Energy sources—uses and management

Fossil fuels are non-renewable energy sources formed from ancient organic matter over millions of years, including coal, oil, and natural gas.

They are finite (non-renewable on human timescales) and cause major environmental impacts, especially climate change and air pollution.

Extraction can cause habitat destruction (mines, drilling sites, pipelines) and water pollution (oil spills, fracking contamination, acid mine drainage).

Greenhouse gas emissions (mainly CO2) driving climate change.

Coal, oil (petroleum), and natural gas.

Oil is most associated with transport because it is refined into petrol, diesel, and jet fuel and is highly energy-dense and portable.

Sulfur dioxide (SO2) which causes acid rain, and nitrogen oxides (NOx) which contribute to smog; particulates are also important.

Coal is generally most polluting because it has high carbon content and produces more CO2 and air pollutants (SO2, particulates, mercury) per unit of energy.

Combustion releases CO2 (climate change) and air pollutants such as SO2/NOx/particulates (acid rain, smog, respiratory disease).

It produces less CO2 and far fewer SO2/particulates than coal when burned, though methane leakage during extraction can reduce its climate advantage.

Peak oil is the point when global oil production reaches its maximum and then begins to decline as reserves become harder to extract.

Methane is a potent greenhouse gas; leaks during extraction and transport can offset the lower CO2 emissions from burning gas compared to coal.

Use consistent criteria such as GHG emissions, air pollution, water use, land use, reliability, cost, and impacts across the life cycle.

EROI is energy output divided by energy input. As easy reserves are depleted, EROI tends to decline (more effort/energy needed per unit gained).

Common questions include comparing fossil fuels by impacts, explaining why fossil fuel use is unsustainable, and describing trends in energy consumption from data.

Renewable energy is energy from sources that are naturally replenished on human timescales. Examples include solar power and wind power.

Hydroelectric power uses flowing or falling water to spin turbines, converting kinetic energy into electrical energy, usually in a dam or run-of-river system.

Solar and wind are intermittent sources because their output varies with sunlight and wind speed.

PV converts sunlight directly into electricity using semiconductors, while CSP uses mirrors to concentrate sunlight to heat a fluid and generate electricity via turbines.

Solar: intermittent; Wind: intermittent; Hydro: ecosystem disruption and site limits; Geothermal: location-limited; Biomass: sustainability and air pollution concerns (any three with a correct limitation).

Large dams can flood habitats, block fish migration, and displace communities; reservoirs can also produce methane from decomposing organic matter.

Hydro (with reservoirs), geothermal, and biomass are commonly considered more reliable/baseload compared with solar and wind.

Because heat from Earth’s interior is continuously available, allowing steady electricity generation or direct heating independent of daily weather conditions.

Advantage: no greenhouse gas emissions during operation and widely available. Disadvantage: intermittent supply (no sun at night) so storage or backup is needed.

Advantage: low emissions during operation and relatively cheap. Disadvantage: intermittent output and potential impacts such as visual/noise concerns or bird/bat mortality.

Large hydro can flood habitats, disrupt river ecosystems, block fish migration, and displace communities, so its environmental and social costs can be high.

Geothermal power is location-limited to regions with accessible heat (often near tectonic boundaries) and can have issues such as gas release (e.g., H2S) or induced seismicity.

Compare energy sources using consistent criteria such as greenhouse gas emissions, reliability, cost, land use, water use, and impacts on biodiversity.

Biomass is only carbon-neutral if new plant growth absorbs as much CO2 as is released when the biomass is burned; if biomass causes deforestation or regrowth is slow, net emissions can be high.

Because solar and wind are intermittent: solar output depends on sunlight and wind output depends on wind speed, so supply does not always match demand without storage or backup generation.

Nuclear fission is the splitting of a heavy atomic nucleus (such as uranium-235) into smaller nuclei, releasing energy and additional neutrons.

Advantages include low greenhouse gas emissions during operation and reliable baseload electricity generation (high capacity factor).

Most current fission reactors use enriched uranium, especially uranium-235 (or fuel that produces plutonium-239 in some designs).

It can run continuously at high output regardless of weather, providing a steady electricity supply.

Fission releases heat, which boils water into steam; the steam turns turbines connected to generators, producing electricity. Control rods and moderators help control the chain reaction.

Disadvantages include long-lived radioactive waste and the risk of severe accidents; high construction and decommissioning costs are also major issues.

Key concerns include radioactive waste management and the risk of severe accidents; high costs and proliferation risk are also common concerns.

Because it generates electricity with very low direct greenhouse gas emissions during operation, helping reduce CO2 from fossil-fuel electricity.

A chain reaction occurs when neutrons released by one fission event trigger further fission in other nuclei, sustaining energy release; in reactors it is kept controlled.

A small mass of nuclear fuel releases a very large amount of energy compared with fossil fuels, so little fuel produces lots of electricity.

Proliferation risk is the possibility that nuclear technology, materials, or expertise could be diverted to develop nuclear weapons.

Because nuclear is low-carbon like renewables but differs due to finite fuel and radioactive waste, so evaluating trade-offs is a common exam theme.

High-level radioactive waste can remain hazardous for thousands of years, requiring secure storage and management over very long time periods.

Technocentric perspectives are more likely to support nuclear because they emphasise technological solutions and value reliable low-carbon power.

It is low-carbon because it produces no direct CO2 during operation, but it is non-renewable because uranium is finite and can be depleted.

Technocentric EVSs often support large-scale technology solutions such as nuclear power and CCS, while ecocentric EVSs emphasise demand reduction, efficiency, and small-scale distributed renewables.

Common criteria include greenhouse gas emissions, air pollution, water use, land use, reliability (capacity factor), cost, scalability, and EROI (any five).

You can evaluate energy sources using criteria such as emissions, pollution, reliability, cost, land use, water use, EROI, feasibility, and scalability (any four).

Challenges include intermittency of solar/wind requiring storage, and the need to upgrade grid infrastructure to manage variable supply and new demand patterns.

EROI (energy return on investment) is the ratio of energy output to energy input for an energy source. Higher EROI generally indicates a more efficient source.

Because all energy sources involve trade-offs across environmental, economic, and social criteria, so choices require balancing competing priorities.

Technocentric: nuclear power or CCS. Ecocentric: demand reduction/efficiency and small-scale renewables.

Because impacts occur across extraction, construction, operation, and decommissioning. Lifecycle analysis compares total emissions and impacts, not just operation.

Stranded assets are fossil-fuel infrastructure or reserves that lose economic value as policies and markets shift toward low-carbon energy.

They are reliable, scalable, and often cheap, but they perform poorly on greenhouse gas emissions and air pollution and are non-renewable.

Examples include carbon pricing (tax or cap-and-trade), renewable energy targets/subsidies, fossil fuel subsidy reform, and investment in R&D (any two).

Barriers include intermittency and storage needs, grid upgrades, high upfront costs, political resistance, and infrastructure lock-in (any two).

Because vested interests, infrastructure lock-in, costs, public acceptance, and lifestyle expectations influence how quickly and fairly energy systems can change.

Some renewables (especially large solar or wind farms) require large areas or specific sites, which can compete with other land uses and impact habitats, even if emissions are low.

Define sustainability and criteria, compare multiple sources using the same criteria, link preferences to EVSs, then conclude with a balanced justified energy mix.