Energy resources, but bitesize.

Part 1Energy resources

Everything we do — heating homes, running cars, charging phones — needs energy. We get that energy from energy resources: the raw materials and natural sources we tap into to release useful energy.

The main ones you need to know are fossil fuels (coal, oil and natural gas), nuclear fuel, and the renewables: wind, solar, hydroelectric, tidal, geothermal and biomass. Right now, most of the world's energy still comes from burning fossil fuels.

Part 2What are fossil fuels?

The three fossil fuels are coal, oil (crude oil) and natural gas. They are called "fossil" fuels because they formed from the remains of living things — dead plants and tiny sea creatures — that were buried millions of years ago.

Over millions of years, heat and pressure from the rock above squashed and cooked those remains into coal, oil and gas. The energy locked inside them originally came from the Sun, captured by those plants and creatures when they were alive. When we burn a fossil fuel, we are releasing ancient, stored sunlight.

Because they take millions of years to form, fossil fuels are finite — once we have used them, they are gone on any human timescale. We say they are non-renewable: they are being used up far faster than they can ever be replaced.

Part 3Why burning them is a problem

When we burn a fossil fuel, the carbon inside it joins with oxygen from the air and releases carbon dioxide (CO₂). Carbon dioxide is a greenhouse gas — it traps heat in the atmosphere, and releasing more of it is causing climate change (global warming).

Burning fossil fuels also releases other pollutants, such as sulfur dioxide (which causes acid rain) and tiny soot particles that harm our lungs. So fossil fuels are useful and reliable, but using them comes at a real cost to the environment.

Part 1The power-station recipe

Most power stations work in almost exactly the same way, whatever fuel they use. Coal, gas and nuclear stations all follow the same chain — only the way they make the heat is different.

Here is the recipe. A fuel is burned (or nuclear fuel releases energy) to heat water. The water boils into high-pressure steam. The steam rushes past the blades of a turbine and makes it spin. The spinning turbine turns a generator, which produces electricity. The electricity then travels out along the National Grid to homes and businesses.

fuel → heat → water → steam → turbine → generator → electricity

Part 2Electricity is generated, not dug up

This is the key idea, and it trips a lot of people up. Electricity is not a fuel and it is not an energy resource. You cannot dig up electricity or drill for it. It has to be generated from an energy resource — by spinning a generator.

So coal is a fuel; electricity is what we make from it. The same is true of wind: the wind is the resource, and a wind turbine generates electricity from it. Whenever you describe the process, get the chain the right way round: resource → generator → electricity.

Part 1Two groups of resources

Energy resources split into two groups. Renewable resources will not run out — they are replaced as fast as we use them (or faster). Non-renewable resources are finite — once used, they are gone.

The renewables are: wind, solar (the Sun), hydroelectric (falling water in dams), tidal (the rise and fall of the sea), geothermal (heat from inside the Earth) and biomass (burning plants or plant waste, which can be re-grown).

The non-renewables are the fossil fuels (coal, oil, gas) and nuclear fuel. Nuclear is not a fossil fuel, but its fuel (uranium) is still mined and finite, so it counts as non-renewable.

Part 2Weighing up pros and cons

No single resource is perfect — each is a trade-off. A fair comparison looks at several things: how much it costs to build and run, how reliable it is (can we use it whenever we want?), how much carbon dioxide it produces, and its impact on land and views.

Fossil fuels are cheap and very reliable, but release lots of CO₂. Renewables release little or no CO₂ while running, but many depend on the weather (no wind, no sun, no power) and can take up a lot of land or change the landscape. The table below sums it up.

Part 1Power ratings

Every electrical appliance has a power rating — how much energy it transfers each second. It is measured in watts (W) or kilowatts (kW), where 1 kW = 1000 W. The bigger the power rating, the more energy the appliance uses every second it is switched on.

A phone charger might be 5 W. A laptop, about 50 W. A kettle is a big one — often 2 to 3 kW. A typical fridge runs at about 100 W but is on all day. You will often need to convert: divide watts by 1000 to get kilowatts (so 2000 W = 2 kW).

Part 2The kilowatt-hour (kWh)

Joules are tiny, so they are awkward for an electricity bill — a single kettle boil is hundreds of thousands of joules. Instead, energy companies use a bigger unit of energy: the kilowatt-hour (kWh), sometimes called a "unit".

One kilowatt-hour is the energy used by a 1 kW appliance running for 1 hour. To find the energy used in kilowatt-hours, multiply the power (in kW) by the time (in hours):

energy (kWh) = power (kW) × time (hours)

So a 2 kW heater on for 3 hours uses 2 × 3 = 6 kWh. Easy — as long as the power is in kW and the time is in hours.

Part 3Working out the cost

The electricity company charges a fixed price for each kilowatt-hour. To find the cost of running an appliance, first work out the energy it uses in kWh, then multiply by the price per kWh:

cost = energy used (kWh) × price per kWh

Use the FIFA method to lay it out cleanly — Formula, Insert the numbers, Fix any units (get power into kW and time into hours), Answer with the unit (£ or p).

Part 1Energy flows hot to cold

Put a cold spoon into a hot cup of tea and the spoon warms up while the tea cools down. Energy always flows from the hotter object to the cooler one — never the other way round.

This continues until both objects reach the same temperature. At that point there is no temperature difference to drive the flow, and the energy stops moving (overall). We say the two objects have reached thermal equilibrium.

Part 2Three ways heat travels

Energy can travel from a hotter place to a cooler place in three ways:

Conduction — through solids. The particles vibrate and pass the energy on to their neighbours, like a row of dominoes. Metals are especially good conductors.

Convection — in liquids and gases. Warm fluid rises (it is less dense), cool fluid sinks to take its place, and this sets up a circulating convection current.

Radiation — by invisible infrared waves. This needs no particles at all, which is how the Sun's energy reaches us across empty space.

Part 3Insulation & keeping homes warm

We cannot stop energy flowing from hot to cold, but we can slow it down. That is what an insulator does — it is a poor conductor of heat, so energy escapes through it much more slowly.

Homes lose heat to the colder outside, so we insulate them to keep that energy in. Loft insulation and cavity wall insulation use trapped air (a great insulator) to slow conduction. Double glazing traps air or gas between two panes of glass. All of this cuts the energy needed for heating — saving money and reducing the fuel we burn.