Year 9 Science · Unit 3 · Lesson 24
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Learning Goals
1. Find the odd one out in each group, and explain why it does not belong.
| # | Group | Odd one out, and why |
|---|---|---|
| 1 | Conduction · Refraction · Convection · Radiation | |
| 2 | Series circuit · Parallel circuit · Nuclear fission · Short circuit | |
| 3 | Coal seam gas · Solar PV · Wind turbine · Geothermal | |
| 4 | Kinetic · Gravitational potential · Elastic potential · Temperature | |
| 5 | Energy use per person · Energy intensity · Ohm’s law · Total energy use |
Scenario: an off-grid roadhouse
A roadhouse on the Stuart Highway is 300 km from the nearest power line, so it must make and store all of its own electricity. It has fuel pumps, a kitchen, a cool room for food, air-conditioned motel rooms and outdoor lights, and it is open 24 hours a day, all year.
2. The cool room’s walls are thick foam panels covered on each side with a sheet of shiny metal. Explain how this design slows the heat entering the cool room.
3. Should the lights in the 12 motel rooms be wired in series or in parallel? Explain, using voltage and what happens when one lamp fails.
Data: the roadhouse’s electrical loads
Table 1 lists the main loads at the roadhouse on a typical day.
| Load | Average power (kW) | Hours used per day |
|---|---|---|
| Cool room | 3.0 | 24 |
| Fuel pumps | 1.5 | 16 |
| Kitchen | 8.0 | 6 |
| Motel air conditioning | 6.0 | 10 |
| Outdoor lights | 1.2 | 12 |
Source: sample values for this worksheet.
4. Use E = P × t to find the energy each load uses per day, and the roadhouse’s total.
Roadhouse kWh
5. On an average day, each kW of solar panels at the roadhouse produces about 6 kWh. (a) What size of solar farm, in kW, does the roadhouse need? (b) Why must the roadhouse also store energy, and when would it use the stored energy?
(a) Panels kW
6. Design the roadhouse’s energy system. Choose its energy sources and its storage, justify each choice using ideas from the unit, and explain how you would keep the cool room running through a long run of cloudy days in the wet season.