Energy resources | IB MYP Physics notes

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Almost every way we generate electricity turns a turbine. What differs is what turns it — steam from burning coal, falling water, wind, or the heat of the Earth — and those differences decide the cost, the reliability and the damage to the planet.

🎯What you need to be able to do

Distinguish renewable from non-renewable energy resources.
Describe how a thermal power station generates electricity.
Explain how hydroelectric, wind, solar, geothermal, tidal and biofuel resources work.
Compare resources on reliability, cost, efficiency and environmental impact.
Calculate the fuel needed from the power output and efficiency of a power station.

♻️Renewable and non-renewable

A non-renewable resource is used up faster than it can be replaced: the fossil fuels (coal, oil and natural gas, formed over millions of years from buried organisms) and nuclear fuel (uranium). A renewable resource is replaced naturally as fast as we use it: sunlight, wind, flowing water, waves, tides, geothermal heat and biofuels from plants.

Almost all of these trace back to the Sun. Fossil fuels and biofuels store energy that plants captured by photosynthesis; wind and waves are driven by the Sun heating the Earth unevenly; rain that fills dams was lifted by evaporation. The exceptions are nuclear, geothermal (heat from radioactive decay inside the Earth) and tidal (the Moon’s gravity).

🏭How a thermal power station works

Block diagram of a thermal power station: fuel is burned in a boiler, which turns water into high-pressure steam; the steam spins a turbine, which turns a generator, which sends electricity through a transformer to the national grid. A cooling tower condenses the steam back to water, releasing waste heat. — Chemical (or nuclear) store → thermal store of steam → kinetic store of the turbine → electrical transfer.

Fuel is burned (or, in a nuclear station, uranium nuclei split) to heat water in a boiler.
The water becomes high-pressure steam, which spins a turbine.
The turbine turns a generator, which induces a voltage by electromagnetic induction (Topic 15).
A transformer steps the voltage up for the national grid.
The steam is condensed back to water in cooling towers or by sea water. This step wastes over half the input energy as heat, so a coal station is only about 35% efficient.

🌬️The other resources

Resource	How it works	For	Against
Coal, oil, gas	burned to make steam (gas can also drive a turbine directly)	reliable, on demand; existing infrastructure	CO₂ (climate change), SO₂ (acid rain), particulates; will run out
Nuclear	fission of uranium heats water	no CO₂ in operation; huge output from little fuel; reliable	radioactive waste for thousands of years; accident risk; expensive to build and decommission
Hydroelectric	water from a dam falls through turbines	no fuel cost; fast response to demand; can store energy	floods valleys and villages; disrupts rivers and fish
Wind	wind turns the blades of a turbine	no fuel, no emissions in use	intermittent; visual and noise impact; needs many turbines
Solar photovoltaic	solar cells convert light directly to electricity	no moving parts; works on rooftops and in remote islands	nothing at night; output falls with cloud; around 20% efficient
Geothermal	hot rock heats water to steam underground	reliable, runs day and night	only in volcanic regions; can release gases
Tidal and wave	moving sea water turns turbines	tides are predictable	few suitable sites; harms estuary habitats; costly
Biofuel	plant material or biogas is burned	roughly carbon-neutral if replanted	uses land that could grow food; can drive deforestation

Indonesia is a good case study because it has nearly all of them: large coal reserves, some of the world’s biggest geothermal potential along its volcanic arc, hydroelectric rivers in Sumatra and Sulawesi, strong sunshine, and palm-oil biodiesel — with the deforestation debate that comes with it.

✏️Worked example: how much coal?

A coal-fired power station delivers 600 MW of electrical power with an efficiency of 35%. Coal releases 24 MJ of energy per kilogram. How much coal does it burn each second, and each day?

1. Input power. Efficiency = output ÷ input, so \[ P_{\text{in}} = \frac{600}{0.35} = 1714\ \text{MW} \]

2. Coal per second. 1714 MW = 1714 MJ every second: \( 1714 \div 24 = 71.4 \) kg/s.

3. Coal per day. \( 71.4 \times 86\,400 = 6.2 \times 10^{6} \) kg — about 6200 tonnes, or roughly a hundred railway wagons, every day.

Sanity check: the waste heat is 1714 − 600 = 1114 MW — almost twice the useful output, which is why power stations need rivers, the sea or cooling towers beside them.

The trap: multiplying by the efficiency instead of dividing. The input must be bigger than the output, so divide by 0.35.

🌎Science in context: the energy trilemma

Energy planners talk about a “trilemma”: electricity should be secure (always available), affordable and sustainable, and no single resource achieves all three. Solar is sustainable but not available at night without storage; coal is cheap and reliable but drives climate change. In a Criterion D response, name the trade-off explicitly and reach a judgement for a specific place — a remote island, a big city — rather than for “the world”.

🧠Quick check

1. Name two renewable resources that do not depend on the Sun.

Geothermal (heat from inside the Earth) and tidal (driven by the Moon’s gravity).

2. Why is a thermal power station only about 35% efficient?

Most of the energy is lost as heat when the steam is condensed back to water (and some in the boiler flue gases and by friction). That waste heat cannot be turned into electricity.

3. Give one advantage of hydroelectricity over wind power.

It can be switched on within minutes whenever demand rises, and the dam stores energy; wind only generates when the wind blows.

4. Why can biofuels be described as "carbon neutral", and why is that claim questioned?

The CO₂ released on burning was absorbed from the air by the plants as they grew. But fertiliser, transport and processing emit extra CO₂, and clearing forest to plant crops releases a great deal.

5. A 2.0 MW wind turbine produces on average 30% of its maximum. How much energy does it deliver in a day?

Average power = 0.6 MW; energy = 0.6 × 10⁶ × 86 400 = \( 5.2 \times 10^{10} \) J.

6. Suggest why solar panels suit remote Indonesian islands.

Strong sunshine all year; no fuel has to be shipped in; small systems can be installed without connecting to a national grid.

📝Worksheet

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