Every energy source we use is a trade-off. Something is cheap but dirty, or clean but only works when the sun shines, or reliable but leaves waste that stays dangerous for thousands of years. This page walks through each source, what it is good at, what it is bad at, and why “renewable” and “sustainable” are not the same word.
📘 What you need to know
Energy sources are split into renewable and non-renewable, based on whether they can be replaced within a human lifespan.
Renewables: wind, solar, tidal, biomass, geothermal, hydropower. Non-renewables: coal, oil, natural gas and nuclear fuel.
Most renewables give off no greenhouse gases while running — biomass is the exception because you burn it.
Every source has a downside. Learn one clear advantage and one clear disadvantage for each.
Sustainable means meeting today’s energy needs without wrecking the ability of future generations to meet theirs.
Renewable does not automatically mean sustainable — building the equipment has its own environmental cost.
What makes a source renewable?
The dividing line is simple, and it is about time. Can nature replace the source as fast as we use it, within a human lifetime? If yes, it is renewable. If no, it is non-renewable.
Wind keeps blowing whether we use it or not. Sunlight arrives every morning. Tides come in twice a day. Nothing we do uses these up. Coal is different: the coal we burn this morning took roughly 300 million years to form, and once it is gone, it is gone for every generation after us.
The test
Renewable = replaced by natural processes within a human lifespan
The split is about replacement speed, not about how clean a source is. Keep those two ideas separate in your head.
A quick check you can do in the exam: ask “will there still be some of this left in 200 years if we keep using it?” Wind, yes. Oil, no. That one question sorts almost every source correctly.
The six renewables at a glance
All six share two big advantages, so learn these once and reuse them: they cut our dependence on fossil fuels and on foreign suppliers, and the industry creates jobs in building, installing and maintaining the kit. After that, each source has its own personality.
Source
How it makes electricity
Biggest plus
Biggest minus
Wind
Moving air spins turbine blades, which drive a generator
Costs have fallen a lot; land underneath still usable for farming
Intermittent — no wind, no power
Solar
Photovoltaic (PV) panels turn sunlight straight into an electric current
Works at any scale, from one roof to a huge farm
Nothing at night; storage needed
Tidal
Rising and falling tides push water through a turbine
Predictable — tide times are known years ahead
Very few suitable sites; harms fish migration
Biomass
Wood and other organic matter is burnt for heat or electricity
Available almost anywhere, especially rural areas
Releases carbon dioxide and air pollution when burnt
Geothermal
Water pumped underground returns as steam and turns a turbine
Works day and night, in all weather
Only possible where hot rock sits near the surface
Hydropower
Water falling through a dam spins turbines
Can be switched up fast to meet a sudden demand spike
Dams flood habitats and displace people
Wind
Large blades catch the kinetic energy of moving air and spin a generator. Turbines can go offshore, out at sea, which keeps them away from houses and gets stronger, steadier wind. The complaints are noise, the look of them, the money needed up front, and birds and bats flying into the blades.
Solar
PV panels have got steadily cheaper and better, and they can be bolted onto buildings that already exist. They are also brilliant in remote places with no grid connection, such as solar street lighting in rural areas. The catch is land: a big solar farm covers ground that could have grown food.
Tidal
Tides are driven by the Moon, so they are the most predictable renewable there is. A tidal barrage traps water at high tide and lets it run back out through turbines. Underwater turbines are almost invisible and last a long time. But sites are limited, building costs are high, and barrages block the routes fish use.
Biomass
Burning wood is called carbon neutral if the trees are replanted, because the new trees soak up roughly the carbon dioxide the old ones released. That “if” is doing a lot of work. If forests are cut faster than they regrow, you get deforestation, habitat loss and a real rise in carbon dioxide.
Geothermal
The Earth’s interior is extremely hot. Water is poured down a shaft, heated by the rock, and comes back up another shaft as steam or hot water. The steam turns a turbine; the hot water can heat homes directly. It runs constantly, which most renewables cannot do, and the power station takes up very little land. The problem is geography: you need hot rock close to the surface, so Iceland can do it easily and most countries cannot.
Hydropower
Water held behind a dam has gravitational potential energy. Let it fall through a turbine and you get electricity, on demand, within minutes. Dams also give flood control and irrigation. But building a reservoir floods the valley behind it, blocks fish migration, and can force whole communities to move. Droughts linked to climate change are now making some reservoirs less reliable too.
Non-renewables: fossil fuels and nuclear
Fossil fuels
There are three: 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 buried and squashed for millions of years.
🤔 Why fossil fuels are really just old sunlight
Plants captured energy from the Sun by photosynthesis and stored it as chemical energy. Animals ate the plants and took on that store. Those bodies were buried, heated and compressed over millions of years into coal, oil and gas. So when you burn petrol, you are releasing sunlight that fell on the Earth before the dinosaurs. That is exactly why it cannot be replaced in a human lifespan — the process that made it takes geological time.
FOSSIL FUELS — ADVANTAGES
Our whole transport and electricity system is already built around them
Readily available day to day
High energy density — a lot of energy per kilogram
Historically reliable for large-scale generation
FOSSIL FUELS — DISADVANTAGES
Carbon dioxide adds to the greenhouse effect
Sulfur dioxide causes acid rain
Oil spills damage marine life over huge areas
Prices swing wildly, and conflicts disrupt supply
Finite — often quoted as running out within about 200 years
Carbon and sulfur can be captured as the fuel burns, so they never reach the atmosphere. The technology exists. It is just expensive, which is the honest reason it is not used everywhere.
Nuclear
Splitting a heavy nucleus in two releases a huge amount of energy. This is nuclear fission. The energy heats water, the steam turns turbines, and you get electricity, exactly like a fossil fuel station except the heat comes from the atom rather than a flame.
Nuclear is low-carbon but non-renewable. There is a finite amount of uranium ore, so it belongs in the non-renewable box even though it barely emits greenhouse gases. It is reliable, it runs on very small amounts of fuel, and it improves energy security. Against that: radioactive waste stays hazardous for thousands of years and is expensive to store safely, an accident can spread contamination over a wide area, and shutting a plant down at the end of its life (decommissioning) costs an enormous amount.
Careful with the wording. “Nuclear produces no pollution” is only true for air pollution during normal operation. It certainly produces waste. Examiners notice the difference.
What sustainability actually means
DefinitionEnergy sustainability = meeting today’s energy demand without reducing the ability of future generations to meet theirs
Two things decide how sustainable a source is: whether it is renewable, and what its environmental impact is. You need both. A source can be renewable and still do damage, which is the point students most often miss.
The environmental cost of non-renewables
Extraction: coal mining and oil and gas drilling destroy habitats, cause soil erosion and contaminate water.
Refining crude oil: releases harmful chemicals and pollutes air and water.
Liquefying natural gas so it can be shipped emits carbon dioxide and other greenhouse gases.
Uranium mining is energy-hungry and leaves radioactive waste behind before a single unit of electricity is made.
Nuclear waste has to be stored safely for thousands of years, which no one has fully solved.
The hidden cost of renewables
Renewables genuinely have a lower impact overall. But “lower” is not “none”, and the costs are hidden because they happen before and after the clean bit in the middle.
This life-cycle view is the single most useful thing to bring into an “evaluate the sustainability of…” question.
Two examples worth memorising:
Wind turbines need rare earth elements such as neodymium for their magnets and motors. At the end of their life the blades are very hard to recycle and often end up in landfill.
Solar panels need mined silicon and rare earths, last around 20 to 30 years, and need careful disposal to avoid chemical pollution.
Tidal barrages disrupt local ecosystems and are huge, expensive structures to build and maintain.
Rare earth elements
Electric vehicles and wind turbines rely on rare earth elements to convert energy efficiently. Getting hold of them is the sustainability weak spot:
Energy-intensive extraction: mining machinery burns a lot of fuel, so the greenhouse gases start before the turbine ever turns.
Water contamination: processing releases toxic chemicals into surface water and groundwater.
Habitat destruction: land is cleared for the mine and its access roads, causing deforestation.
Dust pollution: cutting, drilling and blasting throws up dust, which raises the risk of respiratory disease in nearby communities.
EXAM-STYLE
Outline two reasons why a wind turbine is not completely environmentally friendly. [2]
Point 1 — before it runs
Making a turbine needs rare earth elements such as neodymium. Mining and refining these damages habitats and contaminates water.
Point 2 — after it runs
Turbine blades are very difficult to recycle, so at the end of their life many go into landfill.
2 marks: one impact from manufacture, one from disposalDo not waste the marks on “it kills birds” alone — that is true, but a question about environmental friendliness is really asking about the whole life cycle.
EXAM-STYLE
Explain why biomass is classed as renewable but is still criticised. [3]
Why renewable
Trees regrow within a human lifespan, so the source can be replaced as fast as it is used.
Why criticised
Burning it releases carbon dioxide and air pollutants straight away, unlike the other renewables.
The condition
It is only close to carbon neutral if replanting keeps pace with cutting. If it does not, you get deforestation and habitat loss on top of the emissions.
3 marks: renewable, emits CO₂, only neutral if managedThe word “sustainably managed” is worth a mark on its own here.
💡 Exam tip
Learn one advantage and one disadvantage per source, not six of each. Breadth beats depth in this topic.
Say “during operation” when you claim a renewable produces no greenhouse gases. That one phrase shows you know about manufacturing emissions.
Use named examples. Iceland for geothermal, offshore wind farms, solar street lighting in rural areas — specifics score.
For “discuss sustainability”, always cover both halves: is it renewable, and what is its environmental impact?
Intermittent is the technical word for wind and solar. Use it rather than “unreliable”, which is vaguer.
Geothermal and tidal are the two renewables that are not intermittent. That is a common comparison question.
⚠ Common mix-up
“Renewable means sustainable.” No. Renewable is about running out; sustainable is about total impact including manufacture and disposal.
“Nuclear is renewable because it is low-carbon.” Low-carbon and renewable are different things. Uranium ore is finite, so nuclear is non-renewable.
Forgetting biomass emits carbon dioxide. It is the odd one out among the renewables and gets asked about for exactly that reason.
Mixing up tidal and hydropower. Tidal uses sea tides driven by the Moon; hydropower uses river water held behind a dam.
Saying solar “does not work in winter”. It works, just less well. Say output falls, not that it stops.
Listing advantages with no drawbacks in an evaluate question. Evaluate means both sides plus a judgement.
Up next: Energy Demand and the Choices We Make — why global energy use keeps climbing, and what actually decides which sources a country picks.
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