Green energy choices: Wind power under the microscope

A new report of the International Resource Panel evaluates the relative environmental merits of power generation options. I am co-editor of the report and lead author of the chapter on wind power. In this blog post, I share some insights from the report as well as own reflections on environmental aspects of wind power.

Wind turbines are driven by the energy possessed by moving air – that is, wind. In fundamental contrast to exhaustible energy stocks like oil and gas, wind is a renewable energy flow. What is more, it is available in ample quantities around the globe. Still, wind power deployment is not without environmental concerns.

Assessment approach

The International Resource Panel (IRP) report takes a two-fold approach to assessing the impacts and resource requirements of power supply:

First, comprehensive life cycle assessments are conducted to quantify environmental impacts, such as climate change, toxic effects and air pollution. Second, some impact types are essentially non-quantifiable, as agreed-upon methods for quantification do not exist. The report addresses such impact types by means of a qualitative discussion. Examples of non-quantifiable effects of wind power include bird mortality and visual intrusion in landscapes.

Great potential for reducing pollution

Overview of life cycle impacts for different power generation options. Source: Hertwich et al. (eds.). Green Energy Choices. Summary For Policy Makers. UNEP International Resource Panel. The summary report is available here.

In a life-cycle perspective, wind power causes harmful emissions, just as does any other way of power generation. Looking at the life cycle assessment results of the IRP report, one result is striking: Wind power shows excellent performance by all the assessed impact types caused by pollution, outperforming the global electricity mix by one or two orders of magnitude.

This is evident from the figure above, showing a comparison of estimated impacts for different technologies. (I am afraid image size is small. You may click on image to increase size somewhat, or see the IRP summary report.) Observe, for example, that the greenhouse gas emissions of wind power amount to only 2% of that of the average global electricity. Similarly, wind power causes adverse effects on human and ecosystem health (due to air pollution or toxic contamination of soil and water) corresponding to 4-5% of that of the global electricity.

Bird and bat fatalities

Try a Google search for “wind”, “birds” and “myth”, and you will find websites portraying wind turbines as a major threat to birds. And you will find websites presenting it as a myth that wind turbines is a significant threat to birds.

Such contrasting perceptions probably come about for a variety of reasons. It is clear though, that one explanation is that some people look at the total number of birds killed by wind turbines in comparison to buildings, transmission lines and cats, while other people focus on effects on local bird populations. The former perspective tends to put wind power in a more favourable light, because – true – in the aggregate wind power is only a minor bird-killer compared to other man-made structures. The latter perspective tends to put wind power in a less favourable light, because – also true – wind farms can do harm to local bird populations that are small or vulnerable, or valued by humans. Wind turbines tend to kill different types of birds (for example, eagles) than buildings (for example, songbirds).

Measures exist for reducing the risk of bird collisions and have demonstrated some success, which is encouraging. Perhaps in particular, careful spatial planning and optimized wind farm siting can reduce negative effects on birdlife.

Not to forget, there is also another (and very different) type of flying animals, bats. For reasons not entirely understood, some bat species seem to be attracted to wind turbines – putting the bats at increased risk of injury or death caused by moving turbine blades. There are concerns that wind turbines have become or are about to become a serious mortality factor for bats in some regions.

Land use

How much land area does a wind farm occupy? Here also, views differ greatly. For the IRP report, a choice was made to count only the area used exclusively by turbines with foundations, and access roads. The basic reason for this choice is that the spacing between turbines can be used by humans for other purposes or by terrestrial wildlife. A wind farm area can, within some limits, coexist with agricultural crops, animal grazing or wildlife. The same cannot be said for the land used by open-pit coal mines or bioenergy crops.

With the approach used in the IRP report, the life cycle land use associated with wind power is very small compared with competing technologies, as is evident from the overview of impacts in the figure above. However, as is discussed in the report, a much larger area could also be regarded as impacted, especially because wind turbines are tall structures that may be visually dominating in landscapes. Concerns about degradation of scenic attributes of landscapes can be legitimate, and should not generally be dismissed as a “not in my back-yard”-type problem.

Real benefits arise when worse alternatives are displaced

Life cycle assessments and other literature often assume, explicitly or implicitly, that one unit of wind power delivered implies one unit of fossil fuel-based power avoided. I have some reservations concerning this.

First, I am currently not able to see a basis for a priori assumptions that wind power deployment automatically reduces fossil fuel power use on a one-to-one basis. Second, it appears to be an artificial premise that wind power competes solely with fossil fuel power. It could also be seen as facilitating growth in electricity demand or as competing with other renewable options or with energy efficiency, especially in a future-oriented context assuming high carbon prices.

The IRP report shows that wind power has a great potential for reducing greenhouse gas emissions and other pollution. At the same time, realizing this potential depends on the degree to which fossil fuels are displaced. This again depends on energy and climate policies whose combined effect is to avoid fossil fuel use.

The full report, including the chapter on wind power, is available here. A summary report is available here. Other materials related to the report are available from A Norwegian version of this blog post is here.


Benefits of variable renewables outweigh costs

Replacing fossil fuel power with variable wind and solar power means that more energy storage and power transmission capabilities are necessary. Despite this, we find large climate benefits and a range of other pollution benefits of switching to renewables.

Solar Panel

The variability of wind and solar power makes their large-scale integration into power systems challenging. The wind does not blow on demand. The sun does not always shine. Still, power demand must be met at all times and for all locations. Our new study, lead-authored by one of our Master’s students last year, Peter Berrill, assesses the environmental impacts of high penetration renewable energy scenarios for Europe. By bringing together life cycle assessment (LCA) and power grid modelling, the study is able to capture both life cycle effects and variability issues in one single analysis.

While increased needs to store energy and to transfer electricity over large distances cause additional impacts in systems dominated by renewables, these impacts are small in comparison to the benefits of deploying renewables.

Former estimates present an incomplete picture

Results of LCAs are frequently used to compare the environmental performance of electricity generation options. One example is this graphic from the IPCC, juxtaposing life cycle emission estimates for different power generation options. However, these estimates do not consider impacts associated with accommodating large shares of variable supply in electricity networks.

Considering both life cycle effects and variability issues in one coherent assessment involves a substantial methods and data challenge. The basic reason for this is that impacts occurring as a result of variability is a property of whole systems, not of individual technologies.

How so? Well, we know that the wind does not always blow. This constitutes a challenge, because customer demand for electricity must always be satisfied. Now, we can deal with the challenge in a number of ways. We can expand transmission grids, to exploit the fact that the wind (almost) always blows somewhere. We can combine wind and solar deployment to reduce overall fluctuations. We can invest in energy storage, such as batteries or pumped hydro. We can invest in surplus capacity of flexible natural gas power, ready to be used when needed. Or – as will be the case in the real world – we can combine these measures in one way or another. Then, the impacts that arise as a result of variability depend on how all technologies are combined. The impacts cannot be determined by considering any single technology in isolation.

Our attempt to get a fuller picture

In order to capture both life cycle effects and variability effects, you need both a power system model capable of simulating the operation of entire power systems, and an LCA model capable of estimating life cycle impacts of different power system layouts, and to combine the two in a sound manner.

Our study does exactly this. First, 44 scenarios describing power system configurations for Europe in 2050 were generated by a power system optimization model, REMix, operated by DLR in Germany. Next, the scenarios were examined using NTNU’s prospective LCA modelling framework, THEMIS. This combination allows us to present the first LCA of entire electricity systems while taking into account the effects of variability on storage and transmission requirements, and losses.

Findings: Large climate benefits

Wind turbines in Copenhagen. Photo: NTNU/Maren Agdestein
Wind turbines in Copenhagen. Photo: NTNU/Maren Agdestein

The findings indicate large climate benefits and a range of other emissions reduction benefits of switching to renewables. Adopting variable renewables on a large scale does lead to additional storage and transmission capacity requirements – and hence additional environmental impacts – but these are not large enough to significantly undermine the benefits of renewable power displacing fossil fuel-based power.

Another finding is that solar photovoltaic (PV) power tends to induce larger impacts than wind power, for two main reasons. First, the supply chains of solar power plants generally involve more emissions-intensive material processing and manufacturing activities than that of wind power plants. Second, as wind power plants on average operate closer to their full capacity, systems dominated by wind power show lower needs for storage than solar-dominated systems.

Our findings can help to alleviate fears that large-scale adoptions of variable renewable energy will cause large unintended emissions. At the same time, it is worthwhile to keep in mind that simplifications and assumptions were necessary, and this contributed to uncertainty. Some of the simplifications and assumptions may be replaced by more sophisticated modelling or better data in the future.

The study is reported in Environmental Research Letters.