The Cost of Running Household Appliances, Grade 9 Project
Your Grade 9 textbook prices electricity at 89,52 cents a unit. In 2026 it is about 355 cents.
That is the problem with the prescribed electricity project: the worked example is a municipal account from 2012, VAT on it is 14 %, and the whole task is about what a family pays today. Every answer a learner produces from those figures is roughly four times too low.
This page gives the project with current tariffs, VAT at 15 %, and its prescribed 30 marks, plus a safe way to find the geyser's rating that does not involve climbing into a ceiling.
Where this fits in the curriculum
| Subject | Natural Sciences |
|---|---|
| Grade | 9 |
| Term | 3 |
| Strand | Energy and change |
| Topic | Topic 15, Cost of electrical power |
| Status | This is the prescribed Grade 9 PROJECT |
| Marks | 30, prescribed |
Do not climb into the ceiling
The textbook illustrates this project with a photograph of a boy climbing into a roof space to read the power rating of the geyser, and the first question reminds learners not to forget the geyser "which is usually inside the ceiling".
Ceiling boards do not carry a person's weight, and a geyser sits next to mains wiring and hot pipes.
| Three safe ways to get the number |
|---|
| Ask an adult who knows, or who can check safely |
| Read the paperwork. A plumber's certificate or the geyser manual gives the element rating |
| Use the typical value. Most South African domestic geysers have a 3 kW or 4 kW element, and that is all the calculation needs |
The 2026 tariffs
Eskom direct, effective 1 April 2026, VAT included:
| Tariff | c/kWh including VAT |
|---|---|
| Homepower prepaid, combined rate | 355,56 |
| Homepower, energy charge only | 322,06 |
| Homelight 20A | 270,30 |
| Homelight 60A | 343,61 |
City of Johannesburg, effective 1 July 2026, residential prepaid:
| Block | c/kWh |
|---|---|
| 0 to 350 kWh | 272,37 |
| 351 to 500 kWh | 333,18 |
| Above 500 kWh | 413,06 |
Eskom's tariffs rose 8,76 % in April 2026 and municipal tariffs rose 9,01 % in July. Every municipality is different, so a learner should use their own household's bill or their own municipality's published schedule wherever possible.
Notice the blocks. The last unit a household uses in a month costs more than the first. That is worth a sentence in any project: saving electricity saves it at the highest rate, not the average one.
VAT is 15 %, and has been since 1 April 2018. Any textbook still printing 14 % predates that.
The arithmetic
Energy (kWh) = power (kW) × time (hours)
Cost = energy (kWh) × price per kWh
Watts to kilowatts: divide by 1 000. A 2 000 W kettle is 2 kW. Forgetting this is the commonest mistake in the whole project, and it makes every answer a thousand times too big.
Worked example: the kettle
| Step | Working |
|---|---|
| Power | 2 000 W = 2 kW |
| Used | 30 minutes a day = 0,5 h |
| Energy per day | 2 × 0,5 = 1 kWh |
| Energy per month | 1 × 30 = 30 kWh |
| Cost per month | 30 × R3,55 = R106,50 |
Typical power ratings
| Appliance | Typical rating |
|---|---|
| Geyser | 3 000 to 4 000 W |
| Kettle | 2 000 W |
| Iron | 1 000 to 2 000 W |
| Heater | 1 000 to 2 000 W |
| Stove plate | 1 500 to 2 000 W |
| Washing machine | 500 W, plus the geyser if it draws hot water |
| Television | 50 to 150 W |
| LED light | 5 to 10 W |
| Phone charger | 5 to 20 W |
A geyser does not run 24 hours a day. The thermostat switches the element off once the water is hot. Three to four hours of element time a day is a realistic figure for a family, and at least one printed exam question gets this wrong by assuming 24.
The answer the project always arrives at
| 3 kW geyser, 3 hours a day | 10 W LED bulb, 5 hours a day | |
|---|---|---|
| Energy per month | 270 kWh | 1,5 kWh |
| Cost at R3,55 per kWh | about R958 | about R5,33 |
The geyser costs roughly 180 times what the light costs. That comparison is the whole point of the project: the appliances that matter are the ones that make heat, not the ones that are switched on longest.
What has happened to the price since the textbook was printed
| 2012, in the textbook | 2026 | |
|---|---|---|
| Per kWh | 89,52 c | about 355 c |
| The kettle example above | R26,86 a month | R106,50 a month |
| The geyser example above | R241,70 a month | R958,50 a month |
About four times, in fourteen years. Working that out is one line of arithmetic and it teaches more about household economics than the rest of the chapter.
How the marks work
This project has an official mark allocation, so we have not invented one.
| Section | Marks |
|---|---|
| List the appliances | 2 |
| Table of ratings, hours and costs | 10 |
| Total monthly cost | 2 |
| Which appliance costs most, with reasons | 4 |
| What your answers tell you | 2 |
| Compare with the household bill | 2 |
| Ways to reduce the cost | 4 |
| Presentation and referencing | 4 |
| Total | 30 |
Mark the method, not the household. A learner from a home with four appliances can produce a perfect project, and a learner who cannot get hold of a bill can work from the published tariff.
Safety
- Nobody climbs into a ceiling or roof space
- Nobody opens an appliance, a plug or a distribution board
- Nobody touches the geyser isolator or its cover
- If a label cannot be read safely, use the typical value from the table above
Free project sheet and marking memo
Both free, no sign up, straight to the PDF.
- Project sheet, the prescribed 30 marks plus a 20-mark extension. Part A reproduces the assessed project exactly. Part B works the geyser, the bulb and the fourteen years of price rises
- Marking memorandum, with worked answers and the three answers that look right and score nothing
Related practicals
- Series and parallel circuits, Grade 9. The same term, with real circuits
- What changes the resistance of a wire, Grade 9. Why a heating element is made of nichrome, which is where all this energy goes
- The atmosphere and the greenhouse effect, Grade 9. Where the electricity comes from, and what burning coal to make it does
What you need to run it
Nothing from us. This is a paper project.
A learner needs their household's electricity bill or prepaid slips, a list of appliances with their power ratings, and a calculator. The project sheet and the memo above are free.
One thing would improve it, and we do not sell it yet: a plug-in energy meter, which sits between the socket and the appliance and measures the kilowatt hours actually used. It turns the project from an estimate into a measurement. We are pricing one.
This page is updated every April and July, when Eskom and the municipalities change their tariffs. If you are reading it long after those dates and the numbers look stale, check your own bill: that figure always beats ours.