Responsible Energy Production and Use

The Spanish electricity mix for one year can be approximated as follows: wind power $25\ \%$, nuclear power $20\ \%$, solar power $17\ \%$, combined cycle gas $15\ \%$, hydro power $12\ \%$ and other sources $11\ \%$, as shown in the graph.

1. a) Considering wind, solar and hydro power as renewables, what percentage of Spanish electricity was renewable?
2. b) Check that all the percentages in the mix add up to $100\ \%$.

Classify these energy sources as renewable or non-renewable, and justify your choice in each case: wind, coal, uranium, Sun, natural gas and biomass.

Producing $1\ \text{kWh}$ of electricity in Spain emits an average of about $0,15\ \text{kg}$ of $\text{CO}_2$ into the atmosphere. If a household consumes $300\ \text{kWh}$ in a month, how many kilograms of $\text{CO}_2$ correspond to that consumption?

Spain's annual electricity demand is about $250\ \text{TWh}$. With last year's approximate mix (wind power $25\ \%$, solar power $17\ \%$):

1. a) How many $\text{TWh}$ were produced by wind power?
2. b) How many $\text{TWh}$ were produced by solar power?
3. c) How many $\text{TWh}$ did both add up to together?

A household consumes $3200\ \text{kWh}$ of electricity per year and the emission factor of the Spanish mix is $0,15\ \text{kg}$ of $\text{CO}_2$ per $\text{kWh}$.

1. a) Calculate the kilograms of $\text{CO}_2$ corresponding to that annual consumption.
2. b) Express it in tonnes.

A petrol car consumes $6\ \text{L}$ per $100\ \text{km}$ and travels $12000\ \text{km}$ per year. Burning one litre of petrol emits $2,3\ \text{kg}$ of $\text{CO}_2$.

1. a) How many litres does it consume in a year?
2. b) How many kilograms of $\text{CO}_2$ does it emit in a year? Express the result in tonnes as well, rounding to one decimal place.

A solar panel installation costs $5000\ \text{€}$ and produces $4000\ \text{kWh}$ per year that the family no longer buys at $0,16\ \text{€/kWh}$.

1. a) How many euros does it save per year?
2. b) How many years does it take to pay for itself? Round to one decimal place.
3. c) If a grant covers $30\ \%$ of the installation, what is the new payback period?
4. d) The panels last about $25\ \text{years}$. How much money will have been saved in total over that time (without a grant)? Comment on whether the investment is worthwhile.

In an entrance hall, $10$ incandescent $60\ \text{W}$ light bulbs are replaced with $9\ \text{W}$ LEDs. They are switched on for $4\ \text{h}$ a day for $365$ days a year.

1. a) How many $\text{kWh}$ are saved in a year? Round to one decimal place.
2. b) If the price is $0,16\ \text{€/kWh}$, how many euros are saved per year?

A nuclear power plant with a capacity of $1000\ \text{MW}$ operates for $8000\ \text{h}$ per year.

1. a) How much electrical energy does it produce in a year, in $\text{MWh}$? Express it in $\text{TWh}$ as well.
2. b) If that same energy were produced by burning gas, which emits $0,45\ \text{kg}$ of $\text{CO}_2$ per $\text{kWh}$, how many tonnes of $\text{CO}_2$ would be emitted? Nuclear power emits virtually no $\text{CO}_2$ when operating: how many tonnes does it avoid per year compared to gas?
3. c) State two advantages and two drawbacks of nuclear energy, and finish by giving your reasoned opinion on whether it should be part of the electricity mix.

A petrol car ($6\ \text{L}$ per $100\ \text{km}$; $2,3\ \text{kg}$ of $\text{CO}_2$ per litre) is compared with an electric car ($16\ \text{kWh}$ per $100\ \text{km}$; $0,15\ \text{kg}$ of $\text{CO}_2$ per $\text{kWh}$ with the current Spanish mix).

The graph shows the cumulative $\text{CO}_2$ for each car depending on the distance driven:

1. a) Calculate the kilograms of $\text{CO}_2$ per $100\ \text{km}$ for each car.
2. b) How many kilograms does each one emit per year if they cover $15000\ \text{km}$?
3. c) Manufacturing the electric car's battery emits about $6000\ \text{kg}$ of $\text{CO}_2$ more than manufacturing the petrol car. Using the emissions savings per $100\ \text{km}$, calculate after how many kilometres the electric car offsets the manufacturing of its battery. Round to the nearest thousand.
4. d) Using these results, write a short paragraph arguing when an electric car is worthwhile from an emissions point of view.