Sources of Energy, Grade 7: Renewable, Non-Renewable and the South African Picture

A capital letter is the difference between a power station and a torch bulb.

You will see South Africa's wind farms credited with "a combined 3 400 mw", and its solar with "about 3 500 mw". mW is the milliwatt. MW is the megawatt. They differ by a factor of a billion.

And the same page gets Cahora Bassa right at 1 920 MW, two paragraphs away. So the capital letters are there; they just are not consistent. It is the cheapest correction in the grade and the one most likely to cost a mark in a test.

Units and symbols, since this topic runs on them

Symbol What it is Scale
mW Milliwatt A thousandth of a watt. About what a digital watch uses
W Watt A bulb, a phone charger
kW Kilowatt A thousand watts. A kettle is about 2 kW
MW Megawatt A million watts. This is the unit power stations are measured in

The rule is simple: lower case for small, capital for the person it is named after. The watt is named after James Watt, so W is always capital. The prefix in front of it is lower case up to kilo and capital from mega upwards. 3 400 mW would run a few calculators.

Where this fits in the curriculum

Subject Natural Sciences
Grade 7
Term 3
Strand Energy and Change
Topic Sources of energy
Status Class activities and research. Nothing here is formally assessed
Marks The topic revision is 25. Our worksheet is 40

Coal is not a fossil fuel because it is underground

You will see a caption reading, more or less, that coal is a fossil fuel because it is found below Earth's surface.

That is not why, and the body text one paragraph above it says so correctly.

Gold is below the surface. So are diamonds, rock salt, iron ore and groundwater. None of them is a fossil fuel.

Coal is a fossil fuel because it formed from the remains of living things, in coal's case plants that grew in swamps and were buried before they could rot away. That is the whole definition, and it is the one a learner needs, because the next question is always whether uranium is a fossil fuel.

It is not. Uranium is an element that was in the rock from the beginning. Nothing ever lived in it.

Renewable or not: the test that actually works

Non-renewable Renewable
The test Once it is used, it is gone on any human timescale It replaces itself as fast as we use it, or faster
Examples Coal, oil, natural gas, uranium Sun, wind, water, waves, tides, geothermal heat, biomass
South African examples Coal from Mpumalanga, gas at Mossel Bay, uranium for Koeberg Cahora Bassa hydropower, the Northern Cape solar farms, the Eastern Cape wind farms

Two that catch learners out. Biomass is renewable because you can grow more trees, but only if you actually replant: a forest cut faster than it regrows is being used like coal. And uranium is non-renewable even though a nuclear station emits no carbon dioxide, because the fuel itself runs out. Renewable and clean are two different questions, and this topic is the place to separate them.

What checks out, and what needs a date on it

Claim Verdict
Cahora Bassa produces about 1 920 MW Correct
The world's largest hydropower plant is in China and makes about ten times as much Correct. Three Gorges is around 22 500 MW
Koeberg is in the Western Cape Correct
Concentrated solar power melts salt to about 565 °C and can generate after dark Correct, and it is the best fact in the topic
"Eskom generates 95 % of South Africa's electricity" Out of date. Independent producers have taken a growing share, and the figure moves every year. Any percentage here needs the year attached to it
"Coal reserves of 50 000 million tons" That is the resource, not the reserve. A resource is all the coal known to be there; a reserve is the part that can actually be dug up at a profit with today's technology, and it is far smaller
PetroSA at 45 000 barrels a day That is the plant's nameplate capacity, which is what it could do when running flat out. It has been largely idle in recent years, so quote it with a date or not at all

The Sun does not burn

You will read that the Sun will eventually "burn out".

Burning is a chemical reaction with oxygen. There is no oxygen in space and the Sun is not on fire.

The Sun fuses hydrogen into helium. Four hydrogen nuclei are squeezed together hard enough to make one helium nucleus, and the tiny amount of mass left over comes out as energy. That is nuclear fusion, and nothing is being consumed by oxygen anywhere.

It matters here because this topic asks whether solar energy is renewable. On any timescale a person cares about, yes: the Sun has about five billion years of hydrogen left. Calling it burning makes it sound like a fire that could go out this century.

Our Grade 8 solar system page corrects the same wording, so the two pages agree with each other and not with the printed version.

The Karoo fracking case study, which is good and has two errors in it

The case study itself is balanced and genuinely local, which is rare. Two statements in it do not hold.

What it says What is actually the case
"Explosives are used to break up the rock" Hydraulic fracturing breaks rock with high-pressure fluid. That is what hydraulic means. Small shaped charges are used to perforate the steel casing so the fluid can get out, but they do not fracture the rock formation
"Banned in Canada and France, and the USA is considering banning it too" France banned it in 2011, which is right. Canada has not: Quebec, Nova Scotia and New Brunswick have, while Alberta and British Columbia frack heavily. The USA has no national ban under consideration, though New York, Vermont and Maryland have state bans

And three different lifetimes are given for South Africa's coal across this book: 200 years, 150 years, and a reserve figure that works out at about ten weeks. They cannot all be right. Worth asking a class which one they can check, and how.

If the research goes wrong

Problem Cause Fix
Two sources give wildly different coal reserves One is quoting the resource, the other the reserve Make the learner write down which they found, and the year
The Eskom percentage is different everywhere It changes every year Always record the year with the figure. A percentage with no date is not a fact
A learner writes 3 400 mw Copied straight off the page MW. Capital M, capital W
Nuclear gets classified as renewable It makes no carbon dioxide, so it sounds renewable Clean and renewable are different questions. Uranium runs out
Biomass gets classified as non-renewable It is burnt, like coal It is renewable if it is replanted. That condition is the answer
A learner says the Sun will burn out The wording in front of them It fuses. Five billion years of hydrogen left

How the 40 marks are made up

Part Marks
Units and symbols: mW against MW 8
Renewable against non-renewable, and the two that catch people out 10
South African sources and where they are 8
Fracking, and the claims that do not hold 8
The Sun as a source 6

Nothing in this topic is formally assessed. The topic revision is 25 marks and it adds up correctly. Our worksheet is 40 and the split above is ours.

Free worksheet and marking memo

Both free, no sign up, straight to the PDF.

Related practicals

What you need to run it

Nothing, and we would rather say so.

This is a reading and research topic. It needs an atlas, somewhere to look things up, and a teacher willing to ask for the year beside every percentage. There is no apparatus and we are not going to invent any.

The one thing worth having on the wall if you teach the whole Energy and Change strand is a wall chart, and the one thing worth buying for the strand as a whole is a thermometer, which the next topic explains properly.

If a supplier tells you this topic needs a kit, they are selling you something.