Year 9 Science · Unit 3 · Lesson 16
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Learning Goals
1. A student says: “Hydroelectricity is not renewable, because building a dam damages river habitats.” Explain what the student has mixed up.
Order the steps: from a wind farm to a kettle
Number the steps from 1 to 7. Step 1 happens first.
| Order | Step |
|---|---|
| At a substation near the city, a step-down transformer lowers the voltage for the distribution network. | |
| A kettle changes electrical energy into thermal energy. | |
| A step-up transformer at the wind farm raises the voltage. | |
| A transformer on a pole in the street lowers the voltage to the level used in homes. | |
| The wind turns the turbine, and its generator changes kinetic energy into electrical energy. | |
| Distribution lines carry the electricity along the streets of a suburb. | |
| High-voltage transmission lines carry the electricity hundreds of kilometres. |
Scenario: a spring afternoon in South Australia
On a sunny, windy spring afternoon, South Australia’s wind farms, solar farms and rooftop solar panels can together produce more electricity than the whole state is using. The surplus flows to Victoria through an interconnector: a high-voltage line that links the two states’ grids. Big batteries, such as the Hornsdale Power Reserve, can respond within a fraction of a second when the grid suddenly needs more or less power.
2. Name three sources that supply South Australia’s electricity on an afternoon like this, and say what each one contributes.
3. The wind suddenly drops across the state. Name two things in the scenario that help keep the grid steady, and explain how each one helps.
Data: the interconnector on the same day
Table 1 shows the average flow of electricity through the interconnector in five 3-hour periods.
| Time period | Average flow (MW) | Direction of flow | Energy moved (MWh) |
|---|---|---|---|
| 6 am to 9 am | 200 | Victoria to SA | 600 |
| 9 am to 12 noon | 300 | SA to Victoria | |
| 12 noon to 3 pm | 450 | SA to Victoria | |
| 3 pm to 6 pm | 100 | SA to Victoria | |
| 6 pm to 9 pm | 350 | Victoria to SA |
Source: sample values for this worksheet.
4. Use E = P × t to complete Table 1. The first row is done for you: 200 MW × 3 h = 600 MWh. Then calculate the total energy South Australia sent to Victoria, and the total it received from Victoria, over these 15 hours.
Sent to Victoria MWh
Received from Victoria MWh
5. Explain why the flow changes direction during the day. Then suggest what a large battery in South Australia could do with the midday surplus instead of sending all of it to Victoria, and how that would change the evening flow.
6. What would have to change for South Australia to run on renewable electricity 24 hours a day, every day of the year? Use Table 1 and what you know about storage and the grid.