Energy Resources

Flick a switch and the light comes on. But that electricity had to come from somewhere — and somewhere, at that very moment, something was working to make it. Every joule of usable energy we pour into our homes, factories and phones is drawn from an energy resource: a store in the natural world that we tap to do work for us.

The huge question of our century is which resources to use. Some we can burn today and the sun will refill tomorrow; others took the Earth hundreds of millions of years to make and, once we've burned them, are simply gone. Some are clean; some choke the sky with \text{CO}_2. Some hum away reliably day and night; others sleep when the wind drops. This page is about that choice — and the trade-offs hiding inside it.

Two families: renewable and non-renewable

Every energy resource falls into one of two families, and the dividing line is a single question: will it run out?

Renewable resources are replenished as fast as we use them (or faster), so on any human timescale they won't run out. The sunshine, the wind and the tides keep arriving whether we harvest them or not: solar, wind, hydroelectric (falling water), tidal, wave, geothermal (heat from deep in the Earth) and biomass (wood, crops and other plant matter we grow and burn).
Non-renewable resources exist in a fixed, finite amount that took the Earth an unimaginably long time to lay down. Burn them and the store shrinks; it is not being refilled. These are the three fossil fuels — coal, oil and natural gas — plus nuclear fuel (uranium), which is dug up and used up just like a fuel even though it isn't burned.

Fossil fuels are, quite literally, ancient sunshine: plants and tiny sea creatures that grew in sunlight, died, and were pressed and cooked underground for 300 million years into concentrated stores of chemical energy. That is exactly why they are so finite — we are spending a fortune that took the whole planet aeons to save up, and there is no way to earn it back on any timescale that matters to us.

Nuclear power stations don't set fire to anything. Instead, atoms of uranium are split apart (fission), and the energy locked in the nucleus pours out as heat — a staggering amount from a tiny pellet. So nuclear fuel produces almost no \text{CO}_2, which makes it a powerful low-carbon resource.

But there is only so much uranium ore in the ground, and once an atom has been split it can't be un-split and used again. The store shrinks every year, exactly like coal or oil — so nuclear sits firmly in the non-renewable family. "Low-carbon" and "renewable" are two different questions, and nuclear is a neat reminder that a resource can be one without being the other.

How the electricity is actually made

Here is a fact that surprises almost everyone: nearly every power station on Earth makes electricity in the same way. Coal, gas, nuclear, biomass, hydro, wind, tidal, wave, geothermal — under the bonnet they all do one thing: they spin a turbine, and the spinning turbine drives a generator that pushes out electricity. The whole art is finding something to turn the shaft.

Coal, gas, biomass, nuclear and geothermal all boil water into high-pressure steam, and the steam rushing past the blades spins the turbine. The only difference is the source of the heat — burning coal, burning gas, burning wood, splitting uranium, or hot rock underground.
Wind pushes the blades directly; hydro, tidal and wave use moving water to shove the turbine round. No boiler, no fire — just a moving fluid turning a wheel.

There is one true exception. Solar photovoltaic (PV) panels have no turbine and no moving parts at all: sunlight knocks electrons loose inside the silicon and drives them straight out as an electric current. It is the odd one out — every other resource on the list is, at heart, a clever way to turn a magnet inside a coil.

A generator is a coil of wire near a magnet. Whenever the magnetic field through the coil changes — because the magnet is spinning — a voltage appears across the wire and current flows. That's it. Move a magnet past a wire and you make electricity; spin it thousands of times a minute and you light a city.

So a wind turbine's job isn't really to "make energy" — it's to catch the wind's \text{kinetic energy} and use it to keep a magnet whirling inside a coil. A modern offshore turbine's blades can be longer than a football pitch, and just one can power thousands of homes. The wind does the pushing; physics from the 1830s does the rest.

The trade-offs: comparing the resources

No resource is perfect. Choosing an energy mix means weighing four things against each other: how much carbon it releases, how reliable it is, how quickly it can be switched on, and its wider cost and impact. Read the table across each row and you'll see there is always something to give up.

Resource	Renewable?	\text{CO}_2	Reliable?	Start-up	Main drawback
Coal	No	Very high	Yes (base-load)	Slow	Worst for climate; air pollution
Gas	No	High	Yes	Fast	Still a fossil fuel; finite
Nuclear	No	Very low	Yes (base-load)	Very slow	Radioactive waste; high build cost
Wind	Yes	Very low	No (intermittent)	—	Stops when the wind drops; land/sea use
Solar	Yes	Very low	No (intermittent)	—	Nothing at night or in cloud
Hydro	Yes	Very low	Yes	Fast	Floods valleys; needs the right geography
Tidal / wave	Yes	Very low	Tidal: predictable	—	Expensive to build; few good sites
Biomass	Yes	Medium	Yes	Medium	Burns, so still emits; needs land to grow

Notice the pattern. The fossil fuels are dependable and easy to turn up on demand, but they are finite and they wreck the climate. The renewables are clean and never run out, but the two biggest — wind and solar — are intermittent: they only work when nature cooperates. Nuclear is the unusual one: clean and steady, but non-renewable and painfully slow to build.

Base-load, peak demand, and why start-up time matters

A country's electricity demand is never flat. There is a base-load — the steady minimum being used at 3 a.m. when almost everyone is asleep — and there are peaks, like the surge every evening when millions of kettles and ovens switch on at once. The grid has to match supply to demand minute by minute, or the lights flicker.

This is where start-up time becomes the deciding factor:

Nuclear and coal are slow to warm up and hate being stopped and started, so they are run flat-out around the clock to cover the base-load — the reliable floor under everything.
Gas and hydro can spin up in minutes, so they are the grid's firefighters: held in reserve and fired up to chase the peaks, or to plug the gap the instant the wind drops and the solar fades.
Wind and solar can't be commanded at all — you take their energy when it arrives. That's why a grid leaning heavily on them also needs fast back-up (usually gas today) or big \text{batteries} to store the surplus for later.

So "which resource is best?" has no single answer — the grid needs a mix: cheap clean renewables doing the heavy lifting when nature allows, steady base-load underneath, and something quick on its feet to cover the peaks and the calm, cloudy days.

Have a go: run the grid

You are in charge of a country's power. The coloured bar is your energy mix — the share coming from each resource. Slide the resources up and down and watch two meters respond: the carbon your grid pumps out, and its reliability (how much comes from always-on sources versus the intermittent wind and sun).

Try to make the grid both low-carbon and reliable at once — you'll quickly feel the tension. Pile on the fossil fuels and reliability soars but so does carbon. Go all-in on wind and solar and the carbon collapses, but reliability sags, because on a still, dark evening there's nothing there. A clever mix leans on renewables while keeping some steady base-load underneath.

"Renewable" does not mean "no environmental impact." Renewable only means the resource won't run out. A hydroelectric dam still floods a whole valley; wind farms take up land or sea and can affect birds; making solar panels uses energy and materials. Clean is not the same as harmless — every resource has a footprint.
Low-carbon is not the same as renewable. Nuclear emits almost no \text{CO}_2, yet it is non-renewable because uranium is finite. Don't file it with the renewables just because it's clean.
Electricity is not an energy resource. It's a secondary energy carrier — a convenient way to move energy around after you've made it from a real source (coal, wind, sunlight…). Asking "should we use coal or electricity?" is a category error: the electricity came from a resource. The real question is always which resource made it.

The great shift away from fossil fuels

For over a century, coal and then gas ran the world — they were cheap, concentrated and dependable. But two facts have changed everything: they are finite, and burning them releases \text{CO}_2 that traps heat and warms the planet. So the whole world is now steering, as fast as it can, away from fossil fuels and towards low-carbon resources.

The change is real and quick. Renewables have plummeted in cost — in many places solar and wind are now the cheapest electricity ever built — so grids that once ran almost entirely on coal now draw huge shares from wind and sun. The UK, for instance, went from over half its power from coal to almost none in barely a decade. The engineering puzzle of the next few decades isn't whether to switch, but how to keep the lights on reliably while the mix tips towards resources that come and go with the weather — with storage, smart grids, and a steady low-carbon base-load doing the balancing act.