Wind energy – more than just hot air

Wind energy has attracted substantial media coverage the past month. While news of Boris Johnson’s early-October announcement to power every British household with offshore wind by 2030 quickly spread amongst environmental groups and energy-sector executives, this was quickly overshadowed by incumbent U.S. President Donald Trump, who drew global attention last Thursday for claiming that wind turbines kill "all the birds" during the final presidential debate. With neither politician being a scientist, can we believe their claims?

Once again, we begin by assessing the present circumstances surrounding wind energy before delving into the technicalities. It is easily observable that the sector is amongst the fastest-growing renewable energy technologies in 2019. Having increased its global generation capacity by 10% (59GW) from 2018, wind energy alone comprised over a third of annual expansion in renewable power capacity, ranking it second only to solar.

Source: IRENA, 2020

The appeal of wind energy is primarily attributable to both its rising affordability and low life-cycle carbon emissions. A 2020 study of mature markets in Northern Europe shows that offshore winds projects in Germany and the Netherlands are already subsidy-free, even though prices for their electricity generated have been decreasing by 11.9±1.6% annually between 2015-2019 in the region. While geographically restricted, these successes demonstrate that long-term financial viability for wind energy can be already achieved by leveraging on economies of scale, providing strong justification for other countries seeking to embark on similar energy transition pathways.

As for its environmental benefits, the figure below illustrates the low emission intensity of both wind energy varieties even relative to other renewable energy options, let alone conventional fossil-fuels. Though offshore wind farms are more energy-intensive to construct than their onshore counterparts, the average energy payback period (duration of operations needed to recoup the initial energy expenditure) is 7.8 months for the former compared to 6.8 months in the latter, which is by no means a deal-breaker.

Source: Kaldellis & Apostolou, 2017: 82

Enough has been said of its positive aspects – time to investigate the downsides of wind energy, such as Trump’s allegations! That wind farm operations cause bird fatalities is an undeniable truth – in fact, bats are also common casualties. What Trump casually omitted, however, was that the number of birds directly killed by other human activities dwarfed those from wind turbines, with approximate figures for the USA summarized in the table below.

Source: Saidur et al., 2011: 2426

Furthermore, the above figures neglect any indirect causes of bird fatalities, such as poisoning from toxic waste or habitat degradation through climate change. Attempting to account for these factors, like how Sovacool did in his 2009 publication, suggests that fossil-fuels are far more destructive for bird populations than wind turbines per unit of energy output, with details in the table below. Regardless whether Sovacool’s conclusions are accurate, it can be established that wind energy is not a key contributor to human-induced bird fatalities. However, these negative impacts can certainly be diminished, by reducing turbine operations amidst low wind speeds or utilizing selective stopping mechanisms when birds or bats are detected nearby. By sacrificing <1% of annual wind power output, the former action reduced nightly bat mortality by up to 93% , whereas the latter halved the number of griffon vulture deaths. While deciding between trade-offs is never easy, these empirical studies present strong cases to opt for the minuscule losses in electricity generation.

Source: Sovacool, 2009: 2247

Perhaps more significant than directly killing flying animals, would be the role of wind farms in contributing to habitat losses. Reiterating the point of low land-use efficiency in across renewable energy technologies, power output of wind farms typically range between 0.5–2 We/m2, which is less than a quarter of the 2–10 We/m2 for solar power plants. While wind farms have greater compatibility with other domestic land uses like agriculture, its onshore installation necessarily requires removal of vegetation cover and smoothing of terrain to give way for energy infrastructure, rendering these areas less hospitable for wildlife. In the western USA, onshore wind farms are encroaching on shrublands where large mammalian herbivores like mule deer or elk reside, resulting in protracted ecological damage given the difficulty of restoring shrubland ecosystems in dry climates.

Offshore wind farms may avoid some of these controversies on land-use allocation or degradation of terrestrial habitats, at the expense of migratory birds and bats to which they may pose additional safety hazards. Similar to floating solar farms, most of the ecological damage appears to occur during the construction phase from sedimentation, underwater noise emission and marine habitat destruction, but effects during its dominant operational phase are wrought with ambiguity and vary depending on the species in question. While noise from wind turbine operations is of sufficiently low magnitude to avoid impairing hearing in marine mammals, the resultant noise and electromagnetic fields have nonetheless demonstrated their negative effects on most other marine species, though these detrimental impacts might diminish in relative significance where substantial human activities like maritime trade or commercial fishing were formerly occurring.

Source: Bergström et al., 2014: 5

Yet, by allowing marine ecosystems within their operational areas to be cordoned off from fisheries, offshore wind farms prevent populations of fishes and their mammalian predators from being overfished or hunted to extinction. Meanwhile, structural foundations of wind turbines facilitate formation of artificial reefs, supporting both a greater variety and abundance of wildlife. However, as the structural foundations of wind turbines can differ substantially from naturally occurring sandy substrates, these gains in biodiversity may have stemmed from colonization by invasive species, as observed for the Telmatogon japonicus insect in the southern Baltic Sea. To ensure that native species can continue surviving in these modified ecosystems, regular monitoring – and possibly further active intervention – should be conducted to prevent excessive population declines.

My personal take is that the ecological costs of wind turbines in killing wildlife are dwarfed by the scale of their benefits, in providing clean (even by renewable energy standards) and relatively affordable electricity, especially since their negative impacts can already be significantly diminished through negligible losses in power output. But let me know your opinions too!