PHYSICS · Stage 8 · Chapter 9: Energy Resources
Physics 9.4 Renewable resources: solar and geothermal energy
5 min read 6 parts Lesson 4 of 7
Lesson summary
Physics 9.4 Renewable resources: solar and geothermal energy — Alhussan International Academy — Physics (Stages 7–9) notes: Describe how energy from the Sun and from the Earth can be used to generate electricity and to heat water.Solar energy — It is mainly used for heating homes…
- Solar (photovoltaic) cell
- Connection
- Efficiency
- Satellites
- Solar panel
- Temperature
Section 1 of 6Using energy from the Sun
- Solar energy
- It is mainly used for heating homes and water, and for generating electricity using solar cells.
- Mithapur
- This Indian solar power station has over 100 000 solar cells covering 0.4 square kilometres.
- India
- It has about 300 sunny days a year and could generate much of its electricity using solar cells.
Section 2 of 6Solar cells
- Solar (photovoltaic) cell = a cell that converts the energy of light directly into a voltage.
- Unlike a generator, it has no moving parts.
- Connection
- Each cell produces a small voltage, so many cells are connected to make a big voltage.
- Efficiency
- The efficiency of solar cells has increased from 5% in the 1970s to more than 30% today.
- This means that fewer cells are now needed to produce the same voltage.
- Satellites
- For some objects, such as satellites, solar is the only source of energy.
| Advantages | Disadvantages |
|---|---|
| Renewable and will not run out | Do not work at night |
| Can be used in individual houses and small low-power devices | Expensive to produce |
| Can be used in remote locations | Greenhouse gases are made during production |
| Can work on cloudy days | Output falls when cloudy |
Section 3 of 6Solar water heating
- Solar panel
- It heats water directly and does not use solar cells.
- Design
- Pipes inside a glass-topped panel are painted dull black and are usually copper.
- Black absorbs the most energy from the Sun.
- Copper is a good conductor, so energy passes to the water.
- Action
- Cold water from a tank flows through the pipes, is heated by the Sun and flows back to the tank as hot water.
- Glass
- It lets sunlight in and helps trap thermal energy in the panel.
Section 4 of 6Geothermal power
- Geothermal energy = energy from the heat of the Earth.
- Temperature
- The rocks beneath the surface are hot, and the temperature rises by about 25 °C for each kilometre of drilling.
- Geothermal power station
- Water is pumped into pipes deep underground.
- The water is converted into steam.
- The steam drives a turbine, which drives a generator.
- Limits
- Suitable sites are where hot rocks are near the surface, and drilling is expensive.
| Advantages | Disadvantages |
|---|---|
| Renewable and will not run out | Expensive to build |
| No greenhouse gases while running | Greenhouse gases released during building |
| Available all day and in all weathers | Limited to suitable sites |
Section 5 of 6Heat pumps
- Heat pump = a system that pumps water through pipes in the ground to heat or cool a house.
- Winter
- The water gains a little thermal energy from the ground, which is transferred to heat the house.
- Summer
- The ground is cooler than the house, so the same system cools the house.
Section 6 of 6Comparison with a coal power station
- Similarity
- Both use steam to drive a turbine and generator.
- Difference
- A coal station burns a non-renewable fuel and releases carbon dioxide, whereas a geothermal station burns no fuel and uses heat from inside the Earth.
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