MCQ Answers
1. B — Energy cannot be created or destroyed, only transferred or transformed.
2. C — In parallel, voltage across each branch equals the source voltage (12 V).
3. C — Hydroelectric dams are the most efficient at ~90%.
4. A — Parallel architecture allows multiple generators to feed the same grid voltage independently.
5. D — Social media popularity is not a scientific evaluation criterion.
SAQ 1 — Energy Journey (3 marks)
Marking Criteria: 1 mark — traces at least 4 transformations. 1 mark — identifies one transfer. 1 mark — mentions conservation of energy at each step.
Model answer: The journey from sunlight to LED light involves multiple energy transformations and transfers:
1. Sun → Solar panel: Light energy from the sun strikes photovoltaic cells in a rooftop solar panel, where it is transformed into electrical energy (DC). Some energy is lost as heat in the cells (~80% efficient).
2. Solar panel → Battery or grid: The electrical energy is either transferred directly to the home or transformed into chemical energy in a battery for storage. When discharged, chemical energy transforms back to electrical energy.
3. Battery → Inverter: DC electrical energy from the battery is transformed into AC electrical energy by an inverter, compatible with household appliances (~95% efficient).
4. Inverter → LED bulb: AC electrical energy flows to the LED bulb, where it is transformed into light energy and some heat (~90% efficient, far better than incandescent bulbs).
At every stage, the total energy is conserved — what is not transformed into the desired output becomes heat, sound, or other forms. The overall efficiency from sunlight to LED light is approximately 20% × 95% × 90% = 17%, meaning 83% of the original solar energy is lost as heat at various stages.
SAQ 2 — Batteries vs Pumped Hydro (4 marks)
Marking Criteria: 1 mark — two valid advantages of batteries with Australian example. 1 mark — two valid disadvantages of batteries. 1 mark — two valid advantages of pumped hydro with Australian example. 1 mark — two valid disadvantages of pumped hydro.
Model answer:
Lithium-ion batteries excel at short-duration storage (1–4 hours) and provide the fastest grid response — milliseconds to seconds. The Hornsdale Power Reserve in South Australia (150 MW / 194 MWh) demonstrated that batteries can stabilise grid frequency faster than traditional power stations, preventing blackouts. Batteries are also modular — they can be installed quickly in distributed locations.
However, batteries have limitations. Their round-trip efficiency is 85–95%, but they are best suited for hours, not days. The materials (lithium, cobalt) have supply chain and environmental concerns, and batteries degrade over 10–15 years. Large-scale multi-day storage would require enormous numbers of battery cells.
Pumped hydro is superior for long-duration storage (6 hours to several days). It can store vast amounts of energy — Snowy 2.0 will provide 350,000 MWh, enough to power 3 million homes for a week. Once built, pumped hydro has a 50–100 year lifespan and low ongoing costs. The terrain of the Snowy Mountains provides the elevation difference needed.
However, pumped hydro requires specific geography (two reservoirs at different heights) and has high upfront construction costs ($5–10 billion for Snowy 2.0). It also has lower round-trip efficiency (70–85%) than batteries and can impact local ecosystems during construction.
For Australia's 2050 grid, both technologies are essential: batteries for daily cycling and grid stability, and pumped hydro for seasonal backup during extended renewable lulls.
SAQ 3 — Australia's Net-Zero Pathway (5 marks)
Marking Criteria: 1 mark — references energy conservation/efficiency principles. 1 mark — discusses renewable sources with targets. 1 mark — explains grid upgrades. 1 mark — references emerging technologies. 1 mark — cites 3+ specific Australian projects/policies with detail.
Model answer: Australia can achieve net-zero emissions by 2050 while maintaining prosperity through a five-pillar strategy grounded in the science studied in this unit.
1. Energy Conservation and Efficiency: The law of conservation of energy tells us we cannot "save" energy that is never used. Improving efficiency is the cheapest and fastest decarbonisation strategy. Australia's energy intensity has fallen 20% since 2000, but further gains are possible through better building insulation, efficient appliances (Energy Rating Labels), and industrial process optimisation. Every kWh not consumed is a kWh that does not need to be generated.
2. Renewable Sources: Solar and wind are now the cheapest new electricity sources in Australia. The government target of 82% renewable electricity by 2030 is achievable given Australia's world-class resources. The New England Solar Farm (720 MW) and Silverton Wind Farm (200 MW) demonstrate utility-scale deployment. Rooftop solar — already the highest per-capita uptake globally — reduces grid demand directly.
3. Grid Upgrades: The Rewiring the Nation program ($20 billion) is upgrading transmission lines to connect remote renewable zones to cities. The NEM's parallel architecture allows new generators to connect without disrupting existing supply. Snowy 2.0 (2,000 MW pumped hydro) will provide the long-duration storage needed for a high-renewable grid.
4. Emerging Technologies: Green hydrogen produced in the Pilbara and Gladstone can replace fossil fuels in steelmaking, shipping, and aviation — sectors difficult to electrify. The Hydrogen Energy Supply Chain pilot has already shipped liquid hydrogen to Japan. While hydrogen's round-trip efficiency is only ~35%, its role is in applications where direct electrification is impossible.
5. Policy and Economics: The Safeguard Mechanism requires Australia's largest emitters to reduce emissions progressively. ARENA and the CEFC have invested over $17 billion in clean energy commercialisation. These policies create market certainty that drives private investment.
Achieving net-zero while maintaining prosperity is not just possible — it is already underway. The key is combining conservation, renewables, grid infrastructure, storage, and emerging technologies in a coordinated national strategy.