Weighing a Wind Farm's Net Benefit
A 200 MW wind farm is proposed on farmland. At a 35% capacity factor it would generate about 613 GWh per year. The regional grid currently produces 0.75 t CO2-e per MWh, so the farm could displace about 460,000 t CO2-e annually. Construction emits an estimated 90,000 t CO2-e, and the turbines have a 25-year life. Concerns raised include bird strike, noise, visual impact on a nearby town, and the land footprint. A councillor argues the farm is pointless because construction emissions and variability mean it cannot reliably replace baseload coal.
1. Calculate the lifetime avoided emissions and evaluate the councillor's claim.
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Annual generation: 200 MW × 0.35 × 8,760 h ≈ 613,000 MWh (613 GWh).
Annual avoided emissions: 613,000 MWh × 0.75 t/MWh ≈ 460,000 t CO2-e.
Lifetime avoided: 460,000 × 25 ≈ 11.5 Mt CO2-e, minus 0.09 Mt construction ≈ 11.4 Mt net.
Payback time: 90,000 / 460,000 ≈ 0.2 years, i.e. under three months of operation.
Evaluating the claim:
- The 'pointless' argument fails on emissions: construction is repaid in months, and net lifetime savings are large.
- The variability point is valid but not fatal: wind output varies, so it needs backup, storage, or grid balancing. It reduces the firm capacity value, not the emissions benefit.
- 'Cannot replace baseload coal' conflates energy and capacity. The farm supplies energy and reduces coal running hours; reliability is a system-design issue, addressed by diversified generation and storage.
2. Recommend what information the council should require before deciding, and explain how you would weigh the trade-offs.
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Information required:
- Site-specific bird and bat survey data (seasonal, at least one year) and collision-risk modelling.
- Noise contour modelling at the nearest dwellings against standards.
- Visual impact assessment, including viewshed analysis from the town.
- Grid connection study and expected curtailment.
- Land-use plan showing continued farming between turbines.
- Updated emissions factor for the grid over the project life, since a cleaner grid reduces future avoided emissions.
Weighing trade-offs:
- Quantify what can be quantified (emissions, noise levels, land use) and use structured assessment for what cannot (amenity, landscape).
- Compare alternatives, including solar or offshore wind, on the same criteria.
- Apply mitigation hierarchy: avoid, minimise, rehabilitate, offset.
Judgement: the emissions case is strong (≈11.4 Mt net), but approval should be conditional on acceptable bird-risk and noise outcomes and a credible grid plan; benefits do not automatically override local impacts.