhouse gases during operation.

• Solar and wind energy produce no direct emissions but require land and materials for infrastructure.
• Hydroelectric dams can disrupt aquatic ecosystems and displace communities.
• Tidal energy has minimal emissions but may affect marine life.
• Geothermal energy emits low levels of gases but can cause land subsidence.
• Biofuels can reduce net CO₂ emissions but may compete with food production and cause deforestation.

Choosing an energy generation method involves balancing renewability, availability, reliability, scale, and environmental impact.

Renewable sources are preferred for sustainability and environmental reasons but may require backup systems due to variability.

Non-renewable sources provide reliable, large-scale power but have significant environmental and resource depletion concerns.

• Energy policy must consider local resource availability and environmental regulations.
• Diversifying energy sources can improve reliability and reduce environmental impact.
• Technological advances may improve efficiency and reduce drawbacks of various sources.

Energy transfer efficiency is a measure of how well energy supplied to a system is converted into useful energy output. It is expressed as a percentage and indicates the proportion of input energy that performs the desired work.

Efficiency = (Useful Energy Output / Total Energy Input) × 100%

Here, 'Useful Energy Output' is the energy converted into the desired form (e.g., kinetic energy, electrical energy), and 'Total Energy Input' is the total energy supplied to the system. Both quantities are measured in joules (J).

• Efficiency is always less than or equal to 100%.
• 100% efficiency means no energy is wasted.
• Efficiency is a dimensionless quantity expressed as a percentage.

To calculate efficiency, use the formula: Efficiency (%) = (Useful Energy Output / Total Energy Input) × 100.

Example: A machine receives 500 J of energy and delivers 350 J of useful work. Calculate its efficiency.

Step 1: Write the formula: Efficiency = (Useful Energy Output / Total Energy Input) × 100% = (350 J / 500 J) × 100% = 70%.

• Always ensure energy values are in the same units before calculation.
• Efficiency cannot exceed 100%.
• Common error: forgetting to multiply by 100 to convert to percentage.

In real systems, some energy is lost to the surroundings, usually as heat, sound, or vibration, reducing efficiency.

For example, in an electric motor, electrical energy is partly converted to heat due to resistance in wires.

Reducing energy losses improves efficiency. This can be done by using better insulation, lubricants to reduce friction, or more efficient components.

• Energy losses are often due to friction, air resistance, electrical resistance, or sound.
• Improving efficiency conserves energy and reduces waste.
• No machine is perfectly efficient due to unavoidable energy losses.

Efficiency helps compare different devices or systems to choose the most energy-saving option.

High efficiency means less fuel or energy is needed for the same output, reducing costs and environmental impact.

Understanding efficiency is essential in designing engines, electrical appliances, and renewable energy systems.

• Efficiency guides energy conservation efforts.
• It influences economic and environmental decisions.
• It is a key factor in sustainable technology development.

Solar radiation is electromagnetic energy emitted by the Sun, reaching Earth primarily as visible light and infrared radiation. It is measured in watts per square metre (W/m²) and provides the energy that sustains life and drives many natural processes on Earth.

Most energy resources on Earth ultimately derive their energy from solar radiation. This includes fossil fuels, biofuels, wind, hydroelectric, and wave energy, which depend directly or indirectly on the Sun's energy.

However, some energy sources do not rely on solar radiation. These exceptions are geothermal energy, nuclear energy, and tidal energy, which have different origins.

• Solar radiation is energy from the Sun reaching Earth.
• Measured in watts per square metre (W/m²).
• Primary energy source for most energy resources.
• Exceptions: geothermal, nuclear, tidal energy.

Solar radiation heats the Earth's surface unevenly, causing air movement and weather patterns. This drives wind energy, where moving air turns turbines to generate electricity.

Solar energy also powers the water cycle: evaporation, condensation, and precipitation. This cycle feeds rivers and reservoirs, enabling hydroelectric power generation by water flowing through turbines.

Plants use solar energy for photosynthesis, creating biomass energy stored chemically in organic matter. Burning biomass releases this stored solar energy as heat.

• Wind energy results from solar-driven air movement.
• Hydroelectric power depends on solar-driven water cycle.
• Biomass energy stores solar energy chemically via photosynthesis.

Geothermal energy originates from heat stored within the Earth's interior, produced by radioactive decay and residual heat from planetary formation. It is independent of solar input.

Nuclear energy is released from nuclear reactions, such as fission of uranium atoms in reactors. This energy is stored in atomic nuclei and does not come from solar radiation.

Tidal energy arises from gravitational interactions between the Earth, Moon, and Sun, causing periodic sea level changes. It is driven by gravitational forces, not solar radiation.

• Geothermal energy comes from Earth's internal heat.
• Nuclear energy is from atomic nucleus reactions.
• Tidal energy is caused by gravitational forces, not solar radiation.

Recognising solar radiation as the primary energy source for most resources helps understand the interconnectedness of Earth's energy systems.

Renewable energy sources like wind, hydroelectric, and biomass depend on solar energy, making them sustainable as long as the Sun shines.

Geothermal, nuclear, and tidal energy provide alternative energy sources independent of solar input, useful for diversifying energy supply.

• Solar radiation underpins most renewable energy sources.
• Non-solar energy sources diversify energy supply.
• Understanding energy origins aids in energy resource management.

Nuclear fusion is the process that powers the Sun, occurring in its core where temperatures reach approximately 15 million degrees Celsius and pressures are extremely high. Under these conditions, hydrogen nuclei (protons) overcome their electrostatic repulsion and collide with sufficient energy to fuse together.

The primary fusion reaction in the Sun is the proton-proton chain, where four hydrogen nuclei combine through a series of steps to form one helium nucleus. This process releases energy because the mass of the resulting helium nucleus is slightly less than the total mass of the four original protons.

The difference in mass, called the mass defect, is converted into energy according to Einstein's equation E = mc², where E is energy, m is mass, and c is the speed of light (approximately 3.0 × 10⁸ m/s).

• Fusion occurs in the Sun's core at ~15 million °C.
• Hydrogen nuclei (protons) fuse to form helium nuclei.
• Mass defect is converted into energy (E = mc²).

The proton-proton chain involves several steps: two protons fuse to form a deuterium nucleus (one proton and one neutron), releasing a positron and a neutrino.

The deuterium nucleus then fuses with another proton to form helium-3 (two protons and one neutron), releasing gamma radiation.

Finally, two helium-3 nuclei combine to form helium-4 (two protons and two neutrons), releasing two protons back into the plasma to continue the cycle.

• Step 1: p + p → deuterium + positron + neutrino
• Step 2: deuterium + p → helium-3 + gamma ray
• Step 3: helium-3 + helium-3 → helium-4 + 2p

The energy released during fusion is emitted as electromagnetic radiation, primarily visible light and heat, which travels through space to Earth.

This energy sustains life by providing warmth and enabling photosynthesis in plants.

The Sun's fusion process is extremely efficient and has been ongoing for about 4.6 billion years, with enough hydrogen fuel to continue for several billion more years.

• Energy emitted as light and heat.
• Supports life on Earth.
• Fusion sustains the Sun's energy output over billions of years.

Fusion requires extremely high temperatures to provide particles with enough kinetic energy to overcome electrostatic repulsion between positively charged protons.

High pressure increases the likelihood of collisions between nuclei.

The Sun's core provides these conditions naturally, but replicating them on Earth is challenging and a focus of ongoing research.

• High temperature (~15 million °C) provides kinetic energy.
• High pressure increases collision frequency.
• Conditions are unique to the Sun's core and difficult to reproduce artificially.

Einstein's equation E = mc² explains how a small amount of mass lost during fusion is converted into a large amount of energy.

For example, if the mass defect is 0.007 times the mass of the original hydrogen nuclei, the energy released can be calculated by multiplying this mass by the square of the speed of light.

This principle underlies the enormous energy output of the Sun despite the small mass difference in fusion reactions.

• Mass defect (m) converted to energy (E) by E = mc².
• Small mass loss produces large energy due to c² factor.
• Explains the Sun's powerful energy output.

Nuclear fusion is a nuclear reaction in which two light atomic nuclei combine to form a heavier nucleus. This process releases a large amount of energy because the mass of the resulting nucleus is less than the sum of the original masses. The 'missing' mass is converted into energy according to Einstein's equation E = mc², where E is energy, m is mass, and c is the speed of light (approximately 3.0 × 10⁸ m/s).

Fusion reactions power the Sun and other stars, where hydrogen nuclei fuse to form helium under extremely high temperature and pressure conditions.

• Fusion combines light nuclei to form a heavier nucleus.
• Mass difference converts to energy via E = mc².
• Fusion powers stars like the Sun.

The energy released in fusion comes from the difference in binding energy per nucleon between the reactants and the products. Light nuclei such as isotopes of hydrogen (deuterium and tritium) have lower binding energy per nucleon than helium, so when they fuse, the excess energy is released.

This energy can be harnessed to produce heat, which can then be used to generate electricity through conventional methods such as driving turbines connected to generators.

• Energy release due to difference in nuclear binding energy.
• Fusion of hydrogen isotopes releases significant energy.
• Heat from fusion can drive turbines for electricity generation.

Achieving controlled nuclear fusion on Earth requires replicating the extreme conditions found in stars: very high temperatures (millions of degrees Celsius) and pressures to overcome the electrostatic repulsion between positively charged nuclei.

Two main approaches are being researched: magnetic confinement fusion (e.g., tokamaks) and inertial confinement fusion (using lasers). Maintaining stable plasma and achieving net energy gain (more energy output than input) remain major challenges.

Materials must withstand intense neutron radiation and heat loads, and the process must be sustained safely and economically for practical power generation.

• Fusion requires extremely high temperature and pressure.
• Magnetic and inertial confinement are main research methods.
• Challenges include plasma stability, net energy gain, and material durability.

If successfully developed, fusion power could provide a nearly limitless source of energy from abundant fuels like deuterium extracted from seawater.

Fusion produces no greenhouse gas emissions during operation and generates less long-lived radioactive waste compared to nuclear fission.

Fusion reactors would have a lower risk of catastrophic accidents since fusion reactions are difficult to sustain without precise conditions.

• Abundant fuel supply (e.g., deuterium from water).
• No greenhouse gas emissions during operation.
• Less long-lived radioactive waste than fission.
• Lower risk of runaway reactions or meltdowns.

Experimental fusion reactors such as ITER (International Thermonuclear Experimental Reactor) are under construction to demonstrate the feasibility of fusion power at large scale.

Research continues worldwide to improve plasma confinement, heating methods, and materials.

Commercial fusion power plants are not yet available, but progress is ongoing with the goal of practical electricity generation in the future.

• ITER is a major international fusion experiment.
• Research focuses on plasma control and materials.
• Fusion power plants are still in development stage.

Efficiency is a measure of how well a system converts input energy or power into useful output energy or power.

It is defined as the ratio of useful energy output to total energy input, multiplied by 100% to express it as a percentage.

Alternatively, efficiency can be defined using power, as the ratio of useful power output to total power input, also multiplied by 100%.

• Efficiency = (Useful energy output / Total energy input) × 100%
• Efficiency = (Useful power output / Total power input) × 100%

Energy is measured in joules (J), and power is measured in watts (W), where 1 watt = 1 joule per second.

Efficiency is a dimensionless quantity expressed as a percentage, so it has no units.

Since efficiency is a ratio of output to input, its value ranges from 0% (no useful output) to 100% (perfect conversion with no losses).

• Energy input and output in joules (J)
• Power input and output in watts (W)
• Efficiency expressed as a percentage (%)

Consider an electric motor that consumes 500 J of electrical energy and delivers 400 J of useful mechanical energy.

Using the formula: Efficiency = (Useful energy output / Total energy input) × 100%

Substitute values: Efficiency = (400 J / 500 J) × 100% = 0.8 × 100% = 80%

• Formula: Efficiency = (Useful energy output / Total energy input) × 100%
• Substitution: (400 J / 500 J) × 100%
• Answer: 80% efficient
• Common error: Forgetting to multiply by 100 to convert to percentage

The efficiency formula can be rearranged to find any one of the three variables if the other two are known.

For example, to find useful energy output: Useful energy output = (Efficiency × Total energy input) / 100

To find total energy input: Total energy input = (Useful energy output × 100) / Efficiency

• Useful energy output = (Efficiency × Total energy input) / 100
• Total energy input = (Useful energy output × 100) / Efficiency

No real system is 100% efficient because some energy is always lost to the surroundings, usually as heat, sound, or vibration.

Common causes of energy loss include friction, air resistance, electrical resistance, and heat dissipation.

Improving efficiency involves reducing these losses through better materials, lubrication, insulation, or design improvements.

• Energy lost as heat, sound, or vibration
• Friction and resistance reduce efficiency
• Design improvements can increase efficiency