Energy Resources

Everything a modern society does — heating homes, lighting streets, running factories, charging phones, moving trains — needs a supply of energy, and that energy has to come from somewhere. The natural sources we draw on are called energy resources, and one of the biggest global challenges of our time is choosing which of them to rely on. Some, like coal and oil, are being used up far faster than they form and release harmful gases; others, like the wind and the Sun, will never run out but cannot always be relied on to deliver power exactly when it is needed. This lesson sorts energy resources into renewable and non-renewable, weighs each against the others on reliability, environmental impact, cost and start-up time, and examines the trade-offs a country must balance.

By the end of this lesson you should be able to name the main renewable and non-renewable energy resources, explain what "renewable" means, compare resources in terms of their reliability, environmental impact and cost, and discuss the trade-offs involved in choosing an energy mix.

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Renewable and Non-renewable Resources

An energy resource is described as renewable if it is replenished (refilled) as fast as it is used, so it will not run out on any human timescale. A resource is non-renewable if it is being used up much faster than it forms, so the supply is finite and will eventually be exhausted.

Non-renewable resources:

• Coal, oil and (natural) gas — the three fossil fuels. They formed over hundreds of millions of years from the remains of dead organisms and are burnt to release energy. Once used, they are gone on any practical timescale.
• Nuclear fuel (uranium) — not a fossil fuel, but still non-renewable, because the supply of uranium ore is finite.

Renewable resources:

• Solar — energy from the Sun, captured by solar cells (electricity) or solar heating panels (hot water).
• Wind — moving air turns the blades of wind turbines.
• Hydroelectric (hydro) — water stored behind a dam falls through turbines.
• Tidal — the rise and fall of the tides drives turbines in a tidal barrage.
• Wave — the up-and-down motion of waves at sea generates electricity.
• Geothermal — heat from hot rocks deep underground heats water to make steam.
• Bio-fuel — fuels such as wood, biogas or ethanol grown from plants (or animal waste); the carbon dioxide released was recently absorbed by the plants, so they are broadly carbon-neutral over their life cycle.

The distinction between renewable and non-renewable comes down to a simple question of timescales: is the resource being replaced as fast as we use it? Sunlight, wind, waves and tides are constantly renewed by natural processes, so no matter how much we use today there is just as much available tomorrow — they are renewable. Fossil fuels, by contrast, did form from natural processes, but processes that took hundreds of millions of years, so on any human timescale they are effectively a one-off inheritance that cannot be replaced once spent. Bio-fuels are an interesting case that shows why the timescale is what matters: a crop grown for fuel can be regrown within a single year, so it counts as renewable, and because the growing plants absorb roughly as much carbon dioxide as is later released when the fuel is burnt, bio-fuels are also broadly carbon-neutral. Keeping this "rate of replacement" idea firmly in mind will help you classify any resource correctly, and will stop you from making the very common error of assuming that "low-carbon" and "renewable" mean the same thing.

Exam Tip: "Renewable" does not mean "clean" or "free" — it means the resource is replenished as fast as it is used. Nuclear power produces very little carbon dioxide but is still non-renewable because uranium is a finite resource.

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Comparing Energy Resources

Choosing an energy resource means weighing several factors against one another. No single resource wins on every count, which is why countries use a mix of resources. The main factors are reliability, environmental impact, cost and start-up time.

Resource	Renewable?	Reliability	$\text{CO}_2$CO2​ emissions	Other environmental impact	Start-up time
Coal	No	Reliable	High	Sulfur dioxide (acid rain); mining scars land	Slow
Oil/Gas	No	Reliable	High (gas lower than coal)	Oil spills; extraction impacts	Gas fast; oil slower
Nuclear	No	Very reliable	Very low	Radioactive waste; risk of accidents	Very slow
Solar	Yes	Unreliable (no Sun at night/cloud)	Very low in use	Land use for large solar farms	Fast
Wind	Yes	Unreliable (needs wind)	Very low in use	Visual/noise impact; hazard to birds	Fast
Hydro	Yes	Reliable	Very low in use	Flooding valleys destroys habitats	Slow to build
Tidal	Yes	Predictable (follows tides)	Very low in use	Barrage damages estuary habitats	Slow to build
Wave	Yes	Fairly unreliable	Very low in use	Can obstruct shipping	Moderate
Geothermal	Yes	Reliable	Very low	Limited to volcanic regions	Slow
Bio-fuel	Yes	Reliable (fuel can be stored)	Broadly carbon-neutral	Land used for fuel not food	Moderate

Reliability

A reliable resource can deliver energy whenever it is needed. Fossil fuels, nuclear and geothermal are reliable because the fuel or heat is always available. Solar and wind are unreliable (often called intermittent) because they depend on the weather and time of day — no electricity from solar cells at night, and none from turbines on a still day. Tidal power is unusual: it is intermittent but predictable, because the tides follow a known timetable even though power is only generated as the water flows.

Environmental Impact

Burning fossil fuels releases carbon dioxide, a greenhouse gas that contributes to climate change; coal and oil also release sulfur dioxide, which causes acid rain. Nuclear power emits almost no carbon dioxide but produces radioactive waste that must be stored safely for a very long time, and carries a small risk of a serious accident. Renewables produce very little carbon dioxide in use, but they are not impact-free: hydroelectric dams flood valleys and destroy habitats, wind turbines can be considered noisy or unsightly and are a hazard to birds, and tidal barrages can damage the mudflats that wading birds feed on.

Cost and Start-up Time

Cost has two parts: the set-up (capital) cost of building the power station, and the running cost of fuel and maintenance. Renewables such as wind and solar have a high set-up cost but a very low running cost because the "fuel" (wind or sunlight) is free. Fossil-fuel stations are cheaper to build but have ongoing fuel costs. Nuclear stations are extremely expensive to build and, at the end of their life, expensive to decommission (safely dismantle).