11-CS-3 Engineering Management · May 2017
Nivaar worked solution (AI-drafted; not reviewed by a licensed engineer)
National Exams — May 2017 — 11-CS-3 Sustainability, Engineering and the Environment. Closed book; approved calculator permitted. Any four questions constitute a complete paper; all questions are of equal value (25 marks each).
Question text not reproduced: the examination questions are © Engineers and Geoscientists BC. Open the official past paper (linked at the top of this page) to read the question, then follow the worked solution below.
Order-of-magnitude basis for a 200 MW plant: at an 80% capacity factor a thermal plant generates about 200 × 8,760 × 0.80 ≈ 1.4 million MWh per year. Wind and solar farms need more nameplate capacity (or accept less energy) because their capacity factors are only about 25–35% and 15–20%.
| Heading | Wind turbines | Nuclear plant (one) | Solar PV farm | Coal-fired plant (one) |
|---|---|---|---|---|
| Land requirement | H: about 57 turbines of 3.5 MW must be spaced several rotor diameters apart, so the farm spans tens of km². Only about 2–5% is physically occupied, and farming continues between turbines. | L: a compact site of a few tens of hectares plus an exclusion zone. Upstream uranium mining and tailings add some land, but little per MWh. | H: about 1.5–2.5 ha per MW, i.e. roughly 300–500 ha of panels fully covering the ground, plus mining for silicon and metals. | M: the plant itself is modest, but coal mines (often open-pit), rail lines and ash-disposal ponds add a large, long-lasting disturbed area. |
| Fuel requirement | L: none; wind is free and renewable. | L–M: only tonnes of enriched uranium a year, but mining, milling, conversion and enrichment are an energy-intensive upstream chain. | L: none; sunlight is free and renewable. | H: about 0.5–0.6 million tonnes of coal a year (heat rate ≈ 10 GJ/MWh, coal ≈ 25 GJ/t), mined and hauled continuously. |
| Greenhouse-gas emissions | L: none in operation. Life-cycle emissions of about 10–15 g CO₂e/kWh come from steel, concrete and blades. | L: none in operation. Life-cycle emissions of about 10–20 g CO₂e/kWh come from fuel-cycle energy and construction concrete. | L: none in operation. Life-cycle emissions of about 30–50 g CO₂e/kWh come mainly from energy-intensive silicon purification. | H: about 0.95 t CO₂ per MWh, i.e. roughly 1.3 million tonnes of CO₂ a year, plus methane from the coal mines. |
| Health risks to local populations | L: noise, shadow flicker and ice throw affect nearby residents, and birds and bats are killed. No air pollution. | M: routine releases are very small, but there is a low-probability, high-consequence accident risk, spent-fuel storage, and radon and tailings near uranium mines. | L: no emissions in operation. Chemical hazards (e.g. cadmium or lead in some panels) sit upstream in manufacturing and at disposal. | H: PM2.5, SO₂, NOₓ and mercury cause respiratory and cardiac illness downwind. Coal dust affects miners, and ash ponds can leach metals. |
| Initial cost | M: roughly 2 million dollars per MW, installed. | H: the highest capital cost per MW, because of containment, safety systems, licensing and long construction times. A 200 MW unit is SMR-scale, so costs are uncertain. | M: panel prices have fallen steeply, but more MW must be installed to deliver the same energy. | M–H: boiler, turbine and pollution-control equipment (scrubbers, precipitators, SCR) are costly, though less so than nuclear. |
| Operating cost (excluding fuel) | L: remote monitoring, gearbox and blade maintenance, small staff. | M–H: large, highly trained staff, security, regulatory oversight, waste management and decommissioning funds. | L: panel cleaning, inverter replacement, vegetation control. | M: large staff, ash handling, scrubber reagents (limestone), and boiler and turbine maintenance. |
Once upstream processes are included, the four technologies separate into two groups. Coal is worst on almost every environmental heading. It needs a continuous, very large fuel supply, emits by far the most greenhouse gas, and imposes the highest routine health burden on local populations through air pollution. Wind and solar need no fuel and emit almost nothing in operation. Their costs are mostly initial rather than operating, and their main impact is land: they take large areas because their energy is diffuse and intermittent. Nuclear is compact and low-carbon, like the renewables on GHG, but it carries the highest capital cost and a distinctive risk profile: very low routine exposure, a small chance of a severe accident, and long-lived radioactive waste. It therefore rates M rather than L for local health risk. For a jurisdiction choosing among them, the table shows that the choice is really a trade-off between land use (renewables), long-term waste and accident risk (nuclear), and climate and air-quality damage (coal).
