23-CS-3 Sustainability, Engineering and the Environment · December 2019
Nivaar worked solution (AI-drafted; not reviewed by a licensed engineer)
National Exams — December 2019 — 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.
| Technology | Capital cost | Fuel cost | Land | GHG emissions | Health risk to neighbours |
|---|---|---|---|---|---|
| Wind farm | M–H: turbines are moderately priced per MW of nameplate, but a ~35% capacity factor means roughly 850 MW of turbines (plus transmission and backup) to deliver an average 300 MW | L: the wind is free; only O&M costs | H: turbines need wide spacing (tens of km²), although farming or grazing can continue between towers | L: no combustion; only the embodied emissions of steel, concrete and blade manufacture upstream | L: no air emissions; minor nuisance (noise, shadow flicker) and bird/bat impacts |
| Nuclear | H: reactor, containment and safety systems make it the most capital-intensive option, with long construction times and overruns | L: uranium is energy-dense, so fuel is a small share of the cost even after mining, enrichment and fabrication | L: compact site; upstream uranium mining and waste storage add modest land | L: no combustion; small upstream emissions from mining, enrichment and construction | L–M: negligible routine exposure, but a low-probability, high-consequence accident risk, spent-fuel storage, and uranium-mine tailings upstream |
| Natural gas turbines | L: gas turbines (simple or combined cycle) are the cheapest and quickest to build per MW | M–H: fuel is the dominant, market-volatile cost | L: compact plant; upstream wells, pipelines and fracking pads add a modest dispersed footprint | M: about half of coal’s CO₂ per MWh, plus upstream methane leakage from wells and pipelines | L–M: NOₓ is the main stack pollutant (little SO₂ or PM); upstream fracking raises local air and water concerns |
| Wood pellets | M: boiler, steam turbine and particulate controls, much like a solid-fuel steam plant | M–H: harvesting, drying, pelletizing and hauling a bulky, lower-energy fuel is costly | H: sustained supply needs a very large area of managed forest (hundreds of km²) | M: combustion CO₂ is high per MWh and is only offset over decades of regrowth; harvesting, pelletizing and transport add fossil emissions | M: fine particulates, CO and NOₓ from combustion, plus heavy truck traffic |
| Coal-fired | M–H: large boiler, coal handling, and SO₂/PM/NOₓ controls | M: coal is cheap per GJ, but large tonnages must be mined and hauled by rail | M: plant plus coal storage, ash ponds and upstream strip mines | H: the highest CO₂ per MWh (about 1 t/MWh), plus mine methane | H: PM₂.₅, SO₂, NOₓ and mercury emissions, ash-pond failures, and coal-dust from mines and rail |
Each rating in the table is justified in its own cell and covers both the plant and its upstream fuel or material chain. Wind: no fuel and almost no emissions, but capital-intensive per delivered MW and land-extensive. Nuclear: very high capital, cheap fuel, compact and near-zero carbon; the social concern is accident and waste risk rather than routine exposure. Natural gas: cheap to build but exposed to fuel prices, with medium GHG (about half of coal) and low local pollution. Wood pellets: a moderate-capital steam plant whose fuel chain is costly and land-hungry, and which is only conditionally low-carbon while emitting particulates locally. Coal: land for plant and mines, the highest GHG, and (through particulates, SOₓ, NOₓ and mercury) the highest health risk to neighbours. Considering the triple bottom line and upstream processes: wind and nuclear are the true low-carbon options (trading land or capital/risk), gas is a lower-carbon fossil bridge, biomass is only conditionally low-carbon and adds local pollution, and coal is worst overall.
