Generating electricity and saving energy

What is a power station? Explain in your own words what is done there: where does the electricity it produces come from?

In a thermal power station, the following steps occur, but they are out of order: steam moves a turbine; coal is burned; the generator produces electricity; heat heats water and turns it into steam.

1. a) Order the sequence from start to finish.
2. b) What type of energy is stored in coal before it is burned?

In nature, we hardly ever find "free" electricity ready to use, except for lightning: it has to be generated by transforming other forms of energy.

1. a) Write down the complete chain of transformations in a thermal power station, from the energy stored in coal to electricity.
2. b) Using this chain, explain why we say electricity is very convenient to use, but must always be "paid for" with another form of energy.

In a hydroelectric power station, there is a reservoir with water stored at height, as shown in the figure.

Explain where this power station gets its energy from and what device moves when the water falls.

Look at the wind turbine in the figure:

What moves the blades of a wind turbine? What energy does a wind farm utilise? In what type of locations do you think these wind turbines are installed?

Solar panels on roofs and satellites produce electricity without moving or making noise, like the one in the figure.

What energy do they receive, and what do they transform it into?

Classify these energy sources into renewable and non-renewable: the Sun, wind, coal, water in a reservoir, natural gas, and uranium. Explain the difference between the two groups.

A nuclear power plant heats water like a thermal power plant, but without burning anything.

1. a) What "fuel" does a nuclear power plant use?

1. b) State one advantage and one disadvantage of this type of power plant.

State one advantage and one disadvantage of each of these types of power station: wind and solar. Think about what happens on windless days and at night.

A valley with a fast-flowing river wants to generate its own electricity and is deciding between a hydroelectric dam and a gas-fired thermal power station.

1. a) State one advantage of each option.
2. b) State one disadvantage of each option.
3. c) Which would you choose for the valley? Justify your choice using your previous answers.

Andrea says: "We should produce all our electricity using renewable energy." Bruno replies: "That's not possible, because the Sun and the wind are sometimes unreliable."

1. a) Explain what each person is right about.
2. b) Name two ways to store or obtain energy for times when the Sun and wind are unavailable.
3. c) Which opinion do you agree with more? Give reasons for your answer.

A region produces its electricity as follows: $40\ \%$ from hydroelectric power stations, $30\ \%$ from wind farms, $20\ \%$ from solar power plants, and $10\ \%$ from a thermal power station. Look at the graph:

1. a) What percentage of the electricity is renewable?
2. b) If the region produces $2000\ \text{GWh}$ per year, how many $\text{GWh}$ correspond to wind energy?
3. c) How many renewable $\text{GWh}$ does it produce in total?

Put these stages of electricity's journey to your house in order: the sockets in your room, the power station, the cables on high-voltage pylons. Explain what happens at each stage.

Describe the complete journey of electricity from dammed water in a reservoir to your bedside lamp, naming all the steps: what moves when the water falls, what device generates the current, and how it reaches your home.

A town wants to supply itself with electricity using only solar panels.

1. a) What problem will it face at night and on very cloudy days?
2. b) Propose two solutions to have electricity during those times as well.

Nadia's family installs solar panels on their roof, but remains connected to the electricity grid.

1. a) Why do they not completely disconnect from the grid?
2. b) What do you think happens to the excess energy produced around noon on a sunny day?
3. c) What is the advantage of remaining connected to the grid in addition to having solar panels?

An LED bulb of $10\ \text{W}$ gives out the same light as an old bulb of $60\ \text{W}$.

1. a) Which one uses less energy to provide the same amount of light?
2. b) How many times more energy does the old bulb use compared to the LED?

A mobile phone charger plugged into the mains consumes $1\ \text{W}$, even when no phone is connected.

1. a) How many hours does it spend plugged in if it is not unplugged for an entire week?
2. b) How much energy does it consume in that week, in $\text{Wh}$? Hint: multiply power by time.

The internet router consumes $10\ \text{W}$ and is turned on all day, every day of the year.

1. a) How much energy does it consume in one day, in $\text{Wh}$?
2. b) How much does it consume in a year of $365$ days, in $\text{Wh}$?
3. c) Convert the annual result to $\text{kWh}$, knowing that $1\ \text{kWh} = 1000\ \text{Wh}$.

Why does turning off the light when leaving a room save energy, even if the bulb is small? Explain it by considering the amount of time it stays on.

In the living room of a house, there are $5$ light bulbs turned on.

1. a) If they are old bulbs, of $60\ \text{W}$ each, what is the total power consumption?
2. b) If they are replaced with LED bulbs of $10\ \text{W}$, which give the same light, what total power do they consume now?
3. c) How much power is saved by making the change?

A TV switched off with the remote control is left with a little red light on: this is standby consumption, or "stand-by".

1. a) Do you think it uses energy even though it seems to be off? Justify your answer.

1. b) How would you make it use no energy at all without taking the TV apart?

Household appliances have an energy rating label with a letter, from A (those that consume the least) to G (those that consume the most), like the one in the figure.

1. a) Between two fridges of the same size, one rated class A and another rated class F, which would you buy considering the electricity bill?
2. b) The class A fridge is more expensive to buy; why might it be worthwhile in the long run?
3. c) Why does efficiency matter so much specifically for a fridge, which is plugged in $24$ hours a day?

Write an energy-saving plan for your school featuring four measures (think about lights, heating, computers, and blinds).

1. a) Explain why each measure saves energy.
2. b) Which of your measures do you think will save the most energy? Give reasons for your answer.

Unit challenge. Become your home's energy advisor! To consolidate what you have learned, you will investigate electricity from the atomic scale to the national grid in three phases:

1. Electrification and measurement: Rub a pen with wool and use a ruler to measure the maximum distance $d$ at which it attracts paper confetti ($5$ repetitions). Consider the instrument's uncertainty ($\pm 0.1\text{ cm}$), record the data in a table with the mean, draw its scatter plot, and explain which particles are transferred.

2. Domestic circuits: Draw the standardised electrical diagram of two light bulbs in your house controlled by a switch. Justify whether the circuit should be in series or in parallel based on its practical operation.

3. Mix and energy saving: Check the Red Eléctrica de España (REE) website for today's renewable generation percentage (\%). Then, find the power rating of a kitchen appliance in your home, calculate its estimated monthly consumption ($E = P \times t$, in $\text{kWh}$), and draft two realistic, well-reasoned energy-saving measures.

Present your work in a short report with calculations, the graph, and the diagram.

Evaluation criteria:

• Rigour in collecting home measurements, stating uncertainty ($\pm 0.1\text{ cm}$), and graphical preparation.

• Conceptual and symbolic accuracy in the circuit diagram.

• Rigorous data extraction from REE and physical feasibility of the proposed energy-saving measures.