SPI Physics · Energy Sources
Power Plants and Clean Energy
A power plant changes one form of energy into electrical energy, and a source is clean when using it gives out no smoke, harmful gases or dangerous waste.
Why this matters
Five questions in the bank, four EASY and one MODERATE: the order of energy changes in a nuclear plant, which source is not clean, which pollutes least, why a dam site needs care, and what solar cells are made of. Each is one fact, so the mark goes to whoever knows the drawback of each source.
Concept 1 of 3: The chain of energy changes in each power plant
Almost every power plant ends the same way: something spins a turbine, and the turbine turns a generator that makes electricity. What differs is where the energy starts. Follow it from the start to the wire and you can answer any 'energy transformation' question.
Definition
- In a thermal plant, coal or gas is burnt. Its chemical energy becomes heat, the heat boils water into steam, the steam spins the turbine, and the generator gives electrical energy.
- In a nuclear plant, the fuel (uranium) splits in a reaction called fission. The nuclear energy released comes out as heat, and from there the steps are the same as in a thermal plant.
- In a hydroelectric plant, water stored high behind a dam has potential energy. As it falls it gains kinetic energy, which spins the turbine.
- A solar cell is different: it changes light straight into electricity, with no turbine at all.
| Plant or device | Energy at the start | Chain of changes |
|---|---|---|
| Thermal power plant | Chemical energy of coal | chemical → heat → kinetic (turbine) → electrical |
| Nuclear power plant | Nuclear energy of uranium | nuclear → heat → kinetic (turbine) → electrical |
| Hydroelectric plant | Potential energy of stored water | potential → kinetic → electrical |
| Wind mill generator | Kinetic energy of wind | kinetic → electrical |
| Solar cell | Light energy of the Sun | light → electrical |
Electrical energy is always the LAST link, never the first.
Practice this conceptself-check · 4 quick reps
The same idea in a practice question:
Practice questionEasy
Example 1 · Energy Sources · Power Plants and Clean Energy
In the nuclear power station, the energy transformation occurs as
Putting electrical energy in the middle
Electrical energy is what a power plant delivers, so it is always the last step. Any chain that starts with electrical energy, or turns electrical energy into something else on the way, is wrong.
Skipping the heat step in a nuclear plant
Fission does not make electricity directly. It releases heat, the heat makes steam, and the steam drives the turbine, just as in a coal plant.
Concept 2 of 3: Clean and polluting sources, and the drawback of each
Every source has a cost. Burning coal gives smoke, a nuclear plant leaves dangerous waste, and even a dam floods land. A question on clean energy is really asking which cost you know for each source.
Definition
- A clean source gives out no smoke, no harmful gases and no dangerous waste while making energy. Solar, wind, tidal and hydroelectric energy are clean in this sense.
- Solar energy pollutes least of all: sunlight is used directly, nothing is burnt and nothing is left over.
- Nuclear energy is not clean. It gives no smoke, but it leaves radioactive waste that stays dangerous for thousands of years, and a leak can harm people.
- Thermal power burns coal and gives out smoke, carbon dioxide and other gases.
- Geothermal plants use the heat of hot rocks underground, but they can let out gases such as hydrogen sulphide.
- A hydroelectric dam burns no fuel, but it floods a large area. Forests, farms, homes and the plants and animals of the region are lost, so the site must be chosen with care.
| Source | Clean while making energy? | Main drawback |
|---|---|---|
| Solar | Yes, the least polluting | Weak at night and on cloudy days |
| Wind | Yes | Needs steady strong winds and a lot of land |
| Tidal | Yes | Few coastal sites are suitable |
| Hydroelectric (dam) | Yes, no fuel is burnt | Floods land and harms the plants and animals of the region |
| Geothermal | Mostly | Can release gases such as hydrogen sulphide |
| Nuclear | No | Radioactive waste and the risk of radiation leaks |
| Thermal (coal) | No | Smoke, carbon dioxide and other gases |
No smoke is not the same as clean: nuclear power gives no smoke and is still not clean.
Practice this conceptself-check · 4 quick reps
The same idea in a practice question:
Practice questionModerate
Example 2 · Energy Sources · Power Plants and Clean Energy
Which of the following is not a clean source of energy?
Calling nuclear energy clean because it gives no smoke
A nuclear plant gives out no smoke, but its radioactive waste stays dangerous for thousands of years. That is why nuclear energy is not counted as a clean source.
Saying a dam pollutes the air
A hydroelectric plant burns no fuel, so it does not give out carbon monoxide or carbon dioxide while working. Its real cost is the land and living things lost under the water.
Concept 3 of 3: Solar cells and what they are made of
A solar cell is a thin slice of a special material that gives out electricity when light falls on it. The material is a semiconductor, which is neither a good conductor like copper nor an insulator like glass.
Definition
- A solar cell changes light energy directly into electrical energy.
- It is made of a semiconductor. Silicon is the one used most today; selenium was used in the earliest cells.
- Many cells joined together make a solar panel. Solar cells power satellites, road signs and calculators.
- A solar cell has no moving parts and gives out no pollution, but it makes nothing at night.
| Question | Answer |
|---|---|
| Energy change in a solar cell | Light energy into electrical energy |
| Kind of material | Semiconductor |
| Elements used | Silicon (most common), selenium (earliest cells) |
| Many cells joined together | A solar panel |
| Common uses | Satellites, road signs, calculators |
Practice this conceptself-check · 3 quick reps
The same idea in a practice question:
Practice questionEasy
Example 3 · Energy Sources · Power Plants and Clean Energy
Name any one element which is used in making solar cells.
Picking a familiar metal
Lead and tin are metals, not semiconductors, and are not what solar cells are made of. The elements to remember are silicon and selenium.
Summary — formulas & gotchas at a glance
A revision cheat-sheet for the formulas and gotchas above. Click any concept name to jump back to its full explanation.
Reference tables (3)
The chain of energy changes in each power plant5 rows
| Plant or device | Energy at the start | Chain of changes |
|---|---|---|
| Thermal power plant | Chemical energy of coal | chemical → heat → kinetic (turbine) → electrical |
| Nuclear power plant | Nuclear energy of uranium | nuclear → heat → kinetic (turbine) → electrical |
| Hydroelectric plant | Potential energy of stored water | potential → kinetic → electrical |
| Wind mill generator | Kinetic energy of wind | kinetic → electrical |
| Solar cell | Light energy of the Sun | light → electrical |
Electrical energy is always the LAST link, never the first.
Clean and polluting sources, and the drawback of each7 rows
| Source | Clean while making energy? | Main drawback |
|---|---|---|
| Solar | Yes, the least polluting | Weak at night and on cloudy days |
| Wind | Yes | Needs steady strong winds and a lot of land |
| Tidal | Yes | Few coastal sites are suitable |
| Hydroelectric (dam) | Yes, no fuel is burnt | Floods land and harms the plants and animals of the region |
| Geothermal | Mostly | Can release gases such as hydrogen sulphide |
| Nuclear | No | Radioactive waste and the risk of radiation leaks |
| Thermal (coal) | No | Smoke, carbon dioxide and other gases |
No smoke is not the same as clean: nuclear power gives no smoke and is still not clean.
Solar cells and what they are made of5 rows
| Question | Answer |
|---|---|
| Energy change in a solar cell | Light energy into electrical energy |
| Kind of material | Semiconductor |
| Elements used | Silicon (most common), selenium (earliest cells) |
| Many cells joined together | A solar panel |
| Common uses | Satellites, road signs, calculators |
Watch out for (5)
- Putting electrical energy in the middle→ The chain of energy changes in each power plant
- Skipping the heat step in a nuclear plant→ The chain of energy changes in each power plant
- Calling nuclear energy clean because it gives no smoke→ Clean and polluting sources, and the drawback of each
- Saying a dam pollutes the air→ Clean and polluting sources, and the drawback of each
- Picking a familiar metal→ Solar cells and what they are made of
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