Energy sources and resources, fuels and environmental impact Notes

How Do Different Energy Resources Generate Electricity? Why Do Energy Choices Affect The Environment?

1. Modern life depends on a continuous flow of energy for lighting, heating, transport, communication, and industry.
2. Physics helps us track where that energy comes from, how it is converted into useful forms (especially electrical energy), and what trade-offs exist between different energy resources.

What Is an Energy Resource?

1. An energy resource is something that can be used to provide energy.
2. Energy resources are used to generate electricity, heat buildings, and power transport.
3. Most electricity is produced by converting energy from one form into electrical energy.

Most Usable Energy On Earth Ultimately Comes From The Sun

1. A powerful way to organize energy sources is to ask: "What is the original source of the energy we are using?"
2. For almost everything humans use at Earth's surface, the answer is the Sun.
3. Sunlight warms the Earth directly.
4. Sunlight drives photosynthesis, storing energy in plant matter as chemical energy.
5. Sunlight drives the water cycle: evaporation, rainfall, and rivers, which create gravitational potential energy that can become electricity in hydroelectric systems.

Why do some energy resources eventually run out?

Fossil Fuels

1. Fossil fuels include coal, oil, and natural gas.
2. They were formed from dead plants and animals over millions of years.
3. The energy stored in fossil fuels originally came from the Sun through photosynthesis.

Coal-Fired Power Stations

1. Coal is burned to release chemical energy.
2. The energy heats water to produce steam.
3. Steam turns a turbine.
4. The turbine drives a generator to produce electricity.
5. Large amounts of energy are lost as thermal energy to the surroundings.

Power and Efficiency in Power Stations

1. Power stations convert input power from fuel into useful electrical power.
2. Not all input power becomes useful output.
3. Efficiency shows how effective this conversion is.

$$\text{Efficiency} = \frac{\text{useful power output}}{\text{total input power}} \times 100\%$$

The Typical Thermal Power Station Energy Chain

1. A simplified conversion chain is: chemical (or nuclear) energy → thermal energy → kinetic energy → electrical energy
2. Each arrow represents a conversion, and each conversion loses some energy to less useful forms (mainly heating the surroundings).
3. That is why the overall efficiency is well below 100%.

Environmental Impact of Fossil Fuels

1. Burning fossil fuels releases carbon dioxide.
2. Carbon dioxide is a greenhouse gas that traps thermal energy in the atmosphere.
3. This contributes to global temperature increase and climate change.

Why Are Renewable Resources Considered More Sustainable?

1. Renewable resources can be replaced naturally in a short time.
2. They rely on continuous natural processes.
3. Most renewable resources ultimately depend on the Sun.

1. Hydroelectric Power

1. Uses falling or flowing water to turn turbines.
2. Water gains gravitational energy when stored at height.
3. This energy is transferred into kinetic energy and then electrical energy.
4. Depends on rainfall and geography.

2. Wind Power

1. Wind is caused by uneven heating of Earth’s surface by the Sun.
2. Moving air has kinetic energy.
3. Wind turbines convert kinetic energy into electrical energy.
4. Power output depends on wind speed.

3. Solar Power

1. Solar panels convert light energy directly into electrical energy.
2. No fuel is burned during operation.
3. Power output depends on sunlight intensity and weather.

4. Geothermal Energy

1. Uses thermal energy from Earth’s interior.
2. Hot water or steam is used to turn turbines.
3. Limited to regions with high geothermal activity.

5. Tidal Energy

1. Caused by the gravitational pull of the Moon.
2. Rising and falling sea levels move water through turbines.
3. Very predictable but location-dependent.

6. Biomass And Biofuels

1. Some power stations can use biofuels, fuels produced from plants over a short timescale.
2. Examples include:
   1. Biogas (mainly methane) from rotting organic waste in landfill.
   2. Bioethanol made by fermenting plant matter (such as sugar-rich crops).
3. Because new crops can be replanted as they are used, these are considered renewable, although their overall environmental impact depends on land use, farming practices, and transport.

Why is nuclear power both useful and controversial?

1. Nuclear power stations use nuclear fission.
2. Fission releases very large amounts of energy from small amounts of fuel.
3. Energy is used to heat water and generate steam.

Advantages of Nuclear Power

1. Produces large amounts of energy.
2. Does not produce carbon dioxide during electricity generation.
3. Reliable energy output.

Disadvantages of Nuclear Power

1. Radioactive waste needs careful long-term storage.
2. The risk of accidents can have serious and long-lasting consequences.

What is nuclear fission?

1. In nuclear fission, a heavy nucleus splits into smaller nuclei and releases a very large amount of energy.
2. A striking comparison of energy density is:
   1. $1\ \text{kg}$ of coal can release about $3 \times 10^7\ \text{J}$.
   2. $1\ \text{kg}$ of uranium-235 can release more than $8 \times 10^{13}\ \text{J}$.
3. That is a factor of millions more energy per kilogram for uranium-235.

Matching Supply To Demand Requires Energy Storage

1. Electricity demand varies with time of day and season (for example, higher demand for heating and lighting in winter, and typically higher household use in evenings and weekends).
2. Power stations try to respond, but when supply does not match demand, either energy is wasted or the grid becomes unstable.
3. A major challenge is that electricity is not easy to store directly on a large scale.

Pumped Hydroelectric Storage

1. Used when the electricity supply is greater than the demand.
2. Surplus electricity pumps water to a higher reservoir.
3. Water is released later to generate electricity.

Compressed Air Energy Storage (CAES)

1. Surplus electricity compresses air into an underground cavern or deep-sea vessel.
2. Later, the high-pressure air drives a turbine to produce electricity.

Why Does The Choice Of Energy Resource Matter For The Environment?

1. Burning fuels releases gases and particles.
2. Carbon dioxide contributes to the greenhouse effect.
3. Other pollutants affect air quality and human health.
4. Greenhouse gases trap thermal energy in the atmosphere.
5. Increased greenhouse gas concentration leads to global warming.
6. Fossil fuels are a major source of greenhouse gases.

Environmental Impacts of Renewable Energy

1. Renewable resources also have environmental effects.
2. Hydroelectric dams can flood habitats.
3. Wind turbines may affect wildlife and landscapes.
4. Solar farms require large areas of land.

Sustainability in Energy Use

1. Sustainable energy meets current needs.
2. It does not prevent future generations from meeting their needs.
3. It balances environmental, social, and economic factors.

Reducing Environmental Impact

1. Increasing efficiency reduces energy waste.
2. Using renewable resources reduces emissions.
3. Storing energy improves supply management.

Environmental Impacts Depend On What Is Released And What Is Changed

When comparing energy resources, consider both local and global impacts.

Fossil Fuels: Greenhouse Gases And Pollution

1. Burning fossil fuels produces carbon dioxide (CO$_2$), a greenhouse gas. Increased greenhouse gases are linked with concerns about long-term climate change.
2. Burning also produces other pollutants (depending on fuel and technology), which can affect air quality.

Renewables: Intermittency, Land Use, And Ecosystems

1. Wind: variable output, visual and noise concerns, wildlife impacts.
2. Hydroelectric: alters river systems and habitats, may require flooding land.
3. Solar: variable output (day-night and weather), material and land-use considerations.
4. Geothermal: location-limited, can release some underground gases depending on site.
5. Biomass: combustion emissions and land-use pressure.

How Does Earth’s Atmosphere Control How Much Energy Is Retained?

1. The Sun transfers energy to Earth as solar radiation.
2. Some incoming energy is reflected by clouds and the atmosphere.
3. The rest is absorbed by Earth’s surface.
4. Earth emits energy back as infrared (heat) radiation.

Role of Greenhouse Gases

1. Greenhouse gases absorb some of the outgoing infrared radiation.
2. They re-emit heat energy in all directions.
3. Some of this re-emitted energy returns to Earth’s surface.
4. This increases the average temperature of Earth.