Section 1 of 9The Sun as the main energy source
1
Almost all energy resources are driven by the Sun, which transfers energy by electromagnetic radiation produced by nuclear fusion.
2
The energy warms the atmosphere and oceans, evaporates water, drives the winds and is captured by plants in photosynthesis.
3
Fossil fuels are remains of ancient plants and animals that stored the Sun's energy.
4
Resources that do not depend on the Sun are nuclear fission, geothermal and tidal energy.
5
Renewable resources are replaced as fast as they are used and non-renewable resources have a finite supply.
6
Solar and wind energy are renewable.
Section 2 of 9Solar cells and panels
1
Solar cells (photovoltaic cells) convert light energy directly into electrical energy.
2
Many cells joined together form solar panels that supply homes, calculators, satellites and remote devices.
3Solar heating panels are different
- Solar heating panels are different sunlight heats water flowing through pipes in a dark panel, transferring energy to the thermal store of the water.
4Power produced
Power produced intensity × area × efficiency.
- Intensity at the ground on a clear day can reach about 1000 W/m², but the daily average is much lower.
Section 3 of 9Solar energy — advantages and disadvantages
| Advantages | Disadvantages |
|---|---|
| Renewable | Output depends on weather and is zero at night |
| No fuel cost | Large areas are needed for large power |
| No carbon dioxide or pollutant gases in operation | High initial cost per unit of power |
| Useful in remote places with no grid | Manufacture uses energy and materials |
| Long life and low maintenance | Storage for night use needs batteries |
Section 4 of 9Wind energy
Uneven heating of the air by the Sun creates wind.
Energy chain
- Energy chain kinetic energy of moving air, then kinetic energy of the turbine blades, then electrical energy from the generator.
The wind turns the blades, and the rotating shaft drives a generator.
Power rises rapidly with wind speed because the kinetic energy of air depends on v² and the volume of air arriving each second is proportional to v.
Longer blades sweep a larger area and capture more energy.
Section 5 of 9Wind energy — advantages and disadvantages
| Advantages | Disadvantages |
|---|---|
| Renewable | Works only when the wind is at a suitable speed |
| No fuel cost | Noise and visual impact |
| No emissions in operation | Can harm birds |
| Can be built offshore or on hills | High building cost |
| Land between turbines can still be farmed | Energy cannot easily be stored |
Section 6 of 9Reliability and the energy mix
1
Solar and wind output changes with weather and time of day, so they are intermittent.
2
Other sources or storage are needed to cover calm or dark periods.
- Gas power stations can be switched on quickly.
- Pumped storage saves energy as gravitational potential energy.
3
A mix of sources lowers the risk of shortages.
4
Compare resources by reliability, cost, environmental impact and whether they are renewable.
Section 7 of 9More from the specification
More from the specification
Solar Energy as the Primary Energy Source
- Most renewable energy resources on Earth—including wind, waves, biofuels,
- and hydroelectric power—originate from solar radiation driving atmospheric winds and the hydrologic water cycle.
Hydroelectric and Tidal Power Generation
- In a hydroelectric power station, gravitational potential energy of stored reservoir water drives turbines connected to electrical generators without emitting greenhouse gases or sulfur dioxide.
Environmental Comparison of Fossil Fuels and Renewables
- Burning fossil fuels releases sulfur dioxide and carbon dioxide (a greenhouse gas that traps thermal radiation to contribute to global warming),
- (causing acid rain)
- whereas solar and wind power do not emit atmospheric pollutants.
Solar Photovoltaic vs Solar Thermal Systems
- Solar photovoltaic cells directly convert incident solar light into electrical current,
- while solar thermal collectors absorb radiation to heat water into steam to heat domestic supplies or generate electricity.
Hydroelectric
- Electricity from water flowing down from a high reservoir.
Biofuel
- Fuel made from recently living plant or animal material.
Global warming
- Rise in the average temperature of the Earth.
Hydroelectric power
- Electricity generated from water flowing down from a reservoir.
Section 8 of 9Key terms
| Term | Meaning |
|---|---|
| Renewable | A resource replaced as fast as it is used. |
| Non-renewable | A resource that will run out because it is not replaced quickly. |
| Solar cell | Device that converts light energy directly into electrical energy. |
| Wind turbine | Machine in which wind turns blades that drive a generator. |
| Intermittent | Available only some of the time. |
| Photovoltaic | Producing a voltage from light. |
Section 9 of 9Exam technique
1
Saying renewable energy has no environmental effect — building and siting affect land and wildlife.
2
Mixing up solar cells (electricity) and solar heating panels (thermal energy).
3
Thinking wind turbines work in all weather — they need a suitable wind speed.
4
Saying "it is free" without noting the equipment is costly.
5
Forgetting that the Sun is itself powered by fusion.