Almost every energy source we use is sunlight that has been stored in a different way. Some of it arrived this morning, some of it arrived three hundred million years ago. That single difference — how long ago the energy was captured, and how long it takes to replace — is what splits energy sources into renewable and non-renewable.
📘 What you need to know
Energy sources are classed as renewable or non-renewable depending on whether they regenerate within a human lifespan.
Renewables: wind, solar, tidal, biomass, geothermal and hydropower.
Non-renewables: fossil fuels (coal, oil, natural gas) and nuclear (uranium).
Once running, renewables release no greenhouse gases — except biomass, which is burned.
You must be able to give advantages and disadvantages of each source, not just name it.
Energy sustainability means meeting today’s energy demand without stopping future generations meeting theirs.
Non-renewables carry costs at extraction, refining and disposal, not only when burned.
Renewables have hidden costs too: manufacturing, rare earth mining and end-of-life recycling.
The line between renewable and non-renewable
The test is speed of replacement, measured against a human lifetime.
The classification ruleRenewable = regenerates within a human lifespan, so it will not run out Non-renewable = takes far longer than that to form, so supplies are finite
Coal is the clearest case. The energy in a lump of coal is sunlight that was captured by plants, buried, and squeezed for millions of years. Burn it and you release energy that took an unimaginable time to store. Nothing replaces it on any timescale that matters to us, so it is non-renewable.
Wind is the same sunlight, arriving today. The sun heats the air unevenly, air moves, and a turbine takes a share of that movement. Tomorrow the sun does it again.
Tracing each source back to where the energy came from is the fastest way to remember which category it belongs in.
The renewable sources, one by one
You need a sentence on how each one works, plus at least two advantages and two disadvantages. Learn them as pairs — almost every advantage has a matching drawback.
Wind
Moving air turns large blades, the blades turn a generator, and the kinetic energy of the wind becomes electrical energy.
Advantages
Disadvantages
Abundant, and no greenhouse gases or air pollutants while running
Intermittent — no wind, no power
The land underneath can still be farmed, and turbines can go offshore
Visual and noise pollution for people living nearby
Costs have fallen sharply, so it now competes with fossil fuels
High initial capital cost for turbines and grid connections
Works at small scale (one turbine) or large scale (a wind farm)
Birds and bats can be struck by the blades, and farms need a lot of land
Solar
Photovoltaic (PV) panels transfer energy from sunlight into an electrical current.
Advantages
Disadvantages
Abundant, with no emissions or air pollutants during operation
Intermittent — nothing at night, less under cloud
Works at any scale, from one rooftop to a huge solar farm
Needs storage to cover night-time and cloudy days
Can be fitted to existing buildings, and is getting cheaper and more efficient
Solar farms take up land that could grow food
Can power remote places with no grid, such as rural street signs
Manufacturing and disposal create pollution and electronic waste
Tidal
Rising and falling tides push water through a turbine, usually built into a barrage across an estuary. Water is trapped at a height and released through the turbine as the tide turns.
Advantages
Disadvantages
Predictable and reliable — tides follow a known cycle
Very high initial construction costs
No emissions in operation, and large output at short notice
Only a few coastlines have a suitable tidal range
Little visual impact when the turbines sit underwater
Barrages disturb marine ecosystems and block fish migration
Long lifespan with little maintenance needed
Underwater repairs are difficult, and shipping lanes may be affected
🧩
Predictable is not the same as constant
Tidal power is intermittent but predictable: it stops four times a day, and you know exactly when. Wind and solar are intermittent and unpredictable. That distinction is worth a mark in any question about reliability.
Biomass
Organic material, usually wood, is burned to release heat or generate electricity.
Advantages: renewable if replanted, and considered carbon neutral when managed sustainably, because regrowing plants take back the carbon released. Widely available, especially in rural areas.
Disadvantages: it is the one renewable that emits carbon dioxide and air pollutants when burned. If harvesting outpaces replanting it drives deforestation and habitat loss, and indoor burning without ventilation damages health.
Geothermal
The Earth’s interior is extremely hot. Water is pumped down a shaft, heated underground, and returns up a second shaft as hot water or steam. The steam turns a turbine; the hot water can heat homes directly.
Advantages:constant and reliable, available day and night whatever the weather. Small land footprint compared with wind or solar, long plant lifespan and low running costs.
Disadvantages: strictly site-specific — you need geothermal activity near the surface. High drilling and exploration costs, possible release of underground gases, and risks of small earthquakes or ground subsidence.
Hydropower
Water held behind a dam is released through turbines, so the stored gravitational potential energy of the water becomes kinetic energy and then electricity.
Advantages: reliable and predictable, low emissions in operation, long lifespan with low running costs. It can be turned up within minutes to meet a surge in demand, and dams also give flood control and irrigation.
Disadvantages: dams break up river ecosystems and block fish migration, construction costs are enormous, flooding a valley destroys habitat and can displace whole communities, and droughts driven by climate change are making reservoir levels less dependable.
The advantage they all share. Every renewable reduces dependence on fossil fuels and on imported energy, which improves energy independence and security. The industry also creates jobs in manufacturing, installation, operation and maintenance. Those two points fit almost any renewable question.
The non-renewable sources
Fossil fuels
Coal, crude oil (refined into petrol, diesel and other fuels) and natural gas (mostly methane, used in boilers and cookers). All three formed from the remains of plants and animals, and the chemical energy locked inside them originally came from sunlight captured by photosynthesis.
Advantages: existing transport and electricity systems are built around them and they are readily available day to day. They have a high energy density, meaning a lot of energy per kilogram, and they have historically been reliable for large-scale generation.
Disadvantages: they take millions of years to form, so they are finite — current predictions suggest supplies could be exhausted within about 200 years. Rising demand against falling supply pushes prices up, and prices swing sharply. Burning them releases carbon dioxide, which adds to the greenhouse effect, and sulphur dioxide, which causes acid rain. Both can be captured at the point of burning, but doing so is expensive. Oil spills during transport damage marine environments over huge areas, and conflict or political disputes can cut supply off entirely.
Nuclear
Splitting a large nucleus in two — nuclear fission — releases the energy stored inside it. That heat makes steam, the steam turns a turbine, and electricity is generated. Nuclear power is low-carbon and low-emission, but non-renewable, because uranium ore is finite.
Advantages: no polluting gases released into the atmosphere, and reliable large-scale output that can be made available as needed. Only small amounts of uranium are required and reserves are large. It cuts reliance on fossil fuels and improves energy security. Reactors are safe while operating correctly, which is why safety checks and procedures are so strict.
Disadvantages: uranium supplies are finite. The radioactive waste stays hazardous for thousands of years and must be stored safely, which is expensive. An accident can spread radioactive material over a wide area, and decommissioning a plant at the end of its life costs a great deal.
Notice how often “reliable” and “clean” pull against each other. Fossil fuels and nuclear are reliable but carry serious costs; wind and solar are clean but come and go. Almost every energy essay is really about how a country balances those two things — say so, and you are already writing an evaluation.
How sustainable is each source, really?
DefinitionEnergy sustainability = meeting current energy demand without reducing the ability of future generations to meet their own
Sustainability depends on two things: whether the source is renewable, and what environmental damage it causes. A source can be renewable and still do harm, which is where most students lose marks.
The environmental cost of non-renewables
Stage
What it does
Extraction
Mining coal and drilling for oil and gas destroys habitats and causes soil erosion and water contamination
Refining crude oil
Releases harmful chemicals and adds to air and water pollution
Liquefying natural gas
Turning gas into liquid so it can be shipped emits carbon dioxide and other greenhouse gases
Mining uranium
Energy-intensive, and leaves radioactive waste behind at the mine site
Nuclear waste
Remains hazardous for thousands of years, so long-term storage is difficult and costly
The hidden cost of renewables
Renewables have a lower environmental impact overall. Lower is not zero. The damage simply happens at a different point in the life of the equipment.
The blocks are not to scale. The point is the shape: coal does its damage continuously, a turbine does it once at each end.
Manufacturing: building renewable energy devices needs energy and raw materials, and that causes environmental damage before a single unit of clean electricity is produced.
End-of-life management: recycling solar panels, turbine components and batteries is expensive and not always efficient, so waste and pollution result.
Wind turbines: need rare earth elements such as neodymium for magnets and motors, and the blades are difficult to recycle, so many end up in landfill.
Solar panels: production needs mined silicon and rare earth elements, and panels last only 20 to 30 years before needing careful disposal to avoid chemical pollution.
Tidal barrages: large, expensive to build and maintain, and they disrupt the ecosystems of the estuaries they are built across.
Rare earth elements: the problem behind the problem
Wind turbines and electric vehicles rely on rare earth elements for efficient energy conversion, and these are difficult to mine and refine.
Energy-intensive extraction: mining machinery uses a lot of energy, which itself produces greenhouse gases.
Water contamination: processing releases toxic chemicals into nearby surface water and groundwater.
Habitat destruction: clearing land for mines and access roads destroys ecosystems and causes deforestation.
Dust pollution: cutting, drilling and blasting throws up dust that settles across the surrounding area, raising the risk of respiratory disease in nearby communities.
Who carries the cost? The mining usually happens in one country and the clean electricity is enjoyed in another. When a question asks you to evaluate how sustainable renewable energy is, that gap between where the damage lands and where the benefit lands is one of the strongest points you can make.
Worked examples
WE 1
Distinguish between renewable and non-renewable energy sources
Distinguish between renewable and non-renewable energy sources, using examples. (3 marks)
Point 1: the rule
Sources are classified by whether they can regenerate within a human lifespan.
Point 2: renewable
Renewables will not run out on that timescale, for example wind, solar, tidal, geothermal, hydropower and biomass.
Point 3: non-renewable
Non-renewables took millions of years to form or exist in finite reserves, so they will eventually run out — coal, oil, natural gas and uranium.
The test is the rate of replacement, not whether it is dirty or cleannuclear catches people out: low-carbon, but still non-renewable
WE 2
Evaluate the use of wind power in a coastal region
Evaluate the use of wind power to supply electricity to a coastal region. (4 marks)
For: emissions
No greenhouse gases or air pollutants during operation, and it reduces dependence on imported fossil fuels, improving energy security.
For: practicality
Coastal and offshore sites have strong, steady wind; land beneath turbines can still be farmed, and costs have fallen enough to compete with fossil fuels.
Against: reliability and cost
Output is intermittent, so storage or a backup supply is needed, and the initial capital cost is high.
Against: local impacts
Visual and noise pollution affect residents, birds and bats are struck by blades, and turbines need rare earth metals plus blades that are hard to recycle.
Suitable here, provided storage covers the still days“evaluate” needs both sides plus a judgement at the end — an unbalanced answer caps at half marks
WE 3
Explain why renewable energy is not automatically sustainable
Explain why renewable energy devices may be less sustainable than they first appear. (3 marks)
Point 1: manufacturing
Producing the devices needs energy and raw materials, including mined rare earth elements such as neodymium, causing emissions and habitat damage.
Point 2: mining impacts
Rare earth extraction contaminates water with toxic chemicals, destroys habitat and creates dust pollution that harms nearby communities.
Point 3: end of life
Recycling panels, blades and batteries is expensive and inefficient, so turbine blades and 20 to 30 year old solar panels become waste.
Clean while running, but not clean across the whole life cycleexaminers specifically warn against assuming renewable automatically means green — this is the answer they want
💡 Exam tips
Define the categories by regeneration within a human lifespan, not by pollution.
Learn two advantages and two disadvantages for each of the six renewables plus fossil fuels and nuclear.
Use the right word: intermittent for wind and solar, predictable for tidal, constant for geothermal.
Say “no emissions during operation” — the extra three words show you know about the life cycle.
Remember biomass is the renewable that does emit carbon dioxide when burned.
For sustainability questions, cover extraction, manufacturing, operation and disposal.
⚠ Common mix-ups
Calling nuclear renewable. It is low-carbon, but uranium is finite.
Saying renewables produce no emissions at all. Manufacture and transport of the equipment do.
Treating biomass as emission-free. It is carbon neutral only if what is harvested is replanted.
Confusing intermittent with unreliable. Tidal stops regularly, but you know exactly when.
Forgetting hydropower’s social cost. Reservoirs can displace entire communities.
Listing advantages with no drawbacks. Evaluate questions need both sides.
Up next: Energy Demand and the Choices We Make. You now know what each source can do. The next question is why the world still runs mostly on the dirtiest of them, and what actually decides a country’s energy mix.
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